A non-invasive genetics insight into population structure and recolonization dynamics of the Eurasian otter (Lutra lutra) at the boundary of its Italian core range

During the past century the Eurasian otter (Lutra lutra) suffered a drastic decline throughout the rivers of the Italian peninsula, surviving only in Southern Italy. Recent surveys have revealed irrefutable signs (i.e. faeces' presence) of otter expansion in Central Italy and, specifically in the last 15 years, along rivers of Abruzzo region. Gradually expanding along the Sangro river, otters have also recolonized the Abruzzo, Lazio and Molise National Park (PNALM). To explore both the dispersal dynamics from Southern Italy to Abruzzo and the potential factors that may limit gene flow with PNALM population, we collected faeces (spraints) and anal jelly samples from rivers in Abruzzo and Molise, as well as tissue samples from Southern Italy. We identified 52 specimens using 11 microsatellite loci. Results revealed a significant genetic differentiation between Southern and Central Italy, suggesting a stepping-stone recolonization process. Genetic structure analysis and gene flow estimation indicated that otters followed different recolonization routes, dispersing across the hinterland and along coastal areas. Population structure in Abruzzo is weak and genetic diversity low, consistent with a recent colonization and a founder effect. The Ne estimated could indicate the presence of few breeding adults in the PNALM population, but Nc estimated and the 18 unique genotypes in the protected area, suggested the hosting of a higher number of individuals than initially assumed. Although otter group in PNALM is showing a favourable conservation status, its genetic diversity is low, making it vulnerable to demographic and environmental stochastic factors. Accordingly, interventions are recommended to favour movements of otters and increase the likelihood of stabilization and expansion of Central Italy's population.