ASB 194 Lecture 4new.doc

ASB 194 Lecture 4new.doc - Lecture 4. I. Behavior as...

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Lecture 4. I. Behavior as Phenotypic plasticity: Many behavioral tendencies show high heritability, thus they constitute phenotypes that can evolve by natural selection. Heritability measures percentage of variation in phenotype accounted for by genetic variation (given the range of environments of the sample) A recent metanalysis of more than 400 studies of heritability of behavior and personality traits in twins and adopted siblings suggests the mean heritability is about 41% (Malouf et al 2008). The range of heritabilities for particular traits ranges from ~25% to about 70%. Trans 4.0 heritabilty of some behavioral traits (from Plomin et al 1997). But behavior consists of sets of flexible, facultative responses, decisions, or strategies that occur in relation to varying environmental conditions. Behavior is often “appropriate” in the sense that the response maximizes survival or reproduction. For example, male soapberry bugs show variation in whether they guard females after copulation. When sex ratios are highly female biased the males don’t guard females but instead rapidly search for a new mate after copulation. When females are rare, the males stay with a female after copulation and guard her from mating with other males (thus displacing their own sperm). The reaction norm for mate guarding takes the form--- "guard if females are rare, don’t guard if females are common". Trans 4.1 reaction norms in mate guarding (Boyd and Silk 1997:84-85) This ability to change phenotypes depending on the situation is itself genetically determined and favored only in areas where the male/female sex ratio shows variation from one season to the next. Thus, behavioral responses that are adaptive can be thought of as reaction norms in which the phenotypic adjustment is rapid and not permanent. There are well understood physiological reaction norms due to a few genes--- eg. red blood cell density increases under high altitude . Slide of girl in Andes with bright red cheeks And there are complicated reaction norms due to many genes--- eg. people seek shade when the sun is hot . But in all cases the phenotypic flexibility is what is adaptive, the ability to adapt appropriately is coded by the genes.
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It is the ability to react appropriately that is coded by the genes. Behavioral responses and strategies often proceed as if they were based on a set of decision rules about how to behave in a particular situation. For example, consider a baby’s response to food with different tastes. Babies typically act as if they had an inborn strategy that specifies: 1) if the food tastes bitter, spit it out; 2) if the food tastes sweet, it is good to eat. Swallow or spit is the reaction norm produced by a few ‘food preference genes’. Consider also our response to being situated in precarious situations of great
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ASB 194 Lecture 4new.doc - Lecture 4. I. Behavior as...

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