Genetic Consequences of Range Expansions

TLDR

Range expansions have repeatedly occurred across species, yet their genetic consequences remain poorly understood, despite theoretical and simulation work indicating they differ from simple demographic expansions and can shape molecular diversity patterns. Spatial expansions can create allele‑frequency gradients, promote surfing of rare variants, generate low‑diversity sectors, and cause extensive introgression—patterns once attributed to selection that underscore the importance of dynamic range changes in evolution.

Abstract

Although range expansions have occurred recurrently in the history of most species, their genetic consequences have been little investigated. Theoretical studies show that range expansions are quite different from pure demographic expansions and that the extent of recent gene flow conditions expected patterns of molecular diversity within and between populations. Spatially explicit simulation studies have led to unexpected and fascinating results about genetic patterns emerging after a range expansion. For instance, spatial expansions can generate allele frequency gradients, promote the surfing of rare variants into newly occupied territories, induce the structuring of newly colonized areas into distinct sectors of low genetic diversity, or lead to massive introgression of local genes into the genome of an invading species. Interestingly, most of these patterns had been previously attributed to distinct selective processes, showing that taking into account the dynamic nature of a species range can lead to a paradigm shift in our perception of evolutionary processes.