"Locally adaptive inversions in structured populations"Mackintosh, CarlChromosomal inversions are a type of recombination-suppressing structural variant that have been proposed to facilitate local adaptation by linking together locally coadapted alleles at different loci. Prior work addressing this theoretically has considered the spread of inversions in “continent-island” scenarios in which there is a unidirectional flow of maladapted migrants into the island population. In this setting, inversions capturing locally adaptive haplotypes are most likely to invade when selection is weak, because stronger local selection i) more effectively purges maladaptive alleles, and ii) generates linkage disequilibrium between adaptive alleles, thus lessening the advantage of inversions. We extend this model by studying the establishment of inversions in a more general two-deme context, which explicitly considers the dynamics of allele frequencies in both populations linked by bidirectional migration. In this scenario, stronger selection increases the allele frequency divergence between demes thereby increasing the frequency of maladaptive alleles in migrants, ultimately favouring inversions—the opposite of the pattern seen in the asymmetric continent-island scenario. Furthermore, we account for the likelihood that a new inversion captures an adaptive haplotype in the first instance. When considering the combined process of capture and invasion in “continent-island” and symmetric scenarios, relatively strong selection increases inversion establishment probability. Overall, our analysis suggests inversions that are favoured because they capture locally adaptive alleles are likely to harbour larger effect alleles that experience relatively strong selection. |
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