How often does sympatry affect sexual isolation in Drosophila?

A new method of estimating a lower bound of how often sympatric species interactions elevate prezygotic isolation in Drosophila is presented. The conclusion of an earlier study that prezygotic reproductive isolation in sympatric Drosophila species pairs was greater than in allopatric pairs of similar genetic divergence was affirmed, as sympatry with closely related species was found to be associated with elevated sexual isolation among Drosophila species. Such elevations were also found to be not a rare occurrence, as sympatry was found to have increased sexual isolation of Drosophila species in >21% of the phylogenies which fit the model's criteria.