Cryptic diversity and speciation in endemic Cytherissa (Ostracoda, Crustacea) from Lake Baikal

Lake Baikal (Siberia) is the most ancient and deepest of all ancient lakes on Earth. It holds a (mostly endemic) diversity of thousands of animal species, including a speciose radiation of ostracods of the genus Cytherissa. Applying molecular tools to this crustacean group reveals that several morphological species are actually species clusters. Based on combined 16S and 28S DNA sequence data from thirteen classic Cytherissa species and one subspecies sensu Mazepova (1990), we recognize 26 different genetic Cytherissa species, 18 with morphological variation and eight truly cryptic species. These results suggest that the actual specific diversity of Cytherissa in Lake Baikal might easily be double of what is presently known. Baikalian endemic species most likely live in the cradle in which they originated and this opens perspectives to infer modes of speciation. Our current distribution data of Cytherissa species provide first indications for both geographic (lakes basins and shores) and ecological (sediment type, water depth) separation. Our present data thus provide the first steps towards future, rigorous testing of focussed hypotheses on the causality of speciation through either allopatric isolation or parapatric ecological clines