Albia Dugger • Miami Dade College

Cecie StarrChristine EversLisa Starr

www.cengage.com/biology/starr

Chapter 39Animal Behavior

(Sections 39.1 - 39.4)

39.1 An Aggressive Defense

• Bee stings are highly painful and even a single sting can be fatal to someone allergic to honeybee venom

• Africanized bees respond aggressively to chemical alarm signals (pheromones); they attack in great numbers, sting with little provocation, and pursue intruders persistently

• pheromone• Intraspecific chemical communication signal

Hybrid Africanized Honeybees

Ecology

• Scientists investigate proximate causes of behavior (genetic and physiological factors) and ultimate causes (environmental factors that favored evolution of a behavior)

• Interactions among organisms and their environment are part of the study of ecology

• ecology • Study of organism–environment interactions

39.2 Behavior’s Genetic Basis

• Animal behavior requires a capacity to detect stimuli

• Structure of the nervous system determines the types of stimuli an animal can detect, and types of responses it can make

• stimulus• Environmental cue that a sensory receptor responds to

How Genes Can Influence Behavior

• Much variation in behavior within or among species results from inherited differences

• Behavior can be influenced by genes that affect the structure and activity of the nervous system, and by genes that affect metabolism or physical traits

• Example: Genes that specify beak structure in African seedcrackers determine which species eat large seeds and which species eat small seeds

Genetic Variation Within a Species

• One way to investigate the genetic basis of behavior is to examine behavioral and genetic differences among members of a single species

• Example: Garter snakes of the Pacific Northwest • Snakes in coastal forests prefer to eat banana slugs that

are common on the forest floor• Snakes that live inland prefer to eat fishes and tadpoles• When offered a slug, newborn offspring of coastal snakes

ate it, but offspring of inland snakes ignored it• Newborn coastal snakes associate slug scent with food

Coastal Garter Snake and Banana Slug

Genetic Variation Within a Species (cont.)

• Example: Fruit fly larvae eat yeast on decaying fruit• 70% are “rovers” (move as they feed)• 30% are “sitters” (stay in one place)

• The proximate cause of different behaviors is the gene foraging, which encodes an enzyme for olfactory cues• Dominant allele = rover phenotype• Homozygous recessive = sitter phenotype

• The ultimate cause of behavioral variation is natural selection: a rover does best when surrounded by sitters, and vice versa

“Rovers” and “Sitters”• Genetic polymorphism for foraging behavior in fruit fly larvae

Fig. 39.3, p. 658

yeast

A Rovers (genotype FF or Ff ) move often as they feed. When a rover’s movements on a petri dish filled with yeast are traced for 5 minutes, the trail is relatively long.

B Sitters (genotype ff ) move little as they feed. When a sitter’s movements on a petri dish filled with yeast are traced for 5 minutes, the trail is relatively short.

“Rovers” and “Sitters”

Genetic Variation Among Species

• Comparing behavior of related species can clarify the genetic basis of a behavior

• Example: In voles, inherited differences in hormone receptors influence mating and bonding behavior• Most voles are promiscuous, some are monogamous• Brains of monogamous species have many receptors for

the hormone oxytocin• Also, males of monogamous species have more arginine

vasopressin (AVP) receptors

Voles

• Vole species vary in mating and bonding behavior, and in the number and distribution of receptors for the hormone oxytocin

Oxytocin Receptors in Vole Brains• Monogamous • Promiscuous

Human Behavior Genetics

• Most human behavioral traits have a polygenic basis and are influenced by the environment

• Effects of a single gene among many may show a small statistical correlation between a particular allele and an increased tendency toward a particular human behavior

• Animal studies sometimes inspire human studies: Investigators are looking at possible connections between oxytocin and autism, a disorder involving social attachments

Key Concepts

• Genetic Foundations• Genes that affect the ability to detect stimuli or to respond

to nervous or hormonal stimulation influence behavior• Studying behavioral differences within and between

species allows scientists to determine the behavior’s proximate and ultimate causes

