A DNA-sequence based phylogeny for triculine snails (Gastropoda: Pomatiopsidae: Triculinae), intermediate hosts for Schistosoma (Trematoda: Digenea): Phylogeography and the origin of Neotricula

Abstract

Partial (DNA) sequences were examined for one nuclear (28S rRNA gene) and one mitochondrial (16S rRNA) locus for nine species of pomatiopsid snail (Gastropoda: Rissooidea: Pomatiopsidae) from south-east Asia and south-west China. Fresh field samples were collected for the following taxa: Delavaya dianchiensis (Triculinae: Triculini) from Dianchi lake, Yunnan Province, China; Neotricula aperta (Triculinae: Pachydrobiini) from north-east Thailand; Neotricula burchi from northern Thailand; Oncomelania hupensis robertsoni (Pomatiopsinae: Pomatiopsini) from south-west China; Tricula bambooensis (Triculinae: Triculini) from Dianchi lake; Tricula bollingi from northern Thailand; Tricula hortensis from Sichuan Province, China; Tricula ludongbini from Dianchi lake; and Tricula xiaolongmenensis from Dianchi lake. This work represents the first published DNA-sequence data for the Dianchi lake taxa and the first 28S sequence data for all nine taxa. All of these taxa with the exception of N. burchi and the Dianchi taxa transmit Schistosoma in nature; N. aperta and O. h. robertsoni transmit Schistosoma to humans. The data were used to estimate phylogenies using the maximum likelihood method, a Bayesian method, and the maximum parsimony method. The paper aims to examine the relationships between N. aperta, N. burchi and T. bollingi and the relationship between the Chinese taxa and the south-east Asian taxa; these relationships being important in evaluating certain historical biogeographical hypotheses. Good congruence was found between the phylogenies estimated by the three methods for both the 16S and 28S loci. However, poor congruence was found between the phylogenies based on the 16S and 28S data when the maximum likelihood and Bayesian methods were used. The lack of congruence is explained as a consequence of a rapid, recent, endemic radiation of the Yunnanese Tricula spp.; this hypothesis is consistent with current historical biogeographical models for the Triculinae. The paper puts forward dispersal hypotheses, based on palaeogeographical changes, as possible explanations for the phylogenetic relationships estimated here and for the current biogeography of these taxa.