Substantial genetic differentiation within and between populations of the European adder (Vipera berus) in Baden-Württemberg, Germany

Abstract

Habitat destruction and fragmentation are the main threats to species' long-term survival, they isolate populations geographically and genetically. Over the last centuries, the European adder (Vipera berus) has experienced a decline in abundance and an increase in population extinctions within its entire distribution area. In our study, we aimed to infer whether these trends that are also observed in Baden-Württemberg, Germany have affected the genetic constitution of adders in this region. We therefore genotyped 141 adders using 10 microsatellite markers. Adders were sampled at eight sites, six in the northern Black Forest, one in the southern Black Forest and one in the Swabian Jura. We analyzed genetic diversity, genetic differentiation within sites, average pairwise relatedness and sibling relationships at each site. We additionally applied population STRUCTURE analyses on all and to a subset of individuals and we assessed genetic differentiation between sites. Genetic diversities inferred were like those found in other European regions. We detected signs of genetic erosion across all sites, that is, an excess of homozygotes, positive FIS values, large mean pairwise relatedness values and/or the presence of full and half sib dyads. At one site, we found clear evidence for a within-site differentiation by STRUCTURE and sibship clustering, which we attribute to a barrier to gene flow, that is, a road bisecting the site. We inferred high genetic differentiation between all sites, indicating low gene flow between sites. Our findings indicate that conservation measures should increase population sizes and restore gene flow within and between adder populations in Baden-Württemberg.