Rapid adaptation with gene flow via a reservoir of chromosomal inversion variation?

Abstract

The increased recognition of frequent divergence with gene flow has renewed interest in chromosomal inversions as a source for promoting adaptive divergence. Inversions can suppress recombination between heterokaryotypes so that local adapted inversions will be protected from introgression with the migrants. However, we do not have a clear understanding of the conditions for which adaptive divergence is more or less likely to be promoted by inversions when the availability of inversion variation is considered. Standing genetic variation, as opposed to new mutations, could offer a quick way to respond to sudden environmental changes, making it a likely avenue for rapid adaptation. For a scenario of secondary contact between locally-adapted populations, we might intuit that standing inversion variation would predominate over new inversion mutations in maintaining local divergence. Our results show that this is not always the case. Maladaptive gene flow, as both a demographic parameter and the cause for selection that favors locally-adapted inversions, differentiates the dynamics of standing inversion variation from that of segregating point mutations. Counterintuitively, in general, standing inversion variation will be less important to the adaptation than new inversions under the demographic and genetic conditions that are more conducive to adaptive divergence via inversions.