Individual variation in dispersal associated with phenotype influences fine-scale genetic structure in weasels

In general, landscape genetic studies have ignored the potential role that the phenotype of individuals plays in determining fine-scale genetic structure in species. This potential over-simplification ignores an important component that dispersal is both condition- and phenotype-dependent. In order to investigate the relationship between potential dispersal, habitat selection and phenotype, we examined the spatial ecology, body mass and fine-scale genetic structure of weasels (Mustela nivalis) in Bia?owie?a Forest in Poland. Our study population is characterized by an almost three-fold phenotypic variation in adult body mass and weasels were segregated in certain habitats according to size. We detected significant genetic structuring associated with habitat within the studied area and analyses of radio-tracking and re-capture data showed that the maximum extent of movement was achieved by weasels of medium body size, whereas the smallest and largest individuals exhibited higher site fidelity. With the unrestricted movement of the medium-sized individuals across optimal habitat, genetic admixture does occur. However, the presence of a barrier leads to unidirectional gene flow, with larger individuals outcompeting smaller individuals and therefore maintaining the genetic break in the study area. This highlights the importance of considering both intrinsic (phenotype) and extrinsic (environmental) factors in understanding dispersal patterns and ultimately, gene flow in complex landscapes.