Genetic Structure Inferred from Mitochondrial 12S Ribosomal RNA Sequence of Oncomelania quadrasi, the Intermediate Snail Host of Schistosoma japonicum in the Philippines

Species and subspecies of the Oncomelania hupensis species complex are recognized as intermediate hosts of Schistosoma japonicum. Of these species and subspecies, O. quadrasi is distributed throughout the Philippines. This study used 12S ribosomal RNA sequences to explore the genetic structure of O. quadrasi populations in the Philippines. Three subspecies, O. h. hupensis, O. h. formosana, and O. h. chiui of this group were also examined. The phylogenetic tree and haplotypes network showed that O. quadrasi separated from the subspecies. Ten O. quadrasi haplotypes (Oq1-Oq10) clustered in relation to their geographic origin. Genetic differentiation (F-ST) and estimated gene flow (Nm) among populations showed significant differences, ranging from 0.556-1.000 to 0.00-0.74, respectively. Genetic differences among groups (F-CT = 0.466), populations within a group (F-SC = 0.727), and populations (F-ST = 0.854) were observed. These results indicate that the O. quadrasi populations in the Philippines have a substructure associated with their geographic origin.