Animals - Advanced

Douglas Wilkin, Ph.D. Jennifer Blanchette Jean Brainard, Ph.D.

Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) AUTHORS Douglas Wilkin, Ph.D. To access a customizable version of this book, as well as other Jennifer Blanchette interactive content, visit www.ck12.org Jean Brainard, Ph.D.

EDITOR Douglas Wilkin, Ph.D. CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-source, collaborative, and web-based compilation model, CK-12 pioneers and promotes the creation and distribution of high-quality, adaptive online textbooks that can be mixed, modified and printed (i.e., the FlexBook® textbooks).

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Printed: January 24, 2016 www.ck12.org Chapter 1. Animals - Advanced

CHAPTER 1 Animals - Advanced CHAPTER OUTLINE 1.1 Animals - Advanced 1.2 Classification of Animals - Advanced 1.3 Evolution of Animals - Advanced 1.4 Animal Behavior - Advanced 1.5 Evolution of Animal Behavior - Advanced 1.6 Innate Behavior in Animals - Advanced 1.7 Learned Behavior in Animals - Advanced 1.8 Social Behavior in Animals - Advanced 1.9 Communication Behavior in Animals - Advanced 1.10 Animal Migration - Advanced 1.11 Circadian Rhythms - Advanced 1.12 Animal Aggression - Advanced 1.13 Animal Competition - Advanced 1.14 Animal Mating Systems - Advanced 1.15 Animal Courtship - Advanced 1.16 Parental Care in Animals - Advanced 1.17 References

Introduction

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Do all animals have a head and limbs? Do you know what these greenish, blob-like shapes are? Would it surprise you to learn that they are animals? They don’t look anything like the animals you are probably familiar with —animals such as dogs, deer, fish, and frogs. But the greenish blobs are animals nonetheless. They belong to a phylum called Cnidaria, but you may know them as jellyfish. They are very simple animals and, in fact, are not fish at all. How can an organism as simple as a jellyfish be considered an animal? How are animals defined? What traits must an organism have to be classified in the animal kingdom? In these concepts, you will learn the answers to these questions. You will find out just what it means to be an animal.

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1.1 Animals - Advanced

• Describe the characteristics of animals and how they differ from the characteristics of organisms in other kingdoms.

What do all animals have in common? The ability to smile? No. But they are all eukaryotic, heterotrophic, and multicellular. All organisms on earth are divided up, or classified, into six primary groups called kingdoms. The six kingdoms of organisms are:

• Archaebacteria. • Eubacteria. • Protista. • Fungi. • Plantae. • Animalia.

In these concepts we will examine the animal kingdom. Members of the animal kingdom have a number of characteristics that distinguish them from organisms within other kingdoms, such as the internal organization of their cells and how they obtain nutrients. The animal kingdom is subdivided into a number of different groups called

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phyla. In the three Animals concepts, we will explore the characteristics of animals, the classification of animals into different phyla, and the major trends that can be seen in the evolution of animals.

Characteristics of Animals

There is enormous variation among the different species that make up the multicellular organisms of the animal kingdom, as shown in the Figure 1.1. Despite this variation, there are a number of basic characteristics that are shared by all animals. In this section, we will first consider how it is that such a diverse group of organisms are evolutionarily related to each other, and then we will examine the common traits that exist among all animals.

FIGURE 1.1 Examples of some of the many diverse species that make up the animal kingdom. (A) Sponge, (B) Flatworm, (C) Flying Insect, (D) Frog, (E) Tiger, (F) Gorilla.

How are All Animals Related to Each Other?

All organisms on earth descend from a single common ancestor. (See http://sci.waikato.ac.nz/evolution/Anima lEvolution.shtml .) This ancestor is thought to have originated approximately 3.5 to 4 billion years ago. Over long periods of time, the process of evolution and natural selection led to a divergence of the descendants of this ancestor. Divergence is the evolutionary process by which some individuals within a species develop traits - due to random mutations - that make them different from other members of the species. Divergent evolution results in the formation of a new species when these differences become so large that the different individuals can no longer interbreed with the original members of the species. This process is called speciation. Over time, divergence and speciation ultimately result in the diversity of species that we see on earth today (see the Concept Evolution (Advanced) chapter). All members of the animal kingdom are more closely related to each other than to organisms in any other kingdom because they diverged more recently from each other than they did from members of other kingdoms. This can be compared to the difference between siblings and cousins. You are related to your cousins, but you have to go back to two generations, to your grandparents, to find an ancestor that you all share. You are more closely related to your siblings because you only have to go back one generation to find a common ancestor: your parents. Of course, all animals have to go back an enormous number of generations to reach their shared common ancestor, but not as far back as an animal and a plant would have to go to find a common ancestor. As a result of this comparatively close relationship, members of the animal kingdom share a number of basic traits. They are all defined as multicellular organisms that must obtain organic nutrients by consuming other organisms and whose cells do not have cell walls. In the next three subsections, we will examine this description in more detail, and we will consider a number of other characteristics that distinguish animals from organisms within the other five

4 www.ck12.org Chapter 1. Animals - Advanced kingdoms. These characteristics are roughly divided into three categories: structure, function, and reproductive life cycle.

Animal Structure

Animal cells are eukaryotic. This trait is shared with organisms of three other kingdoms: plants, fungi, and protists. Cells of the bacterial kingdoms are prokaryotic. The major difference between a prokaryotic cell and a eukaryotic cell is the presence of a nucleus. The nucleus is a membrane-bound organelle within the cell that contains genetic information in the form of chromosomes composed of DNA. In prokaryotic cells the chromosomes are not enclosed by a membrane compartment. There are generally other membrane-bound organelles within a eukaryotic cell that are specialized for specific cellular functions. An example of a prokaryotic and a eukaryotic cell are shown in the Figure below. These cell types are extensively discussed in the Concept Cell Biology (Advanced) chapter.

FIGURE 1.2 A prokaryotic bacterial cell (top) and a eukaryotic animal cell are shown (bottom) for comparison. Various internal struc- tures are labeled. Note the many or- ganelles within the eukaryotic cell that are not present in the prokaryotic cell. The most prominent of these organelles is the cell nucleus, which contains the genetic material.

The cells of plants, fungi, some protists, and some prokaryotes have a cell wall. A cell wall is a rigid layer that surrounds the cell membrane and is usually composed primarily of carbohydrate molecules. The cell wall functions to provide structural support and protection to the cell. Animal cells do not have a cell wall. This allows them to have more flexibility and to adopt different shapes. Some animal cells, such as the neuron shown in the Figure 1.3, have an extremely elongated shape that is essential to their function. In the case of neurons, an extended cell shape is necessary for transmitting nerve signals over long distances. This shape would not be feasible if the cell were surrounded by a rigid wall. Neurons are discussed in the The Nervous System concepts under Anatomy and Physiology.

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FIGURE 1.3 A diagram of a neuron, illustrating the extended shape and specialized cell regions such as the dendrites (that receive information) and the axon (that transmits information to the next cell).

Most animals have specialized tissues and organs that carry out specific functions within the animal, such as the nervous system and the muscular system. These are discussed in the next section.

Animal Function

In addition to the absence of a cell wall, animals differ from plants in another important way. Plants are capable of using the energy from the sun to generate their own organic nutrients from inorganic molecules by photosynthesis. An organism that can synthesize its own nutrients is called an autotroph. In contrast, animals are heterotrophs. Heterotrophs obtain organic nutrients by consuming either autotrophs or other heterotrophs. At some stage in their life cycle, all animals are capable of movement. For most animals, it is the adult stage that is motile. This is mediated by the muscular system. The muscular system allows animals to actively seek food resources as well as mating partners for reproduction. It also allows them to escape from predators. Movement would not be possible, however, without a nervous system. Nearly all animals have some type of nervous system. It consists of a network of tissue that enables animals to sense what is going on in their environment and to respond to these events. Animals detect stimuli from their environment using sensory organs. This information is transmitted between cells of the nervous system through both electrical impulses and biochemical molecules released by the cells. As the information is transmitted and processed, the nervous system mediates behavioral responses, such as movement. The organization of the nervous system ranges from a very simple net of nerve cells (jellyfish, for example) to a highly complex network with a centralized brain, such as that of vertebrates. Another feature unique to animals is internal digestion. While many other organisms absorb nutrients directly from their environments, most animals eat other organisms. They must first digest their food and then absorb the nutrients derived from the digestion process. This requires an internal digestive system made up of a digestive cavity. Similar to the variety in the nervous system, digestive systems can also range from very simple systems to highly complex systems. These will be discussed in The Digestive System concepts.

Animal Reproduction and Life Cycle

Throughout most of its life cycle, an animal is generally diploid. Diploid refers to having two copies of the genetic material, or chromosomes, one copy from the female parent and one copy from the male parent. Most animals reproduce by sexual reproduction. This involves the formation of two types of gametes: eggs and sperm. Each gamete is formed from specialized reproductive organs in the animal, through a process called meiosis. Gametes contain half of the genetic information within the parental cells and are therefore haploid. Haploid means having only one copy of each chromosome. Sexual reproduction occurs when a sperm cell fuses with an egg cell to generate a diploid cell. This process is called fertilization. A fertilized egg, called a zygote, then undergoes a number of cleavage events to form a mass of cells known as an embryo. The embryo goes on to develop into a new individual. This cycle is shown in the Figure below. For more information on meiosis, see the Meiosis concepts. Animals generally develop through several different embryonic stages. These stages include the formation of a blastula and gastrulation. A blastula is a hollow sphere of cells. Gastrulation is the process by which one region of

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FIGURE 1.4 Animal Life Cycle. An animal life cycle that includes only sexual reproduction is shown here. Some animals also repro- duce asexually. How does the animal life cycle compare with the life cycle of a plant?

the ball retracts, or invaginates, into the hollow space. You can imagine this looking similar to pushing your finger into a partially deflated balloon. The resulting embryo is shaped like a sac encircled by two cell layers. Further cell division and cell differentiation result in a fully developed organism. In the Animals: Evolution (Advanced) concept we will consider how these embryonic stages reflect the steps that occurred during the evolution of the earliest animals. For a general overview of the characteristics of animals, see http://www.youtube.com/watch?v=wd-QnKlfZHI

MEDIA Click image to the left or use the URL below. URL: http://www.ck12.org/flx/render/embeddedobject/139429

Vocabulary

• autotroph: An organism that produces organic compounds from an energy source (often light) and simple inorganic molecules; autotrophs are also known as producers.

• blastula: A hollow sphere of cells formed early in development.

• cell wall: A rigid layer that surrounds the plasma membrane of prokaryotic cells, plant cells, and fungal cells; the cell wall helps support and protect the cell.

• diploid: The state of a cell containing two sets of chromosomes; in human somatic cells, two sets is 46 (23 pairs) chromosomes, 2n.

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• divergence: Divergent evolution.

• eukaryotic cells: Cells that have a nuclei and membrane-bound organelles. They are typical of multi-cellular organisms and are usually larger than prokaryotic cells.

• fertilization: The joining of gametes during reproduction.

• gastrulation: The development of different layers of cells in an embryo; in humans, gastrulation generally occurs during the second week after fertilization.

• haploid: The state of a cell containing one set of chromosomes; in human gametes, one set is 23 chromosomes, n.

• heterotroph: Organisms which must consume organic molecules; they are also known as consumers.

• nucleus (plural, nuclei): The membrane-enclosed organelle found in most eukaryotic cells that contains the genetic material (DNA); it is the control center of the cell.

• prokaryotic cells: Cells that lack nuclei and membrane-bound organelles. They are typical of simple, single- celled organisms, such as bacteria.

• sexual reproduction: Reproduction involving the joining of haploid gametes, producing genetically diverse individuals.

• speciation: The process which results in new, separate and genetically distinct groups of organisms; the formation of a new species.

• zygote: A fertilized egg; the first cell of a new organism.

Summary

• All organisms on earth descend from a single common ancestor, but animals are more related to each other than to bacteria, fungi, protists, or plants. • Animals are multicellular organisms that are made up of eukaryotic cells without cell walls. • Animals are heterotrophs and usually reproduce through sexual reproduction.

Practice

Use this resource to answer the questions that follow. http://animalspeek.blogspot.com/2006/02/characteristics-of-a nimals.html

1. How many species of animals have scientists identified? 2. What are some important characteristics used to describe animals?

Practice Answers

1. Scientists have identified over 1 million species of animals although estimates for the total number of species range from 3 to 30 million. 2. Basic characteristics such as body symmetry, directions of the body, pattern of body development, and formation of germ layers are important descriptions used when studying animals.

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Review

1. Which four kingdoms contain organisms with eukaryotic cells? 2. What characteristic of animal cells makes it possible for nerve cells to have their elongated shape? 3. Why are animals capable of movement, at least in some stage of their life cycle? What system common to all animals makes movement possible? 4. How do most animals reproduce?

Review Answers

1. Animals, plants, fungi, and protists are all organisms with eukaryotic cells (bacterial cells are prokaryotic). The major difference between a prokaryotic cell and a eukaryotic cell is the presence of a nucleus. 2. Animal cells do not have cell walls, which allows for the cells to be more flexible and adopt different shapes. 3. Animals are capable of movement because they are heterotrophs and need to consume other organisms for energy. Almost all animals have a nervous system that enables them to sense what is going on in their environment and to respond to these events through movement. 4. Most animals reproduce through sexual reproduction. This involves the formation of two types of gametes: eggs and sperm.

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1.2 Classification of Animals - Advanced

• Describe how animals are classified into different phyla.

Insect? Yes. But what type? This insect would be classified as a beetle. The order Coleoptera, otherwise known as the beetles, means “sheath wings,” a reference to the hardened forewings which cover the insect’s body.

Classification of Animals

Despite the general characteristics that animals have in common, they are an enormously diverse group of organisms. Animals exhibit great variation in structure and function. They include simple animals, such as sponges, as well as highly complex animals, such as humans. The members of the animal kingdom are subdivided into more than 30 different groups called phyla. There are 7 major hierarchies, or ranks, in animal classification. Kingdom is the highest and most inclusive rank. Phylum is the rank below kingdom, and species is the most fundamental rank. The hierarchy of the ranks is shown in the Figure 1.5. The subdivision of the animal kingdom into different phyla is based on the evolutionary relationships within and between the species of each phylum. The organisms within a phylum are considered to be more closely related to each other than they are to organisms of other phyla. As was discussed in the Animals: Characteristics (Advanced) concept, the relatedness of two organisms has to do with how recently they diverged from a common ancestor. In the following sections we will look at two ways in which scientists determine how closely related two animal species are to each other, and then we will examine the major phyla that make up the animal kingdom. More on classification is discussed in the Concept Invertebrates (Advanced) chapter and the Concept Vertebrates (Advanced) chapter.

Traditional versus Molecular Phylogeny

Traditional phylogeny divides animals into hierarchical categories based on structural similarities. This assumes that these similarities reflect a shared evolutionary history. In other words, it is assumed that all animals having a particular trait, such as a segmented body plan, evolved that trait from the same recent common ancestor. The problem with this method is a process called convergent evolution. Convergent evolution is when organisms that

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FIGURE 1.5 Major hierarchical rankings in animal classification. For more information, see the Classification concepts.

are not closely related to each other independently develop the same trait over time. This can happen when two unrelated organisms have to adapt to similar environmental pressures. Molecular phylogeny can often resolve these classification problems. In molecular phylogeny, the evolutionary relatedness of two organisms is determined by comparing the molecules that make up their genetic material. It is changes in the genetic code of an organism that lead to the changes we observe in their outward appearance. However, not all changes in the genetic code lead to observable changes in the appearance of an organism. Therefore, molecular phylogenetics can detect relationships that are not reflected in shared, observable traits.

Animal Phyla

There is some controversy in the field of phylogenetics based on the conflicts between traditional and molecular phylogeny. This controversy can lead to different estimates of the number of animal phyla. Depending on the classification scheme, there are roughly 34 animal phyla. There are nine phyla that are considered the major phyla, and these are listed in the Major Phyla of the Animal Kingdom Table. This Table also includes a description of the major evolutionary changes that arose with these phyla and some of the members of each phylum. Each of these phyla contain at least 10,000 different species, with the phylum arthropoda containing over one million species. For more information on the major phyla, visit http://waynesword.palomar.edu/trnov01.htm.

TABLE 1.1: Major Phyla of the Animal Kingdom

Phylum Evolutionary Developments Porifera Multicellularity Cnidaria True tissue, radial symmetry Platyhelminthes Mesoderm, bilateral symmetry

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TABLE 1.1: (continued)

Phylum Evolutionary Developments Nematoda Complete digestive system, pseudocoelom Arthropoda Segmented body Annelida Closed circulatory system, segmented body Mollusca Highly developed brain in cephalopoda class Echinodermata Deuterostomes Chordata Notochord

Vocabulary

• convergent evolution: Evolution whereby distantly related species each independently develops the same trait over time.

