Population genetics and genetic variability of Bulinus globosus (Gastropoda: Planorbidae) from the two main river systems in Zimbabwe

are grateful to the technical and field staff of Blair Re-search Laboratory. Without their cooperation this study would have been Impossible. This study was fi-nancially supported by the Danish Bllharziasls Laboratory. Journal of Heredity 1996:87:288-294; 0022-1503/96/J5.00 Bulinus globosus is the only known vector of Schistosoma haematoblum in Zim-babwe. The population genetic structure of this vector snail from the two main river drainage systems, represented by 27 localities, was determined from starch gel Isoenzyme electrophoretic data. Out of 11 enzyme systems screened eight loci were resolved, and six of them were polymorphic In at least one of the populations sampled. Genotyplc distributions showed deviations from Hardy-Weinberg pro-portions due to deficiency of heterozygotes and this was attributed to selflng. The Save River drainage system, which falls under the high rainfall area, revealed a higher proportion of gene diversity than the Sanyatl River drainage system. Hier-archical analysis showed that differentiation within the populations In the two drain-ages (F3R = 0.085) was higher than between the two drainages (FRT = 0.011). This highlights the role of ecological factors (drought/desiccation and floods), genetic drift, and seasonal gene flow as the main factors influencing the genetic structure of these populations. Bulinus globosus, the only known natural vector of Schistosoma haematobium, is widespread in Zimbabwe, yet no informa-tion is available regarding the genetic structure and possible genetic variation of populations of this vector snail. The genetic structure of populations of B. globosus has not been intensively stud-ied. Studies have been carried out on pop-ulations of B. globosus and B. truncates in Cote-D'Ivore and Niger (Njlokou 1992), B. cemicus in Mauritius (Rollinson an