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Home , Mate choice, Mating, Mating system, Polygynandry, Polygyny, Reproductive system

contents Principles of 171 underlies many behaviors.

The greater sage grouse (Centrocercus urophasianus). sage grouse evaluate males as sexual partners on the basis of the ornaments and the males' elaborate displays. Stephen J. Krasemann/Science Source.

Topics Covered in this Module

Mating as a Risky Behavior

Major Objectives of this Module

Describe factors associated with specific patterns of and history strategies of specific mating patterns. Describe how contributes to behavioral such as mating. Describe the selection factors influencing behaviors like mate choice.

page 882 of 989 3 pages left in this module

contents Principles of Biology

171 Mate Choice Mating as a Risky Behavior Different have different mating patterns. Different species have evolved a range of mating behaviors that vary in the number of individuals involved and the length of time over which their relationships last. The most open type of relationship is , in which all members of a community can mate with each other. Within a promiscuous species, an animal of either gender may mate with any other male or female. No permanent relationships develop between mates, and cannot be certain of the identity of their . Promiscuous behavior is common in ( paniscus), as well as their close relatives, the (P. troglodytes). Bonobos also engage in sexual activity for activities other than reproduction: to greet other members of the community, to release social tensions, and to resolve conflicts. Test Yourself

How might promiscuous behavior provide an evolutionary advantage for males?

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Some demonstrate polygamous relationships, in which a single individual of one gender mates with multiple individuals of the opposite gender. In polygynous relationships, one male mates with multiple , while in polyandrous relationships, one female mates with multiple males. is the most common type of relationship in the animal world. Of the two forms of polygamy, is far more common than . Polygynous species range from toads, , and cuttlefish to aardvarks, elks, seals and whales. A single male elephant seal may maintain a of 40 or more females, all with whom he mates (Figure 1). Evolutionarily, polygyny increases the opportunities for a dominant male to transmit his to future generations through multiple females.

Figure 1: Elephant seals (Mirounga leonina). A single male elephant seal may maintain a harem of as many as 40 females. Craig K. Lorenz/Science Source.

Polyandry has been observed in a variety of species, including Harris' hawks, acorn , spotted sandpipers (Figure 2), and red-necked phalaropes. Tree toads, field crickets, agile , marmosets, bandicoots, , and a number of other animals also practice polyandry. Among in particular, polyandry occurs in two forms: simultaneous and sequential. In simultaneous polyandry, a female maintains more than one nest and acts as a mating partner with more than one male at the same time. In sequential polyandry, a female mates and nests with one male partner after another.

Figure 2: A spotted sandpiper (Actitis macularius). Spotted sandpipers polyandrous behavior. Jim Zipp/Science Source.

In a polygynandrous relationship, multiple females and multiple males live and breed together where there are exclusive relationships between two or more males and two or more females. , Eastern box turtles, swallows, warthogs, , and Tasmanian devils, among other species, demonstrate . Polygynandry has a number of advantages over other types of mating relationships, as males face less competition for mates and younger members of the group receive greater protection. For example, male and female spectacled caimans (Figure 3) breed together before females build their nests, where they guard their and young, together with a male. Figure 3: A spectacled caiman (Caiman crocodilus). Male and female spectacled caimans breed and protect their eggs and young together. Gregory Ochocki/Science Source.

Some animal species are monogamous, that is, two animals bond exclusively with each other for an extended period of time. A monogamous relationship may extend over a single mating season or for many years. Some monogamous relationships endure for twenty years or more. Many species favor monogamous relationships, including giant river otters, meerkats, white rhinoceroses, agile gibbons, greater flamingos, Magellanic penguins (Figure 4), mute swans, and shingleback . Human beings often engage in monogamous relationships, although those relationships may take the form of serial . In serial monogamy, a pair of individuals remain together for an extended period of time before ending their relationship and beginning new monogamous relationships with a different partners. Figure 4: Magellanic penguins (Spheniscus magellanicus). Magellanic penguins mate for long periods of time. There is at least one report of a pair sharing the same nest for 16 years. Art Wolfe/Science Source.

