Without the evolution of some

Without the - speciation 3 if populations come into secondary contact no gene flow(= speciation complete If no gene flow after secondary contact

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Without the evolution of some intrinsic barrier to gene exchange, fusion of the two incipient species would be one likely outcome (populations would blend back into one), or extinction of one or the other lineages (one population out competed [at the individual level!] the diverged sister population leaving only one population). MODELS OF SPECIATION There are may models which have been proposed that enable barriers to gene exchange to evolve; as argued by Ernst Mayr, geographic isolation provides the most effective barrier. We thus consider the allopatric model : 1. continuous distribution split into two (or more) sub populations 2. differentiation in allopatry (different selection regimes; not necessarily selection for
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Unformatted text preview: speciation) 3. if populations come into secondary contact, no gene flow (= speciation complete) If no gene flow after secondary contact, speciation was completed in allopatry . Speciation would then be viewed as a byproduct of divergence in allopatry . What happens after secondary contact is a matter of great debate: If the two differentiated forms mix or hybridize this may provide the context for selection for assortative mating also called reinforcement of premating isolation (reinforcement hypothesis). In this case speciation was not completed in allopatry and fate of the two populations depends on the outcome of the interaction upon secondary contact....
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This note was uploaded on 11/06/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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