animal behavior 1. proximate vs. ultimate causes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

ANIMAL BEHAVIORANIMAL BEHAVIOR

1. Proximate vs. Ultimate Causes

2. Environment Influence + Genetic Component

3. Natural Selection favors behaviors that increase survival and reproductive

success

4. Inclusive fitnessaltruistic behavior


• Concept 51.1: Behavioral ecologists distinguish between proximate & ultimate causes of behavior

• The scientific questions that can be asked about behavior can be divided into two classes

– Those that focus on the immediate stimulus and mechanism for the behavior (how)

– Those that explore how the behavior contributes to survival and reproduction (why)


• What Is Behavior? =what an animal does in response to some env. stimulus and how it does it

Figure 51.2: African cichlid raising its fins in response to a threat.

Dorsal fin

Anal fin


• Proximate, or “how,” questions about behavior

– Focus on the environmental stimuli that trigger a behavior

– Focus on the genetic, physiological, and anatomical mechanisms underlying a behavioral act

• Ultimate, or “why,” questions about behavior

– Address the evolutionary significance of a behavior


• Example - bird migration• Proximate causes

– External stimuli- changes in day length

– Internal stimuli - hormone levels

• Ultimate causes - birds that migrate have a selective advantage over birds that don't/didn't, selected for over time; could be due to long term climate changes, glaciation, disease, taking advantage of food sources, mating.


ORGANISMS

GenePool

Phenotypes

EnvironmentalStimuli

Behavior

Nat.Sel.


2 Components of Behavior

• Nature/innate: instinct and genes determine behavior

• Nurture/learned: experience and learning influence behavior

These are not working AGAINST each other.


• Innate

Programmed by genes

Sterotyped (similar each time)

Developmentally fixed

Examples: kinesis, taxis, fixed-action pattern

Parental feeding - brood parasites like cuckoo bird take advantage of parents’ innate feeding of baby birds in their nest


• Learned behavior

More of a change in a behavior based on experience

Still has a genetic component (“disposition”)


• A fixed action pattern (FAP)

– Is a sequence of unlearned, innate behavior that is unchangeable

– Once initiated, is usually carried to completion


• A FAP is triggered by an external sensory stimulus (= sign stimulus)

In male stickleback, the stimulus for attack behavior is the red underside of an intruder

Figure 51.3a

(a) A male three-spined stickleback fish shows its red underside.


• When presented with unrealistic models

– As long as some red is present, the attack behavior occurs

Figure 51.3b

..

Will this fish illicit a response?


• Proximate and ultimate causes for the FAP attack behavior in male stickleback fish

ULTIMATE CAUSE: By chasing away other male sticklebacks, a male decreases the chance that eggs laid in his nesting territory will be fertilized by another male.

BEHAVIOR: A male stickleback fish attacks other male sticklebacks that invade its nesting territory.

PROXIMATE CAUSE: The red belly of the intruding male acts as a sign stimulus that releases aggression in a male stickleback.


Directed Movements

• Many animal movements are under substantial genetic influences


•A kinesis is a change in random activity (e.g., turning rate) in response to changes detected in the environment•Ex: Sow bugs become more active in dry areas and less active in humid areas (but still randomly move)

Dry open area

Moist site under leaf

Kinesis increases the chance that a sow bug will encounter and stay in a moist environment—improves gas exchange, chances of finding food


• Taxis is an oriented movement toward(+) or

away (-) from a stimulus

• Many stream fish exhibit positive rheotaxis whereby they automatically swim in an upstream direction

Figure 51.7b

Direction

of river

current


Migration

• Many features of migratory behavior in birds have been found to be genetically programmed

Figure 51.8


Animal Signals and Communication

• In behavioral ecology a signal can cause a change in another animal’s behavior

• Communication = the reception of and response to signals


• Animals communicate using

– Visual, auditory, chemical, tactile, and/or electrical signals (can you think of ex?)

