Population genetic structure of Biomphalaria glabrata in a schistosomiasis-endemic region in Brazil

The population genetic structure of the freshwater snail, Biomphalariaglabrata, was assessed in the municipality of Virgem das Graças(Minas Gerais, Brazil), a schistosomiasis-endemic area. Theseven microsatellite loci that were used to genotype 326 individualsfrom 17 collection sites within a 3-km radius revealed highgenetic variability. However, we found a deficit of heterozygotesrelative to Hardy–Weinberg expectations for most of theloci and in many collection sites, indicating a high level ofinbreeding. This may be the result of founder effects and sib-mating.A high level of overall population genetic differentiation amongB. glabrata collection sites suggested low gene flow at thisrelatively small spatial scale in this region. However, subsequentanalyses also indicated that these patterns may also resultfrom founder events and that an exchange of individuals betweenparticular collection sites does exist. The isolation-by-distancecorrelation between collection sites of B. glabrata was foundto be significant. However, only approximately 6% of the variancein F_ST was explained by geographic distances suggesting thatthere are other factors affecting genetic differentiation amongthese collection sites. It is likely that the current populationgenetic structure reflects patterns of both migration and founderevents. Results from this study are important for understandingthe potential for local adaptation between schistosomes andtheir snail hosts at this epidemiologically relevant scale.