• molecular phylogeny: The evolutionary relatedness of two organisms, determined by comparing the molecules that make up their genetic material.

• phylogeny: The evolutionary history of a group of genetically related organisms.

Summary

• There are 7 major hierarchies, or ranks, in animal classification. Kingdom is the highest and most inclusive rank, and species is the most fundamental rank. • The subdivision of the animal kingdom into different phyla is based on the evolutionary relationships within and between the species of each phylum. • Controversy between tradition and molecular phylogeny has lead to different estimates of the number of animal phyla.

Practice

Use this resource to answer the questions that follow. "Animal Phylogeny" at https://www.boundless.com/biolog y/the-animal-kingdom/animal-phylogeny/animal-phylogeny/.

1. What are clades? 2. If we traced all animals back far enough, what was our common ancestor? What are its closest living relatives today? 3. What animals belong to the clade known as Eumetazoa?

Practice Answers

1. Clades are groupings that consist of an ancestor organism and all its descendants (and nothing else). 2. Animals are generally considered to have a common ancestor, evolving from a flagellated eukaryote. Their closest known living relatives are the choanoflagellates, which are collared flagellates that are morphologically similar to the choanocytes of certain sponges. 3. Eumetazoa is a clade comprising all major animal groups except sponges and placozoa. Characteristics include true tissues that are organized into germ layers and an embryo that undergoes a gastrula stage.

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Review

1. How many hierarchies are there for animal classification? What are they? 2. How were animals originally classified? What are some problems with the older form of classification? 3. Why is there controversy over the number of phyla in the animal kingdom? Roughly how many are there?

Review Answers

1. There are 7 major hierarchies for animal classification: kingdom, phylum, class, order, family, genus, and species. 2. Traditional phylogeny divides animals into hierarchical categories based on structural similarities which, in theory, were supposed to reflect a shared ancestor. One problem with this type of classification is convergent evolution: when unrelated organisms evolve the same characteristics, perhaps due to similar environmental pressures. Molecular phylogeny solves these problems. 3. There is some controversy in the field of phylogenetics based on the conflicts between traditional and molec- ular phylogeny. Depending on the classification scheme, there are roughly 34 animal phyla.

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1.3 Evolution of Animals - Advanced

• Identify and describe the major trends that are seen throughout the evolution of animals.

Are alligators and crocodiles prehistoric creatures? That depends on your definition of prehistoric. It is true that these crocodilians roamed the Earth along with the dinosaurs. Crocodilians first appeared in the late Cretaceous period about 84 million years ago. They very closely resembled modern day reptiles such as crocodiles, caimans, and specifically alligators. Dinosaurs went extinct about 65 million years ago.

Major Trends in Animal Evolution

Animal evolution is a fascinating subject. The slow, step-wise evolutionary changes that link the earliest-known and simplest animals to the most recently evolved, highly complex animals is truly a remarkable process. Several critical steps in animal evolution take place within the large number of invertebrate phyla. These will be discussed in detail throughout the Concept Invertebrates (Advanced) chapter. In this section we will summarize those trends, and we will focus on evolutionary changes that occur between invertebrates and vertebrates within the phylum chordata.

From a Single Cell to Multi-Celled Organisms

The first animals likely evolved from marine protists. Protists are mostly single-celled organisms, some of which grow clumped together as cellular aggregates called colonies. The evolution of multicellular organisms may have occurred when the cells within a protist colony began to become specialized for different functions. The individual cells would then be dependent on other cells within the colony for survival. This would represent the first primitive multicellular animal. Strong support for this hypothesis comes from the most primitive animals: sponges. One group of specialized cells within a sponge, called choanocytes, bears a striking resemblance to a class of protists called choanoflagellates. Choanoflagellates are single-celled organisms that have a long, thin fiber protruding from their bodies called a flagellum. The flagellum beats like a whip, and this motion allows the organism to move through the water. Choanocytes also have a flagellum that is used to bring water into the sponge’s body. Both choanocytes and choanoflagellates also share another distinct feature called a collar. The collar is a circle of smaller projections called microvilli that surround the flagellum. In both organisms the collar is used to trap small food molecules. The

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Figure 1.6 shows the strong similarities between choanocytes and choanoflagellates. This is further discussed in the Concept Invertebrates (Advanced) chapter.

FIGURE 1.6 Choanoflagellate and choanocytes. On the right is the single-celled protist called a choanoflagellate. On the left is a diagram of a cross-section through a sponge body wall, illustrating the layer of choanocytes lining the digestive cavity. Note the structural similarities between the choanoflagellate and the choanocyte.

The transition from a colony to an animal likely involved the invagination of some of the cells within the aggregate in order to form a digestive cavity. This is similar to the stage of embryonic development called gastrulation that we discussed in the Animals: Characteristics (Advanced) concept. In an evolutionary theory known as recapitulation, some scientists hypothesize that steps in the process of an animal’s embryonic development resemble, or “recapit- ulate,” the evolutionary history of the species. For example, the gastrula stage of development in higher animals resembles the adult stage of primitive animals from which they evolved, such as sponges. While general similarities between embryonic development and evolutionary history do exist, modern evolutionary science rejects the theory of recapitulation. This is because these stages are not truly equivalent to the adult stages of evolutionary ancestor species. For example, there is no stage of human embryonic development that can be considered the functional equivalent of a “fish” stage, even though fish are evolutionary ancestors of humans.

The Cambrian Explosion: An Explanation for Multicellular Organisms

When did the transition from colony-forming protists to multicellular animals take place? We are not entirely sure, because of our incomplete fossil record. The first strong evidence of multicellular animals in the fossil record occurs roughly 630 million years ago, during a geological time period called the Ediacaren. The Figure 1.7 shows a timeline of the geological periods associated with the early fossil record. One striking feature of the fossil record is a massive increase in the number and diversity of fossilized animals beginning in the Cambrian period. Within roughly 40 million years, fossils from nearly all phyla of the animal kingdom first appeared. This sudden burst of animal diversity in the fossil record is known as the Cambrian explosion. There are a number of scientific theories that may explain this seemingly rapid evolution. These theories are primarily based on hypothesized atmospheric conditions during and prior to the Cambrian period. For example, one theory postulates that a sudden rise in atmospheric oxygen levels facilitated the rapid evolution of animal species. However, it is not even agreed upon that this increase in the fossil record actually reflects a period of rapid evolution. Based on evolutionary time scales estimated by molecular phylogenetics, it is thought that the first animals arose several hundred million years prior to the Cambrian explosion. Yet, there is no fossil record for the existence of multicellular animals dating to that time. In this case, the fossils found in the Cambrian period may not reflect the

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FIGURE 1.7 A geological timeline. This figure shows a portion of a geological timeline with approximate dates. This section includes parts of the Neoproterozoic and Paleozoic eras. The Cambrian explosion occurred approximately 540 million years ago.

first appearance of many of those animals. Rather, there may just be a large segment of time that is completely missing fossils of the species that lived at that time. One possible explanation for the lack of a fossils of these earlier animals is that their physical composition or the geological conditions during that time did not allow fossil preservation. This debate is currently unresolved among scientists, and it will likely require additional research to determine the most likely cause of the so-called Cambrian explosion. In addition to periods of increased diversity, the fossil record also shows periods of extinction, some on a very large scale. Extinctions occur when changing environmental conditions do not allow a species to survive. Sometimes this is a result of competition from a species which is better adapted to the environment. There are a great number of extinctions that occur throughout the evolution of animals. In fact, the organisms present on the earth today represent only 0.1% of all of the species that have existed through time. These extinct species, however, remain a critical part of the evolutionary history of the animal kingdom.

Invertebrates to Vertebrates

Many major evolutionary developments occurred in the animal kingdom prior to the development of a notochord, the defining feature of the phylum chordata. These developments include the following:

• Bilateral symmetry. • True tissue and organ systems. • A body cavity. • Centralized nervous system. • Complete digestive system with separate openings for the mouth and the anus. • A segmented body plan.

Each of these steps were essential for the evolution of higher organisms, such as mammals. They will be discussed in detail in the concepts on invertebrates. The phylum chordata reflects the development of the notochord. A notochord is a rod-shaped, semi-rigid support structure that forms between the dorsal nerve cord and the gut of an animal. A diagram showing the placement of the notochord within a chordate body is shown in the Figure 1.8. The notochord serves as a major step in the evolution of both the internal skeleton and backbone found in vertebrates. The notochord not only provides structural support for the animal, but it also provides a place for muscle attachment. The force of muscle contractions opposing the notochord allow movement, much like how the contraction of muscles attached to our internal skeleton causes us to move. Other features that are specific to members of the phylum chordata include a dorsal nerve cord, pharyngeal slits, an endocyst, and a post-anal tail. Pharyngeal slits and the endocyst are structural features of the pharynx that assist in feeding. In humans, none of these features persist to adulthood, but all are present at various stages during development.

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FIGURE 1.8 The anatomy of a chordate from the sub- phylum cephalochordata, illustrating the location of the notochord within the body plan. Anatomical features are numbered as follows: 1. brain like blister, 2. noto- chord, 3. dorsal nerve cord, 4. post-anal tail, 5. anus, 6. digestive canal, 7. blood system, 8. abdominal pore, 9. overphar- ynx lacuna, 10. gill slit, 11. Pharynx, 12. mouth lacuna, 13. mimosa, 14. mouth gap, 15. gonads (ovary/testicle), 16. light sensor, 17. nerves, 18. abdominal ply, 19. liver-like sack.

Vertebrates are one of three major subphyla of chordata. The other two subphyla consist of invertebrates. Vertebrates include over 50,000 different species. More than half of these species are fish. The defining feature of vertebrates is an internal skeleton that includes a backbone and a cranium. The classes within the subphylum vertebrata are listed in the Subphylum Vertebrata (Phylum Chordata) Table.

TABLE 1.2: Existing Classes within the Subphylum Vertebrata (Phylum Chordata)

Class Members Example Myxini Hagfish (Jawless)

Hyperoartia Lampreys (Jawless)

Chondrichthyes Cartilaginous fish

Actinopterygii Ray-finned fish

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TABLE 1.2: (continued)

Class Members Example Sarcopterygii Lobe-finned fish

Amphibia Amphibians

Sauropsida Reptiles

Aves Birds

Mammalia Mammals

Within the vertebrates we see the evolution of increasingly complex fish, beginning with jawless fish. The jawless fish evolved to form jawed, cartilaginous fish and eventually bony fish. Animals that we commonly think of as vertebrates, four-legged (or two legs and two wings) backboned animals, arose from bony fish. These tetrapod classes include the following:

• Amphibians. • Reptiles. • Birds. • Mammals.

Water to Land

A major evolutionary event that occurred within the vertebrates was the transition from water to land. This required a number of physiological changes to compensate for the differences between an aquatic environment and a terrestrial environment. On land, animals need systems to conserve water, exchange gases internally, and move from place to place on the ground. In addition, land animals cannot rely on water currents to disperse their gametes in order to

18 www.ck12.org Chapter 1. Animals - Advanced sexually reproduce. These changes began to be seen as amphibians evolved from a bony fish called a lobe-finned fish. Lobe-finned fish had what are called proto-lungs and proto-limbs. The proto-lungs enabled them to surface from the water and breath air for a short time. The proto-limbs, or lobed fins, enabled them to walk out of the water and on land for short distances. From the lobe-finned fish, amphibians evolved true lungs and true limbs for survival on land. However, most amphibians are still dependent on water to lay their eggs. Amphibian eggs are not able to survive in a non-aquatic environment because they do not have a waterproof covering. This adaptation arose with the reptiles. Reptiles have what is called an amniotic egg. In an amniotic egg, the embryo is surrounded by layers of membranes and a solid, water-impermeable shell. This allows the embryo to survive on dry land. Reptiles mark the full transition from water to land. It is important to realize, however, that chordates were not the first animals to make the water to land transition. Arthropods had achieved this step independently and through evolutionary changes that were quite distinct form those of vertebrates. For example, arthropods dealt with the problem of retaining water partly by using a physical feature that they had already evolved, or pre-adapted, called the exoskeleton.

FIGURE 1.9 From Lobe-Finned Fish to Early Amphib- ian. Lobe-finned fish evolved into the earliest amphibians. A lobe-finned fish could breathe air for brief periods of time. It could also use its fins to walk on land for short distances. What similarities do you see between the lobe-finned fish and the amphibian?

Birds and Mammals

Mammals and reptiles both evolved from the same amniotic-egged ancestor. This ancestor diverged into two major groups: the synapsids (mammalian-like reptiles) and the sauropsids (reptiles). The vertebrate class mammalia evolved from the synapsids. Dinosaurs and subsequently birds (class aves) evolved from reptiles of the class sauropsid. Both birds and mammals are warm-blooded vertebrates. Warm-blooded animals have the ability to regulate internal body temperature. Birds have wings and feathers, and they lay their eggs for external development. Mammals are defined by the presence of milk-producing mammary glands in females. Additional features of mammals include hair, three middle ear bones, and a specialized region of the brain called the neocortex. Most mammals also exhibit vivipary. Vivipary means that, instead of laying eggs that develop outside of the mother, the embryo develops inside of the mother’s body. Human beings, the species Homo sapiens, belong to the primate order within the class mammalia. Scientists estimate that Homo sapiens arose roughly 200,000 years ago. It is important to consider that evolution is a continual process, and humans are continuing to evolve. The slow rate of evolution makes it essentially impossible to study as it is occurring, however, it is interesting to speculate on the future of human evolution. This brings up questions about the environmental pressures that will lead to the divergence of humans into new species and what this divergence will look like.

Vocabulary

• amniotic egg: An egg with a water-impermeable amniotic membrane surrounding a fluid-filled amniotic cavity; This type of egg permits embryonic development on land without the danger of water-loss.

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• Cambrian explosion: The abrupt emergence of many new species during the Cambrian Period; within roughly 40 million years, fossils from nearly all phyla of the animal kingdom first appeared.

• choanocytes: Specialized digestive cells, which line the spongocoel, that filter and take in food; they are also known as collar cells. • choanoflagellates: Single-celled organisms that have a long, thin fiber protruding from their bodies called a flagellum.

• notochord: A rod-shaped, semi-rigid support structure that forms between the dorsal nerve cord and the gut of an animal.

• vivipary: When the embryo develops inside of the mother’s body, instead of laying eggs that develop outside of the mother.

Summary

• The first animals likely evolved from marine protists that clumped together in colonies. • The transition from a colony to an animal likely involved the formation of a digestive cavity via the invagina- tion of some of the cells within the aggregate. • The first strong evidence of multicellular animals in the fossil record occured roughly 630 million years ago during a geological time period called the Ediacaren. • Major developments that occurred within the animal kingdom include bilateral symmetry, true tissue and organ systems, a body cavity, a centralized nervous system, a complete digestive system, a segmented body plan, and a notochord. • The notochord serves as a major step in the evolution of both the internal skeleton and backbone found in vertebrates. • Vertebrates include over 50,000 different species. More than half of these species are fish. • A major evolutionary event that occurred within the vertebrates was the transition from water to land.

Practice

Use this resource to answer the questions that follow. "Plant and Animal Evolution" at http://sci.waikato.ac.nz/evo lution/AnimalEvolution.shtml.

1. Explain what the theory of endosymbiosis is and how it may have led to the evolution of animals. 2. What is one possible reason animals did not migrate to land sooner? 3. When did multicellular animals appear in the fossil record for the first time? 4. What were the earliest types of fish? When did they appear? 5. Some of us may have the conception that amphibians were the first animals to venture on land. Is this true?

Practice Answers

1. Endosymbiosis is a theory for how animal cells gained organelles such as mitochondria. The theory postulates that larger cells ingested mitochondria-like cells and formed a symbiotic relationship. Animal cells can produce energy thanks to this prehistoric symbiotic relationship. 2. Animals remained in the sea for 600 million years in part because there wasn’t a protective ozone layer against UV radiation. An ozone layer formed only once there was sufficient atmospheric oxygen produced by plants. 3. Between 620 and 550 million years ago (during the Vendian Period) relatively large, complex, soft-bodied multicellular animals appeared in the fossil record for the first time. The animals are generally known as Ediacaran fauna.

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4. Agnathans, or jawless fish, were the earliest fish. An excellent fossil of Haikouichthys ercaicunensis dates back to about 530 million years (to the Cambrian). 5. Arthropods were the first animals to become colonists on land. The arthropods were pre-adapted to life on land because by the time they moved ashore, they had already evolved lighter bodies and slim, strong legs that could support them against the pull of gravity. Their hard outer exoskeletons also provided protection and would help to retain water.

