Animal Behavior

Animal Behavior

41

Chapter 41 Animal Behavior

Key Concepts

• 41.1 Behavior Has Proximate and Ultimate Causes

• 41.2 Behaviors Can Have Genetic Determinants

• 41.3 Developmental Processes Shape Behavior

Chapter 41 Animal Behavior

Key Concepts

• 41.4 Physiological Mechanisms Underlie Behavior

• 41.5 Individual Behavior Is Shaped by Natural Selection

• 41.6 Social Behavior and Social Systems Are Shaped by Natural Selection

Chapter 41 Opening Question

How can a single gene be responsible for a complex behavior?

Concept 41.1 Behavior Has Proximate and Ultimate Causes

Four questions in studying animal behavior:

• Causation: What is the immediate stimulus for the behavior?

• Development: How does behavior change with age and learning—what experiences are necessary for it to be displayed?

• Function: How does the behavior affect chances for survival and reproduction?

• Evolution: How does the behavior compare with similar behaviors in related species, and how might it have evolved?


Causation and development refer to proximate causes—genetic, physiological, neurological, and developmental mechanisms.

Function and evolution refer to ultimate causes—evolutionary processes that produced the capacity and tendency to behave in certain ways.


Two classical schools of animal behavior focused on proximate causes.

Behaviorism—derived from Pavlov’s work on conditioning; neural reflexes could be modified by experience to respond to an unnatural stimulus.

Ethology—study of instinctive behaviors—genetically determined fixed action patterns. These are not learned and resist modification.

Figure 41.1 The Conditioned Reflex (Part 1)

Figure 41.1 The Conditioned Reflex (Part 2)


Fixed action patterns are usually triggered by simple stimuli such as color, smell, or sound.

The triggers are called releasers.

Example: Gull chicks respond to a red dot on their parents’ bills to initiate pecking behavior to get food.

Figure 41.2 Releasing a Fixed Action Pattern (Part 1)

Figure 41.2 Releasing a Fixed Action Pattern (Part 2)


Behavioral ecologists study why particular behaviors have evolved in a species.

Environmental conditions may put selective pressures on an animal.

Reproductive fitness can be affected by behaviors, such as choices of nest location, mate, defense of a territory or food source.

Concept 41.2 Behaviors Can Have Genetic Determinants

Breeding experiments can test if behavioral phenotypes are genetically determined.

Honeybees demonstrate hygienic behavior when removing larvae killed by a bacterium.

In backcrosses, nonhygienic behavior is dominant, yet intermediate behavior also occurs—components controlled by separate genes.

Figure 41.3 Genes and Hygienic Behavior (Part 1)

Figure 41.3 Genes and Hygienic Behavior (Part 2)


Mutants with altered behaviors allow studies to identify the genes involved.

Male courtship behavior in fruit flies is under control of a single gene, fruitless (fru)—results in male sexual behavior.

The fru product is also a transcription factor for other genes involved in sexual differentiation and behavior.

Alterations in fru lead to a variety of effects on a male’s sexual behavior.


Knockout experiments can reveal the roles of specific genes.

Mice have a small olfactory organ adjacent to the nasal passages—the vomeronasal organ.

Male mice engineered to lack a receptor for pheromones could not distinguish between males and females.

Figure 41.4 The Mouse Vomeronasal Organ Identifies Gender (Part 1)

Figure 41.4 The Mouse Vomeronasal Organ Identifies Gender (Part 2)

Concept 41.3 Developmental Processes Shape Behavior

The development and expression of behavior can be controlled by hormones.

In rats, males and females adopt different sexual behaviors:

Females—lordosis, a receptive posture

Males—copulate with receptive females


Experiments with neutered rats receiving hormone treatments concluded:

• Male sexual behavior requires exposure to testosterone, but female behavior does not require estrogen, in newborns

• Testosterone masculinizes the nervous systems of both sexes


• Exposure to sex steroids as adults is necessary for normal behavior, but only if brains were exposed as newborns

Thus, sex steroids present at birth determine pattern of behavior; steroids present as adults determine when behavior is expressed

Figure 41.5 Hormonal Control of Sexual Behavior (Part 1)

Figure 41.5 Hormonal Control of Sexual Behavior (Part 2)


Imprinting—the animal learns a set of stimuli during a critical period, such as recognition of parents and offspring.

Learning of stimuli takes place during a limited time called the critical period, or sensitive period.

Emperor penguins lay eggs far inland in Antarctica.

Imprinting allows males to find their chicks after they have returned from feeding in the ocean.


Some behaviors result from both inheritance and learning.

Male songbirds have species-specific songs that must be learned during a limited developmental time frame.

White-crowned sparrows must hear the song when they are nestlings, even though they don’t sing it for a whole year.


