SEQUENCING METHODOLOGY AND PHYLOGENETIC ANALYSIS - CYTOCHROME-B GENE SEQUENCE REVEALS SIGNIFICANT DIVERSITY IN CHINESE POPULATIONS OF ONCOMELANIA (GASTROPODA, POMATIOPSIDAE)

The evolution of the snail species Oncomelania hupensis, a vector for transmission of Schistosoma japonicum in Asia, is tightly linked to th e evolution of its parasite. We report here on studies of the evolutio n of O. hupensis on the mainland of China, using sequence divergence o f the mitochondrial cytochrome b gene. The cytochrome b gene was ampli fied by PCR, cloned in pBluescript, and sequenced; these methods are d escribed in detail. The sequences for three populations of two subspec ies of this prosobranch gastropod were aligned and used in reconstruct ing phylogenetic trees. The phylogenetic analyses confirm the divergen ce of Chinese Oncomelania into subspecies and provide a finer tool for further genetic discrimination. Comparison of Oncomelania cytochrome b sequences to published sequences for two pulmonate gastropods shows a greatly increased divergence rate in the pulmonates relative to that of Oncomelania and of other metazoan groups.