Phylogenetic relationships of snails of the genera Oncomelania and Tricula inferred from the mitochondrial 12S rRNA gene

The Schistosoma japonicum group and S. sinensium utilize intermediate snail hosts belonging to the genera Oncomelania and Tricula (Gastropoda: Pomatiopsidae). In the present study, partial sequences of the mitochon- drial 12S rRNA gene from 7 subspecies of O. hupensis, two species of Tricula (T. bollingi and T. humida )a ndO. minima were examined to infer a phylogeny for these. Nucleotide differences among subspecies of O. hupensis were less than 6.5% and among species from different genera, 10-12%. The phylogenetic tree obtained in this study indicates that O. hupensis subspecies fell into four distinct clades ; that is, O. h. quadrasi from the Philip- pines, O. h. lindoensis from Indonesia, O. h. hupensis from Yunnan, China and the remaining 5 subspecies (O. h. hupensis from other parts of China, O. h. robertsoni from China, O. h. formosana from Taiwan, O. h. chiui from Taiwan and O. h. nosophora from Japan). The phylogenetic tree also showed that O. minima was placed as sister to all of the subspecies of O. hupensis. Possible evolutionary relationships among the snail hosts were discussed.