Persistence of Anopheles arabiensis during the severe dry season conditions in Senegal: an indirect approach using microsatellite loci

Variation at nine microsatellite loci was investigated to understand how An opheles arabiensis populations survive the dry season in the sahelian regio n of Senegal. Low estimates of genetic differentiation (F-ST = 0.012, R-ST = 0.009) between two populations, 250 km apart, suggested extensive gene fl ow across this distance. Despite extreme seasonal fluctuation in abundance with dry season minima in which mosquitoes virtually disappeared, allele fr equencies remained stable over time in the village of Barkedji from August 1994 to December 1997 (including four rainy seasons and three dry seasons). The effective population size (Ne) was estimated to be 601 with 95% CI (28 1, 1592), providing strong evidence against annual bottlenecks. Differences in measures of genetic diversity and linkage disequilibrium between the dr y and the rainy seasons were not detected. These results suggest that despi te extreme minima in local density, An. arabiensis maintains large permanen t deme spread out over large area.