Pervasive genetic differentiation among Central European populations of the threatened Arnica montana L. and genetic erosion at lower elevations

Knowledge of within-species genetic diversity can improve effectiveness of conservation measures. These include the mitigation of extinction risks caused by habitat fragmentation, environmental change or diseases as well as site selection for in situ conservation that considers a thorough representation of genotypes. Based on genotyping at twelve nuclear microsatellites we assess genetic diversity of the endangered grassland species Arnica montana . In addition to presenting large scale patterns of genetic diversity, we studied differentiation and inbreeding along altitudinal and latitudinal gradients as well as in relation to population size. Thirty populations (561 individuals) were sampled to represent the species through Central Europe. A broad range of genetic diversity ( H e ) from 0.383 to 0.662 and high levels of genetic differentiation ( F ST = 0.27) were detected. Most variation was found within populations (73%) and not among populations (27%). The majority of populations showed private alleles and a significant pattern of isolation-by-distance. Bayesian analyses of shared ancestry revealed a high number of 24 distinct clusters. Populations at low altitude showed signs of genetic erosion and a tendency for increased clonal reproduction. The strong genetic differentiation of A. montana suggests restricted gene flow among populations. Due to high genetic diversity and no inbreeding, the southern and higher altitude populations in the Alps seem genetically unaffected from genetic erosion despite strong genetic differentiation. The results indicate that in particular lowland populations will depend on human intervention such as assisted gene flow and population reinforcement to avoid further genetic erosion.