As males approach maturity, they begin singing and improve as they match their song with the stored memory.

If a bird is deafened before starting to sing, it will not develop species-specific song.

If deafened after singing, he will continue to sing normally—behavior is crystallized.

There are two critical periods for learning— as a nestling and near sexual maturity.

Figure 41.6 Sensitive Periods for Song Learning


Males also hear songs of other species while they are nestlings.

Deprivation experiments have shown that young male sparrows do not learn songs of other species.

Brief exposure to their own species song is enough for imprinting.


Hormones have an influence on behavior through their influence on development and the physiological state of an animal.

Male and female songbirds both hear and recognize the songs, but only the males sing.

When females were injected with testosterone in the spring, they too learned to sing.


In the spring, increased testosterone causes parts of the brain to enlarge.

Individual neurons get larger and grow longer extensions, and number of neurons increases.

Hormones can control behavior by changing brain structure and function.

Concept 41.4 Physiological Mechanisms Underlie Behavior

Biological rhythms coordinate behavior with environmental cycles.

Circadian rhythms are daily cycles of activities.

Length of a cycle is the period—any point on the cycle is a phase of the cycle.

If two rhythms completely match, they are in phase.


If a rhythm is shifted to an earlier or later time it is phase-advanced or phase-delayed.

The period of a circadian rhythm is not exactly 24 hours, so it must be phase-shifted every day.

The rhythm has to be entrained to match the environmental cycle of light and dark.


If an animal is kept in constant conditions, its circadian clock will run according to its natural period—free-running.

The free-running period is under genetic control.

Environmental signals entrain the free-running period to the light-dark cycle.

Figure 41.7 Circadian Rhythms Are Entrained by Environmental Cues


In mammals the master circadian “clock” consists of two clusters of neurons—the suprachiasmatic nuclei (SCN).

If the SCN are destroyed, the animal becomes arrhythmic.

Circadian rhythms were restored experimentally with transplanted SCN tissue—recipients now had the rhythms of the donor tissue.


The molecular mechanism of the circadian clock involves negative feedback loops.

When clock genes are expressed in the SCN, mRNA is translated in the cytoplasm.

The protein products combine into a dimer—it returns to the nucleus, then acts as a transcription factor to stop clock gene expression.

This cycle lasts about a day.


Animals must be able to find their way in their environment.

Piloting involves knowing and remembering the structure of the environment.

Gray whales find their way from Mexico to the Bering Sea by following the coastline as a cue.

Figure 41.8 Piloting


Homing is the ability to return to a specific location from long distances.

Pigeons can fly from remote sites where they have never been before.

They can navigate without visual cues from the environment, detecting the Earth’s magnetic field.


Humans use two systems of navigation:

Distance-direction navigation—requires knowing in what direction and what distance the destination is.

Bicoordinate navigation (true navigation)—requires knowing longitude and latitude of the current position and destination.


Many animals seem to have a compass sense and can use environmental cues to determine direction.

Others appear to have a map sense to determine their position.


Many animals are capable of bicoordinate navigation—a circadian clock may give information about time of day, and sun position may give map coordinates.

Pigeons showed that they orient by means of a time-compensated solar compass.

Figure 41.9 A Time-Compensated Solar Compass


Many animals are active at night, including many migrating birds.

Stars offer two sources of information about direction—moving constellations and a fixed point.

Birds learn to identify the fixed point in the sky.

Figure 41.10 Coming Home (Part 1)

Figure 41.10 Coming Home (Part 2)


When animals interact, they exchange information—systems of information exchange evolve into communication.

Behaviors may be elaborated as signals if both sender and receiver benefit.

A display is favored if it increases the sender’s probability of passing on his genes, and sexual selection occurs.


Animals use multiple modalities to communicate.

Pheromones are chemical signals between individuals.

Diverse molecular structures mean very specific communication—used for alarms, territory-marking, trail-marking, and to attract mates.


Visual signals offer rapid delivery and accurate position of the sender.

Visual signals require light—not effective at night.

Some species signal with light-emitting mechanisms (e.g., fireflies signal for mates).

Some predatory species of fireflies imitate the flashes of other species to attract prey.


Acoustic signals are not as complex as visual ones, but can be used at night and in dark environments.

The receiver does not have to be focused on the sender—more useful over long distances and in complex environments such as forests.

Information content of acoustic signals can be increased and adapted to specific habitats by varying the frequency.


Mechanosensory signals involve touch.

Dance of honeybees—foragers return to hive and communicate with hive-mates by dancing on vertical walls of hive in the dark.

Other bees follow and touch the dancer to interpret the signals.


If the food source is more than 100 meters away, the bee performs a waggle dance, which gives information about distance and direction.

