| Drosophila melanogaster has two partially reproductively isolated races in the incipient stages of speciation. The Z (Zimbabwe) behavioral group is found in southern Africa, and Z females rarely mate with M (cosmopolitan) males. Whereas males and M females exhibit no mating preference. M flies have a global distribution, and it is unknown whether the behavioral differences arose within Africa or after D. melanogaster migrated out of Africa in the recent past. In this study we resequenced the genome for pools of Z, African M, and non-African M flies and describe genomic patterns of differentiation between the three groups. We find that populations separated by behavior are more differentiated than those separated by geography. Furthermore, for sites that are differentiated between the pools, around 75% support a tree based on behavior compared with only 20% that cluster based on geography. We, therefore, conclude that the Z-M behavioral split occurred within Africa with the M-type subsequently colonizing the rest of the world. These results have implications for previous studies that estimated parameters of the out-of-Africa migration using Zimbabwe flies without regard to mating behavior. |
