Zoology 445 Fall 2006Speciation II Handout2. Genetic and ecological divergence of the isolated gene pools.a. The two gene pool diverge so they have different niches and hybrids have reducedfitness.Divergence is the result of three processes:1. Genetic drift2. Natural selection3. Sexual selection1. Genetic DriftOriginal populationFitness surface based on floral charactersBeeMothHummingbirdFounder population2. Natural selectionClassic example is in the apple maggot fly, Rhagolitis pommonella.Divergence occurs because the hosts differ in scent cues and temporal availability- Host conditioning emerging adults appears to prefer the host species on which they emerge. Thus apple adults preferentially migrate to apples and hawthorn adults to hawthorn.- Allochronic development. Apples are available for oviposition before hawthorns. Thus individuals from the apple host emerge from pupae 1½ to 2 weeks before hawthorn race. Thus they have mated before the bulk of the hawthorn flies have emerged.AM Jarosz 1Zol 445 Jarosz3. Sexual selectionTheoryDifferent mutations occur in the two populations while in isolation, and sexual selection operateson these mutations in a manner that causes the mating behavior of the two populations to diverge.One apparent example of this is in the Drosophila on the Hawaiian islands. D. silvestris & D. heteroneura.2Zol 445 Jarosz\Evolution Zol 445\2006\Speciation II