If it is less than 100 meters away, she performs a round dance.

Odor on her body also indicates the flower to be looked for.

Figure 41.11 The Waggle Dance of the Honey Bee

Concept 41.5 Individual Behavior Is Shaped by Natural Selection

Habitat selection is one of the most important decisions.

It must provide food, shelter, nest sites, escape routes, etc.

Generally, the cues animals use to select habitat are reliable correlates of good fitness outcomes.


A cost–benefit approach can be used to investigate behaviors.

Assumes animal has a limited amount of energy for its activities; animals cannot perform behaviors that cost more than the benefits they provide.


• Energetic cost is the difference between performing a behavior and not performing it

• Risk cost is the increased chance of being injured or killed performing a behavior

• Opportunity cost is the benefit the animal forfeits by not performing other behaviors during the same time


Territorial behavior is aggressive behavior used to actively deny other animals access to a habitat or resource.

Territorial displays require considerable energy, may make a male more vulnerable to predation, and reduce time for feeding or parental behavior.


An experiment to estimate costs to male lizards of defending a territory:

Testosterone capsules were inserted under skin of males to stimulate territorial behavior. They spent about one-third more energy than control males.

They had less time to feed, stored less energy, and died at a higher rate.

Figure 41.12 The Costs of Defending a Territory (Part 1)

Figure 41.12 The Costs of Defending a Territory (Part 2)


An animal will not defend a resource that cannot be economically defended.

A seabird can defend its nest site, but not the open ocean where it feeds.

For elephant seals, the females are the resource and males defend beach sites in order to mate.


An unusual form of male territorial behavior does not involve defense of food, nest sites, or females.

Males gather in a lek—a communal area to display prowess and impress females.

Males compete for prime sites in the center of the group, where females will come to mate.


Cost–benefit analysis is also used to study food choice.

Costs of foraging are similar to costs of territorial defense.

Other considerations besides energy are the need for essential minerals or foods with medicinal value.

Concept 41.6 Social Behavior and Social Systems Are Shaped by Natural Selection

Evolution of different mating systems can be understood by asking how behavior contributes to individuals’ fitness.

Mating systems may be relatively simple or may involve multiple mates and differences in parental care.


Mating systems maximize fitness of both partners. Different prairie vole species are either:

Monogamous—strong lifelong pair bonds with shared rearing of young

Promiscuous—males mate with many females, females raise young


In polygynous mating systems a male has more than one mate—fitness is increased by having more females.

Polyandry is a mating system where one female mates with many males—rare, seen where increased paternal care improves fitness.

Figure 41.13 Polyandry in a Small Primate


Altruistic acts—behaviors that reduce the performer’s fitness, but increase fitness of the individual being helped.

An animal’s offspring contribute to its individual fitness.

Inclusive fitness is individual reproductive success plus that derived from relative’s success.


Kin selection is selection for behaviors that increase a relative’s success, at a cost to the performer.

Scrub jays demonstrate helping at the nest.

• Helpers are young, prior offspring of the mating pair

• Mating pairs with helpers have increased reproductive success

Figure 41.14 Helpers at the Nest


Hamilton’s rule:

For an altruistic behavior to be adaptive, the fitness benefit of the act to the recipient times the degree of relatedness between recipient and performer has to be greater than the cost to the performer.


Eusocial societies are an extreme example of kin selection.

In honey bees, most females are non-reproductive workers—including soldiers that defend the colony.

Haplodiploidy—diploid individuals are female, haploid are males. Only the queen is fertile, she produces all the offspring in a colony.

Sisters share 75 percent of their genes.


Eusocial species build elaborate nests or burrows.

Eusociality may be favored if it is difficult or dangerous to start a new colony.

Naked mole-rats are the most eusocial mammals. Individuals trying to found a new colony are at risk from predators, and most founding attempts fail.

Figure 41.15 A Eusocial Mammal


A benefit of group living is foraging efficiency, as in wild dogs hunting in packs.

Living in a group can also reduce risk of members becoming prey themselves.

Alarm calling is another means of reducing predation risk.

Figure 41.16 Group Living Provides Protection from Predators (Part 1)

Figure 41.16 Group Living Provides Protection from Predators (Part 2)


Social behavior also has costs.

Foraging in a group may interfere with one another’s ability to get food or to reproduce.

Increased risks from diseases and parasites

Answer to Opening Question

A gene cannot code for a behavior—a gene’s products, though, are proteins.

Proteins have many roles in structure, function, and signaling.

By interfering with any of these roles, a gene can have an effect on a behavior.

Examples: Changes in pheromone receptors in mice, or in hormones in the of songbirds, can produce different behaviors.

Animal Behavior

Documents

Transcript of Animal Behavior