engleski

The mitochondrial genome of stygobitic sponge Eunapius subterraneus: insights into evolution of freshwater sponges

Sponges (Porifera) being the first that branched from the common ancestor of all Metazoa, some 580 million years ago, are excellent model organisms for evolutionary studies. These ancient metazoans mainly inhabit marine ecosystems, but a few taxa within the Demospongiae (suborder Spongillina) live in freshwater. Cave fauna stands out among all other freshwater biota owning peculiar species which are usually distinct from that of surrounding freshwater habitats. Eunapius subterraneus is the only stygobitic member of the suborder Spongillina known from merely six caves near Ogulin, Croatia. Despite of increased research in the recent years phylogenetic relationships among Spongillina are not fully resolved and represent a challenging topic. In this study, we determined and analyzed the complete mitochondrial DNA (mtDNA) sequence of unique stygobitic sponge E. subterraneus, being the second complete mt genome of freshwater sponge (Spongillidae) described so far. Analysis on primary and secondary structure supported with phylogenetic analysis showed remarkable similarity of mtDNA genomes of E. subterraneus and E. muelleri. Our results support hypothesis that endemic sponge species might have originated from a cosmopolitan founder species such as Ephydatia. E. subterraneus mtDNA is 24, 850 bp long ; gene arrangement is identical as in E. muelleri and G. neptuni and similar to all so far sequenced demosponge mt-genomes, thus placing mt genome of E. subterraneus in G4 group. Intergenic regions (IGR) comprise 24.7% of E. subterraneus mtDNA and are abundant with direct and inverted repeats and palindroms. One overlapping gene and tRNA-like structure (trnX) was found. Phylogenetic analysis based on concatenated amino acid sequences from 12 mt protein genes emphasize similarity with E. muelleri mt genome, thus suggesting the close relationship between these two species and their recent diversification.

Porifera; Spongillidae; stygobitic; mitochondrial evolution

nije evidentirano