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Chapter 32: Animal Behavior

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Genetic Basis of BehaviorThe behavior of animals is any action

that can be observed and described.All behavior has a genetic basis, as

demonstrated by various experiments.Lovebirds are small green and pink

African parrots; several closely related species differ by the way they build nests.

Hybrids between species have trouble with carrying nest materials.

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Nest-building behavior in lovebirds

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Several experiments have been done with the garter snake, which has two different populations in California.

Inland populations are aquatic and feed underwater on frogs and fish.

Coastal populations are terrestrial and feed mainly on slugs.

In the lab, inland garter snakes refused to eat slugs but coastal snakes ate them.

Hybrid offspring showed an intermediate acceptance of slugs as food.

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Feeding behavior in garter snakes

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Both the nervous and endocrine systems are responsible for the integration of body systems.

To test whether the endocrine system influenced behavior, the egg-laying behavior of a marine snail Aplysia was examined.

Egg-laying hormone (ELH) causes the snails to lay eggs even without mating.

ELH is thought to control the egg-laying behavior in Aplysia.

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Development of Behavior

Some behaviors seem to be fixed action patterns (FAPs) in which a specific cue sets the behavior in motion.

Experiments with laughing gull chicks show that improvement in motor skills, as well as visual experience, strongly affect development of chick begging behavior.

This suggests that learning, rather than FAPs, may be involved in gull chicks.

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Pecking behavior in laughing gulls

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The Phenomenon of Learning

Operant Conditioning and ImprintingOperant conditioning, one of many forms

of learning, is the gradual strengthening of stimulus-response (behavior-reward) connections.

Imprinting is another form of learning; chicks, ducklings, and goslings will follow the first moving object they see during a sensitive period after hatching.

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Song-Learning in BirdsSong learning in birds is an active area of

research.White-crowned sparrows sing a species-

specific song, but males of a particular region have their own dialect; birds were caged into three groups to see how young birds learn to sing from older members of their species.

Birds in the first group heard no singing; when grown, these birds sang a song that was not fully developed.

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Birds in the second group heard tapes of white-crowns singing; when grown, they sang in a dialect, as long as the tapes had been played during a sensitive period.

Birds in the third group were given an adult tutor; these birds sang a song of even a different species, no matter when the tutoring began.

It appears that social influence, along with genetics, is of great importance in the development of singing.

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Song-learning by white-crowned sparrows

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Adaptiveness of Behavior

Since genes influence the development of behavior, it can be assumed that behavioral traits are among those subject to natural selection.

Investigators studying survival value of a given behavior seek to discover how a given trait might improve reproductive success.

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Males can father many offspring because they produce sperm in great quantity; it would be expected that they inseminate as many females as possible.

Females produce few eggs, so choice of mate becomes an important consideration.

Experiments with satin bowerbirds and birds of paradise support these bases for sexual selection.

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Mating behavior in birds of paradise

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Female ChoiceCourtship displays are rituals that serve

to prepare the sexes for mating; they help male and female recognize each other so that mating will be successful.

Courtship displays also play a role in a female’s choice of a mate.

Female choice can explain why male birds are so much more showy than females; colorful, lengthy plumes might signify health and vigor.

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Male CompetitionEvolution by sexual selection can occur

either when females have the opportunity to select among potential mates, and/or when males compete among themselves for access to reproductive females.

Only if the positive effects of male competition outweigh the negative effects will the animal have reproductive success.

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Dominance HierarchyMale and female baboons within a troop

have separate dominance hierarchies in which a higher-ranking animal has greater access to resources than a lower-ranking animal.

Dominant male baboons generally monopolize females when they are fertile, although males that help rear offspring sometimes have breeding access during less fertile times.

Dominance is decided by confrontations.

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A male olive baboon displaying full threat

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Female choice and male dominance among baboons

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TerritorialityA territory is an area that is defended

against competitors.Territoriality includes the type of

defensive behavior needed to defend a territory.

Vocalization and displays, rather than outright fighting, may be sufficient to defend a territory.

Red deer stags may actually lock antlers and push against each other to repel challengers.

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Competition between male red deer

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Animal Societies

Some animals are solitary, others live in small groups, and still others organize a society in which members cooperate, a behavior extending beyond mating and parental care.

Social behavior in societies requires communication between members.

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Communicative BehaviorCommunication is an action by a sender

that affects the behavior of a receiver.Chemical communication uses chemical

signals, such as pheromones; an advantage is that this form of communication works both night and day.

Auditory (sound) communication is fast and effective, and can be easily modified.

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Use of a pheromone

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A chimpanzee with a researcher

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Visual communication involves signals used by species active during the day.

For example, defense and courtship displays are exaggerated and are always performed in the same way so their meaning is clear.

Tactile communication occurs when one animal touches another.

Honeybees use a combination of methods of communication, but especially tactile ones, to impart information about food distance and direction.

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Communication among bees

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Sociobiology and Animal Behavior

Sociobiology applies the principles of evolutionary biology to the study of social behavior in animals.

It is assumed that a social individual derives more reproductive benefits than costs from living in a society.

Group living protects members from predators and helps in finding food; disadvantages include increased disease and territoriality, and not all members of the group will mate.

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Altruism Versus Self-Interest

Altruism is behavior that has the potential to decrease the lifetime reproductive success of the altruist while benefiting the reproductive success of another member of the group.

Genetic relatedness appears to underlie altruism; an altruistic act is best targeted at a close relative sharing the same genes.

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Direct selection is natural selection that can result in adaptation to the environment when the reproductive success of individuals differs.

Indirect selection is natural selection that can result in adaptation to the environment when individuals differ in their effects on the reproductive success of relatives.

Inclusive fitness of an individual includes personal reproduction and reproduction of relatives.

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Inclusive fitness

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Inclusive fitness is measured by the genes an individual contributes to the next generation, either directly by offspring or indirectly by way of relatives.

Many of the behaviors once thought to be altruistic turn out to be examples of indirect selection and are adaptive.

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Chapter Summary

Various experiments with African lovebirds, California garter snakes, and and the marine snail Aplysia have shown that behavior has a genetic basis, and further that the nervous and endocrine systems control behavior.

The environment influences the development of behavioral responses, and learning occurs.

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Song learning in birds involves various elements, including a sensitive period during which the bird is primed to learn, and the effect of social interactions.

Since genes influence the development of behavior, it can be assumed that behavioral traits, such as mate choice, are among those subject to natural selection.

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Evolution by sexual selection can occur either when females have the opportunity to select among potential mates, and/or when males compete among themselves for access to reproductive females.

Territoriality includes the type of defensive behavior needed to defend a territory.

Vocalization and displays, rather than outright fighting, may be sufficient to defend a territory.

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Animals that form social groups use chemical, auditory, visual, or tactile communication, and communication fosters cooperation that benefits both sender and receiver.

In most cases, individuals of a society act to increase their own reproductive success by helping relatives who share their genes.

Altruistic behavior has a benefit in terms of inclusive fitness.