Detailed genetic structure of European bitterling populations in Central Europe

The European bitterling (Rhodeus amarus) is a small cyprinid fish whose populations declined markedly between 1950 and 1980. However, its range currently expands, partly due to human-assisted introductions. We determined the genetic variability and detailed spatial structure among bitterling populations in Central Europe and tested alternative hypotheses about colonization of this area. Twelve polymorphic microsatellite loci on a large sample of 688 individuals had been used to analyse genetic variability and population structure. Samples originated from 27 localities with emphasis on area of the Czech Republic where three major sea drainages (Black, Baltic, and Northern Sea) meet. Highly variable level of intrapopulation genetic variability had generally been detected and a recent decrease in numbers (“bottleneck”) had been indicated by genetic data among six populations. High level of interpopulation differentiation was identified even within the basins. There was a significant role of genetic drift and indications of low dispersal ability of R. amarus. Surprisingly, the Odra River was inhabited by two distinct populations without any genetic signatures of a secondary contact. Czech part of the Odra (Baltic basin) was colonized from the Danubian refugium (similarly to adjacent Danubian basin rivers including the Morava), while Polish part of the Odra was genetically similar to the populations in the Vistula River (Baltic basin), that has been colonized by a different (Eastern) phylogeographic lineage of R. amarus. Most Czech R. amarus populations were colonized from the Danubian refugium, suggesting potential for a human-mediated colonization of the Odra or Elbe Rivers by R. amarus. One Elbe basin population was genetically mixed from the two (Danubian and Eastern) phylogeographic lineages. In general the Czech populations of R. amarus were genetically stable except for a single population which has probably been recently introduced. This research was supported by Czech Science Foundation no. 13-05872S.