Effects of a range expansion on adaptive and neutral genetic diversity in dispersal limited Hazel grouse (Bonasa bonasia) in the French Alps

Biogeographic range expansions, when related to dispersal limitation, may have counter intuitive effects on genetic diversity. At range margins the relative roles of demographic changes, connectivity and genetic diversity need to be integrated for a successful assessment of population viability. Historically the Hazel grouse (Bonasa bonasia) in France was found in the north of the French Alps and also in a disjunct population in the nearby Jura Mountains. The species has recently undergone a range expansion in a north to south axis in the Alps. Local population size estimates and migration patterns during expansion have previously been studied. In this study, we performed genotyping at neutral (microsatellite) and adaptive (MHC) genetic markers in Hazel grouse. We compared diversity and differentiation (F-ST and D-EST) at three sampling localities along the expansion axis in the French Alps and Jura, as well as at two sampling localities in Sweden, where the population has had a long-term continuous and stable distribution. Strong serial founder effects were found between the French localities, resulting in stronger isolation further south, with a relatively high neutral differentiation (pair-wise F-ST = 0.117). However, the loss of adaptive diversity MHC was slight. No adaptive differentiation (MHC D-EST = -0.015) was observed, thus, the French localities can be considered uniform units with regard to MHC diversity, a criterion to treat populations in these localities as a management unit.