Parasite (Schistosoma mansoni) and host (Biomphalaria glabrata) genetic diversity: population structure in a fragmented landscape.

Random amplified polymorphic DNA (RAPD) markers were used to quantify genetic diversity within and between 5 populations of Schistosoma mansoni within its definitive host (Rattus rattus) and the 5 corresponding populations of the snail intermediate host (Biomphalaria glabrata) from a limited endemic area of murine schistosomiasis on the island of Guadeloupe. Analysis of molecular variance (AMOVA) and canonical correspondence analysis (CCA) were used to test the significance of genetic differentiation between populations. Both methods gave similar results. Of total gene diversity, 15.1% (AMOVA) and 18.8% (CCA) was partitioned between localities for S. mansoni with an absence of association between genetic and geographical distances. Geographical localities accounted for 20.5% (CCA) of the total diversity for B. glabrata populations. The genetic distances between pairs of parasite populations were not correlated with the genetic distances between the corresponding pairs of snail host populations. Such strong patterns of local differentiation of both parasite and snail populations are consistent with predictions based on metapopulation dynamics and may have implications on host-parasite susceptibility relationship through local adaptation processes.