Review

1. What did the first animals likely evolve from? What supports this theory? 2. What is the evolutionary theory known as recapitulation? Why does modern evolutionary science reject this theory? 3. What are some theories that try to explain the Cambrian explosion? 4. What role does the notocord serve in animals? 5. As the first animals began to migrate to land, what were some challenges that their aquatic bodies faced?

Review Answers

1. The first animals likely evolved from marine protists that clumped together in colonies. The most primitive animals (sponges) still have cells that resemble protists called choanoflagellates, giving a lot of support to this theory. 2. Recapitulation was a theory that hypothesized that steps in the process of an animal’s embryonic development resemble, or “recapitulate,” the evolutionary history of the species. It is now rejected because embryonic stages are not truly equivalent to the adult stages of evolutionary ancestor species (there’s no "fish" embryonic stage for humans). 3. Many theories regarding the Cambrian explosion are based on hypothesized atmospheric conditions during and prior to the Cambrian period which might have promoted rapid evolution. There are also theories that postulate conditions prior to the Cambrian period did not support fossilization of animals, leaving a gap in the fossil record during which time animals actually evolved. 4. The notochord provides structural support for the animal and also provides a place for muscle attachment. The force of muscle contractions opposing the notochord allow movement. 5. On land, animals need systems to conserve water, exchange gases internally, and move from place to place on the ground. In addition, land animals cannot rely on water currents to disperse their gametes in order to sexually reproduce. Animals had to adapt in order to overcome these challenges.

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1.4 Animal Behavior - Advanced

• Define animal behavior and ethology. • Identify the four questions that Tinbergen thought should guide studies of animal behavior.

Is hunting a type of behavior? It is. Hunting is a way that organisms interact, so it is a behavior. It may not be a very pleasant behavior for one of the animals involved, but it is still a behavior.

Studying Animal Behavior

Animal behavior includes all the ways in which animals interact with other members of their species, with organ- isms of other species, and with their environment. Several common examples of animal behavior are shown in the Figure 1.10. The study of animal behavior is called ethology.

Ethology

Ethology is the scientific study of animal behavior. Like genetics and ecology, for example, ethology is a branch of biology. Three 20th century European scientists are usually considered to be the founders of ethology: Konrad Lorenz, Karl von Frisch (shown in the Figure 1.11), and Nikolaas (Niko) Tinbergen. All three studied animal behavior for several decades, beginning in the 1920s or 1930s. In 1973, they jointly received the Nobel Prize in Physiology or Medicine for their work. http://nobelprize.org/nobel_prizes/medicine/laureates/1973/press.html Like most other early ethologists, Lorenz, von Frisch, and Tinbergen mainly investigated animal behavior in natural settings rather than in a laboratory. Lorenz studied the behavior of geese and other birds. He is best known for his discovery of imprinting, a type of behavior that is described below. Von Frisch studied the behavior of honeybees. He determined how they communicate with one another (see the Animal Behavior: Communication (Advanced) concept). Tinbergen studied gulls and fish called sticklebacks. He is noted for his contributions to the understanding of instinct, which is also discussed later.

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FIGURE 1.10 This spider is spinning a web. This bird is building a nest. These wolves are hunting together as a pack. This piglet is suckling milk from its mother’s nipple. This dog is herding sheep. These children are playing with marbles.

Understanding Animal Behavior

In addition to his investigations of specific behaviors in animals, Tinbergen identified four basic questions that he thought should be answered to fully understand any animal behavior:

1. What causes the behavior? What is the stimulus (plural, stimuli), or trigger, for the behavior? What body parts and functions are involved when the behavior is performed? 2. How does the behavior develop? Is the behavior present early in life, or does it develop as the animal matures? What experiences are necessary for the behavior to develop? 3. Why did the behavior evolve? How does the behavior affect the fitness of individuals in a species? How does it influence the survival of the species as a whole? 4. How did the behavior evolve? How does the behavior compare with similar behaviors in related species? In what ancestor species did the behavior first appear?

An example of how Tinbergen’s four questions can be applied to the study of a particular animal behavior is described in the Understanding Bird Song Table.

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FIGURE 1.11 Karl von Frisch was one of the founders of ethology, the scientific study of animal behavior.

TABLE 1.3: Understanding Bird Song

Question Answer 1. What causes the behavior? The ability to produce songs is influenced by male hormones and occurs mainly in male songbirds. Songs are produced when air flows from large air sacs in the bronchi through an organ called the syrinx. Certain parts of the brain control song production and are well developed in male songbirds. 2. How does the behavior develop? Young male songbirds first listen to the songs of nearby males of their species. Then they start to practice singing. By adulthood, male songbirds have learned how to produce the song that is characteristic of their species.

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TABLE 1.3: (continued)

Question Answer 3. Why did the behavior evolve? Singing helps male birds attract mates, so it increases the chances that they will reproduce. Singing also helps male songbirds claim a territory and discourage potential competitors. This, in turn, helps ensure that the male songbirds will be able to mate and have enough food to survive. 4. How did the behavior evolve? Almost all species of birds can make vocal sounds, but only those in the suborder Passeri are songbirds. Evi- dence suggests that songbirds evolved about 50 million years ago in what is now Australia, New Zealand, and New Guinea. They later spread around the world.

This table shows how Tinbergen’s four questions have been answered for a particular type of behavior that occurs in many male birds: producing the song that is characteristic of their species.

Vocabulary

• animal behavior: Any way that animals interact with each other or their environment.

• ethology: The scientific study of animal behavior.

• stimulus (plural, stimuli): A physical, chemical, or biotic change –internal or external –which can cause a response.

Summary

• Animal behavior includes all the ways in which animals interact with other members of their species, with organisms of other species, and with their environment. • Tinbergen focused on cause, development, reasons for evolution, and how the evolution occurred.

Practice

Use this resource to answer the questions that follow. "Tinbergen: The Four Questions & Super Stimulus" at http://f reethoughtlebanon.net/2012/02/tinbergen-the-four-questions-super-stimulus/.

1. What are "super normal stimuli," and who explored this concept in detail? 2. How did Tinbergen demonstrate super normal stimuli in his seagull experiment? 3. What were Tinbergen’s opinions on animal behavior and human behavior? How might his study of super stimuli apply to humans?

Practice Answers

1. Super normal stimuli are exaggerated versions of a stimulus which already produces a response, or any stimulus that elicits a response more strongly than the stimulus for which the behavior evolved. It was studied by Tinbergen.

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2. Tinbergen demonstrated that baby chicks responded to contrast, redness, and elongation and produced a perfect beak design using just a long stick painted red and white. The chicks responded much more so to this man-made beak even though it did not resemble their mother’s. 3. Tinbergen was a firm believer in applying his methods to study human behavior as well. Super stimuli might pose a problem for humans in particular because we can create our own super stimuli such as junk food. These super stimuli might test a human’s innate urges.

Review

1. Who were the founders of ethology? 2. What were Tinbergen’s four questions that guided his study of animal behavior?

Review Answers

1. Three 20th century European scientists are usually considered to be the founders of ethology: Konrad Lorenz, Karl von Frisch, and Nikolaas (Niko) Tinbergen. 2. His four questions were the following: What causes the behavior? How did the behavior develop? Why did the behavior evolve? How did it evolve?

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1.5 Evolution of Animal Behavior - Advanced

• State both sides of the nature-nurture debate. • Explain how behavior can evolve. • Describe the differing views of sociobiologists. • Identify criticisms of sociobiology.

Why would an animal do this? This baboon is showing altruistic behavior by removing parasites from another baboon’s back. Is this behavior due to genes? Is it an instinct? Is it a learned behavior? Does it increase the fitness of the population? These are all good questions.

Evolution of Animal Behavior

Many ethologists are interested in how animal behaviors affect fitness (the ability to survive and reproduce) and evolution. This interest in fitness and evolution is clearly seen in Tinbergen’s third and fourth questions. Evidence shows that many animal behaviors are at least partly controlled by genes. However, there are no genes that code directly for behavior. Genes code for proteins (see the Protein Synthesis concepts), and a change in a single protein can cause wide-ranging effects throughout the body. It can dramatically influence an individual’s phenotype, or observable traits (see the Concept Inheritance (Advanced) chapter). On the other hand, the external environment also influences how most genes are expressed. Nonetheless, to the extent that behavior is controlled by genes, it may be subject to natural selection and evolution.

Nature vs. Nurture

As you read below about different examples of behavior, you will see that some behaviors seem to be mainly determined by genes, whereas others appear to be greatly influenced by experiences in a particular environment. Whether behaviors are controlled mainly by genes or by the environment is controversial. The controversy is often

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referred to as the nature-nurture debate. Nature refers to the genes that an individual inherits. Nurture refers to the environment in which the individual lives and the particular experiences the individual has throughout life. Some ethologists have used controlled experiments to investigate the relative importance of genes and the environ- ment in various animal behaviors. For example, they have raised baby animals in controlled environments without contact with other members of their species. If a behavior still appears under these conditions, then it is assumed to be controlled almost completely by genes. Consider the example of a puppy raised by humans, without contact with other dogs. Like all normal dogs, the puppy will drool when it sees or smells food. It does not need to observe other dogs drooling in order to perform this behavior. It also does not need to be repeatedly exposed to food to develop the ability to drool. If a behavior does not appear in a controlled environment, this does not necessarily mean that the behavior has no genetic basis. It may mean only that the stimulus needed to trigger the behavior is not present. For example, a dog does not normally drool without the stimulus of food. However, drooling behavior is still known to be controlled by genes; that is, genes are involved in the production of saliva. The same example shows how the environment can play a major role in shaping behavior. The puppy raised without contact with other dogs will not become socialized enough to interact normally with other members of its species. In fact, it is unlikely to ever interact normally with other dogs. It may always fear other dogs or act aggressively toward them. The tendency to behave toward other dogs in certain ways is probably controlled by genes. However, the behaviors cannot develop in an environment that deprives dogs of opportunities to interact.

How Behaviors Evolve

A behavior that is at least partly under genetic control can evolve through natural selection. However, being controlled by genes is not the only requirement for a behavior to evolve through natural selection. The individual performing the behavior also must have increased fitness due to the behavior. In other words, performing the behavior must increase the individual’s chances of surviving and successfully reproducing. Many behaviors make sense in terms of individual fitness and natural selection. For example, it is easy to see how “selfish” behaviors —such as successfully competing with other members of the same species for food and mates —could increase an individual’s fitness. By obtaining more food and mates, the individual has a greater chance of surviving and reproducing than less competitive members of the same species. Another example that is readily explained by natural selection is cooperative behavior, such as wolves hunting together as a pack. Hunting with the pack is more likely to be successful than hunting alone. Therefore, it could increase the fitness of all the animals in the pack.

Altruism, Sociobiology, and Kin Selection

Other behaviors are harder to explain in terms of individual fitness and natural selection. Altruistic behavior is a prime example. Altruism means doing something for others that puts oneself at risk. Squirrels act altruistically when they make warning sounds to “tell” other squirrels that a predator is near. This is likely to help the other squirrels avoid the predator, which increases their fitness. However, the altruist is more likely to be noticed by the predator, which decreases the altruist’s fitness. If a behavior reduces the fitness of the individual performing it, how could the behavior persist in the species through natural selection? Altruistic behavior is the only type of behavior that Charles Darwin admitted he could not explain through natural selection. In his famous 1859 book, On the Origin of Species, Darwin referred to altruistic behavior as the “one special difficulty, which at first appeared to me insuperable, and actually fatal to my theory.” Sociobiologists have offered explanations for how altruism and similar behaviors evolve. Sociobiology is the study of how behavior increases fitness and evolves through natural selection. Sociobiologists assume that behaviors that persist or increase in frequency must be adaptive. They also assume that genes determine most behavioral traits. Many of the theories of sociobiology were developed by scientists studying the behavior of insects that live in social

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groups. The scientist that established sociobiology as a distinct scientific field, E.O. Wilson (see the Figure 1.12), was an expert on the social behavior of ants. Wilson tried to explain the behavior of other animals, including humans, based on his knowledge of insect behavior.

FIGURE 1.12 E.O. Wilson founded sociobiology as a distinct field of study. He has received many honors and awards for his research and writing on the social behavior of ants. However, his explanations of human be- havior have been criticized by many other scientists.

One way in which Wilson and other sociobiologists have explained the evolution of altruism is through a process called kin selection. Kin selection refers to changes in gene frequencies from generation to generation that occur when biological relatives (kin) influence one another’s fitness. In ants and other insects that live in social groups, individuals in the group are close biological relatives. Therefore, an individual insect performing an altruistic behavior may be increasing the fitness of its kin. Close relatives share many of the same genes, which they have inherited from their common ancestor. As a result, helping out kin actually increases the chances that copies of genes found in the altruist will be passed on to the next generation. In this way, sociobiologists argue, genes that control altruism could be selected for and increase in frequency in a species.

Criticisms of Sociobiology

Other scientists have criticized sociobiology on several grounds. Critics think that it is not valid to base explanations of human behavior on the behavior of insects. They also criticize the assumption of sociobiologists that genes are more influential than the environment in most behaviors. For example, sociobiologists contend that variation in human behaviors such as aggression (see the Animal Behavior: Aggression (Advanced) concept) can be explained by differences in genes. Most experts on human behavior take the opposite view. They think that variation in aggression and other human behaviors can be explained by differences in environments. They cite evidence showing that environmental factors, such as exposure to violence in the media, can influence how aggressively people behave. Sociobiology has also been criticized for using “just-so” stories to explain animal behavior. A just-so story is an explanation that does not rest on any evidence other than its own internal logic. A just-so story can be created to argue for the adaptiveness and evolution of almost any trait. In fact, different sociobiologists have sometimes explained the same trait with opposite just-so stories. Most of these just-so stories rest on the assumption that behavior is genetically controlled and that it must be adaptive simply because it has not died out. In contrast, critics of sociobiology argue that any explanation of behavior must be based on evidence. The evidence must show that the behavior is genetically controlled and that it results in the production of more offspring. Charles Darwin also invented a few “just-so” stories to explain the evolution of certain organisms. The following

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example appeared in his book, On the Origin of Species, although he later deleted it: "In North America the black bear was seen...swimming for hours with widely open mouth, thus catching, like a whale, insects in the water. Even in so extreme a case as this, ...I can see no difficulty in a race of bears being rendered, by natural selection, more and more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale."

Vocabulary

• altruism: Doing something for others that puts oneself at risk.

• kin selection: Behaviors which sacrifice reproductive success or even survival to promote the survival and reproduction of close relatives, who share a significant proportion of the same genes.

• nature-nurture debate: The debate over the extent to which genes (nature) or experiences in a given envi- ronment (nurture) control traits such as animal behaviors.

• sociobiology: The study of how behavior increases fitness and evolves through natural selection.

Summary

• Whether behaviors are controlled mainly by genes or by the environment is controversial. • A behavior that is at least partly under genetic control can evolve through natural selection. However, being controlled by genes is not the only requirement for a behavior to evolve through natural selection. • Sociobiologists assume that behaviors that persist or increase in frequency must be adaptive.

Practice

Use this resource to answer the questions that follow. "Nature vs. Nurture Revisited" at http://www.pbs.org/wgbh/ nova/body/nature-versus-nurture-revisited.html. Although the completion of the Human Genome occurred in 2001, this topic is still relevant.

1. How many genes does the Human Genome contain? How has this raised doubt as to how much behavior is determined by genes? 2. How might genes give expression to more than one characteristic? 3. How does perfect pitch illustrate the importance of nature and nurture?

Practice Answers

1. Humans only have around 30,000 genes. "We simply do not have enough genes for this idea of biological determinism to be right," asserted Craig Venter, president of Celera Genomics. 2. A conservative estimate is that 30,000 human genes produce ten times as many proteins in the human body. These proteins may have a variety of different effects on the body. 3. Perfect pitch has been shown to be inheritable, but the studies also demonstrate a requirement for early musical training (before age six) in order to manifest perfect pitch. Thus, the environment is responsible for the manifestation of the gene.

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Review

1. What is the major controversy over the origins of animal behavior? 2. If you were a behavioral scientist, how could you set out to prove that a behavior is controlled by genes? 3. How can behaviors evolve through natural selection? 4. What behavior did Darwin think was "actually fatal" to his theory of evolution? 5. What is one explanation of altruism? 6. What are some criticisms that have arisen against sociobiologists?

