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 toproximate causes—genetic, physiological, neurological, and developmental mechanisms. • Function and evolution refer toultimatecauses—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.
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.
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.
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.
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
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.
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 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.
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 free-running 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.
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.
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.
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. • Pheromonesare chemical signals between individuals. • Diverse molecular structures mean very specific communication—used for alarms, territory-marking, trail-marking, and to attract mates.