Every Branch in Its Niche: Intraspecific Variation in Habitat Suitability of a Widely Distributed Small Mammal, the Harvest Mouse Micromys Minutus

Climate and land use changes re-shape the distribution of species around the world, so understanding biogeographical patterns is key to protect and manage wildlife, particularly in the case of threatened or declining species. Species with wide ranges are usually considered as common, yet the occurrence of intraspecific variability and adaptation to local conditions may pose serious challenges to their conservation. In this paper, we selected the harvest mouse Micromys minutus as a model species to assess the role of intraspecific genetic variability in shaping the environmental preferences and distribution of a widely distributed mammal across Europe. By applying an integrative approach combining species distribution modelling and phylogenetic reconstruction, we assessed the clade-specific habitat suitability of all mitochondrial clades of the species occurring in Europe, unveiling distinct bioclimatic niches. Most of Central Europe results as suitable to M. minutus, whereas different clades showed distinct distributions of suitable areas across Europe, with limited overlap. We then combined mitochondrial analyses with clade-specific suitability maps to determine the geographic delimitations of Italian and central European clades. We showed that individuals from the northernmost Italian regions actually belong to the central European clade, consistent with the biogeographical patterns of other small mammals, and indicating potential past dispersal between the Italian Peninsula and Central Europe, or human-assisted translocations. Our results highlight the importance of intraspecific variability in shaping biogeographical patterns of widely distributed species, also representing a reproducible exercise to understand their environmental preferences and eventually fostering their conservation.