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Speciation Species have unique combinations of features when similar, usually closely related Species are reproductively isolated when closely related, can hybridize Allopatric & sympatric speciation Allopatric speciation populations evolve in geographic isolation Sympatric speciation populations evolve in geographic proximity Allopatric speciation Geographic isolation produces genetic isolation Allopatric speciation Populations can become geographically isolated when individuals colonize a new habitat Allopatric speciation Populations can also become geographically isolated when a species’ former range is split into two or more distinct areas Sympatric speciation Natural selection can cause populations to diverge even when a small amount of gene flow occurs Sympatric speciation Changes in chromosome number isolate populations genetically Speciation triggered by changes in chromosome number has been especially important in plants (polyploidization) Mechanisms of divergence Genetic drift Natural selection Sexual selection Reinforcement Mechanisms of divergence Genetic drift Drift can produce rapid genetic divergence in small, isolated populations Mechanisms of divergence Natural selection Natural selection can produce genetic divergence in populations subjected to different pressures Mechanisms of divergence Sexual selection Sexual selection acts on characters involved in mate choice Mechanisms of divergence Sexual selection Mechanisms of divergence Sexual selection Changes in sexual selection may isolate populations and cause rapid divergence Mechanisms of divergence Reinforcement Reinforcement leads to assortative mating and the prezygotic isolation of populations Mechanisms of divergence Prezygotic isolation Reinforcement Genetic distance Allopatric Sympatric
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