• The type of signal used to transmit information

– Is closely related to an animal’s lifestyle and environment


• Many animals that communicate through odors emit chemical substances called pheromones

• When a minnow or catfish is injured an alarm substance in the fish’s skin disperses in the water, inducing a fright response among fish in the area (communicates danger)

Figure 51.9a, b

(a) Minnows are widely dispersed in an aquarium before an alarm substance is introduced.

(b) Within seconds of the alarm substance being introduced, minnows aggregate near thebottom of the aquarium and reduce their movement.


Auditory Communication

• Experiments with various insects have shown that courtship songs are under genetic control

Henry, Martínez, and Holsinger crossed males and females of Chrysoperla plorabunda and Chrysoperla johnsoni, two morphologically identical species of lacewings that sing different courtship songs. EXPERIMENT

SONOGRAMS Chrysoperla plorabunda parent

Vibration volleys

Standard repeating unit

Chrysoperla johnsoni parent Volley period

crossed with

Standard repeating unit

The researchers recorded and compared the songs of the male and female parents with those of the hybrid offspring that had been raised in isolation from other lacewings.

Volley period

Results: song similar to one species but interval between each song similar to the other


• Even a variety of mammalian behaviors are under relatively strong genetic control

• Research has revealed the genetic and neural basis for the mating and parental behavior of male prairie voles (see pp. 1135 for more

details)


• Concept 51.3: Environment, interacting with an animal’s genetic makeup, influences the development of behaviors

• Research has revealed that environmental conditions modify many of the same behaviors

• Let’s look at an example.


Dietary Influence on Mate Choice Behavior

• One example of environmental influence on behavior Is the role of diet in mate selection by Drosophila mojavensis

• Lab experiments have demonstrated that the type of food eaten during larval development influences later mate choice in females

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsFigure 51.12

ResultsWhen D. mojavensis had been raised on artificial medium, females

from the Sonoran population showed a strong preference for Sonoran males (a). When D. mojavensis had been raised on cactus medium, the Sonoran females mated with Baja and Sonoran males in approximately equal frequency (b).

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CONCLUSION

• The difference in mate selection shown by females that developed on different diets indicates that mate choice by females of Sonoran populations of D. mojavensis is strongly influenced by the dietary environment in which larvae develop.


Learning

• Learned behavior = a more complex process

• Learning is the modification of behavior

– Based on specific experiences

• Learned behaviors

– Range from very simple to very complex

Examples:


• Imprinting

– includes both learning & innate components and is generally irreversible

– distinguished from other types of learning by a sensitive period = limited phase in an animal’s development that is the only time when certain behaviors can be learned


• An example of imprinting is young geese following their mother

• Konrad Lorenz showed that when baby geese spent the first few hours of their life with him, they imprinted on him as their parent


• There are proximate and ultimate causes for this type of behavior

Figure 51.5

BEHAVIOR: Young geese follow and imprint on their mother.

PROXIMATE CAUSE: During an early, critical developmental stage, the young geese observe their mother moving away from them and calling.

ULTIMATE CAUSE: On average, geese that follow and imprint on their mother receive more care and learn necessary skills, and thus have a greater chance of surviving than those that do not follow their mother.


• Conservation biologists have taken advantage of imprinting in programs to save the whooping crane from extinction

Figure 51.6


• Habituation is a loss of responsiveness to stimuli that convey little or no information;

• Occurs over time and is often referred to as NON-associative learning

• Ex: alarm calls of prairie dogs when humans were around waned over time


• Spatial learning is the modification of behavior based on experience with the spatial structure of the environment


• In a classic experiment, Niko Tinbergen

– Showed how digger wasps use landmarks to find the entrances to their nests

After the mother visited the nest and flew away, Tinbergen moved the pinecones a few feet to one side of the nest.

