In search of speciation: Diversification of Stuckenia pectinata s.l. (Potamogetonaceae) in southern Siberia (Asian Russia)

Although aquatic plants usually are less taxonomically diverse than related terrestrial groups, genetic studies could reveal groups of sibling species and thus increase taxonomic resolution. We hypothesised that different age and environmental diversity of water bodies in southern Siberia caused diversification within Stuckenia pectinata s.l. (Potamogetonaceae). To test this hypothesis we studied nuclear (ITS) and plastid (rpl32-trnL) genetic variation of 37 populations of S. pectinata from eastern Europe, the Russian Far East and southern Siberia with special emphasis on the latter. Plastid DNA variability within S. pectinata s.l. was found to be structured neither geographically nor taxonomically. We revealed strong ITS differentiation within S. pectinata s.l. in southern Siberian water bodies with different combinations of age and salinity. We discuss possible causes of such differentiation. We found a striking contrast between the absence of ITS variability across almost all of Europe colonized by the only ribotype, and relatively high ITS variability in southern Siberia. This contrast could be explained by the different history of young European populations that could have appeared as a result of recent northwards expansion following the Last Glacial Maximum, and the relatively old ones of southern Siberia. The absence of clear correspondence between genetic variation and morphological variability does not sufficiently support delimitation of species within Siberian S. pectinata s.l. (such as S. chakassiensis and S. macrocarpa).