Abstract: | Many ectothermic species are currently expanding their geographic range due to global
warming. This can modify the population genetic diversity and structure of these species
because of genetic drift during the colonization of new areas. Although the genetic
signatures of historical range expansions have been investigated in an array of species,
the genetic consequences of natural, contemporary range expansions have received little
attention, with the only studies available focusing on range expansions along a narrow
front. We investigate the genetic consequences of a natural range expansion in the
Mediterranean damselfly Coenagrion scitulum, which is currently rapidly expanding
along a broad front in different directions. We assessed genetic diversity and genetic
structure using 12 microsatellite markers in five centrally located populations and five
recently established populations at the edge of the geographic distribution. Our results
suggest that, although a marginal significant decrease in the allelic richness was found
in the edge populations, genetic diversity has been preserved during the range expansion
of this species. Nevertheless, edge populations were genetically more differentiated
compared with core populations, suggesting genetic drift during the range expansion. The
smaller effective population sizes of the edge populations compared with central
populations also suggest a contribution of genetic drift after colonization. We argue and
document that range expansion along multiple axes of a broad expansion front generates
little reduction in genetic diversity, yet stronger differentiation of the edge
populations. |