Genetic differentiation between American and European Drosophila melanogaster populations could be attributed to admixture of African alleles.

A total of 48 polymorphic microsatellite loci were characterized in 13 Drosophila melanogaster populations originating from Europe, America, and Africa. Consistent with previous results, the African D. melanogaster populations were the most differentiated populations and harbored most variation. Despite an overall similarity, American and European populations were significantly differentiated. Interestingly, genetic distances based on the proportion of shared alleles as well as FST values suggested that the American D. melanogaster populations are more closely related to the African populations than European ones are. We also detected a higher proportion of putative African alleles in the American populations, indicating recent admixture of African alleles on the American continent.