BSC 385 Lecture 9: Chapter 6

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Chapter 6
Behavioral Ecology
A Case Study: Social Behavior
Alarm calls
o Warn other colony members of a predator’s presence
o Increase the probability that the caller will fall prey
How Does Behavior Evolve?
Behaviors contribute to fitness
Behaviors that are genetically controlled are subject to natural selection
Like other traits, each behavior has both a fitness cost and benefit
Selection favors behaviors for which the benefits outweigh the costs
Behaviors are result of genetic make-up as well as environment and experience of an
individual
o Few behaviors are purely genetically fixed or purely the result of the environment
o Behavioral plasticity is itself an adaptation
The relative contributions of the environment and genetics in behavior can be measured
as heritability
Heritability
Broad sense heritability (H^2): the proportion of the total variation that is due to genetic
differences among individuals
Range 0-1
Phenotypic variation Vp = Vg + Ve
H^2 = Vg/Vp
o Vg genetic variation among individuals
o Ve environmental variation
o Vp total phenotypic variation
Narrow sense heritability (h^2): the proportion of the total phenotypic variance that is due
to additive genetic variance
Range 0-1
h^2 = Va / Va + Vd + Ve
o Va variation due to additive genetic differences between individuals
o Vd the effect of dominance (the masking of recessive genes by dominant ones)
o Ve environmental variation
Estimates of Heritability
h^2 can be measured as the slope of the regression of the average offspring phenotype vs.
the average of the parental phenotypes
Estimates of h^2 can be obtained by comparison of monozygotic and dizygotic twins
raised in different environments
Heritability Affects Evolutionary Rate
Traits with high heritability respond to natural selection more rapidly than traits with low
heritability
R = (h^2)(s)
o Where R is the change in the trait, h^2 is heritability, and s is the selection
coefficient
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