Species involved in different kinds of mating relationships have evolved morphological differences known as sexual dimorphisms (Figure 5). These physical differences allow the to differentiate each other. Typical sexual dimorphisms have evolved because males compete with each other for mates, something females rarely do. Therefore, males typically are larger, have weapons of various sorts for use in subduing competitors, and engage in mate-attracting displays as a result of selection for the ability to dominate rivals and attract females. Sexual dimorphisms are most pronounced among species whose mating practices are primarily polygamous and least pronounced among those who practice monogamy. In polyandric species, such as the garden , the female generally displays more brightly colored markings than a male. In a polygynic species, the male generally displays the more vivid characteristics: a brighter color, larger size, or more pronounced appendages, as in some species. Figure 5: Mating pairs. (a) in spiders. Male and female black spiders (Latrodectus mactans) can vary greatly in size and color. (b) Male and female western grebes (Aechmophorus occidentalis) involved in a dance. Western grebes are monogamous birds with few apparent differences in morphological features. (a) James H. Robinson/Science Source. (b) Phil A. Dotson/Science Source.

Test Yourself

A familiar sexual dimorphism among is the presence of large antlers in males. What form of would be expected in species displaying these dimorphisms?

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As with mating behavior, animals exhibit a wide variety of parenting behaviors. These behaviors appear to be influenced by at least two factors: independence of the young at , and certainty of paternity. In some species, a newborn animal is well developed and can take care of itself at a minimal level. For example, most young stand and walk within minutes of birth, although they rely entirely on their for nourishment. Parental treatment of mammalian young varies widely, depending on the ' stage of development at birth. , for example, carry their completely helpless newborns for months in pouches that contain mammary glands. In an even more extreme case, monotremes lay eggs that incubate in a . After hatching, the young are nourished by milk that is secreted into the pouch through the 's skin rather than through mammary glands. Members of other classes of animals display a similar range of variability in the care of their young. Among , the young are generally on their own shortly after hatching, although may guide the newborn to water if they require an aquatic habitat, or provide some minimal level of protection against predators. For some -laying animals, parents provide protection to the eggs themselves. Either may carry eggs on its backs, under its skin, or even in its mouth to protect against predators. For example, the female (Gastrotheca) carries her eggs in a brood pouch on her back. In such species, the young are essentially responsible for their own survival once the eggs hatch. Similarly, newborn are independent from the moment of birth, so focuses primarily on protecting the eggs. Once thought to be uncommon, parental care among fish is now known to be widespread, with more than 80 of bony fish demonstrating some form of care for their eggs. In some fish species, parents fan the eggs to provide a continuous supply of oxygen, hide the eggs to protect them from predators, or clean the eggs to remove fungal growth and other contamination. Other fish species build nests in which their eggs can be suspended. These nests lie directly on a lake or pond bottom, suspended in aquatic , or are supported by masses of bubbles produced by a parent. In many cases, males are responsible for the care of the eggs. In some cases, this care extends beyond hatching. Male banded jawfish (Opistognathus macrognathus), for example, protect their young by enveloping them in their mouths for a short period of time. Birds have also developed complex systems of parental care for their eggs. Most birds are born helpless, relying entirely on their parents for food and protection for at least a few weeks. In some albatross species, young birds are dependent on their parents for up to five months. For other bird species, the young care for themselves soon after hatching. The megapode birds ( Megapodiidae) represent an extreme example, as their young are born with and can fly within a few hours of their hatching. When both parents care for their eggs and fledglings, parents may share duties equally, or each parent may be responsible for a different set of chores, such as incubating eggs or finding food. In other species of birds, parental care falls to a single parent. Most young become relatively independent once their feathers have developed, although extended care may continue in some bird species. Ducks, swans, loons, and grebes (Figure 6), for example, carry their young on their backs until they have matured further. Figure 6: Eared grebe (Podiceps nigricollis) and its eggs. A grebe hovers over its nest, protecting its eggs. After the eggs hatch, the adult grebe will carry its young on its back until they have matured further. Courtesy of Dave Menke/USFWS. While the mother of a newborn animal always can be identified, since she produces an egg or bears live young, the paternity of the newborn cannot be known with certainty. In cases of , as occurs in most land animals, the act of precedes birth from few weeks to many months. In humans, paternal certainty could not be assured, even in relationships deemed by the participants to be monogamous, until the advent of DNA testing. While other animals do not contemplate their situation through reasoning or technology, would not favor males who raised the offspring of another male. This might explain why is seldom the primary or exclusive pattern among terrestrial animals. Test Yourself

Why might evolution favor males who do not provide parental care for their young in some species?

