Geue JC, Vágási CI, Schweizer M, Pap PL and Thomassen HA 2016. Environmental selection is a main driver of divergence in house sparrows (Passer domesticus) in Romania and Bulgaria. Ecology and Evolution (in press).
Abstract: Both neutral and adaptive evolutionary processes can cause population divergence, but their relative contributions remain unclear. We investigated the roles of these processes in population divergence in house sparrows (Passer domesticus) from Romania and Bulgaria, regions characterized by high landscape heterogeneity compared to Western Europe. We asked whether morphological divergence, complemented with genetic data in this human commensal species was best explained by environmental variation, geographic distance, or landscape resistance ‒ the effort it takes for an individual to disperse from one location to the other ‒ caused by either natural or anthropogenic barriers. Using generalized dissimilarity modeling, a matrix regression technique that fits biotic beta diversity to both environmental predictors and geographic distance, we found that a small set of climate and vegetation variables explained up to ~30% of the observed divergence, whereas geographic and resistance distances played much lesser roles. Our results are consistent with signals of selection on morphological traits and of isolation by adaptation in genetic markers, suggesting that selection by natural environmental conditions shapes population divergence in house sparrows. Our study thus contributes to a growing body of evidence that adaptive evolution may be a major driver of diversification.
Fig. 1 Study region, sampling sites, and generalized dissimilarity modeling (GDM) results. (a) Location of the study region within Eastern Europe, with average temperature of the year (Bio 1). (b) Overview of the study area, with sampling sites (crosses) on a hillshade map and an overlay of percent tree cover. (c-e) GDM results for the second morphological shape component for females (c), the morphological size component in females and the first shape component for males (d), and microsatellites (e). The color difference between two locations along the color bar (c, d), or on the RGB color cube (e) in the GDM maps represents the magnitude of the difference in the biotic response variable, i.e. morphological variable or FST.