Dispersal Beyond Mountains and Borders: Asymmetrical Gene Flow Helps Maintain Brown Bear Metapopulation Connectivity on the Balkan Peninsula.

The Balkan Peninsula is a biodiversity hotspot, harbouring some of the largest transboundary populations of large carnivores such as brown bears. However, most studies to date in this area have addressed bear population dynamics within the confines of country borders, which presents limitations. Our aim was to address this, by investigating the genetic structure and dispersal dynamics of the Eastern Balkan brown bear population and its connectivity with the Dinaric-Pindos population from four mountain ranges and across country borders: Stara-Planina and Rhodope in the east and Stari-Vlah and Sharr Mountains in the west. Using both microsatellite markers and mitochondrial DNA data we detected a primary east-west cline in genetic structure, with additional north-south substructuring and high diversity overall. Evidence of past bottlenecks, historical isolation and ongoing cross-border, and primarily male-mediated gene flow, suggests complex dispersal dynamics shaped by past demographic fluctuations. Results from mitochondrial data further reflected signals from postglacial population contractions, re-expansions of Balkan populations. These findings emphasise the need for conservation strategies that maintain transboundary connectivity in this metapopulation, to ensure the long-term viability of brown bears on the Balkan Peninsula.