Evidence for extensive genetic differentiation among populations of the malaria vector Anopheles arabiensis in Eastern Africa

We describe the geographical population structure of the malaria vector Ano pheles arabiensis in Eastern Africa. Allelic variation at eight microsatell ite loci was scored in samples from nine localities along a 4500 km transec t from Sudan to Mozambique. Highly significant differences in genotype freq uencies were found between all populations separated by more than 200 km. P opulations within Malawi separated by 191 km were indistinguishable, as wer e those within Sudan separated by 134 km. F-ST and rho(ST) gave significant estimates of isolation by distance. These data, lead us to conclude that t here are extensive barriers to gene flow in this region. The high estimates of N-m (9.4 from F-ST and 5.2 from rho(ST)) indicate recent range expansio n in this species rather than extensive contemporary gene flow.