ANIMATION: Hormonal Control of Behavior

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39.3 Instinct and Learning

• All animals are born with the capacity for instinctive behavior – such as the newborn coastal garter identifying a banana slug as food

• instinctive behavior • An innate response to a simple stimulus

Instinctive Behavior: Cuckoos

• A female cuckoo lays her eggs in nests of other birds

• When a cuckoo egg hatches, contact with other eggs stimulates a fixed action pattern: the blind hatchling shoves the eggs out of the nest, eliminating the competition

• fixed action pattern • Series of instinctive movements elicited by a simple

stimulus and carried out with little variation once begun

Cuckoos (cont.)

• Instinctive behavior: A young cuckoo shoves its foster parent’s eggs out of the nest

Cuckoos (cont.)

• The cuckoo’s foster parent responds to the simple stimulus of a chick’s gaping mouth with the fixed action pattern of parental feeding behavior

Time-Sensitive Learning

• A genetic capacity to learn, combined with actual experiences in the environment, shapes most forms of behavior

• Learning may occur throughout an animal’s life, or be restricted to a critical period

• learned behavior • Behavior that is modified by experience

Time-Sensitive Learning (cont.)

• Imprinting is a form of learning that occurs during a genetically determined time period early in life

• Example: Baby geese follow the large object that bends over them in response to their first peep – usually their mother

• imprinting• Learning that can occur only during a specific interval in an

animal’s life

Imprinting• Nobel laureate Konrad Lorenz with geese that imprinted on

him, and a normal imprinting pattern

Time-Sensitive Learning (cont.)

• Example: Songbirds• A male songbird recognizes his species’ song when he

hears older males singing it• Males reared with no model sing a simplified version of

their species’ song• Many birds can only learn the details of their species-

specific song during a limited period early in life

Conditioned Responses

• Most animals are lifelong learners: • They learn to associate certain stimuli with rewards and

others with negative consequences

• Classical conditioning:• An involuntary response to a stimulus becomes associated

with a stimulus that accompanies it• Example: Pavlov’s dog salivated at the sound of a bell

associated with feeding time

Conditioned Responses (cont.)

• Operant conditioning:• An animal modifies its voluntary behavior in response to

consequences of that behavior• Example: A rat that presses a lever and is rewarded with

food presses the lever again; a rat that receives a shock when it enters a particular area avoids that area

Other Types of Learned Behavior

• Habituation:• An animal learns by experience not to respond to a

stimulus that has neither positive nor negative effects• Example: Pigeons in cities learn not to flee from people

who walk past them

• habituation • Learning not to respond to a repeated stimulus

Other Learned Behavior (cont.)

• Spatial learning:• Animals learn about landmarks in their environment that

help them return home

• Social learning:• Animals learn to recognize offspring, competitors, or

mates by appearance, calls, odor, or combinations of cues

• Observational learning:• Animals learn skills by imitating behaviors it observes in

others

Social Learning• Male lobsters battle at their first meeting – the loser will

remember the winner’s scent and avoid him

Observational Learning• A marmoset opens a container using the same method he

observed another use

Key Concepts

• Instinct and Learning• Instinctive behavior can be performed without any practice • Most behavior has a learned component• Even instinctive behavior is often modified over time• Some learning can only occur during a certain portion of

the lifetime

Video: Ducklings Following

Video: Woodpecker Feeding Young

39.4 Adaptive Behavior

• Not all behaviors are adaptive; scientists use experiments to test hypotheses about the adaptive value of a behavior

• Example: • Starlings place sprigs of wild carrot in their nests• Scientists tested the effect of wild carrot sprigs on the

number of blood-sucking mites in nests• Results: Nests with wild carrots had significantly fewer

mites than those with no greenery

Starling Nest Decorating Behavior