The genetic signature of rapid range expansion by flying squirrels in response to contemporary climate warming

Abstract

Climate is an important factor limiting species distributions. Historic climate-change related range movements have modified the genetic diversity of species by the merging and splitting of gene pools and by the effects associated with recurrent founder events. These effects are often inferred, either from retrospective analyses of current genetic patterns or from simulations. Rarely has it been possible for the population genetic effects of range expansion to be examined with contemporaneous demographic data. We characterized the genetic signature of rapid range expansion by southern flying squirrels (Glaucomys volans) and compared these results to a stationary population of the closely related northern flying squirrel (Glaucomys sabrinus) in Ontario, Canada. Samples were taken during an approximately 200 km range expansion by G. volans (1994-2003) and genotyped at 6 (G. sabrinus) and 8 (G. volans) microsatellite loci. For G. volans, but not G. sabrinus, we found evidence of a latitudinal gradient in allele frequencies and a decrease in allelic richness along the axis of expansion. We found no evidence of isolation-by-distance in either species or of genetic bottlenecks in the area of G. volans expansion. These results suggest that serial founder events can cause an immediate reduction in genetic diversity following rapid range expansion with high levels of gene flow giving rise to heterogeneity within what would classically be termed panmixia. Given the pace of anthropogenic climate change, and the increasing incidence of range movements in response, this may be an important, immediate consequence of climate change.

A Phylogeographic and Population Genetic Analysis of a Widespread, Sedentary North American Bird: the Hairy Woodpecker (Picoides Villosus)

“…The number of generations presented here may seem low and may raise questions regarding our ability to detect the signature of a bottleneck or other effects of genetic drift. However, results from previous studies suggest otherwise (e.g., Garroway et al 2011, Harper 2011, Short and Petren 2011, Swaegers et al 2014. Our study provides evidence that continuous gene flow from conspecifics may prevent the loss of genetic diversity from recently established populations at the edge of a species' range.…”

“…In expanding populations, allelic frequency gradients are often present along the axis of range expansion, as Garroway et al (2011) found in the case of southern flying squirrels. Along with the presence of these gradients, a reduction in the effective number of alleles, or allelic richness, starting from the source population and emanating out in the direction of range expansion is sometimes observed.…”

“…Similar patterns of loss of neutral genetic diversity should be found in contemporary range shifts, but since current climate changes are taking place more rapidly, the genetic changes occurring in populations undergoing current expansions should look aberrant when compared with populations in the center of a species' current distribution. Thus far, relatively few empirical studies have investigated the genetic responses of populations undergoing contemporary range expansions or distributional shifts (Garroway et al 2011, Song et al 2013, Swaegers et al 2014.…”

Rapid range expansion increases genetic differentiation while causing limited reduction in genetic diversity in a damselfly

“…Results so far are equivocal. To our knowledge, only two studies reported the expected reduction in genetic diversity (Watts et al, 2010;Garroway et al, 2011), and only one the expected increase in genetic differentiation (Watts et al, 2010). These studies all documented range expansions occurring along a single axis of a relative narrow (o100 km) expansion front.…”

“…Despite its relevance, only very recently the genetic consequences of natural, contemporary range expansions have started to receive attention (Watts et al, 2010;Banks et al, 2010;Garroway et al, 2011;Buckley et al, 2012). Results so far are equivocal.…”