Population genetic structure of stone crayfish in the canton of Aargau
The stone crayfish (Austropotamobius torrentium) is an endangered freshwater species. It suffered sever declines due to habitat degradation as well as the crayfish plague, a lethal pathogen transmitted by North American crayfish species invasive to Switzerland. The aim of this study was to determine the amount of genetic diversity and the genetic differentiation of the few remaining stone crayfish populations in the canton of Aargau. In the largest remaining stone crayfish stock in the brook system of Mettauertal I also investigated the effect of migration barriers on genetic structure of stone crayfish populations by testing for correlations between genetic differentiation (FST‐values) and the number or cumulative height of barriers, correcting for waterway distance. Genetic analysis with microsatellites and subsequent cluster analysis revealed pronounced genetic differentiation among disconnected populations and identified five genetic clusters, one containing three populations. Moreover, the large population in Mettauertal was identified as the genetically most diverse one. Fine‐scale sampling within these populations showed that FST‐values correlated with the number of barriers after applying partial Manteltests to correct for waterway distance and cumulative height of barriers. However, strong correlations between all three independent variables do not permit a clear statement on the effects of barriers relative to distance per se on the fine‐scale genetic structure. Conservation management for Austropotamobius torrentium in the canton of Aargau has already met the prioritization for genetically diverse populations by listing the population of Mettauertal as a nationally important gene pool of conservation value. Its members could be used to improve long‐term evolutionary potential of other populations by translocation. Individuals belonging to the abundant population of Niederwil could be translocated into less dense populations in Mühlau and Lenzburg of the same genetic cluster. This could lower the risk of population decline by stochastic factors. Clarification of their genetic correspondence to the Niederwil population by re‐sampling and an analysis of habitat suitability should however be done in the Lenzburg and Mühlau populations. At four sites from which stone crayfish were reported in earlier surveys, my work did not find any individuals. Even though the potential extinction of these populations needs to be confirmed by more intensive sampling, my observations suggest that the decline of this species in the canton is ongoing. Further efforts to stabilize remaining populations in Switzerland should be executed according to the pragmatically formulated action plan for crayfish of 2011.