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By contrast, aquatic males participate in parenting more readily than their terrestrial counterparts. In an aquatic environment, is much more likely to occur. In many species, males and females deposit their in a common area, where they are more likely to meet than in open water. Observations of different fish species suggest that the more certain a male is that he is the parent of offspring, the more willing he is to assume some type of parental care for the offspring. In addition, paternal care may confer an evolutionary advantage because males with eggs under their control become more attractive to additional females. Data displayed in Figure 7 suggest that fish species that engage in external fertilization have a much higher proportion of males that are involved in parenting than fish species that use internal fertilization. Figure 7: Comparison of external and internal fertilizing fish species with uniparental male or female care. Parental care was exclusively by males in over half (59%) of the more than a hundred fish species studied. © 2012 Nature Education All rights reserved.

How does a mate of one species recognize and choose a suitable mate from the same species? Mate choice is a critical aspect of mating behavior. In most instances, a female in a community can choose a mate from a large number of available males. How does she select a mate that will help transmit her genes to the next generation in the most efficient way? In many species, the female selects a mate based on the exaggerated morphological features of a male, such as color or size. For example, an anole lizard extends the fold under his chin, called a dewlap, for examination by female admirers (Figure 8).

Figure 8: A male anole lizard (Anolis sagrei) with dewlap extended. As with many other species, the female anole lizard selects a mate based on the exaggerated morphological features of a male. John Serrao/Science Source.

Males display their to prospective mates using a variety of behaviors. Many birds have evolved elaborate dancing patterns to attract females, as demonstrated by the blue-footed booby (Figure 9). In other species, a male will produce complex vocalization patterns to demonstrate their superiority over other males. is similar to , but is based on variation in secondary such as colorful , bird songs and other sexual characteristics that are not part of the . Sexual selection occurs when individuals differ in their inherited traits in ways that affect their access to mating partners. For example, sexual selection can occur when males differ in their ability to fight with or dominate rivals for mates, or to attract willing female partners.

Figure 9: Blue-footed booby (Sula nebouxii) performing mating ritual. Many birds have evolved elaborate dancing patterns to attract females. Kevin Elsby/FLPA/Science Source.

A number of factors influence the way an animal makes its choice of mates. For example, many animals prefer a mate that is also attractive to other members of its species, a phenomenon known as mate-choice copying. Mate selection based on mate-choice copying has been observed in experiments involving sailfin mollies (Poecilia latipinna), a species of fish. Imprinting also appears to affect mate choice. The morphological traits of the parents that an animal is raised with at least partially determine the traits of the mate it eventually selects. Researchers have demonstrated this principle with zebra finches. In an experiment, the control group consisted of a pair of zebra finches without any type of head crest. The experimental group consisted of pairs of zebra finches to which a red feather had been attached as an ornamental head crest. The feather was attached to the male of a pair, to the female of the pair, or to both sexes in the pair. These finch pairs then mated and their offspring were observed. The three experimental situations used in the research are summarized below. The presence or absence of the artificial head crest apparently had no effect on male mate choice. As adults, they chose either ornamented or non-ornamented females with equal frequency. Although females were not influenced in their choice of mates by ornamentation by female parents, they were influenced by ornamented male parents. The conclusion from this study is that young female zebra finches imprinted on the sexual characteristics displayed by their very early in their life, and that this imprinting was a factor in their later choice of mates.

Exceptions to the rule. The females of some species mate promiscuously with several males to produce as many offspring as possible. This female drive poses a problem for males whose primary goal is to transmit their genes to future generations by inseminating each female they mate with. This phenomenon consists of behavioral or morphological strategies adapted by males to increase the probability of successful insemination. Males have evolved a variety of strategies in competition. In some species, males gather females together to prevent contact with other males. In other species, males try to fight off other males that attempt to approach a female. Beyond these obvious strategies, males of some species have evolved a number of sophisticated mechanisms to ensure that their sperm will "win out" over those of competitors. For example, males of some species deposit a thick, wax-like material, called a copulatory plug, in a female's genital tract after impregnating her. That plug prevents other males from depositing their sperm in the same female. In the nematode (), the plug originates within the at the end of a male's (Figure 10). This -like structure solidifies after injection into the female. In some cases, the plug contains a that decreases sexual desire in other males and stimulates ovulation and in the female. A host of other mechanisms are also available to males of various species. The black-winged , for example, has a shaped like a brush. During the movements associated with , the penis scrubs out sperm of previous suitors from the female's body, ensuring that the only sperm remaining inside her are his own.

