Genetic architecture and the evolution of local adaptation and differentiation with gene flow
Reinhard Burger (Department of Mathematics, University of Vienna)
(September 24, 2013 10:20 AM - 11:15 AM)
In subdivided populations, adaptation to a local environment may be hampered by maladaptive gene flow from other subpopulations. We study a continent-island model in which an ancestral population sends migrants to a colony exposed to a different environment. At an isolated locus, i.e., unlinked to other loci under selection, a locally beneficial mutation can be established and maintained only if its selective advantage exceeds the immigration rate of alternative allelic types. We show that, if a beneficial mutation arises in linkage to a locus at which a locally adapted allele is already segregating in migration-selection balance, the new mutant can invade and be maintained under much higher immigration rates than predicted by one-locus theory. We deduce the maximum amount of gene flow that admits the preservation of the locally adapted haplotype on the strength of recombination and selection. We calculate the selective advantage of recombination-reducing mechanisms, such as chromosome inversions, which often seem to play a role in speciation. Our analysis provides conditions for the evolution of clusters of locally adaptive genes, or islands of divergence, as found by some empirical studies. For an extended model that allows for epistasis, we discuss how much gene flow is needed to inhibit speciation by the accumulation of Dobzhansky-Muller incompatibilities.