Review Answers

1. It is not clearly understood just how much genetics and the environment play in the development of certain behaviors. This is known as the nature-nurture debate. 2. Some ethologists have used controlled experiments to investigate the relative importance of genes and the en- vironment in various animal behaviors. An individual is separated from any interaction with other individuals of the same species. If a behavior still appears under these conditions, then it is assumed to be controlled almost completely by genes. 3. Performing the behavior must increase the individual’s chances of surviving and successfully reproducing. It must also be at least partly controlled by genes for it to evolve through natural selection. 4. Darwin had trouble explaining altruism using natural selection. 5. Sociobiologists explain altruism through kin selection, which involves animals sacrificing their own fitness to promote the fitness of their kin, who share many genes with the altruist. 6. Some scientists critique how sociobiologists assume that genes are more influential and provide "just-so" explanations instead of evidence.

31 1.6. Innate Behavior in Animals - Advanced www.ck12.org

1.6 Innate Behavior in Animals - Advanced

• Define innate behavior, and describe examples of innate behavior.

How do this bird know what to do? Nest building is an innate behavior in birds. Innate behaviors are also called instincts.

Innate Behavior

One type of behavior that is clearly controlled by genes and subject to natural selection is innate behavior. Innate behavior is behavior that occurs naturally in all members of a species. For innate behavior to occur, it just needs a

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particular stimulus to trigger it. Innate behavior is also called instinctive behavior. Instinct is the ability of an animal to perform a particular behavior in response to a given stimulus the first time the animal is exposed to the stimulus. In other words, an instinctive behavior does not have to be learned or practiced. Innate behaviors are rigid and predictable. All members of the species always perform an innate behavior in the same way, regardless of the environment. Innate behaviors usually involve basic life functions, such as caring for offspring, so they often are necessary for successful reproduction. If animals do not perform innate behaviors correctly, they are unlikely to pass on their genes to the next generation. http://science.jrank.org/pages/3608/Instinct -Classic-examples-animal-instinct.html

Examples of Innate Behavior

Innate behaviors are well known in many species of birds and insects. For example, chicks in many bird species instinctively open their mouths wide when their mother returns to the nest. In response to this stimulus, the mother instinctively spits up food to feed the chicks. In certain other bird species, including the kelp gull shown in the Figure 1.13, when a mother bird taps on the ground with her beak, her chicks instinctively peck at a red spot on her beak. In response to the pecking, the mother instinctively spits up food to feed the chicks. Another example of innate behavior occurs in honeybees. A honeybee performs a “dance” when it returns to the hive after finding a source of food. The dance “tells” the other bees where to find the food. These innate behaviors in birds and honeybees help the animals performing them survive and reproduce, so they are passed down to future generations. Innate behaviors occur in virtually all species of animals. Generally, in species with lower levels of intelligence, a greater proportion of behaviors are innate. The following behaviors are examples of innate behaviors:

• Web making in spiders. • Nest building in birds. • Fighting among male stickleback fish. • Cocoon spinning in insects such as moths. • Swimming in dolphins and other aquatic species.

A well-studied example of innate behavior occurs in ground-nesting water birds, such as graylag geese shown in the Figure 1.13. If one of her eggs rolls out of the nest, a female graylag goose will instinctively use her bill to push the egg back into the nest. The sight of the egg outside the nest triggers the behavior. This type of innate behavior is also called a fixed action pattern. It involves a fixed sequence of actions. Once a fixed action pattern is triggered by a stimulus, the sequence continues until completed, even if the stimulus is no longer present. For example, if the graylag goose’s egg rolls out of the nest and is picked up and taken away, the goose will continue moving her head as though pushing an imaginary egg. The goose will also try to push any egg-shaped object, such as a golf ball, if it is placed near the nest. She will even push a much larger egg-shaped object, such as a volleyball. In fact, a bigger object will trigger larger movements in response. The behavior of the graylag goose demonstrates that innate behaviors do not always increase an animal’s chances of successfully reproducing. Pushing an egg back into the nest increases the goose’s chances of successfully reproducing, but pushing a golf ball wastes time and energy that could be spent on the actual eggs. Therefore, innate behaviors may be too rigid to be advantageous all the time. They may occur even when they are not appropriate.

Do Humans Have Innate Behaviors?

The only animal species in which the existence of innate behaviors is questioned is Homo sapiens. The drives to eat and mate are probably instincts in humans, but the ways in which humans act upon these drives can be consciously controlled and influenced by the environment. The only human behaviors that are undeniably innate are reflex behaviors, several of which occur in infants. An example is the grasping reflex. In the first few months after birth, infants instinctively grasp objects placed on their palm. Did you (or your healthcare provider) ever strike your bent

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FIGURE 1.13 A female graylag goose is followed closely by her gosling (baby geese).

knee just below the knee cap while you were sitting? If your knee was struck in just the right place, your lower leg automatically swung forward. This is another example of a reflex behavior. Apart from reflex behaviors such as these, the behaviors of humans are primarily acquired or shaped through learning.

Vocabulary

• fixed action pattern: A type of innate behavior that involves a fixed sequence of actions.

• innate behavior: Behavior that occurs naturally in all members of a species and is triggered by a particular stimulus.

• instinct: The ability of an animal to perform a particular behavior in response to a given stimulus the first time the animal is exposed to the stimulus.

Summary

• One type of behavior that is clearly controlled by genes and subject to natural selection is innate behavior. • Innate behaviors are rigid and predictable and usually involve basic life functions, such as caring for offspring, so they often are necessary for successful reproduction. • Once a fixed action pattern is triggered by a stimulus, the sequence continues until completed, even if the stimulus is no longer present. • The only animal species in which the existence of innate behaviors is questioned is Homo sapiens.

Practice

Use this resource to answer the questions that follow. "Fixed Action Patterns: Instinctive Behavior of FAPs" at http ://www.scienceprofonline.org/animal-behavior/fixed-action-pattern-instinctive-behavior-FAP.html.

1. What part of the nervous system is responsible for fixed action patterns?

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2. Which ethologist was a pioneer in studying fixed action patterns? 3. Give an example of a fixed action pattern in humans. 4. What is code breaking, and how have some animals taken advantage of this?

Practice Answers

1. The innate releasing mechanism in the neural network is responsible for fixed action patterns. 2. Tinbergen pioneered the study of fixed action patterns through his observations of graylag geese and red- bellied sticklebacks. 3. The act of yawning is a fixed action pattern because the process must usually run its course and is initiated by certain stimuli, such as other people yawning. 4. Code breaking is the process of stimulating another species to undergo a fixed action pattern. Brood parasitism involves one species laying an egg in another species’ nest and then stimulating the owner into taking care of the offspring as its own.

Review

1. How common are innate behaviors in the animal kingdom? Which animals tend to have a greater number of innate behaviors? 2. How can innate behaviors sometimes be disadvantageous for an individual in terms of reproduction? Give an example based on the graylag goose. 3. What kind of innate behaviors do humans exhibit?

Review Answers

1. Innate behaviors can be found in almost all animals. Species with lower levels of intelligence generally have a greater proportion of innate behavior. 2. Because innate behaviors are so rigid, such behavior can occur when it is not appropriate. The graylag goose will push most round objects into its nest, even though they are not its actual eggs. This behavior wastes time and energy that might have been spent on her actual offspring. 3. Humans seem to only exhibit reflex behaviors, such as the instinctive grasping motion at birth. Other behav- iors, such as the drive to eat and mate, can be consciously controlled.

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1.7 Learned Behavior in Animals - Advanced

• Define learning, and describe different ways that animals learn. • Explain how imprinting occurs, and give examples of imprinting.

How do these baby birds know what to do? Some infant animals are really good at playing the game "Follow the Leader." Some baby animals instinctively follow and become attached to whatever large moving object they first see. The moving object is usually their mother. This is an instinctive behavior that results in imprinting. Becoming imprinted on the mother helps ensure their survival.

Learned Behavior

Learning is a change in behavior that occurs as a result of experience. Compared with innate behaviors, learned behaviors are less rigid. Many learned behaviors can be modified to suit changing conditions. For example, drivers may have to change how they drive (a learned behavior) when roads are wet or icy, otherwise they may risk losing control of their vehicle. Because learned behaviors can be modified when the environment changes, they are generally more adaptive than innate behaviors. Species that are more intelligent typically have a greater proportion of behaviors that are learned rather than innate.

Types of Learning

Animals may learn behaviors in a variety of ways. Some ways in which animals learn are relatively simple. Others are very complex. Types of learning include the following:

• Habituation. • Sensitization. • Classical conditioning. • Operant conditioning.

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• Observational learning. • Play. • Insight learning.

Habituation and Sensitization

One of the simplest ways that animals learn is through habituation. In this type of learning, animals decrease the frequency of a behavior in response to a repeated stimulus. This occurs when the behavior does not result in some type of benefit or reward. Habituation has been demonstrated to occur in virtually every species of animal. It is adaptive because responding to a stimulus when there is no benefit or reward is a waste of energy. An example of habituation is the behavior of certain species of small songbirds when presented with a stuffed owl or similar “predator.” If a stuffed owl is placed in their cage, the birds first respond as though it were a real predator. They act frightened and try to escape. Over time, as the stuffed owl remains in the cage without moving, the birds show less response. They become habituated to the presence of the stuffed owl. A similar example of habituation is when coyotes invade human neighborhoods. They have become habituated to humans in these locations, so they are no longer afraid to approach (shown in the Figure 1.14).

FIGURE 1.14 Coyotes are becoming increasingly ha- bituated to humans, especially when hu- mans feed them, so they are no longer afraid to approach human neighborhoods. This can be quite dangerous, as coyotes are known to attack livestock, pets, and, sometimes, even humans.

Sensitization is the opposite of habituation. In sensitization, an animal learns to react more often or more strongly to a repeated stimulus. For example, exposure to painfully loud sounds causes an animal to respond strongly. The animal may act agitated and try to escape from the source of the sounds. If the loud sounds are followed by lesser sounds that are not painful, the animal may respond to them just as strongly. If this occurs, the animal has become sensitized to sounds. Scientists have demonstrated that sensitization occurs because of changes in nerve cells and nerve pathways (see The Nervous System and The Endocrine System concepts). These changes take place after nerves have been stimulated repeatedly. This sometimes occurs in a person who has had a painful injury. With repeated stimulation of the nerves, sensitization occurs, and the pain continues even after the injury is healed.

Classical Conditioning

Classical conditioning is a type of learning in which an animal learns to associate one stimulus with another. In this type of learning, a stimulus that normally produces a particular behavior is linked with a second stimulus. The second stimulus is something neutral to which the animal does not normally respond. If the animal is repeatedly exposed to both stimuli together, it learns to associate the two stimuli. Because of this association, the animal will

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respond to the second stimulus alone in the same way that it responds to the normal stimulus. A well-known example of classical conditioning is the work of the Russian scientist Ivan Pavlov. In the late 1800s and early 1900s, Pavlov investigated behavior in dogs. As mentioned above, dogs instinctively drool when they see or smell food. They also drool when they think that they are about to be fed. Pavlov conditioned dogs to drool when they heard a particular sound, such as a bell or whistle. He made the sound just before he fed the dogs, and the dogs learned to associate the sound with food. In a short time, they started drooling as soon as they heard the sound. Because of Pavlov’s research in this area, classical conditioning is sometimes called Pavlovian conditioning. Another example of classical conditioning is called conditioned taste aversion. Animals may learn not to eat certain foods if they have ever become ill after eating them. This is an adaptive trait because it may help them avoid foods that are poisonous. For example, animals that vomit after eating a particular type of berry may learn to avoid eating berries of this type in the future. They become conditioned to avoid the berries because they have learned to associate the berries with vomiting.

Operant Conditioning

In operant conditioning, an animal learns either to perform a behavior that is rewarded or to stop performing a behavior that is punished. One of the first scientists to investigate this type of learning was Edward Thorndike. In the early 1900s, Thorndike investigated learning in cats. He placed the cats in “puzzle boxes” that he had constructed. It was difficult for the cats to find their way out of the mazelike boxes, but they kept trying because they did not like being confined. When first placed in one of the boxes, a cat needed a long time to find the way out. However, the cat needed less and less time with repeated trials. Through trial and error, the cat learned how to escape from the box. Beginning in the 1930s, another scientist, named B.F. Skinner, did similar research with rats. He placed rats in a box containing a bar. If the rats stepped on the bar, a pellet of food was released. When first placed in the box, a rat did not know that stepping on the bar would release a food pellet. Sooner or later, the rat would accidentally step on the bar and be rewarded with food. Before long, the rat learned that a food pellet would be released each time it stepped on the bar. After that, it stepped on the bar repeatedly in order to get the food. In operant conditioning, the reward may be something positive that is gained (food in the case of Skinner’s rats) or something negative that is avoided (confinement in the case of Thorndike’s cats). In either case, a behavior is learned through trial and error because it is reinforced by a reward. Operant conditioning can also use punishment to discourage a behavior. A punishment is something unpleasant or painful. An example of this occurs when cows are placed in a pasture surrounded by an electrified fence. The fence alone is inadequate to keep them in the pasture. It is just a single strand of wire strung between posts that are several feet apart. However, when the cows touch the fence, they receive an electric shock. They soon learn from the punishment (the shock) to stay away from the fence (the behavior). Can you think of a behavior that you learned from operant conditioning? Maybe you learned that taking notes in class results in better grades on exams. Getting better grades (the reward) may have reinforced note taking (the behavior). You probably also learned to avoid behaviors that were punished. For example, when you were younger, fighting with a sibling may have resulted in a time-out. After repeated time-outs (the punishment), you may have learned to avoid fighting with your sibling (the behavior). Did you ever touch your tongue to a metal object on a cold winter day? If you did, then you know that your tongue “sticks” to the metal and that pulling your tongue away from the metal is very painful. If you learned to avoid this behavior because of the pain, then this is also an example of operant conditioning.

Observational Learning

Perhaps you learned to avoid touching your tongue to a freezing metal object because you saw another child do it and realized how painful it was from the other child’s reaction. If so, then you learned not to do it yourself through observational learning. This type of learning involves observing the behavior of another individual and

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either copying the behavior or avoiding it. Most studies of observational learning have focused on behaviors that are copied. Canadian psychologist Albert Bandura is world renowned for his investigations of observational learning in humans. According to Bandura, learning a behavior by observing it in someone else requires four conditions to be met:

1. An individual (the observer) must pay attention to the behavior of another individual (the model). 2. The observer must be able to remember what the model has done. 3. The observer must have the ability or skills to perform the behavior. 4. The observer must be motivated and have the opportunity to perform the behavior.

Because of these conditions, observational learning requires considerable intelligence and is found most often in humans. However, observational learning has also been observed in many other species of animal. For example, wolves and other predatory animals that hunt in packs learn hunting skills through observational learning. Young animals observe and copy the behavior of older animals when they hunt together. Another example of observational learning involves Japanese macaques (a species of monkey shown in the Figure 1.15). In the 1960s, a group of researchers started placing sweet potatoes on a sandy beach to lure macaques out of a nearby forest. Soon the macaques started coming out on the beach to eat the sweet potatoes. At first, the macaques just brushed the sand off the sweet potatoes before eating them. Then, about a year later, a female macaque was observed washing sweet potatoes in the ocean before eating them. Her behavior was observed and copied by other macaques in the troop. Before long, all the macaques in the troop were washing their sweet potatoes in the ocean. When these monkeys gave birth, their offspring also learned this behavior by observing and copying the behavior of their parents and other adults. Many human behaviors are learned by children through observation and mimicking the behaviors of the people around them. What behaviors have you learned in this way? For example, as a young child, did you learn how to tie your shoes by watching your parents or older siblings tie their shoes? Did you learn how to solve a math problem by watching your teacher solve one like it? Did you learn how to play a video game by observing a friend play the game? If so, you were learning the behaviors through observational learning.

Play

Playing a video game is just one of the many ways in which humans may play. Play involves behaviors that have no particular goal except enjoyment or satisfaction. Play is not restricted to humans. Most mammals and many birds also play when they are young. The drive to play seems to be innate in many species. You have probably seen kittens, like the one in the Figure 1.16, playing with a toy. Play may also involve other animals. For example, kittens often play with their littermates. Like other predatory animals —including lions and some species of bears —kittens chase, pounce on, and wrestle with one another. Prey animals such as deer and zebras play somewhat differently. They run, leap, and kick their hind legs when they play. Play is one way that young animals develop the skills needed during adulthood. How does playing with a toy prepare this kitten for catching mice as an adult? Play has risks and costs. It may increase exposure to predators and lead to injury. It also requires energy. For play to have evolved, it is likely to have significant benefits that outweigh these drawbacks. How could play be beneficial? Play is actually a form of learning. Through play, young animals learn important skills. By chasing, pouncing on, and wrestling with one another, kittens and other young predators are learning how to catch prey (see the adult cat in the Figure 1.17). By running, leaping, and kicking their hind legs, young deer, zebras, and other prey animals are learning how to escape or ward off attacks from predators. Play can also be beneficial by helping young animals develop muscles and improve their physical fitness.

