Strong genetic structure in Cameroonian populations of Bulinus truncatus (Gastropoda : Planorbidae), intermediate host of Schistosoma haematobium

In order to evaluate the snail host contribution on the variability of mollusk/schistosome compatibility, the genetic structure of seven Cameroonian populations of the schistosome vector, Bulinus truncatus, was studied using four variable microsatellite loci. A substantial polymorphism mainly distributed among populations was observed. No heterozygous genotype was scored, confirming the high level of setting rate occurring in B. truncatus populations. Contemporaneous samples were highly and significantly differentiated with a marginally significant correlation with geographical distances (P-value = 0.069). The different sites sampled seemed to rarely exchange migrants with very small Nm (similar to 0.22 or below). The data also suggest that B. truncatus subpopulations might be composed of very small and isolated units at much smaller surfaces than what was investigated. Even if more data (in particular more loci) will be needed to confirm these issues, they suggest that restricted gene flow plays an important role in maintaining differentiation among snail populations in the transmission foci, potentially leading to specific adaptation between each B. truncatus population and its local Schistosoma haematobium population