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Allopatric speciation 3 steps: (1) isolation (2) divergence (3) reproductive isolation

Allopatric speciation 3 steps: (1) isolation (2) divergence (3) reproductive isolation. Isolation without migration, populations can diverge allopatry – Isolation can occur through: colonization of a new habitat - - vicariance –

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Allopatric speciation 3 steps: (1) isolation (2) divergence (3) reproductive isolation

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  1. Allopatric speciation 3 steps: (1) isolation (2) divergence (3) reproductive isolation • Isolation • without migration, populations can diverge • allopatry – • Isolation can occur through: • colonization of a new habitat • - • - • vicariance – • e.g., sinking/rising of land bridge, separation of continents

  2. Allopatric speciation 3 steps: (1) isolation (2) divergence (3) reproductive isolation • Divergence • after isolation, no gene flow, so populations can diverge • Divergence by genetic drift • most pronounced in small populations • small groups of colonizers • small isolated peripheral populations

  3. Allopatric speciation 3 steps: (1) isolation (2) divergence (3) reproductive isolation • Reproductive isolation • after divergence in isolation, populations may no longer be able • to produce viable offspring • postzygotic reproductive isolation – • - • Secondary contact • after divergence in isolation, populations come back together • hybrid matings take place, but offspring are unfit  • reinforcement – • reinforcement completes reproductive isolation • prezygotic reproductive isolation –

  4. Other ways for speciation to work 3 steps: (1) isolation (not necessarily geographic) (2) divergence (not just by drift) (3) reproductive isolation (secondary contact not necessary) • Isolation • without gene flow, populations can diverge • Other methods of isolation: • chromosomal changes including polyploidy • - • sympatric speciation – • - isolation by biology rather than geography especially habitat or food preferences  

  5. Sympatric speciation 3 steps: (1) isolation (different host plants) (2) divergence (natural selection) (3) reproductive isolation • Example:apple maggot flies • mate and lay eggs on apples or hawthorns • each host plant selects for different traits • because mating occurs on host fruit, • assortative mating occurs • and gene flow is prevented

  6. Other ways for speciation to work 3 steps: (1) isolation (not necessarily geographic) (2) divergence (not just by drift) (3) reproductive isolation (secondary contact not necessary) • Other mechanisms of divergence • natural selection – isolated populations experience different env’s • - • sexual selection – isolated populations differ in sexual selection • may diverge until they fail to recognize each other as mates  • prezygotic reproductive isolation • divergence in sympatry – strong selection can allow divergence • - • - assortative mating must prevent most gene flow between groups

  7. Other ways for speciation to work 3 steps: (1) isolation (not necessarily geographic) (2) divergence (not just by drift) (3) reproductive isolation (secondary contact not necessary) • Reproductive isolation • prezygotic reproductive isolation – • can evolve through sexual selection, drift, or natural selection • or by reinforcement • postzygotic reproductive isolation – • - can evolve by drift or natural selection • Secondary contact • not required if…

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