Figure 51.14CONCLUSION

A female digger wasp excavates and cares for four or five separate underground nests, flying to each nest daily with food for the single larva in the nest. To test his hypothesis that the wasp uses visual landmarks to locate the nests, Niko Tinbergen marked one nest with a ring of pinecones.

EXPERIMENT

Nest

When the wasp returned, she flew to the center of the pinecone circle instead of to the nearby nest. Repeating the experiment with many wasps, Tinbergen obtained the same results.

RESULTS

The experiment supported the hypothesis

that digger wasps use landmarks to keep track of their nests.

NestNo Nest


• In Associative Learning

– Animals associate one feature of their environment with another

• Two types:


• Classical conditioning is a type of associative learning in which an arbitrary stimulus is associated with a reward or punishment

• Animals make associations - Pavlov's dog associates bell with food, begins to salivate. Conditioned stimulus -> bell, conditioned response –> salivation w/out food.

Figure 51.15


• Operant conditioning is another type of associative learning in which an animal learns to associate one of its behaviors with a reward or punishment

Figure 51.16

Ouch!I won’t try to eat that again.


Cognition and Problem Solving

• Cognition is the ability of an animal’s nervous system to perceive, store, process, and use information gathered by sensory receptors

• Book says it is a “process of knowing involving awareness, reasoning, recollection and judgement.

• Most complex form of learning


• Problem solving can be learned by observing the behavior of other animals (= social learning)

Figure 51.17


• Behavioral traits can evolve by natural selection

• Because of the influence of genes on behavior, natural selection can result in the evolution of behavioral traits in populations.

• When behavioral variation within a species corresponds to variation in the environment, it may be evidence of past evolution.


Variation in Prey Selection

• Differences in prey selection in populations of garter snakes are due to prey availability and are evidence of behavioral evolution (p. 1135)

• Slugs prevalent coastally but rare inland

Figure 51.18a, b

(a) A garter snake (Thamnophis elegans)

(b) A banana slug (Ariolimus californicus); not to scale


• Observation by Arnold: 73% of young from coastal mothers attacked slugs vs. 35% for the inland snakes

• Proximate cause: coastal snakes recognize the slugs by chemoreception

• Ultimate cause: those inland snakes that colonized coastal took advantage of more abundant food source, passed on their ability to recognize, survived and increased that trait in subsequent populations


• Natural selection favors behaviors that increase survival and reproductive success

• Behavior can affect fitness through its influence on foraging and mate choice

• Optimal foraging behavior

– Do species forage in an efficient manner that maximizes benefits of nutrition and minimizes costs of obtaining food?


Energy Costs and Benefits

• Reto Zach

– Conducted a cost-benefit analysis of feeding behavior in crows

• The crows eat molluscs called whelks

– But must drop them from the air to crack the shells


•Zach determined that the optimal flight height in foraging behavior

– Correlated with a fewer number of drops, indicating a trade-off between energy gained (food) and energy expended

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Height of drop (m)


• In bluegill sunfish

– Prey selection behavior is related to prey density

Figure 51.23

Low prey density High prey density

33%33%33%

32.5%32.5%35%

2%40%

57%

100%

50%35%

14%

33%33%33%

Small preyMedium preyLarge prey



Percentage available

Predicted percentage in diet

Observed percentage in diet

Large prey at far distance

Small prey at middle distance

Small prey at close distance


• Mating Behavior and Mate Choice

– Is the product of a form of natural selection called sexual selection

• The mating relationship between males and females varies a great deal from species to species


• In many species, mating is promiscuous

– With no strong pair-bonds or lasting relationships (sorry, guys not humans)


• In monogamous relationships

– One male mates with one female

(a) Since monogamous species, such as these trumpeter swans, are often monomorphic, males and females are difficult to distinguish using external characteristics only.


• In a system called polygyny

– One male mates with many females

– The males are often more showy and larger than the females

Figure 51.25bAmong polygynous species, such as elk, the male (left) is often highly ornamented.

