Daphnia in the Tatra Mountain lakes: multiple colonisation and hidden species diversity revealed by molecular markers

Abstract

Ecosystems of European mountain lakes may harbour relict populations of boreal aquatic species, including cryptic lineages not easily recognised using traditional taxonomic methods. As a previous genetic study revealed the presence of the cryptic cladoceran species Daphnia lacustris in the area, we explored the species diversity of the Daphnia longispina group (Crustacea: Cladocera: Anomopoda) in lakes of the Tatra Mountains (Central Europe: Slovakia - Poland). Daphnia populations representing various morphotypes from sixteen mountain lakes were analyzed by DNA methods, including restriction fragment length polymorphism of the nuclear ribosomal internal transcribed spacer region (ITS-RFLP) and sequencing of the mitochondrial 12S rDNA gene. Altogether, three Daphnia species of the D. longispina group were found in the region: D. longispina, D. galeata, and D. lacustris; we detected neither their syntopic occurrence nor interspecific hybrids. D. lacustris was found in two neighbouring lakes in the Polish High Tatras (Nizni Toporowy Staw and Wyzni Toporowy Staw); these may represent relict populations, since the closest known extant populations of this species are found in Fennoscandia. Morphologically highly variable populations of D. longispina formed the majority (69 %) of the analysed populations. Relatively high divergence of 12S rDNA haplotypes from various lakes suggests multiple colonisations of the Tatra Mountain region by this species. Similarly, each of the three recorded D. galeata populations is probably of different origin. In addition, we found that the species replacement in one lake, from either D. lacustris or D. longispina to D. galeata, was associated with anthropogenically mediated environmental changes (fish stock increase, eutrophication).