From Local Adaptation to Speciation: Specialization and Reinforcement

Figure 2

Indirect selection on a migration modifier with local adaptation. Sketches how a migration modifier evolves in presence of local adaptation (for the sake of illustration the M allele causes maximal migration (1/2) and the m allele zero migration). Before migration (step 1) consider two habitats with haploid individuals. Before migration (step 1) consider two habitats with haploid individuals. On the left the A allele is favored at a local adaptation locus whereas a is favored on the right. To make things simple we consider these alleles to be fixed where they are beneficial. During migration only individuals with allele M move between habitats (step (2) migrants in red). Half of the M individuals move to the other habitat and the other half stays at home. Importantly migration directly generates LD between the M allele and the locally inferior allele (the locally inferior allele is found only with M and not with m). Finally, selection occurs favoring A on the left and a on the right very strongly in the illustration and carries the m allele with the adaptation locus because of the linkage disequilibrium generated at the previous step (the m overall frequency has raised from 1/2 to 2/3 on the illustration). Note that in a finite population kin selection by contrast favors M [54].