Microsatellite variation and differentiation in African and non-African populations of Drosophila simulans

Drosophila simulans originated in sub-Saharan Africa or Madagascar and colonized the rest of the world after the last glaciation about 10 000 years ago. Consistent with this demographic history, sub-Saharan African populations have been shown to harbour higher levels of microsatellite and sequence variation than cosmopolitan populations. Nevertheless, only limited information is available on the population structure of D. simulans. Here, we analysed X-linked and autosomal microsatellite loci in four sub-Saharan African, one North African, one Israeli, and two European D. simulans populations. Bayesian clustering algorithms combined the North African, Israeli, and European populations into a single cosmopolitan group. The four sub-Saharan populations were split into two separate groups. Pairwise F-ST analysis, however, indicated significant population differentiation between all eight populations surveyed. A significant signal for population reduction in cosmopolitan populations was found only for X-linked loci.