Origin of sexual isolation in Drosophila ananassae due to founder effects.

The origin of sexual isolation is the central event in the evolution of biological species and plays a key role in maintaining biological diversity. Three mass culture stocks of D. ananassae originating from different geographic localities showing no isolation with each other were subjected to different degrees of bottlenecks i.e. one pair, five pairs and ten pairs. These drift lines were passed through flush-crash cycle at every generation with same initial number of founders, and maintained for twenty-seven generations and then the pattern of matings was tested among these nine drift lines involving 36 crosses in total. In 23 of 36 crosses, the difference between homogamic and heterogamic matings was significant and isolation indices were significantly more than zero in one direction only providing evidence for asymmetrical sexual isolation. Further, when Bonferroni test for pair-wise analysis was employed, significant differences between homogamic and heterogamic matings were found in 25 crosses. These findings provide evidence for origin of sexual isolation by founder effects in D. ananassae.