Phylogeography of noble crayfish (Astacus astacus) reveals multiple refugia

SUMMARY 1. Reconstructing the phylogeographic history of a species can aid in defining areas of conservationpriority. For freshwater species, historical river structure plays a significant role in explaining geneticdifferentiation and population structure. However, human-induced translocations can erase thenatural genetic structure, especially for species of commercial interest such as the noble crayfish(Astacus astacus).2. Our aim was to reconstruct the current genetic structure of the endangered noble crayfish incentral Europe to identify refugial areas that are hotspots of genetic diversity. We analysed afragment of the mitochondrial cytochrome oxidase subunit I, and the 16S rRNA from 540 noblecrayfish specimens from 156 sampling sites distributed around five European sea basins.Additionally, we conducted a microsatellite analysis of 289 individuals from 22 sites.3. Both mitochondrial and nuclear markers revealed genetically relatively homogenous populations incentral Europe that had been influenced by anthropogenic translocations. However, some areas (Eidercatchment in northern Germany and Rhineland-Palatinate in south-western Germany) show a distinctgenetic structure with endemic haplotypes and private alleles indicating (i) that these areas wererefugia for A. astacus in central Europe and (ii) that these populations have not been subject to anthro-pogenic translocations. Further, we found the highest genetic diversity in the Black Sea basin and par-ticularly high differentiation between populations from the western Balkans and the remaining BlackSea populations. The split between Western Balkan and the remaining European populations is esti-mated to have occurred approximately 700 k years before present, whereas remaining differentiationsoccurred within the last 450 k years. Using migration modelling, we detected that the North Sea basinand the Baltic Sea basin were colonised independently via different colonisation paths from the easternBlack Sea basin, while the western Balkans did not contribute to this colonisation.4. Our results suggest the existence of at least two refugial areas in south-eastern Europe. To conservemaximum genetic diversity, conservation priorities for noble crayfish should focus on the south-easternEuropean genetic hotspots and on populations in central Europe that hold an autochthonous geneticstructure (e.g. Langsee in the Eider catchment area). We further propose that each river catchmentshould form a separate management unit to reduce anthropogenic genetic homogenisation.Keywords: human-mediated translocation, microsatellite analysis, migration model, mitochondrial DNA,refugial areas