EXTENSIVE GENETIC-VARIATION REVEALED IN ADJACENT POPULATIONS OF THE SCHISTOSOME INTERMEDIATE HOST BIOMPHALARIA-PFEIFFERI FROM A SINGLE RIVER SYSTEM

Random amplified polymorphic DNA (RAPD) analysis was used to study gen etic variation among schistosome hosts of the species Biomphalaria Pfe ifferi The analysed snails came from 15 sites along a 6-km stretch of a Zimbabwean river, providing data on genetic-geographical relationshi ps over, probably, the smallest scale yet studied for any snail interm ediate host species. Only 6% of the DNA fragments were common to all s nails, and snail populations as geographically close as 100 m mere gen etically distinct. The most genetically polymorphic snail populations were those collected within and downstream from human water-contact si tes.