# Substantial Genetic Differentiation Within and Between Populations of the European Adder (Vipera berus) in Baden‐Württemberg, Germany

## TL;DR

European adders in Baden-Württemberg show high genetic differentiation and low gene flow due to habitat fragmentation, requiring conservation action.

## Contribution

The study reveals genetic erosion and within-site differentiation in European adders caused by roads and habitat fragmentation.

## Key findings

- High genetic differentiation and low gene flow were found within and between adder populations.
- Evidence of genetic erosion, including excess homozygotes and sibling relationships, was detected across all sites.
- A road was identified as a barrier to gene flow at one site, causing within-site differentiation.

## 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 F
IS 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.

The number of records of the European adder
Vipera berus
has declined substantially during the last decades in Baden‐Württemberg, Germany from habitat fragmentation and destruction. We genotyped 141 individuals sampled at eight sites in this region and evaluated 10 microsatellite markers. We found high average pairwise relatedness values and close sibling relationships for all sites, indicating high genetic differentiation within sites. Differentiation between sites was also high. In summary, our results indicate genetic erosion and a low gene flow within and between sites and ask for conservation measures to enable long‐term survival of the adder in Baden‐Württemberg.