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FIGURE 1.15 Japanese macaques have learned to wash sweet potatoes in the ocean before eating them. This behavior was first noted in one macaque. Other macaques in the troop soon learned the behavior through observational learning.

FIGURE 1.16 Kittens often play with toys.

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FIGURE 1.17 This adult cat is trying to catch a mouse.

Insight Learning

Several species of animals have been observed using insight learning. Insight learning is the use of past experiences and reasoning to solve problems. Unlike operant conditioning, insight learning does not involve trial and error. Instead, an animal thinks through a solution to a problem based on previous experience. The solution often comes in a flash of insight. Insight learning requires relatively great intelligence. Species most likely to learn in this way

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include species of apes (chimpanzees, gorillas, and orangutans), crows, and humans. Examples of insight learning in apes in the wild include chimpanzees "fishing" for termites. The animals place a “tool” such as a twig in a hole of termite mound, and the termites crawl onto the twig. Then the chimpanzee withdraws the twig from the hole and eats the termites. Chimpanzees may also use leaves to sop up drinking water and rocks to smash nuts. They have even been observed sharpening sticks with their teeth and using them as spears to kill small animals for food. Another example of tool use in chimpanzees in the wild is shown in the Figure 1.18. Gorillas may use tools to solve problems as well. For example, they have been observed using small branches as walking sticks and as measuring sticks to test the depth of water before wading through it. Orangutans use small sticks to get at edible seeds inside prickly fruits without being pricked. They may also use leaves to make rain-hats and roofs over their sleeping nests.

FIGURE 1.18 This chimpanzee is using a stick as a tool to obtain food that is out of reach. This is an example of insight learning.

Crows and related species of birds have large brains relative to their body size and are noted for their intelligence. They also use insight learning to solve problems. For example, a crow was observed placing nuts on the crosswalk of a busy street, where cars would drive over them and crack the shells. After the traffic light turned red, the crow entered the street to retrieve the nutmeats. Crows have also been seen working together to eat food scraps in a trashcan. Some of the crows propped up the lid of the can, while the others ate the scraps inside. Then the crows switched places so that all of them had a chance to eat. Homo sapiens have larger brains (for their body size) and are more intelligent than any other species. Humans are also known for their incredible ability to use insight learning to solve problems, ranging from learning how to start a fire to putting a man on the moon. Think about problems you have solved in the past. Perhaps you learned how to use a new computer program through reasoning and past experience with other computer programs. You may also have used reasoning and previous experience to solve math problems or attain the next level of a video game. For a video on a chimpanzee demonstrating insight learning, visit http://www.youtube.com/watch?v=fPz6uvIbWZE

MEDIA Click image to the left or use the URL below. URL: http://www.ck12.org/flx/render/embeddedobject/139430

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Behavior Influenced by Both Genes and Learning

The ability to learn behaviors in all these different ways depends on intelligence, which is at least partly determined by genes. However, the environment also plays a role in learned behaviors. For example, classical conditioning depends on the presence of a suitable reward or punishment, and observational learning depends on the behavior of potential models. A type of behavior that clearly shows the influence of both genes and environment is imprinting. Like instinct, imprinting results in fixed, lifelong behaviors after exposure to a stimulus. Also like instinct, imprinting leads to full- blown behaviors after the first exposure to the stimulus. However, the environment also plays a role in imprinting. The animal must be exposed to the proper stimulus during a period of development called the critical period. This period is commonly a few days or weeks in early life. In addition, the type of stimulus that triggers an imprinted behavior determines how the behavior is performed. Therefore, imprinting depends on both instinct and learning and may vary with the environment. See also http://www.bookrags.com/research/imprinting-ansc-03/. Imprinting often occurs in species in which the young are fairly mobile early in life. Animals in which imprinting occurs include species of aquatic birds and herbivorous mammals. In these species, baby animals instinctively follow and become attached to whatever large moving object they first see during the critical period. The moving object is usually their mother. Becoming imprinted on the mother helps ensure their survival. They are unlikely to wander off after they have become imprinted on her. However, the infants may become imprinted on any other large moving object if they see it first during the critical period. This could be a balloon blowing across the ground or a human walking nearby. Once attachment to the object occurs through imprinting, the behavior is fixed and cannot be changed. The animal remains attached to the object for life. Moose calves ( Figure 1.19) also imprint on their mothers. If a moose calf were to imprint on a human, it would continue its attachment to humans rather than members of its own species. As an adult, the moose would be likely to try to attract humans, rather than other moose, as mates.

FIGURE 1.19 If a human were the first large moving object a moose calf saw during a critical period in its development, the moose calf would imprint on the human.

There are many other examples of imprinting in animals:

• Puppies must be exposed to humans within the first two or three months of life, or they will never become socialized and be suitable as human companions. • In birds called zebra finches, chicks raised with another species of bird, rather than with other zebra finches,

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will imprint on birds of the other species. As adults, the finches will try to mate with birds of the other species instead of with other zebra finches.

From all of these examples, it appears that imprinting may or may not be adaptive. Whether it is adaptive depends on the timing and type of stimulus that triggers the behavior. If the stimulus occurs during the critical period and is appropriate, then imprinting is likely to be adaptive and increase the fitness of the imprinting animal. If the stimulus occurs outside of the critical period or is inappropriate, then imprinting may not be adaptive and may reduce fitness.

Vocabulary

• classical conditioning: A type of learning in which an animal learns to associate one stimulus with another.

• habituation: A type of learning in which an animal decreases the frequency of a behavior in response to a repeated stimulus.

• imprinting: A type of fixed behavior that occurs only after an animal has been exposed to a particular type of stimulus during a critical period of its development.

• insight learning: A type of learning in which an animal uses past experiences and reasoning to solve problems.

• learning: A change of behavior that occurs as a result of experience.

• observational learning: A type of learning in which an individual learns by observing the behavior of another individual and either copies the behavior or avoids it.

• operant conditioning: A type of learning in which an animal learns either to perform a behavior that is rewarded or to stop performing a behavior that is punished.

• play: Behaviors that have no particular objective in themselves, but seem to give enjoyment or satisfaction and help young animals learn important skills.

• sensitization: A type of learning in which an animal learns to react more often or more strongly to a repeated stimulus.

Summary

• Learning is a change in behavior that occurs as a result of experience, and learned behaviors are usually less rigid than innate behaviors. • Types of learning include habituation, sensitization, classical conditioning, operant conditioning, observa- tional learning, play, and insight learning. • One of the simplest ways that animals learn is through habituation, where animals decrease the frequency of a behavior in response to a repeated stimulus. • Observational learning and insight learning are usually observed in animals with higher levels of intelligence.

Practice

Use this resource to answer the questions that follow.

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Practice Answers

Review

1. What type of learning has been studied in almost all animals? 2. What type of learning is conditioned taste aversion? How does it aid in survival? 3. What is the difference between operant and classical conditioning? 4. What are the four conditions for observational learning that were laid out by Albert Bandura? 5. Which animals are known for insight learning? Why does this type of learning usually involve higher intelligence? 6. When does imprinting usually occur? What does it require?

Review Answers

1. Habituation has been demonstrated in almost every species because responding to a stimulus that provides no benefit is a waste of energy. 2. Conditioned taste aversion is an example of classical conditioning where an animal learns not to eat certain foods that make them become ill. It prevents animals from eating poisonous food in the future. 3. Classical conditioning involves an involuntary association between two stimuli. Operant conditioning involves voluntary behavior in order to achieve a reward. 4. Observational learning requires that the observer pay attention to the model, remember what was observed, have the ability to repeat the behavior, and is motivated to perform the behavior. 5. Species known for insight learning include apes, crows, and humans. Because the solution to a problem is solved using prior experience and reasoning, this type of learning usually involves higher intelligence. 6. Imprinting usually occurs in early development, during a period known as the critical period. Exposure to a proper stimulus during the critical period is required for imprinting to occur.

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1.8 Social Behavior in Animals - Advanced

• Define concepts associated with social living, describe eusociality, and give examples of animal cooperation.

Teamwork? Yes. Some animals, as seen with these ants here, practice teamwork or cooperation to complete a task. Here they are working together to move this piece of food.

Social Living

Social animals are animals that are highly interactive with other members of their own species. They have a recognizable and distinct society. A society is a group of individuals of the same species that are organized in a cooperative manner. Social living is most common in insects, birds, and mammals. Ants, bees, crows, penguins, wolves, and humans are just a few examples of animals that are social. Social behavior is behavior that is directed toward or takes place between members of the same species. (Behaviors such as predation, which involve members of different species, are not usually considered social behaviors.) Social behaviors involve more than just reproducing and caring for offspring. For example, individuals in a social group may help defend or share food with one another. Types of social behavior include cooperation and communication, both of which are discussed below.

Eusociality

Eusociality is an extreme form of social living that occurs in some animal species. Eusocial species have highly organized societies, in which individuals are specialized for different roles. Members of the group cooperate to care for the young, find food, and perform virtually all other important functions. Many species of insects are eusocial, including the majority of ant, termite, and bee species. A few species of crustaceans and mammals are eusocial as well. Ants, like the ones in the Figure 1.20, are known for their highly organized societies, which are called colonies. An ant colony may contain several million ants yet appear to operate as a single unit. The colony makes a nest in the

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soil. This is typically a low mound on and just below the ground with a system of tunnels and chambers (rooms). Most of the ants in a colony are females that never reproduce because they are infertile. The infertile females are divided into castes, or specialized forms. Some belong to the soldier caste and defend the nest against predators, including other insects and birds. The majority of infertile females belong to the worker caste and perform all the rest of the labor for the colony. They build and maintain the nest, forage for food outside the nest, feed and care for the young, and tend to the queen. The queen is the only fertile female and is larger than the other ants. In most ant species, there is just one queen per colony. The queen’s primary function is to lay eggs after mating with one or more fertile male ants, called drones. The drones have no other role and usually die soon after mating. The queen may live as long as 30 years and lay up to 3 or 4 millions eggs each month.

FIGURE 1.20 These ants belong to an ant colony that may number in the millions. The only ants that actually leave the colony’s nest are worker ants.

Termites also live in colonies that may contain several million individuals. Their nests, called mounds, are relatively complex structures, like the one shown in the Figure 1.21. Depending on the species, termite mounds may be more than 10 meters (30 feet) in height, although most are not this tall. A typical colony consists of nymphs, which are semi-mature young, infertile workers and soldiers, and fertile males and females, often referred to as kings and queens. There may be just one king and queen in a colony, or there may be several. Like worker ants, worker termites build and maintain the nest, forage for food, feed and care for the young, and tend to the queen. Soldier termites are specialized to defend the mound from predators, which are most often ants. For example, the soldiers have large jaws for biting. In fact, their jaws may be so large that the soldiers are unable to eat unless fed by workers. Soldiers also have hard heads that they use to block tunnels and keep out invading ants. The primary role of the kings and queens is to reproduce. A mature queen termite may lay more than 2,000 eggs a day. Aside from insects, eusociality is relatively rare in animals. Some shrimp are eusocial, but the only known eusocial vertebrates are mammals called mole rats. There are two species of mole rats. Both species live in burrows in dry areas of sub-Saharan Africa. They form colonies of several dozen individuals each. Each colony has one fertile female (the queen) and one to three fertile males with whom she mates. The other members of the colony are infertile workers. Different workers specialize in different jobs. For example, some workers mainly make burrows, and others primarily defend the colony from predators.

Cooperation

In eusocial species, a colony has a clear division of labor. Only by working together can individual animals perform all the necessary functions of the colony. Working together with others instead of working alone is called cooperation. Cooperation is a hallmark of eusocial animals. It allows colonies to live in environments and exploit food sources that an individual acting alone could not. This is demonstrated by the following two examples of cooperative behavior. First, when a group of ants moves a much larger prey insect back to the nest to feed the colony ( Figure 1.22). A single ant is too small to perform this task alone. Second, when hundreds of ants join together

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FIGURE 1.21 This termite mound stands several meters in height. It is called a cathedral mound because of its shape.

to form a “raft” that floats on the water. This cooperative behavior helps the ants survive floods that would drown individual insects. Cooperation occurs in many other species besides eusocial species. For example, in some species of crows, young males serve as “nannies,” helping to take care of the younger offspring of their parents. In lions, males cooperate to defend the pride, and females hunt and share the kill with other pride members. In meerkats, young females that do not yet have offspring take care of the pups while their parents are away from the burrows gathering food. Some species of groupers, which are fish, hunt cooperatively in pairs. Wolves and some other mammalian predators hunt cooperatively in packs. See also http://www.usatoday.com/news/science/aaas/2002-04-05-coop-behavior.htm

Vocabulary

• cooperation: The behavior that involves working together with others instead of working alone.

• eusociality: An extreme form of social living where individuals become specialized for specific tasks.

• social animals: Animals that are highly interactive with other members of their own species.

• social behavior: Behavior that is directed toward or takes place between members of the same species.

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FIGURE 1.22 These ants are working together to drag their much larger insect prey back to the nest. This is an example of cooperation.

FIGURE 1.23 The brown “substance” floating on the water in this photograph is actually made up of hundreds of ants. This is another ex- ample of cooperation. By joining together, all of the ants are able to float. A single ant would not be able to stay afloat and would probably drown.

• society: A group of individuals of the same species that are organized in a cooperative manner.

Summary

• Social animals are animals that are highly interactive with other members of their own species. • Eusocial species have highly organized societies, in which individuals are specialized for different roles. • Aside from insects, eusociality is relatively rare in animals. • Cooperation is a hallmark of eusocial animals but also occurs in other species.

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Practice

Use this resource to answer the questions that follow. "An Introduction to Eusociality" at http://www.nature.com/sc itable/knowledge/library/an-introduction-to-eusociality-15788128

1. What four traits do eusocial animals share? 2. What is the difference between primitive and advanced eusocial organisms? 3. How does the order hymenoptera determine sex? 4. What are some advantages of eusociality?

Practice Answers

1. Eusocial animals have adults that live in groups, cooperative care of offspring, reproductive division of labor, and overlap of generations. 2. Whereas primitively eusocial organisms show no morphological difference between reproductives and non- reproductives, advanced eusocial organisms may have different morphologies for reproductive and non-reproductive individuals and even specialization within the non-reproductives. 3. Hymenoptera have a haplodiploid sex determination system (whereby females arise from fertilized diploid eggs and males arise from unfertilized haploid eggs), which may contribute to kin selection, favoring altruistic behavior in this group. 4. Eusocial animals benefit from defense against predators, advantages against competitors, and the possibility of inheriting the nest.

Review

1. What is eusociality? What animals exhibit eusociality? 2. Give an example of cooperation in mammals.

Review Answers

1. Eusociality is an extreme form of social living that is characterized by highly organized societies in which individuals are specialized for different roles. Most eusocial species are insects, although some shrimp and mole rats exhibit eusociality as well. 2. Lions exhibit cooperation, as males defend the pride while females hunt. In meerkats, young females tend to the offspring of others.

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1.9 Communication Behavior in Animals - Ad- vanced

• Describe different ways that animals communicate, including auditory and visual communication, display behaviors, and pheromones.

What reptile has a built-in communication device? The rattle of this rattlesnake is used to communicate with other species. The rattle is a warning device for predatory animals that might be a threat to the rattlesnake. It produces a signal to drive them away.

Communication

A necessary condition for cooperation among members of a species is communication. Communication —in the context of animal behavior —refers to any process or behavior that allows organisms to send and receive information. When you think of communication, you many think of human language, but communication is not limited to humans. Every transfer of information between living organisms is an example of communication. Animal communication most often takes place between members of the same species. This is called intraspecies (“within species”) communication. Many examples of intraspecies communication are described below. Animal communication may also take place between members of different species. This is called interspecies (“between species”) communication. An example of interspecies communication is the wriggling “worm” that protrudes from the head of an anglerfish (see the Aquatic Biomes: Marine (Advanced) concept). It serves as a lure to other species of fish. When they try to eat the “worm,” they are captured by the anglerfish. The rattle of a rattlesnake is also an example of interspecies communication. The rattle warns potential predators to stay away from the rattlesnake, which has a poisonous bite. Intraspecies communication is demonstrated by the waggle dance of the honeybees, discussed in the Animal Behavior: Innate (Advanced) concept.

