Genetic drift linked to heterogeneous landscape and ecological specialization drives diversification in the Alpine endemic columbine Aquilegia thalictrifolia

The European Alpine system is an extensive mountain range, whose heterogeneous landscape together with Quaternary climatic oscillations significantly affected organismal diversity and distribution in Europe. The model genus Aquilegia representsa textbook example of a rapid and recent radiation through the Northern hemisphere, with the majority of the European taxa occuring in the Alpine system. However, the processes governing genetic differentiation of the genus in this complex geographicarea are still widely unexplored. In this work, we used 9 microsatellite loci to study the genetic structure and diversity of 11 populations of Aquilegia thalictrifolia Schott & Kotschy, an alpine taxon characterized by a marked ecological specificity.We found that, despite the endemic and fragmented distribution, A. thalictrifolia has overall high levels of heterozygosity, which is consistent to the substantial inbreeding depression that characterizes the genus. Strong spatial genetic structuring ofpopulations suggests a historical prevalence of genetic drift over gene flow, with natural barriers and ecological niche hindering migration. An analytical comparison of fixation and population differentiation indexes allowed us to infer hypothesesof the postglacial history and more recent demographic events that have influenced the genetics of the species. Overall, ourresults indicate allopatry as a major force of differentiation in the European scenario, likely to underlie the development oftaxonomic boundaries in a broader geographic context. This adds to previous notions on the primary evolutionary forcesshaping the Aquilegia radiation in Europe