jan 13: genetics--genes & environment genetics vs ...jan 13: genetics--hybridization...

Jan 13: Genetics--genes & environment

Genetics vs. Environment in Behavioral Development

(Fig. 2.1 from Alcock 6th Ed.)

Two ways to get difference in behavioral phenotype (e.g., song)

Jan 13: Genetics: why genetics matters

Why Genetics Matters in Study of BehaviorEvolutionary issues

Mechanistic issues

• The view that behavior evolves by natural selection assumes a geneticbasis for behavioral traits

• Testing hypotheses about trait evolution may require tests of thisassumption

• Genes have role in development and operation of neural machineryunderlying behavior, hence gene function must be explored as part ofcausal basis of behavior

• The tools of genetics provide ways of dissecting genetic mechanisms

Jan 13: Genetics--Evolution by natural selection

Review of Natural SelectionNatural selection has three components• Variation

• Inheritance

• Differential survival and/or reproduction

¢ Variation in phenotype among members ofsame population

¢ A population is a group of interbreedingindividuals of the same species

¢ “Like begets like”¢ Or, phenotypic differences are produced by

genotypic differences

¢ Some phenotypic variants have higherchance of surviving and reproducing

¢ Or, there are differences in FITNESScorrelated with phenotype

Natural Selection = Differential Success of Inherited Variants

Jan 13: Genetics--How to study role of genes in behavior

Five Ways to Study Role of Genes in ProducingBehavioral Differences Among Animals

• Isolation Experiment

• Compare relatives

• Hybridization studies

• Artificial selection

• Single-gene (molecular genetic) approaches

Can be used to quantify “heritability”: useful for relating toevolutionary questions

Jan 13: Genetics--Isolation experiments

Isolation Experiments

• Basic logic• Goal is to test whether trait depends

upon particular environmental cues orexperiences

• Rear in isolation from these experiences

• Example 1: Garter snakes and banana slugs

Garter snakes from coastalhabitats in CA (but notfrom inland habitats) likebanana slugs

So do UC Santa Cruz students(their school mascot is thebanana slug)


Isolation Experiments-cont’d

• More on garter snakes

• Coastal snakes reared in lab like slugs, but inland snakes don’t• This is not dependent on experience with slugs (or with adult snakes)

Alcock Fig. 3.19


Isolation Experiments-cont’d

• Example 2: Preferred migratorydirection in blackcap warblers

Southbound blackcapsfollow two main routesout of central Europe(Fig. 3.2 from Alcock)

Hand-reared birds orient inpreferred migratory directionduring “migratory restlessness”(Fig 3.1 from Alcock)

Jan 13: Genetics--comparing relatives

Compare relatives

• Basic logic• To test whether “like begets like,”

compare offspring and parents (or otherclasses of relatives; e.g., siblings)

• Ideally, rear in “common garden”--hold environmental conditions constant

• “Heritability” is measure of strength ofgenetic effects

• Classic example: Francis Galton’s study of human traits

Francis Galton(Darwin’s cousin!)


Compare relatives--cont’d

Height in humans: first attempt tomeasure heritability (and first use ofconcept of “regression” *** )

*** The term “regression comes from Galton’s observation that inherited traitsexhibit “regression toward the mean”--offspring of extremely tall or shortparents are not as different from the mean as their parents are. This is evidenceof non-genetic effects on inheritance

Regression line is best fit to data(intermediate heritability)

Perfect heritability

No heritability


Compare relatives--cont’dHeritability of body color of male guppies

And genetic correlation of femalecolor preference with male color

Jan 13: Genetics--hybridization

HybridizationBasic logic

• Breed individuals expressing different phenotypes• Examine phenotypes of offspring are dependent on

phenotypes of parents

Single-locus case (e.g., Mendel's peas):• Two distinct phenotypes continue to be

seen in hybrids and later descendentgenerations

• Behavioral example: “hygenic” behaviorin honey bees


Hybridization--cont’dMultilocus case (far more common for behavioral traits)• Trait results from action of many genes of small effect• Hybrids are typically intermediate in phenotype between the parents

Example: innate migratoryorientation of blackcapwarblers

• Birds from western and easternEurope have different preferredmigratory directions


Hybridization--cont’dMultilocus case (far more common for behavioral traits)• Trait results from action of many genes of small effect• Hybrids are typically intermediate in phenotype between the parents

Example: innate migratoryorientation of blackcapwarblers• Birds from western and eastern Europe

have different preferred migratorydirections

• Their offspring prefer an intermediatedirection

Jan 13: Genetics--Artificial selection

Artificial selectionLogic• If trait evolved by natural selection,

then it should be possible to change itby artificial selection

• A response to artificial selection isevidence of heritable variation for thetrait being selected (and the stronger theresponse to selection, the higher theheritability)

The only difference between artificial selection and naturalselection is that a human breeder, rather than the naturalenvironment, determines which variants have higher success

Jan 13: Genetics--Artificial selection

Artificial selection--cont’dExample of artificial selection Learning speed in honey bees

Bees learn toextend proboscison presentation ofspecific odors

Learning speed can be artificiallyselected, hence is heritable

Rewarded odor

Unrewarded odor

From Brian Smith, OSU

• Flies are shocked in presenceof particular odor

• Can learn to avoid it

Drosophila

Jan 13: Genetics--Single gene approaches

Single Gene/Molecular Genetic ApproachesLogic• Cause mutations in single genes (generate mutant variants)• Screen for behavioral traits affected by mutations• Map gene’s location on the chromosome and determine its product• The main use of this approach is not to determine whether a trait is

under genetic control, but what the genes areMutant flies are bad at remembering(or at learning in the first place)


Hybridization--cont’dMultilocus case: Example 2: cricket song

• Thus pattern of inheritance in hybrids may indicate whether manyor few genes underlie traits

• Also it may provide evidence of genetic correlations among traits

Hybrids of two different cricket speciessing intermediate song (Bentley & Hoy) Hybrid females prefer hybrid song

jan 13: genetics--genes & environment genetics vs ...jan 13: genetics--hybridization...

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