Auditory Communication

The rattle of a rattlesnake is an example of auditory communication. Auditory communication is the use of sounds to send and receive information. Auditory communication is particularly important in birds. They use sounds to

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communicate warnings, attract mates, signal other birds to flock together, and for other important purposes. Some of the sounds made by birds are called birdsongs. Birdsongs are relatively long and melodic and are always more or less the same in a given species (see the Understanding Bird Song Table in the Animal Behavior: Introduction (Advanced) concept). Many other species also use auditory communication:

• Monkeys cry out a warning when a predator is near. The warning call gives other members of the troop a chance to escape. Vervet monkeys have different calls, depending on the predator. • Bullfrogs croak to attract female frogs as mates. In some frog species, the sounds can be heard up to a mile away. • Gibbons use calls to mark their territory. This helps to keep potential competitors away. A paired male and female and even their young may make the calls together.

Visual Communication

In addition to calls and other sounds, gibbons and many other animals use visual communication. Visual communi- cation involves signals that can be seen. Visual communication may include gestures, facial expressions, and body postures. Like gibbons, most other primates use visual communication. For example, chimpanzees communicate a threat by raising their arms, slapping the ground, or staring directly at another chimpanzee. The “grin” on the face of the young chimpanzee shown in the Figure 1.24 actually communicates fear and submission. The “fear grin” is used by young chimpanzees when approaching a dominant male in their troop.

FIGURE 1.24 The “fear grin” on this chimpanzee’s face shows that he is willing to submit to a dominant male.

In many species of monkeys, including baboons and some macaques, the skin around a female’s genitals periodically becomes swollen and brightly colored (usually bright red). This occurs when she is fertile and receptive to mating. This communicates to male monkeys that she may be approached for mating.

Human Communication

Human communication can be considered to be a highly developed form of animal communication. Humans show exceptional skill in communicating with one another through both auditory and visual means. In fact, the human

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ability to communicate may be one of the species’ most important capabilities. It is also key to most of the species’ achievements. The most significant means of human communication is language. Language is the use of symbols to communicate. Although some other animal species are said to communicate through language, human language is far more complex than any other type of animal communication. Words in human languages are symbols that represent objects, actions, emotions, or ideas. All humans, regardless of their genetic makeup or the culture into which they were born, are able to learn any human language, especially if they are exposed to it early in life. During the first few years after birth, humans can learn a language without any formal education and long before they develop many other mental abilities. All it takes is being surrounded by the speech of parents or other people and practicing the language. Humans also communicate a great deal of information visually. Like other primates, humans use facial expressions, gestures, and body postures to send and receive information. In humans, this is called body language. Examples of body language include smiling, shrugging the shoulders, and shaking the head. Can you think of other exam- ples? What body language would you use to express affection? To express fear? Another way in which humans communicate visually is by writing and reading language or using images such as pictures and charts.

Display Behavior

Without communication, social living would not be possible. In fact, many social behaviors serve mainly as a means of communication among members of a species. A special type of social behavior that many species use for communication is called display behavior. Display behavior is ritualized behavior that communicates specific information. A ritual is a fixed set of actions that is symbolic. In other words, the set of actions stands for something else. For example, the honeybee “dances” that were described in the Animal Behavior: Innate (Advanced) concept communicate to other members of the colony where to find food. Another example of display behavior is a peacock (male peafowl) fanning out his big ornamental tail feathers (see the Figure 1.25). This display may be used to warn other peacocks to stay away or to attract peahens (female peafowls) for mating. Many species of birds perform “dances” to attract mates. Display behaviors are described in more detail in later sections in the contexts of aggression and mating.

FIGURE 1.25 By displaying his large fan-shaped tail, this peacock is trying to communicate to peahens that he is an attractive mate. The display may also “tell” other peacocks to stay away.

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Pheromones

Another way many animals communicate is with pheromones. Pheromones are chemicals, secreted by special glands, that trigger responses in other organisms, usually members of the same species. The other organisms smell the pheromones or detect them in some other way. Pheromones are especially important in eusocial insects such as ants and bees, but they are also common in mammals. Pheromones may be secreted in urine, feces, or sweat. For example, when male dogs urinate on fire hydrants or trees, they are using pheromones in urine to mark their territory so other dogs will stay away. Pheromones may also be secreted directly on the ground, on objects, or on other organisms. Ants secrete many different pheromones, and they use their antennae to detect pheromones secreted by other ants. In fact, pheromones explain how ants are able to cooperate and maintain their complex, well-organized societies. Different ant pheromones have different purposes. Some attract mates, others signal all the ants in the colony to come together, and still others warn of danger. For example, when any potential danger —from a spider to a lawnmower —threatens an ant colony, the first ant to detect the threat will secrete a warning pheromone that alerts all the other ants of the danger. Several different pheromones are secreted only by the queen of the colony. One of these prevents young female ants from becoming fertile. When the queen dies and stops producing this pheromone, young females can become fertile, and one is raised by the workers to become the new queen. Other ant pheromones are used to mark trails. When an ant finds a source of food, it marks its trail on the way back to the nest by secreting a pheromone on the ground. Other ants follow the pheromone trail to the food source. On their way back to the nest, they reinforce the trail by secreting more of the pheromone. This continues until the food is gone. Insect pheromones are used to trap insect pests, including Japanese beetles and gypsy moths. For example, a pheromone that Japanese beetles secrete to attract mates is placed on bag traps. Japanese beetles are attracted by the pheromone and fly into the bags. They are unable to get out again because of the way the bags are constructed. Bees are also well known for communicating with pheromones. Like ants, bees use pheromones for a variety of purposes. For example, honeybees release pheromones to mark both food sources and their hives. Other pheromones stimulate bees in a hive to group together in a swarm, like the one shown in the Figure 1.26. Like a queen ant, a queen bee produces a pheromone that interferes with the reproductive systems of other females in the colony. This ensures that the queen is the only fertile female in the hive. The same pheromone also attracts drones to the queen for mating.

FIGURE 1.26 This swarm of bees is preparing for flight. Pheromones from other bees in the hive signaled the bees to swarm.

Some studies suggest that humans secrete pheromones that influence the behavior of other humans. For example, when mature females live in close quarters, such as college dormitories, their menstrual cycles may become synchro-

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nized. In other words, after awhile, their menstrual periods start and stop at the same time. This has led researchers to speculate that human females secrete pheromones around the time of menstruation that influence the menstrual cycles of other females with whom they have close contact. A similar phenomenon occurs in mice. Female mouse reproductive cycles are regulated by pheromones secreted by male mice.

Vocabulary

• body language: The use of facial expressions, gestures, and body postures to send and receive information.

• communication: Any process or behavior that allows organisms to send and receive information.

• display behavior: A ritualized behavior that communicates specific information.

• language: The use of symbols to communicate.

• pheromones: Chemicals that are secreted by special glands and trigger responses in other organisms.

• ritual: A fixed set of actions that is symbolic (stands for something else).

Summary

• Communication is necessary for cooperation among members of a species. • Forms of intraspecies communication include auditory, visual, display rituals, and pheromones. • Examples of animals that use auditory communication include monkeys, bullfrogs, and birds.

Practice

Use this resource to answer the questions that follow. "An Introduction to Animal Communication" at http://www.n ature.com/scitable/knowledge/library/an-introduction-to-animal-communication-23648715.

1. Why is auditory communication very common among animals? 2. What importance does tactile communication have? 3. What are some important functions of communication?

Practice Answers

1. Sound can be adapted to a variety of different environmental situations whereas visual communication is usually reserved for daylight. 2. Tactile communication is often very important in building and maintaining relationship among social animals. Chimpanzees that regularly groom other individuals are rewarded with greater levels of cooperation and food sharing. 3. Animal communication plays important roles in reproduction, resolving conflicts (often territorial conflicts), relocating young, conveying information about potential predators, and maintaining group cohesion.

Review

1. What is the difference between intraspecies communication and interspecies communication? Give examples of both.

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2. Give an example of each of the following: a. Auditory communication. b. Visual communication. c. Display behavior. d. Pheromones. 3. Do humans communicate using pheromones?

Review Answers

1. Intraspecies communication is communications within the same species (e.g. birdsongs or a bullfrog’s croak). Interspecies communication is communication between different species (e.g. the rattle of a rattle snake or the lure of an anglerfish). 2. Examples include: a. Auditory: birdsong, bullfrog croak, language. b. Visual: "fear grin" of chimpanzees, body language of humans. c. Display Behavior: honeybee "dances," the colorful display of a peacock. d. Pheromones: dogs urinating on fire hydrants, ants marking trails. 3. Some studies suggest that humans secrete pheromones that influence the behavior of other humans. For example, when mature females live in close quarters, such as college dormitories, their menstrual cycles may become synchronized. Nothing is conclusive however.

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1.10 Animal Migration - Advanced

• Describe how and why migration occurs.

The Great Migration happens every year. Why? Each year, around 1.5 million wildebeest and 300,000 zebra (along with other antelope) gather up their young and start their long trek north from Tanzania’s Serengeti Plains to Kenya’s Masai Mara National Reserve. They go in search of food and water. Their migration runs in a clockwise circle and the animals cover a distance of around 1800 miles. It’s a tough journey, and every year an estimated 250,000 wildebeest don’t survive.

Migration

In addition to reproductive cycles, animals have other behaviors that occur in regular cycles. One type of cyclic behavior is migration. Other cyclic behaviors are called circadian rhythms. Migration usually refers to seasonal movements of animals from one area to another, typically over long distances. One area is often a breeding site. Migration occurs mainly in birds, fish, insects, and some ocean organisms, including whales. Migration is an innate behavior, but it generally occurs in response to predictable changes in the environment. For example, in the northern temperate zone, bald eagles, which prey on fish, migrate south when ponds and lakes freeze over in the winter. Many other birds also migrate to milder climates from areas with harsh winters, where little food is available. Some species travel incredible distances during these migrations. The Figure 1.27 shows migration routes of birds called bar-tailed godwits. These birds make both the longest nonstop flights of any bird and the longest journeys without food of any animal. Their migration routes are almost entirely over the Pacific Ocean. The birds fly from the Arctic or other areas in the far North (where they breed) to New Zealand or even farther south. They have been known to travel more than 11,000 kilometers (over 6,800 miles) in just nine days. How fast, on average, do they fly to cover this much distance in this amount of time? Some species of whales migrate seasonally as well. Gray whales have the longest known migration route of any whale or other mammal. In the summer, one group of gray whales lives in the Bering Sea near Alaska. Beginning

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FIGURE 1.27 This map shows the migration routes of birds called bar-tailed godwits. In their seasonal migration, they travel farther without feeding than any other species of animal. They also travel fast, given the distance and number of days they fly. For example, traveling over 6,800 miles in nine days requires an average speed of more than 31 miles per hour.

in October, these whales head south, traveling along the western coast of both Canada and the United States. By mid-December, they can be seen off the California coast between Monterey and San Diego. By late December, the whales begin arriving at their destination: the warm waters near Mexico’s Baja Peninsula. The entire trip covers about 10,000 kilometers (6,000 miles). The whales travel day and night and average almost 130 kilometers (80 miles) per day. Once they arrive at their destination, pregnant females give birth, and females that are not pregnant seek males for mating. Migrating to and from areas that are thousands of kilometers apart requires several abilities. Animals must be able to determine their current location, the location of their destination, and how to get from one location to the other. Many species of migratory birds determine the direction in which to fly based on cues such as Earth’s magnetic lines, the position of the sun, or the direction of prevailing winds. In addition to determining the correct direction, they must know how far or how long to travel in that direction. Other species of birds follow landmarks on Earth’s surface, such as rivers, coastlines, or mountain ridges. See 60 Minutes: The Great Migration at http://www.cbsnews.com/video/watch/?id=5362301n for additional information on the great wildebeest migration.

Vocabulary

• migration: The direct, often seasonal movement of a species or population.

Summary

• Migration occurs mainly in birds, fish, insects, and some ocean organisms, including whales. • Migration is an innate behavior, but it generally occurs in response to predictable changes in the environment. • Migrating to and from areas that are thousands of kilometers apart requires several abilities, including the

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ability to determine one’s current location, the location of one’s destination, and how to get from one location to the other.

Practice

Use this resource to answer the questions that follow. "How Animal Migration Works" at http://science.howstuffw orks.com/zoology/all-about-animals/animal-migration.htm

1. What might cause partial migrations? 2. What are some benefits that animals gain by migrating to a breeding site? 3. If an animal migrates in the winter, what migratory cues might the animal be receiving? 4. Explain the two competing theories regarding how migration evolved in animals. 5. How did scientists prove that loggerhead sea turtles migrate along their 8,000-mile migration route using Earth’s magnetic field?

Practice Answers

1. Partial migration is when some members of a species migrate while others stay put. This usually occurs when the species’ range is large enough that some individuals live someplace that is always relatively warm, while others live in a temperate region that gets too cold in the winter. An example of this are Barn owls. 2. Breeding sites usually allow the young to be born in regions with richer food sources and less dangerous predators. 3. There are a variety of migratory cues that might stimulate the animal to migrate, including the shortening of the photoperiod, a drop in temperature, or other internal cues such as circannual rhythms. 4. One theory postulates that population pressure drove some individuals further north during warm months, when the area is still hospitable. When winter came, they were forced to temporarily relocate to warmer areas. Another theory postulates that northern latitudes were originally more hospitable but grew colder due to climate change, forcing species to head south periodically. 5. Scientists subjected loggerhead sea turtles to a variety of magnetic fields that differed from the earth’s own field. The turtles that encountered these different fields went off course. Exposure to a magnet that mimicked the earth’s field put them back on course, proving that turtles can somehow detect Earth’s magnetic field and use this to navigate.

Review

1. What are some common reasons for animal migration? 2. What animal takes the longest journey without food? What is the farthest mammalian migration? 3. How do migratory birds manage to determine their direction and how long they have traveled?

Review Answers

1. Animals usually migrate in order to reach either their breeding site or milder climates where food is more plentiful. 2. The bar-tailed godwits travel the farthest without food out of all animals (over 6,800 miles). Gray whales have the longest migration route of any mammal (about 6,000 miles). 3. Many migratory birds determine their direction using the Earth’s magnetic lines, the position of the sun, or the direction of prevailing winds. They determine how long to travel using landmarks on Earth’s surface.

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1.11 Circadian Rhythms - Advanced

• Define and describe circadian rhythms and biological clocks, and explain what controls them.

What time do you get tired? Everybody falls asleep. Your body needs to rest and recover from the day’s activities. Usually you get tired around the same time every day. This happens because processes in your body occur in a 24-hour cycle.

Circadian Rhythms

Migration is a behavior that usually occurs seasonally. Certain other behaviors, as well as many biological processes, have daily cycles. Circadian rhythms are regular changes in the biology and behavior of individuals that occur in 24-hour cycles. The term circadian comes from Latin words that mean “around a day.” Circadian rhythms occur in virtually all animals. In fact, they occur in most living organisms. In humans, all of the following biological characteristics or processes have roughly 24-hour cycles:

• Brain wave activity. • Hormone secretion. • Urine production. • Blood pressure. • Body temperature.

For example, the average adult human temperature changes in a regular way each day. It reaches its minimum in the middle of the night or very early in the morning. It reaches its maximum late in the afternoon. Circadian rhythms determine patterns of important behaviors in most animals, including feeding and sleeping patterns. In humans and other mammals, sleep patterns are partly controlled by a hormone called melatonin, which causes drowsiness. The hormone is secreted by the pineal gland, located in the brain. The secretion of melatonin changes predictably over a 24-hour cycle. The level of melatonin increases after darkness falls and drops to a very low level during daylight hours.

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Animals have internal biological clocks that help maintain circadian rhythms. The primary biological clock in mammals is a tiny structure called the suprachiasmatic nucleus (SCN). The SCN is located in the hypothalamus near the base of the brain. As shown in the Figure 1.28, light enters the eye and strikes the retina (see The Nervous System and The Endocrine System concepts). The optic nerve carries signals about light from the retina to the SCN. The SCN, in turn, sends out signals that help control biological characteristics and processes, including those listed above. For example, when little or no light enters the eyes, the SCN signals the pineal gland to secrete more melatonin. When light enters the eyes, the SCN signals the pineal gland to secrete less melatonin.

FIGURE 1.28 This diagram shows how light controls many human biological processes and characteristics that have roughly 24-hour cycles, or circadian rhythms. Light en- ters the eye and strikes the retina, which sends signals via the optic nerve to the suprachiasmatic nucleus (SCN). In response, the SCN sends signals that cause changes in many biological pro- cesses. For example, signals sent to the pineal gland change the amount of mela- tonin that the gland secretes. Melatonin, in turn, helps control the sleep-wake cy- cle.

