Intraspecific and interspecific sequence variability in the ITS region of the rDNA of freshwater sponges of Lake Baikal and East Siberia

Abstract

Sponge (Porifera) systematics and phylogeny are complicated due to the limited number of morphological features and lack of information employed for taxonomy. Baikal sponges occur in the families Lubomirskiidae and Spongillidae, with 13 and 4 species in each family, respectively. The aim of this research was to study the variability of internal transcribed spacers (ITS) of rDNA in the families Lubomirskiidae and Spongillidae to determine the effectiveness of using ITS sequences to differentiate species and study the evolution of sponges in Lake Baikal. ITS1 and ITS2 (~950 bp) were amplified and sequenced for 34 samples of Lubomirskiidae and 28 samples of Spongillidae. Phylogenetic reconstructions revealed monophyly of Ephydatia fluviatilis, Ephydatia muellery, and Spongilla lacustris. Intraspecific polymorphisms were much lower than interspecific variability among the species of Spongillidae, despite analyzed samples of each species originating from geographically distant locations. Our findings revealed that ITS1 and ITS2 sequences could be an appropriate tool for phylogenetic study and species identification of Spongillidae. ITS analyses did not support monophyly of the lubomirskiid genera and species, possibly because of incomplete species divergence, indicating that species delimitation is difficult in the case of rapid species radiation within Lubomirskiidae.

Keywords:

• Baikal
• evolution
• freshwater sponges
• ITS1 and ITS2
• Porifera
• species identification

Acknowledgements

We thank Tatjana Butina and Yulija Sapozhnikova (Limno-logical institute SB RAS, Russia) for their help in sample collection. We thank Darja Vladimirova (Irkutsk State University) for technical assistance.