Lect5 - Lecture 4 Behavior as heritable phenotypic...

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Lecture 4. Behavior as heritable phenotypic plasticity: In the previous lecture we finished up by talking about reaction norms. These are ranges of phenotypes that are produced by a single genotype depending on environmental context. Now we will extend this understanding of phenotypic plasticity from morphology and physiology to behavioral traits. In essence adaptive behaviors are rapidly expressed reaction norms whose range of expression is determined by genotypes, but whose actual expression at any moment is determined mainly by the environment. Many behavioral tendencies show high heritability, thus they constitute phenotypes that can evolve by natural selection. Note here that we are referring to tendencies (often personality traits) not to specific behaviors which cant be heritable because they are elicited by environmental cues. The tendency to do X when environmental cue Y is present is something that indeed is heritable from parents to offspring even when eliminating the effects of environmental similarities. Heritability is a biological measure of the 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 ~ 70%. Table- heritabilty of some behavioral and personality traits (from Plomin et al 1997, Yang et al 1996). B ehavior consists of sets of flexible, facultative responses, decisions, or strategies that occur in relation to varying environmental conditions. Behavior is often “adaptive” in the sense that the response maximizes survival or reproduction. Behavior as reaction norm : Soapberry bugs eat soapberries, and males find females near berry patches and then mount them to mate. After mating, males may either dismount and look for another female, or “stick” to a female to prevent her from mating with any other male (who might displace the first male’s sperm from the female’s reproductive tract). Scott Carroll showed that different genetic lines of male soapberry bugs show variation in whether they guard females after copulation. When sex ratios are highly female biased some males don’t guard females but instead rapidly search for a new mate after copulation. When females are rare, these males stay with a female after copulation and guard her from mating with other males. This flexible mate guarding behavior is a “reaction norm”
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The reaction norm for mate guarding takes the form--- "guard if females are rare, don’t guard if females are common". See figure from Carroll and Corneli 1999 (adapted in Boyd and Silk).
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