Jan 24: Development--nature vs. nurture

“Nature vs. Nurture”Just how do genes and environment interact?

• Radical behaviorism (Watson, Skinner): Most complexbehavior is entirely shaped by environment, and only looselyconstrained by genetics

• Classical ethology (Lorenz): Genes and environment makedistinct contributions, so behavioral capacities are either innateor learned (and many complex behavior patterns are largelyinnate)

• Modern view: Genes and environment interact in developmentof all behavioral traits

Jan 15: Behavioral development: two forms

Behavioral development

Learning

• Changes in behavior through ontogeny, as adult behavioral repertoiredevelops

• Adaptive behavioral flexibility at a particular life stage

Two forms of behavioral plasticity in which to explorethe nature/nurture debate

Alcock treats these as two different manifestation of a generalphenomenon: the flexibility of behavior in adapting theindividual to specific environmental conditions

Jan 15: Development--Filial imprinting intro

Case Study 1: Filial Imprinting• Basic function: recognition of parents in

animals with precocial young (e.g., geese,ducks)

• Dependence of recognition on experience(“Nurture”)

• Genetic constraints on development ofrecognition (“Nature”)

¢ Young animal must see model to recognize it¢ Learning is flexible: model may look unlike

own parent or even own species

¢ Sensitive period of exposure to model¢ Learning triggered by specific stimuli (e.g.,

movement, sound)¢ Learning is rapid and long lasting¢ Learning is apparently irreversible

Jan 15: Development--Filial imprinting cont’d

Imprinting-cont’d

• Sensitive period: learning isstrongest when chick is exposedto model during particular timewindow (for ducks, 10-20 hoursafter hatching)

Height of curves indicatesstrength of response to model

• Following of model (and learning)triggered by sight and sound, butsound is more potent than sight

Duckling Hidden loudspeaker

Jan 15: Development--song learning intro

Case Study 2: Song learning in true songbirds*

* See Chap. 2 in Alcock

• Functions of song (to be discussed in detail later incourse)

• Song development• Songs of true song-birds are usually species-specific, but their

development is influenced by experience

• Other bird groups that exhibit vocal learning: hummingbirds, parrots,lyrebirds

• Most other bird species do not need experience to develop normalvocalizations

• Territorial defense (usually by males)• Attraction of mates

Jan 15: Development--song dialects

Dependence of song learning on experience (“nurture”)• Flexibility in development of species

specific song: learned “dialects”

Song learning-cont’d

Dialect 1

Dialect 2

White-crowned sparrow

Jan 15: Development--song isolation exps

• Flexibility in development of speciesspecific song: learned “dialects”

Song learning-cont’d

• Isolation experiments--isolated ordeafened birds develop degradedsong

Normal

Isolated

Deafened

Dependence of song learning on experience (“nurture”)

White-crownedsparrow

Song sparrow

Jan 15: Development--genetic constraints on song

• Sensitive periods: isolatedwhite-crowned sparrows musthear species-specific songbetween days 10 and 50 afterhatching

Song learning-cont’d

• Isolated birds can only learntheir own species’ song

Genetic constraints on development (“Nature”)

Jan 15: Development: song template hypothesis

Song learning: the template hypothesis (P. Marler)*

• Brain encodes a “template” of species-specific song• Template is used for recording correct song in memory

• Open only during senstitive period• Selective for species-specific song (but any variant will do)

• Memorized song is used as basis for comparison duringpractice phase

*The hypothesis that dominated ideas about song learning during 70s and 80s

Jan 15: Development: social cues

Role of social cues in song-learning: challenging thedogma of the template hypothesis

• White-crowned sparrows maychange songs throughout lives(i.e., well after critical period)

• Also, young birds given morenormal social experience (can seeas well as hear other birdssinging) have more flexibility intheir vocal development

White-crowned sparrows givensocial cues can even learn thesong of a different species!

• Thus, original templatehypothesis pertains only tosocially isolated birds

Jan 15: Development: social cues

Beyond the template hypothesis

Jan 15: Development: other songbirds

Vocal development in other songbird species• Some species learn a completely new song repertoire each year (e.g.,

canaries)• Some birds add continually to song repertoire throughout their lives by

imitating songs of other species (e.g., mockingbirds, lyrebirds)• Some birds mimic environmental sounds other than bird songs (e.g.,

parrots, starlings)• In spite of this flexibility, there are still constraints on what can be

learned and under what circumstances it can be learned

Jan 15: Development: other songbirds

Why do species vary in level of vocal flexibility?

• This is a functional question (e.g., what is survival value ofvocal flexibility, and why don’t all birds have same need forit?)

• Some hypotheses:•Advantages of sharing local dialect (favors learning)•Advantages of expanding repertoire size (favors learning)•Costs of having to learn (disfavors learning)

Jan 15: Development: speedy mice

Inbred mice and speed

“Genetic” responses to amphetamine in two inbred mice strains

Cabib et al. 2000 Abolition and reversal of strain differences in behavioralresponses to drugs of abuse after a brief experience. Science 289:463.

Jan 15: hungry/speedy mice

Food deprivation alters strain-specific response

Make mice hungry...

...then test again