Drivers of population structure and connectivity in a mountain biodiversity hotspot: Current patterns and future trends in fire salamander populations

Mountain regions are characterized by complex topographic, climatic, and habitat features where interweaving eco-evolutionary processes generate intricate spatial patterns of biological diversity, especially in organisms with low dispersal abilities. As global changes critically threaten mountain ecosystems, disentangling the contribution of these processes is paramount and increasingly compelling. Here, we evaluated the contribution of mountain landscape features to the shaping of spatial patterns of genetic diversity in a low-dispersing amphibian, the fire-salamander Salamandra salamandra , within a highly heterogeneous mountain region, the Aspromonte massif in Southern Italy. We genotyped 198 fire salamanders from 74 locations at 13 microsatellite loci and assessed the spatial structure of genetic variation by coupling ordination-based and Bayesian clustering approaches. Then, we applied ecological modeling to evaluate the influence of climate, habitat heterogeneity, topography, hydrographic structure, and proximity to old-growth forests on patterns of genetic variation and population connectivity. All landscape predictors correlated with individual genetic differentiation, yet only climatic and habitat heterogeneity remained relevant once we ruled out the confounding effect of topographic distance. Notably, the distribution of old-growth forests was significantly associated with pairwise genetic dissimilarity, suggesting a key role of these areas as ecological refugia through time. Finally, by modeling landscape connectivity, we identified several ecological corridors for salamanders across the massif, although these corridors will dramatically decline under predicted climate change scenarios. This study outlines habitat configuration and climatic variation as major drivers of genetic diversity patterns in mountain regions and highlights the global significance of old-growth forests as refugia from global changes.