The dynamics of underdominant alleles during species range expansions
We investigate clines in allele frequencies that exist where there are no apparent ecological determinants of divergence over space. To understand these patterns of spatial genetic structure and potential species divergence, we model the establishment of clines that occur due to the surfing of underdominant alleles during range expansions. We provide analytical approximations for the fixation probability of underdominant alleles at expansion fronts and demonstrate that gene surfing can lead to clines in 1D range expansions. We extend these results to multiple loci via a mixture of analytical theory and individual-based simulations. We study the interaction between the strength of selection against heterozygotes, migration rates, and local recombination rates on the formation of stable hybrid zones. A key result of our study is that clines created by surfing at different loci can attract each other and align after expansion, if they are sufficiently close in space and in terms of recombination distance. Our findings suggest that range expansions can set the stage for parapatric speciation due to the alignment of multiple selective clines, even in the absence of ecologically divergent selection.
1 Evolution of dispersal can rescue populations from expansion load
2 Transition from background selection to associative overdominance promotes diversity in regions of low recombination
3 Mutation load dynamics during environmentally-driven range shifts