New Approaches to Study Biodiversity and Evolution of Freshwater Sponges in Ancient Lakes

Freshwater sponges (Porifera; Spongillina) include 6 families. Some of them are endemic of ancient lakes Baikal, Tanganyika, Ohrid and Malawi. Others families are cosmopolitan and inhabit inland waters worldwide. Freshwater sponges are important for cleaning of water due their filter activity and are often main part of benthos in the lakes. The taxonomy of freshwater sponges is difficult that complicates an estimation of their biodiversity. Evolution and phylogenetic relationships of these animals also are not well known. Freshwater sponges from lakes Baikal (family Lubomirskiidae), Biwa (family Spongillidae) and Tanganyika (family Potamolepidae) were collected during several Japan-Russian joint expeditions and analyzed by morphology and molecular methods. Several gene regions (18SrRNA gene, COXI gene and internal transcribed spacers of rRNA) were sequenced and analyzed. The obtained results allowed to develop a molecular marker for species identification in Porifera and to study the phylogenetic relationships between endemic and cosmopolitan freshwater sponges. Our results indicated that the endemic family Lubomirskiidae is monophyletic, showing the highest bootstrap support. The genetic distances between Lubomirskiidae species are much lower than those between Spongillidae species. The lower genetic distances between species of Baikalian sponges is indicative of their relatively recent radiation from a common ancestor. The evolutionary age of the family Lubomirskiidae does not exceed the geological age of Lake Baikal, which indicates an autochthonous evolution of sponges in Lake Baikal. The cosmopolitan family Spongillidae is paraphyletic in relation to other freshwater sponges. The genera Radiospongilla and Eunapius are probably monophyletic and the genus Ephydatia is paraphyletic and forms basal branches. The family Potamolepidae is more closely related to common ancestor of all freshwater sponges. The developed molecular method can be useful for identification of species of freshwater sponges. Study of species diversity of this important group of organisms will allow performing an ecological monitoring of lake ecosystems.