Concurrent starling invasions suggest selection on shared genomic regions even after genetic bottlenecks

A species' success during the invasion of new areas hinges on an interplay between the demographic processes common to invasions and the specific ecological context of the novel environment. Evolutionary genetic studies of invasive species can investigate how genetic bottlenecks and ecological conditions shape genetic variation in invasions, and our study pairs two invasive populations that are hypothesized to be from the same source population to compare how each population evolved during and after introduction. Invasive European Starlings (Sturnus vulgaris) established populations in both Australia and North America in the 19th century. Here, we compare whole-genome sequences among native and independently introduced European Starling populations from three continents to determine howdemographic processes interact with rapid evolution to generate similar genetic patterns in these recent and replicated invasions. Demographic models indicate that both invasive populations experienced genetic bottlenecks, and we find that specific genomic regions have differentiated even on this short evolutionary timescale. Despite these bottlenecks, we suggest that genetic drift alone cannot explain differentiation in at least two of these regions, given that within-population nucleotide diversity and neutrality statistics indicate a role for purifying and/or diversifying selection. Instead, the patterns of genetic variation we find are consistent with the hypothesis that this infamous and highly mobile invader adapted to novel selection (e.g., extrinsic factors), perhaps in part due to the demographic boom intrinsic to many invasions.