The phylogenetics of triculine snails (Rissooidea:Pomatiopsidae) from south-east Asia and southern China:: Historical biogeography and the transmission of human schistosomiasis

Partial DNA sequences were examined for one nuclear (18S rRNA) and two mitochondrial (16S rRNA and CO1) loci for six species of pomatiopsid snail (Gastropoda:Rissooidea:Pomatiopsidae) from south-east Asia and south-west China. Fresh field samples were collected for the following taxa: Neotricula aperta (Triculinae:Pachydrobiini) from southern Laos; Neotricula burchi from northern Thailand; Oncomelania hupensis robertsoni (Pomatiopsinae:Pomatiopsini) from south-west China; Robertsiella sp. (Pachydrobiini) from West Malaysia; Tricula bollingi (Triculinae:Triculini) from northern Thailand; and Tricula hortensis from south-west China. Sequences taken from GenBank for Gammatricula fujianensis (Pachydrobiini) were also used. This represents the first published DNA sequence data for N. burchi and Robertsiella. With the exception of N. burchi, all of these taxa transmit Schistosoma in nature; N. aperta, O. h. robertsoni and Robertsiella transmit Schistosoma to humans. All of the above taxa were found to be homogenetic (i.e. showed no sequence variation) at the 18S locus. Phylogenies were estimated using a fully optimized model of nucleotide substitution and either a maximum likelihood or Bayesian method. Good congruence was observed between the phylogenies resulting from the two different methods. The 16S and CO1 trees showed the same topology except for the relationships between G. fujianensis, T. hortensis and the other taxa. The data confirmed the congeneric status of N. aperta and N. burchi; the implications of this for the choice of historical biogeographical model for the Pachydrobiini are discussed.