The Figure 1.29 shows what happens to melatonin levels when a person remains in darkness for 24 hours. Melatonin secretion continues to cycle, but the cycle lengthens. Without light, melatonin secretion and other circadian rhythms operate on a cycle that is closer to 25 hours. Normally, the 24-hour cycle of daylight and darkness regulates the innate rhythms. Each day, light resets the cycle so it is 24 hours long.

FIGURE 1.29 With normal daily changes in light, mela- tonin secretion has a 24-hour cycle (left side of curve). In the absence of light, the same cycle is almost 25-hours long (right side of curve).

Did you ever fly from one time zone to another? If you did, then you may have experienced a disruption of your circadian rhythms called jet lag. For example, if you traveled to a time zone that was three hours earlier than the time zone to which you are accustomed, you may have become sleepy three hours earlier than your usual bedtime.

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It generally takes a few days to adjust to a time difference such as this.

Vocabulary

• biological clock: An internal structure in an animal that helps maintain circadian rhythms.

• circadian rhythms: The approximately 24-hour cycle in most biological processes in organisms; the regular changes in the biology or behavior of an individual that occur in a 24-hour cycle.

Summary

• Many biological processes have daily cycles dictated by each organism’s circadian rhythm. • Circadian rhythms determine patterns of important behaviors in most animals, including feeding and sleeping patterns. • Animals have internal biological clocks that help maintain circadian rhythms.

Practice

Use this resource to answer the questions that follow. "Circadian Rhythms Fact Sheet" at http://www.nigms.nih.gov /Education/Factsheet_CircadianRhythms.htm.

1. What is the difference between circadian rhythm and the biological clocks? 2. Where is the SCN located? Hypothesize about how its location is related to its function. 3. What diseases are related to circadian rhythms?

Practice Answers

1. Circadian rhythms are physical, mental, and behavioral changes that follow a roughly 24-hour cycle, respond- ing primarily to light and darkness in an organism’s environment. The biological clocks control circadian rhythms. 2. The SCN contains about 20,000 nerve cells and is located in the hypothalamus, an area of the brain just above where the optic nerves from the eyes cross. This location might be optimal for receiving information from the optic nerve regarding how much light there is. 3. Abnormal circadian rhythms have been linked to insomnia, obesity, diabetes, depression, bipolar disorder, and seasonal affective disorder.

Review

1. What biological characteristics or processes of humans are regulated by a 24-hour cycle? 2. How does the primary biological clock work in mammals? 3. If left in complete darkness, how long does a human’s circadian rhythm usually last?

Review Answers

1. Human biological characteristics/processes such as brain wave activity, hormone secretion, urine production, blood pressure, and body temperature are all based on roughly 24-hour cycles. 2. When light enters the eye of a mammal and strikes the retina, the optic nerve caries signals about light to the suprachiasmatic nucleus (SCN). The SCN then sends signals that help control biological characteristics and processes such as the secretion of melatonin for sleep.

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3. Without light, melatonin secretion and other circadian rhythms operate on a cycle that is closer to 25 hours. Normally, the 24-hour cycle of daylight and darkness regulates the innate rhythms. Each day, light resets the cycle so it is 24 hours long.

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1.12 Animal Aggression - Advanced

• Define animal aggression, and explain how this behavior might increase fitness and be favored by natural selection.

Why fight? In this intense fight between two male Gemsbok (large antelope) on dusty plains of Southern Africa, the winner will drive the other away. This will increase the overall fitness of the population.

Aggression

In many animal societies, cooperation among members of the society is important and offers many benefits. In eusocial species, cooperation is likely to increase the fitness of individuals and be favored by natural selection. The opposite of cooperation is competition. How might competition and other aggressive behaviors benefit individuals? Why might individuals that act aggressively be more fit to survive and reproduce in their environment? Aggression refers to behavior that is intended to cause harm or pain (behavior that accidentally causes harm or pain is not considered to be aggression.) Aggression may involve physical attacks against other individuals. For example, male deer may clash their antlers together, and ants may attack other ants by biting and stinging. These forms of aggression may lead to serious physical injury and even death. In humans, aggression can be verbal or emotional as well as physical. In many species, display behaviors —rather than actual physical attacks —are used to show aggression. This helps prevent injury and death. For example, sometimes a male mountain gorilla fights another male gorilla and uses his big canine teeth to cause deep wounds. However, this is less common than a display of aggression by the male. In fact, male mountain gorillas have a unique series of display behaviors to show aggression. The behaviors includes beating their chest with cupped hands, running sideways, and thumping the ground with their hands. Dogs may also use display behaviors to show aggression. The behaviors include barking, growling, and baring their teeth. Did you ever hear the expression “its bark is worse than its bite?” As this saying suggests, barking displays aggression but does not necessarily lead to aggressive behavior such as biting. Although the dog shown in the Figure 1.30 looks aggressive, it may not actually attack.

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FIGURE 1.30 This dog is baring its teeth, which is a species-wide display behavior that shows aggression. Like other displays of aggres- sion in dogs, it may be used as a warning to strangers (people or other dogs) to stay away.

Aggression has a biological basis. It is associated with an area of the brain called the amygdala, which is controlled by the hypothalamus. Aggression is also influenced by hormones. For example, the male sex hormone testosterone has been shown to increase aggressive behaviors in mice. Animal research has also shown that a tendency to behave aggressively may be partly inherited, although this has not been demonstrated for Homo sapiens. In fact, for most species, the genetic basis of aggression is still poorly understood. In some species, aggression may increase an individual’s fitness and be favored by natural selection. This is especially likely in species of social animals that have dominance hierarchies (see the Mammals concepts). Animals that are more dominant may be more aggressive than less dominant animals. Dominant animals usually have a higher priority in accessing food and other resources. They may also have more chances to mate or even exclusive rights to mate within their social group. If aggression helps an animal become dominant without serious injury or death, it may increase the animal’s fitness. A behavior that increases fitness and is at least partly controlled by genes will be favored by natural selection. For these reasons, it is likely that aggression is selected for in some species, despite the fact that it may be dangerous for the aggressive animal. However, there is no conclusive evidence that aggression is selected for in human beings.

Vocabulary

• aggression: Any behavior that is intended to cause harm or pain.

Summary

• Aggression may involve physical attacks, display behaviors, and verbal or emotional attacks in the case of humans. • In some species (especially those with dominance hierarchies), aggression may increase an individual’s fitness and be favored by natural selection. • Dominant animals may be more aggressive than less dominant ones.

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Practice

Use this resource to answer the questions that follow. "Territoriality and Aggression" at http://www.nature.com/sc itable/knowledge/library/territoriality-and-aggression-13240908.

1. What is resource holding potential? 2. Explain briefly how game theory can be applied to natural selection and aggression. 3. Why do some animals go through protracted encounters before one individual backs down?

Practice Answers

1. Resource holding potential (RHP) is the ability to defend territories and, in many cases, engage with opponents directly using, for example, weapons or large body size. 2. In game theory, contests between animals are regarded as "games" played out with different alternatives. If one strategy, once adopted by most of the population, is immune to invasion by any of the alternatives in the game, it is called the evolutionarily stable strategy (ESS). In some cases, aggressive behavior without risk to injury or death may result from such games. 3. There are two theories as to why some animals go through protracted display rituals. One theory, known as mutual assessment, postulates that each individual gathers information about the others RHP until they know the other is stronger (this forms the Sequential Assessment Model). Another theory postulates that each individual keeps on fighting until the risk of receiving an injury is too great. This is known as the Energetic War of Attrition.

Review

1. How is aggression usually expressed in most species? Give an example. 2. What part of the brain is aggression associated with? What hormones are associated with aggression? 3. What are some possible evolutionary benefits to aggression?

Review Answers

1. In many species, aggression is usually expressed through display behaviors rather than physical attacks in order to prevent injury and death. Male mountain gorillas beat their chests and thump the ground as display behaviors to show aggression. 2. Aggression is associated with the amygdala in the brain, which is controlled by the hypothalamus. Aggression is also influenced by hormones such as testosterone, which has been shown to increase aggressive behavior. 3. More aggressive individuals are more likely to become dominant in societies that have dominance hierarchies. Dominant animals are then allowed to have more chances to mate and more food resources.

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1.13 Animal Competition - Advanced

• Define competition, and explain how this behavior might increase fitness and be favored by natural selection.

Is there enough water for all? Not always. It is very common to have both interspecies and intraspecies competitions for limiting resources. Here we see zebras drinking at the Serengeti National Park in Tanzania, Africa. Sometimes these watering holes cannot supply enough water for all the animals who need to drink.

Competition

Aggressive behavior often occurs when individuals or groups of individuals are in competition with one another. Competition is rivalry between individuals or groups over something that both sides want or need. Competition occurs naturally between living organisms that coexist in the same environment. For example, animals may compete for territory, water, food, or mates. Competition often occurs between members of the same species. This is called intraspecific competition. This is the type of competition that is the driving force behind natural selection within a species. One reason for intraspecific competition is a scarcity of resources or mates. Another reason is to achieve or maintain high status in a dominance hierarchy. In some species, such as meerkats, an adult female may kill infants of other adult females so that her own offspring will benefit from reduced competition. In many species, a parent (most often the mother) will act aggressively against others that threaten to harm her or his offspring. Aggression may also occur when individuals or groups defend their territory against other members of their species. For example, chimpanzee males may be very aggressive toward males from outside their own troop. Groups of males may patrol the boundaries of their territory looking for lone males and attack them. The lone males are often killed. Competition also occurs between members of different species. This is called interspecific competition. Although a predator tries to kill its prey and the prey may try to fight off its predator, predation is usually not considered to be competition. For example, a cat shows aggression by hissing and arching its back, but it does not behave this way

67 1.13. Animal Competition - Advanced www.ck12.org when it is preying upon a mouse. Instead, the term interspecific competition is generally used to refer to competition between members of different species for the same limited resources. Interspecific competition may or may not involve aggression. For example, individuals of one species may be better suited to exploit the resources that both species need, but members of the two species may not actually fight with one another. For example, cheetahs and lions both feed on the same prey; they compete for this resource. Therefore, if they live in the same area, one or both species will have less food. You might expect them to fight each other over food, but they do not. On the other hand, members of two species may have physical conflicts over resources. For example, some species of ants attack and take over colonies of other ant species. Both types of interspecific competition are likely to play a role in the evolution of species. The better suited or more aggressive species may survive and increase in numbers while the other species declines in numbers and eventually dies out. A species of ants called pavement ants are well known for their aggressive behavior toward other ants. In their quest for new territory and resources, pavement ants brutally attack other ants’ colonies. The resulting battles may leave thousands of ants dead. To view a video on interspecific competition between wolves and bears in Yellowstone, visit http://www.youtube.c om/watch?v=-pd7yTRnYzg (3:21)

MEDIA Click image to the left or use the URL below. URL: http://www.ck12.org/flx/render/embeddedobject/139431

Vocabulary

• competition: The relationship between organisms that strive for the same limited resources.

Summary

• Competition occurs naturally between living organisms that coexist in the same environment and need to compete for territory, water, food, or mates. • Competition between members of the same species is the driving force behind natural selection within a species. • Interspecific competition is generally used to refer to competition between members of different species for the same limited resources and may or may not involve aggression.

Practice

Use this resource to answer the questions that follow. "Competition" at http://www.marietta.edu/~biol/biomes/com petition.htm.

1. What is the principle of competitive exclusion? 2. How do some animals reduce competition between the young and the adults? 3. What is the difference between the two mechanisms of competition: exploitation and interference? 4. How might predators influence competition between different species of prey?

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Practice Answers

1. Competitive exclusion states that two species competing for the same limiting resource in an area cannot coexist. If two similar species are found in the same place, careful examination often finds that the ways they use the resources differ in some critical, but often not apparent, way. 2. Some animals partition the habitat between the young and the adults. Many insects, such as butterflies, feed on different parts of the plant depending on their stage of development. Tadpoles live in the water, feeding on algae, while the adult frogs are carnivorous and, in many species, live away from the water. 3. In exploitation competition, organisms use up resources directly. Once used, the resource is no longer available for other species to use. In interference competition, one organism prevents other organisms from using a resource. Of the two mechanisms, exploitation competition is the more common. 4. Ecologist Robert Paine realized that the Purple Sea Star prey on the most abundant organisms, allowing weaker competitors to have a chance as well.

Review

1. Provide some reasons why competition occurs. 2. What is the difference between intraspecific and interspecific competition? 3. An antelope tries to defend itself against a lion by kicking. Is this considered interspecific competition? 4. Give an example of interspecific competition that doesn’t involve fighting and another that does.

Review Answers

1. Competition occurs naturally between living organisms that coexist in the same environment, usually for territory, water, food, or mates. 2. Intraspecific competition refers to competition between members of the same species. Interspecific competi- tion refers to competition between different species for the same limited resources. 3. Predation is usually not considered to be competition because the two different species are not competing for the same resources. 4. Cheetahs and lions both feed on the same prey; they compete for this resource but do not directly fight each other over food. Pavement ants, on the other hand, aggressively attack other ants for new territory and resources.

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1.14 Animal Mating Systems - Advanced

• Define mating and distinguish among different types of mating systems.

Can all animals show affection? No, but, as seen here with these two tigers, many can. This may be part of the mating ritual among animals and lead to the continuation of the population and species.

Mating Systems

Most animals, and virtually all vertebrates, reproduce sexually. This requires the fertilization of a female’s egg(s) by a male’s sperm. In biology, mating refers to a pairing of a male and female animal that can lead to the production of offspring. In some animals, especially insects, fertilization of the female’s eggs by the male’s sperm occurs outside the female’s body. In most vertebrates, the eggs are fertilized internally by the male depositing sperm inside the female’s reproductive tract. Animals may engage in sexual behavior solely for reproductive purposes, in which case the behavior almost always occurs when the female is fertile. In most species, females are fertile and receptive to sexual behavior only at certain times of the year. However, in some species, including Homo sapiens, sexual behavior may also occur at times when the female is not fertile. Animals may engage in sexual behavior at these time for pleasure. This may strengthen bonds between the male and female. A mating system is the way in which an animal society is organized for mating purposes. The mating system describes which males mate with which females and under what circumstances. The most common mating systems that have been observed in animals are these:

• Monogamy. One male and one female have an exclusive mating relationship with each other. This occurs more frequently in birds and mammals than in most other animals. It is also called pair-bonding, especially if the relationship lasts for a relatively long time. A pair-bond in mammals called voles is pictured in the Figure 1.34.

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• Polygamy. One male has an exclusive mating relationship with more than one female, or one female has an exclusive mating relationship with more than one male. In vertebrates, the most common polygamous system is one in which a male has an exclusive mating relationship with two or more females. A lion pride typically has this type of mating system. • Promiscuity. Any male within the social group may mate with any female in the group. Promiscuous mating systems are more common in invertebrates, but they are also found in vertebrates, including chimpanzees.

FIGURE 1.31 Voles are small, mouselike rodents, some of which have monogamous mating sys- tems. The male and female shown here belong to monogamous pair-bond. Both the male and female provide parental care for their offspring.

In reality, mating systems tend to be somewhat flexible. For example, even in species with monogamous mating systems, mating may occur outside the monogamous pair. In some monogamous species, such as graylag geese, a pair-bond may last for the life of the partners. In other monogamous species, including ducks, a pair-bond may last for just a year or two. Some species tend to have different mating systems under different circumstances. For example, when food resources are spread thinly, so that individuals must spread out over a large area, monogamous mating is more likely than if the population is more densely packed into a smaller area. Some species may normally have different mating systems in different parts of the species’ geographical range. A mix of different mating systems may also normally exist within a species in a single geographic area.

Vocabulary

• mating: The pairing of a male and female sexually reproducing organism that can lead to the production of offspring.

• mating-system: The way in which an animal society is organized for mating purposes.

• monogamy: A mating system in which one male and one female have an exclusive mating relationship with each other.

• pair-bonding: A monogamous relationship between a sexually mature male and female animal, especially if the relationship lasts for a relatively long time.

• polygamy: A mating system in which one male has an exclusive mating relationship with more than one female, or one female has an exclusive mating relationship with more than one male.

• promiscuity: A mating system in which any male within a social group may mate with any female in the group.

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Summary

• In biology, mating refers to a pairing of a male and female animal that can lead to the production of offspring. • The mating system describes which males mate with which females and under what circumstances. • Common mating systems include: monogamy, polygamy, and promiscuity. • In reality, mating systems tend to be somewhat flexible depending on factors such as the environment.

