Unformatted text preview: • The lack of fertility of the offspring of hybrids that are not completely sterile is usually attributed to hybrid breakdown • Postzygotic reproductive isolation imposes a considerable fitness cost. • Natural selection should normally favor the preemption of fitness costs associated with interspecific fertilization. 6.3 – Geographical Separation of populations fosters speciation • Geographically separated populations are called allopatric, evolutionarily independent. • Speciation may still not occur upon barrier removal. • Selection will strongly favor mating only within species upon reunification of allopatric species if there is established postzygotic reproductive isolation due to fitness costs. • Natural selection actively favors the maintenance of multiple laters of mechamisms for reproductive barriers between species 6.4 The genetic mechanisms of allopatric speciation may be adaptive or nonadaptive •...
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- Spring '08
- Evolution, postzygotic reproductive isolation