(b)


• Vs. in polyandrous systems

– One female mates with many males

– The females are often more showy than the males

Figure 51.25c(c) In polyandrous species, such as these Wilson’s phalaropes, females

(top) are generally more ornamented than males.


• The needs of the young

– Are an important factor constraining the evolution of mating systems

• The certainty of paternity

– Influences parental care and mating behavior


• In species that produce large numbers of offspring

– Parental care is at least as likely to be carried out by males as much as females

Figure 51.26

Eggs


Sexual Selection and Mate Choice

• In intersexual selection

– Members of one sex choose mates on the basis of particular characteristics (like a courtship song by males toward females)

• Intrasexual selection

– Involves competition among members of one sex for mates


• Mate Choice by Females

• Male zebra finches

– Are more ornate than females, a trait that may affect mate choice by the females

Figure 51.27


• Imprinting of female chicks on males with more ornamentation

– Affects mate selection as adults

Figure 51.19

Experimental Groups Control Group

Parents not ornamented

Both parents ornamented

Malesornamented

Femalesornamented

Results

Females reared byornamented parentsor ornamented fatherspreferred ornamentedmales as mates.

Females reared byornamented mothers ornonornamented parentsshowed no preferencefor either ornamented ornonornamented males.

Males reared by all experimental groups showed nopreference for either ornamented or nonornamentedfemale mates.


• Male competition for mates is a source of intrasexual selection that can reduce variation among males

• Such competition may involve agonistic behavior, an often ritualized contest that determines which competitor gains access to a resource (e.g.,mate)

Figure 51.30


• Applying Game Theory: evaluates alternative behavioral strategies in situations

– Where the outcome depends on each individual’s strategy and the strategy of other individuals

– Different behavioral strategies by males shows that success is relative and changes depending on the others

– These lizards behave differently dep. on their coloration.


•Mating success of male side-blotched lizards

– Was found to be influenced by male polymorphism and the abundance of different males in a given area (“rock, paper, scissors”)

Figure 51.22

Orange = aggressiveBlue = defend smaller area and after less femalesYellow=sneaky

See p. 1133


• Concept 51.6: The concept of inclusive fitness can account for most altruistic social behavior

• Many social behaviors are selfish b/c natural selection favors behavior that maximizes an individual’s survival and reproduction

• On occasion, some animals behave in ways that reduce their individual fitness but increase the fitness of others altruism, or selflessness


• In naked mole rat populations

– Nonreproductive individuals may sacrifice their lives protecting the reproductive individuals from predators

Figure 51.33


Inclusive Fitness

• Altruistic behavior can be explained by inclusive fitness

– The total effect an individual has on proliferating its genes by producing its own offspring and by providing aid that enables close relatives to produce offspring


Hamilton’s Rule and Kin Selection

• Hamilton proposed a quantitative measure

• For predicting when natural selection would favor altruistic acts among related individuals

• The three key variables in an altruistic act are

– The benefit to the recipient

– The cost to the altruist

– The coefficient of relatedness


• The coefficient of relatedness

– Is the probability that two relatives may share the same genes

Figure 51.34

Parent A Parent B

OR

Sibling 1 Sibling 2

1/2 (0.5) probability

1/2 (0.5) probability


• Natural selection favors altruism when the benefit to the recipient

– Multiplied by the coefficient of relatedness exceeds the cost to the altruist

• This inequality

– Is called Hamilton’s rule


• Kin selection is the natural selection

– That favors this kind of altruistic behavior by enhancing reproductive success of relatives


• An example of kin selection and altruism– warning behavior observed in Belding’s ground

squirrels (related females closer in distance when sounding the alarm)

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Figure 5129


Reciprocal Altruism

• Altruistic behavior toward unrelated individuals

– Can be adaptive if the aided individual returns the favor in the future

• This type of altruism

– Is called reciprocal altruism (“tit for tat”more game theory)

animal behavior 1. proximate vs. ultimate causes

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