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41
Animal Behavior
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?
Concept 41.1 Behavior Has Proximate and Ultimate Causes
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.
Concept 41.1 Behavior Has Proximate and Ultimate Causes
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)
Concept 41.1 Behavior Has Proximate and Ultimate Causes
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)
Concept 41.1 Behavior Has Proximate and Ultimate Causes
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)
Concept 41.2 Behaviors Can Have Genetic Determinants
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.
Concept 41.2 Behaviors Can Have Genetic Determinants
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
Concept 41.3 Developmental Processes Shape Behavior
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
Concept 41.3 Developmental Processes Shape Behavior
• 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)
Concept 41.3 Developmental Processes Shape Behavior
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.
Concept 41.3 Developmental Processes Shape Behavior
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.
Concept 41.3 Developmental Processes Shape Behavior
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
Concept 41.3 Developmental Processes Shape Behavior
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.
Concept 41.3 Developmental Processes Shape Behavior
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.
Concept 41.3 Developmental Processes Shape Behavior
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.
Concept 41.4 Physiological Mechanisms Underlie Behavior
If a rhythm is shifted to an earlier or later
time it is phase-advanced or phasedelayed.
The period of a circadian rhythm is not
exactly 24 hours, so it must be phaseshifted every day.
The rhythm has to be entrained to match
the environmental cycle of light and dark.
Concept 41.4 Physiological Mechanisms Underlie Behavior
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 freerunning period to the light-dark cycle.
Figure 41.7 Circadian Rhythms Are Entrained by Environmental Cues
Concept 41.4 Physiological Mechanisms Underlie Behavior
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.
Concept 41.4 Physiological Mechanisms Underlie Behavior
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.
Concept 41.4 Physiological Mechanisms Underlie Behavior
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
Concept 41.4 Physiological Mechanisms Underlie Behavior
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.
Concept 41.4 Physiological Mechanisms Underlie Behavior
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.
Concept 41.4 Physiological Mechanisms Underlie Behavior
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.
Concept 41.4 Physiological Mechanisms Underlie Behavior
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
Concept 41.4 Physiological Mechanisms Underlie Behavior
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)
Concept 41.4 Physiological Mechanisms Underlie Behavior
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.
Concept 41.4 Physiological Mechanisms Underlie Behavior
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.
Concept 41.4 Physiological Mechanisms Underlie Behavior
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.
Concept 41.4 Physiological Mechanisms Underlie Behavior
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.
Concept 41.4 Physiological Mechanisms Underlie Behavior
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.
Concept 41.4 Physiological Mechanisms Underlie Behavior
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.
Concept 41.5 Individual Behavior Is Shaped by Natural Selection
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.
Concept 41.5 Individual Behavior Is Shaped by Natural Selection
• 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
Concept 41.5 Individual Behavior Is Shaped by Natural Selection
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.
Concept 41.5 Individual Behavior Is Shaped by Natural Selection
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)
Concept 41.5 Individual Behavior Is Shaped by Natural Selection
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.
Concept 41.5 Individual Behavior Is Shaped by Natural Selection
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.
Concept 41.5 Individual Behavior Is Shaped by Natural Selection
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.
Concept 41.6 Social Behavior and Social Systems Are Shaped by
Natural Selection
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
Concept 41.6 Social Behavior and Social Systems Are Shaped by
Natural Selection
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
Concept 41.6 Social Behavior and Social Systems Are Shaped by
Natural Selection
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.
Concept 41.6 Social Behavior and Social Systems Are Shaped by
Natural Selection
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
Concept 41.6 Social Behavior and Social Systems Are Shaped by
Natural Selection
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.
Concept 41.6 Social Behavior and Social Systems Are Shaped by
Natural Selection
Eusocial societies are an extreme example
of kin selection.
In honey bees, most females are nonreproductive 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.
Concept 41.6 Social Behavior and Social Systems Are Shaped by
Natural Selection
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
Concept 41.6 Social Behavior and Social Systems Are Shaped by
Natural Selection
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)
Concept 41.6 Social Behavior and Social Systems Are Shaped by
Natural Selection
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.