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 1 www.ck12.org 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. 2 www.ck12.org Chapter 1. Animals - Advanced 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 3 1.1. Animals - Advanced www.ck12.org 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. 5 1.1. Animals - Advanced www.ck12.org 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.