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Unformatted text preview: in determining the outcome of speciation (or fusion). The cricket hybrid zone (fig. 16.8, page 438) is in fact the result of allopatry followed by secondary contact (my personal knowledge), but Ridley does not let you know this. Non-allopatric models of speciation are controversial but not impossible. Sympatric speciation can be modeled with a two locus polymorphism, one locus (A) affecting fitness (in this case by affecting fitness in terms of survival on one of two alternative hosts/patches), and another locus (B) affecting mate choice which is crucial in the evolution of assortative mating , a barrier to gene exchange (proposed by John Maynard-Smith in 1966) AA Aa aa BB Bb bb host 1 1+s 1 1 mate w/ AA no preference mate w/ aa host 2 1 1 1+t...
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