Practice

Use this resource to answer the questions that follow. "Mating Systems in Sexual Animals" at http://www.nature.co m/scitable/knowledge/library/mating-systems-in-sexual-animals-83033427.

1. What is the major advantage of sexual reproduction? 2. How does Bateman’s principle explain why most males have greater elaboration of behavior and structures? 3. Why are females more likely to be choosier than males when it comes to selecting partners? 4. What are leks? 5. When does sperm competition usually occur in animals?

Practice Answers

1. The major advantage of sexual reproduction comes from genetic recombination, which allows an organism’s offspring to be genetically diverse. This increases the chances of acquiring favorable genes. 2. Bateman’s principle stems from the understanding that females can fertilize all their eggs with one mating, while males can mate several times, increasing how many times their genes are passed on. Thus females become satisfied with one mating, whereas males gain increasing fitness from multiple matings. Males need to attract more mates in order to be fitter, hence the greater elaboration. 3. In most species, females are choosier when picking a mate than males because of the higher investment females make in each gamete than males. Additionally, in most species, females are more likely to provide parental care. Females that carefully select their mates are at a lower risk of losing their reproductive invest- ment. 4. A lek is an aggregation of males that are each seeking to attract a mate. Within a lek, males typically perform sexual displays. Unlike most other mating systems, leks are not associated with resources. It is thought that males form leks because they attract more females than an isolated males would. 5. If more than one male mates with a female in a short time period, competition can occur after the males have released their sperm. This is often apparent in animals that use external fertilization. In aquatic animals that release their gametes into the water, animals that release the largest amount of sperm, and sperm that are highly capable of swimming, are likely to produce the most offspring.

Review

1. What are three common mating systems? How is each different? 2. What animals exhibit monogamy? Promiscuity? 3. Why would one species have multiple different mating systems?

Review Answers

1. Monogamy is a mating system where one male and one female have an exclusive mating relationship with each other for an extended period of time. Polygamy is a mating system where one individual of a gender has an exclusive mating relationship with more than one of the other gender. Promiscuity is when any male and female can mate in a group.

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2. Monogamy occurs more frequently in birds and mammals than in other animals. Promiscuity occurs more frequently in invertebrates, although vertebrates such as chimpanzees also exhibit such behavior. 3. Some species tend to have different mating systems under different circumstances. For example, when food resources are spread thinly, so that individuals must spread out over a large area, monogamous mating is more likely than if the population is more densely packed into a smaller area.

73 1.15. Animal Courtship - Advanced www.ck12.org

1.15 Animal Courtship - Advanced

• Describe courtship behaviors among various types of animals.

Do all females wish to be wined and dined? No, but courtship rituals are prevalent among many species. This peacock, with his tail fully fanned, is showing off for the females of the population. This is part of the courtship routine among peacocks.

Courtship

Females typically put much more time and energy into reproduction than do males. Therefore, females are likely to be more selective than males when choosing mates. In fact, it is most often the females of a species that decide who mates with whom, not the males. Males, for their part, try to attract females for mating. In many species, females tend to select males that are larger in size or have more pronounced male traits than other males. To attract females, males may perform display behaviors or engage in physical combat with other males. These behaviors are called courtship behaviors. They get the attention of females and give the males a chance to show off their traits and abilities. Generally, the more impressive males are in these displays, the greater chance they have being selected by females as mates. In many animal species, males gather together in a neutral area for competitive mating displays. This type of behavior is called lekking. By gathering together in one area, the males can get the attention of more females and show their advantages over other males. The males may assemble daily in the same location, called a lekking arena, both before and during the mating season. Within the lekking arena, each male takes and defends a small territory. While assembled, the males put on courtship displays and may fight one-on-one with nearby males within the arena. An example of a lekking species in which males use visual displays is the peafowl. During the display, the peacock fans out and shakes his large tail feathers. Besides peafowls, lekking occurs in many other bird species, including birds of paradise and prairie chickens. Lekking occurs in some mammals as well, including waterbucks and topi (both African herbivores). It has also been observed in some species of fish and insects. In some lekking species, males perform “dances” or “gymnastics” to impress females with their physical abilities. They may also use vocal displays instead of, or in addition to, visual displays.

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In nonlekking species, males do not gather together in one place and put on displays together. Instead, males perform courtship behaviors individually. For example, to attract a mate, a male bowerbird builds an elaborate nest (called a bower). Each bowerbird male spends many hours constructing his nest. He gathers and carefully decorates the nest with hundreds of small objects, such as shells and bits of glass, most of which are bright blue in color (see the Figure 1.32). A female bowerbird typically inspects the nests of many males before deciding on a mate. She selects the male whose nest she prefers.

FIGURE 1.32 The nest created by a male bowerbird is decorated with carefully chosen and placed bright blue objects. The nest is prepared for the purpose of attracting a mate.

Many individual courtship displays involve elaborate “dances.” For example, a male jumping spider performs complex sideways and zigzag movements as part of his courtship. The courtship dance of the blue-footed booby, a species of seabird, consists of the male spreading his wings, stomping on the ground, and flaunting his blue feet. In some species that form lifelong monogamous relationships, both members of the pair-bond engage in an interactive courtship dance. The first time this occurs, the dance helps form the pair-bond. Later, the dance helps reinforce the pair-bond. This type of courtship behavior occurs in the laysan albatross. The courtship dance in this species includes more than two dozen different moves, one of which is shown in the Figure 1.33.

FIGURE 1.33 The male and female laysan albatross pictured here are involved in their elab- orate courtship dance. The albatross on the right is performing a dance move called the “sky call.”

Individual courtship displays may also involve vocal behaviors. For example, some songs of humpback whales

75 1.15. Animal Courtship - Advanced www.ck12.org appear to have the purpose of attracting mates. Mandrills, a species of monkey, also use vocal courtship behaviors. During courtship, a male mandrill walks behind a female and makes various soft sounds. If the female likes what she hears, she will mate with him. Vocal courtship behaviors are very common in birds. For example, African birds of prey called secretary birds have courtship behaviors that include croaking sounds. The croaking of bullfrogs is also a vocal courtship behavior.

Vocabulary

• courtship behaviors: Behaviors performed by a sexually mature animal, usually a male, for the purpose of attracting a mate or reinforcing a mating relationship.

• lekking: A behavior in which males gather together in a neutral area for competitive mating displays.

Summary

• Females typically put much more time and energy into reproduction than do males. Therefore, females are likely to be more selective than males when choosing mates. • To attract females, males may perform display behaviors or engage in physical combat with other males. • Many individual courtship displays involve elaborate “dances" and/or vocal behaviors.

Practice

Use this resource to answer the questions that follow. "Public Displays of Affection May Have Evolutionary Benefits" at http://www.livescience.com/27245-sexual-displays-increase-reproductive-fitness.html.

1. Why are mating displays evolutionarily costly for an animal? 2. What is one evolutionary advantage to monogamy? 3. What effect did covering mating displays have on offspring?

Practice Answers

1. Mating displays are costly because they require lots of energy and make animals more visible to predators. 2. Scientists noted that in monogamous species, paired-up animals are better at raising more offspring. In other words, two individual birds may be able to raise one chick at a time, but a couple can raise more than two chicks together. 3. Researchers found that covering up a mate’s mating displays made the partner less invested in the offspring.

Review

1. Why do females usually select males instead of the other way around? 2. What kind of behavior are males exhibiting if they assemble during mating season and defend small territories? Give examples of animals that exhibit this behavior. 3. Why might monogamous animals still undergo courtship dances?

Review Answers

1. Females typically put much more time and energy into reproduction than do males. Therefore, females are likely to be more selective than males when choosing mates.

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2. The behavior of males gathering together in a neutral area for competitive mating displays is known as lekking. Peafowls, many other bird species, waterbucks, and topi all exhibit lekking behavior. 3. Animals such as the laysan albatross go through courtship dances in order to find a mate and then reinforce the pair-bond.

77 1.16. Parental Care in Animals - Advanced www.ck12.org

1.16 Parental Care in Animals - Advanced

• Describe types of parental care among various types of animals.

Are there animals that just leave their young after birth? Yes. There are many that even leave their young prior to birth. But there are also many that raise their young. This penguin is protecting her chick and will continue to do so until the chick is able to protect itself.

Parental Care

Mating refers not only to sex and courtship behaviors. It may also include the cooperative rearing of offspring by the parents. Parental care refers to any behaviors on the part of either or both parents that help their offspring survive. In many birds, parental care includes building a nest and feeding the young. Parental care generally is longest and most complex in mammals, in which it always involves the mother feeding milk to the young (see the Mammals concepts). Parental care in mammals may also involve teaching the young important skills that they will need when they are older and no longer cared for by the parents. For example, meerkat adults teach their pups how to eat scorpions. They show the pups how to safely handle the poisonous insects and how to remove the stingers. In contrast, many invertebrates and some vertebrates provide no parental care at all. Adults in most species of fish, for example, simply release gametes (eggs or sperm) into the water and have nothing to do with any resulting offspring. However, some fish species do provide parental care, a few in unique ways. For example, tilapia practice a behavior called oral brooding. The mother carries the eggs in her mouth until they hatch. This behavior protects the eggs and allows them to receive more nutrients, so it increases their chances of survival. When parental care does occur in a species, it is most often the mother that provides it. However, in some species both parents or just the father may be involved. Who provides parental care tends to vary with the type of mating system. In species with a monogamous mating system, especially one in which the parents stay together for a long time, both parents are likely to cooperate in caring for their offspring. This is true of the species of voles shown in the Figure 1.34. A mating system in which one female mates with two or more males is typically associated with males taking the sole or main parental role. On the other hand, a mating system in which one male mates with two or more females is usually associated with males having little or no involvement in parental care. Males are also rarely involved in parenting in promiscuous mating systems.

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FIGURE 1.34 Voles are small, mouselike rodents, some of which have monogamous mating sys- tems. The male and female shown here belong to a monogamous pair-bond. Both the male and female provide parental care for their offspring.

Vocabulary

• parental care: Any behaviors on the part of either or both parents that help their offspring survive.

Summary

• Parental care varies greatly from one species of animal to another. • Many invertebrates provide almost no care, whereas mammals usually provide the most parental care. • Animal parental care can be provided by the female or the male.

Practice

Use this resource to answer the questions that follow.

• The Animal Kingdom’s Most Devoted Dads at http://www.livescience.com/14651-animal-kingdom-devo ted-dads.html.

1. Describe the parenting role of the male seahorse. 2. Describe the parenting role of the male penguin. 3. Describe the parenting role of the male emu.

Practice Answers

1. A male seahorse not only gets pregnant, brooding eggs in their pouch, but they’re monogamous and so they mate with just one female for life. 2. Male penguins incubate eggs for weeks, fasting during this time. 3. The male emu watches over the incubating eggs for about 60 days, and then, as a single parent, the male cares for his emu chicks for up to two years.

79 1.16. Parental Care in Animals - Advanced www.ck12.org

Review

1. Which animals usually provide the most care for their offspring? 2. Explain how mating systems are usually related to which gender takes care of the offspring.

Review Answers

1. Mammals usually provide the most care for their offspring, in part because it always involves the mother feeding milk to the offspring. 2. In species with a monogamous relationship, both parents usually take care of the offspring. A mating system in which one female mates with two or more males is typically associated with males taking the sole or main parental role. On the other hand, a mating system in which one male mates with two or more females is usually associated with males having little or no involvement in parental care.

Summary

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1.17 References

1. Derek Keats; prilfish; ian hughes; U.S. Fish and Wildlife Service Headquarters; cc-content.net; Roger Luijten. A) Sponge https://www.flickr.com/photos/dkeats/6163164373; (B) Flatworm https://www.flickr.com/photo s/silkebaron/297217127; (C) Flying Insect https://www.flickr.com/photos/36463157@N08/4843619362/; (D ) Frog https://www.flickr.com/photos/usfwshq/13999033450/; (E) Tiger https://www.flickr.com/photos/cc-co ntent/7583177418/; (F) Gorilla https://www.flickr.com/photos/66555186@N02/6312198231/ . CC BY 2.0 2. Mariana Ruiz Villarreal (User:LadyofHats/Wikimedia Commons) for CK-12. Top: http://commons.wiki media.org/wiki/File:Prokaryote_cell_diagram.svg; Bottom: http://en.wikipedia.org/wiki/File:Animal_cell_s tructure.svg . CC-BY-NC-SA 3.0 original public domain 3. LadyofHats. http://commons.wikimedia.org/wiki/File:Nerve.nida.jpg . Public Domain 4. LadyofHats for CK-12 Foundation. CK-12 Foundation . CC-BY-NC-SA 3.0 5. Peter Halasz. http://en.wikipedia.org/wiki/Image:Biological_classification_L_Pengo.svg . Public Domain 6. LadyofHats for CK-12. (Left) http://en.wikipedia.org/wiki/File:Monosiga_Brevicollis_Phase.jpg; (Right) htt p://commons.wikimedia.org/wiki/File:Ascon_anatomia.jpg . CC-BY-NC-SA 3.0 7. CK-12 Foundation. . CC-BY-NC-SA 3.0 8. Piotr Jaworski. http://commons.wikimedia.org/wiki/Image:Lancetnikinside.png . CC-BY-SA 9. LadyofHats for CK-12. CK-12 Foundation . CC-BY-NC-SA 3.0 10. katsrcool ; Tony Alter; Ronnie Macdonald; Kabsik Park; SheltieBoy; Tup Wanders. a)https://www.flickr.com /photos/katsrcool/9683249122 b)https://www.flickr.com/photos/78428166@N00/7429511676 c)https://www.f lickr.com/photos/ronmacphotos/11065841524/ d)https://www.flickr.com/photos/royalty-free-images/139764663 / e)https://www.flickr.com/photos/montanapets/7298181720 f) http://commons.wikimedia.org/wiki/File:Child ren_marbles.jpg . CC-BY 2.0 11.. http://en.wikipedia.org/wiki/Image:Nikolass_Tinbergen.gif . Public Domain 12. Acghost. http://en.wikipedia.org/wiki/File:EOWilsonCntr.jpg . CC BY 3.0 13. Hunter Desportes. https://www.flickr.com/photos/hdport/4710923235 . CC BY 2.0 14. Raquel Baranow. https://www.flickr.com/photos/666_is_money/4591215888/ . CC-BY-2.0 15. Mark Dumont. https://www.flickr.com/photos/wcdumonts/12112708786/in/photostream/ . CC BY 2.0 16. Belal Khan. Kittens often play with toys. . CC BY 2.0 17. Olivier62. This adult cat is trying to catch a mouse. . CC-BY 18.. http://en.wikipedia.org/wiki/Image:Chimpanzee_and_stick.jpg . Public Domain 19. Casey Brown. https://www.flickr.com/photos/cbrown1023/2667419275 . CC BY 2.0 20. David Lofink. https://www.flickr.com/photos/lofink/4833472120/ . CC BY 2.0 21. RachTHeH. https://www.flickr.com/photos/21834956@N04/4782015284/ . CC BY 2.0 22. Fallows C, Gallagher AJ, Hammerschlag N. http://en.wikipedia.org/wiki/Oecophylla_smaragdina#mediaview er/File:Red_weaver_ants_(Oecophylla_smaragdina)_feeding_on_a_dead_African_giant_snail_(Achatina_fuli ca)_-_journal.pone.0060797.g001-F.png . CC BY 2.5 23. Maggie. https://www.flickr.com/photos/nile_red/5729195926/ . CC-BY-2.0 24. Frans de Waal. http://commons.wikimedia.org/wiki/Image:Young_male_chimp.png . CC-BY 2.5 25. Brad Hammonds. https://www.flickr.com/photos/bradhammonds/8698806505 . CC BY 2.0 26. John Clift. https://www.flickr.com/photos/johnnydante/5772886471 . CC BY 2.0 27.. http://en.wikipedia.org/wiki/Image:Bar-tailed_Godwit_migration.jpg . Public Domain 28.. www.ninds.nih.gov/img/sleep-2.gif . Public Domain 29.. pubs.niaaa.nih.gov/publications/arh25-2/85-93.html . Public Domain 30. Greg Westfall. https://www.flickr.com/photos/imagesbywestfall/8406415395 . CC BY 2.0 31. Peter Trimming. https://www.flickr.com/photos/peter-trimming/6065071438 . CC-BY 2.0 32. Dfrg.msc. http://en.wikipedia.org/wiki/Image:BBNest.jpg . CC-BY 2.5

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33.. www.absc.usgs.gov/.../LAAL_pair_Wang.jpg . Public Domain 34. gailhampshire. https://www.flickr.com/photos/gails_pictures/4509871925/ . CC-BY-2.0

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