Figure 10: Copulatory plug in the nematode Caenorhabditis elegans. The plug is located within the vas deferens at the end of the nematode’s tail. It consists of a sponge-like structure that solidifies after injection into the female. © 2008 Nature Publishing Group Palopoli, M. F., et al. Molecular basis of the copulatory plug in Caenorhabditis elegans. Nature 454, 1019–1022 (2008) doi:10.1038/nature07171. Used with permission.

IN THIS MODULE

Mating as a Risky Behavior Summary Test Your Knowledge

SCIENCE ON THE WEB

Under the Feathers Browse this web resource about the mating systems of birds

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contents Principles of Biology

171 Mate Choice Summary OBJECTIVE Describe factors associated with specific patterns of mating and life history strategies of specific mating patterns. Mating behavior between animals can be classified as promiscuous, polygamous, or monogamous. In promiscuous behavior, one individual mates with many other individuals, which may be of the same or opposite sexes. In polygamous behavior, one individual mates with two or more members of the opposite . In polygynous behavior, one male mates with multiple females, while in polyandrous behavior, one female mates with multiple males. Polygynandrous behavior involves mating patterns with multiple males and multiple females. Monogamous behavior refers to the exclusive mating of two individuals.

OBJECTIVE Describe how genetics contributes to behavioral phenotypes such as mating. Genetics contributes to mating phenotypes and sexual selection. For example, males who engage in polygynous behavior increase the likelihood of passing their genes to the next generation. Polygynous males are also less likely to be territorial about offspring. Female mate choice from a large number of available males is also an evolutionary advantage. In many species, the female selects a mate based on the exaggerated morphological features of a male, such as color or size, which may indicate increased likelihood of passing her genes to the next generation. Another evolutionary strategy is the favoring of inherited traits that allow a male to fight with or dominate rivals so that it acquires exclusive access to females in a .

OBJECTIVE Describe the selection factors influencing behaviors like mate choice. Animals use a variety of means to select mates. In most cases, males display traits to attract to females. These traits may include pronounced appendages, dancing behaviors, or displays of physical prowess. Imprinting influences mate selection, with experiments showing females of some species seeking out mates with physical traits corresponding to their male parents. Mate-choice copying, in which an individual’s choice of mates is influenced by the behaviors of other same-sex individuals toward prospective mates, also influences mate selection.

Key Terms mate choice Selection of a member of the opposite sex to mate with.

mate-choice copying Many animals select a mate that is also attractive to other members of the species.

monogamous Two individuals bond exclusively with each other.

polyandrous One female mates with two or more males. polygamous Single individual of one gender mates with several members of the other gender. polygynous One male mates with two or more females. promiscuous Individuals of either gender may mate with any other individual. sexual dimorphism A term that describes the phenomenon that members of the same species have different physical characteristics based on sexual identity. sexual selection Subset of natural selection in which selection is based on of individuals rather than survival.

IN THIS MODULE

Mating as a Risky Behavior Summary Test Your Knowledge

SCIENCE ON THE WEB

Under the Feathers Browse this web resource about the mating systems of birds

page 884 of 989 1 pages left in this module

contents Principles of Biology

171 Mate Choice

Test Your Knowledge

1. For what purpose do bonobos practice promiscuous sexual behavior?

for sexual pleasure only as a way of resolving conflicts with other animals only as a way of greeting other bonobos only All reasons are correct.

2. A female bird that maintains five separate nests with five different males at the same time is practicing what kind of sexual pattern?

simultaneous polyandry monogamy promiscuity sequential polyandry polygyny

3. Which type of parenting behavior is not found in fish?

oxygenating eggs carrying eggs on a parent's body nest building placing eggs in a hidden place guiding the newborn to water

4. A polygynandrous relationship is most like which of the following relationships or mating systems?

a polygynous relationship sequential polyandry a monogamous relationship simultaneous polyandry a promiscuous relationship

5. A group of warthogs living together consists of three males, five females, and their offspring. What type of mating group does this arrangement constitute?

polygyny simultaneous polyandry polygynandry monogamy sequential polyandry

6. A researcher studies five groups of animals, recording physical traits of one male and one female in each species. Which species pair does NOT exhibit sexual dimorphism?

A male bird has red feathers on its head, and the female has brown feathers there. A male has antlers, and the female lacks antlers. A female fish has a colorful tail, and the male is dull colored. A male frog makes a loud trill, while a female has no call. None of the answers are correct. Submit

IN THIS MODULE

Mating as a Risky Behavior Summary Test Your Knowledge

SCIENCE ON THE WEB

Under the Feathers Browse this web resource about the mating systems of birds

page 885 of 989