Meeting Abstract
Females in many species follow sensory clues received from males to make reproductive decisions. Although chemical clues (e.g., pheromones, seminal fluid proteins) have been studied extensively, much less is known about the role of tactile clues in directing male-female reproductive interactions. The epandrial posterior lobes (PLs) are male-specific cuticular projections of the external genitalia that have evolved recently among the four species of the Drosophila melanogaster complex and have diverged morphologically among these species. The PLs insert between two abdominal segments of the female during mating, and variation in PL size and shape affects female oviposition amounts. Using a collection of interspecific genetic introgression lines between D. sechellia and D. mauritiana, we test the hypothesis that the loci that specify male PL morphology and female egg-laying behavior are genetically linked, which facilitates their rapid divergence between species. We find that pure species D. sechellia females mated with introgression males possessing divergent PL morphology lay fewer eggs compared to matings with pure species control males. In contrast, introgression line females mated with males of the same introgression line lay normal numbers of eggs, a result that is consistent with either tight linkage of loci that specify male and female traits, or pleiotropic effects of a single locus. We have also identified a series of mechanosensory bristles at the PL insertion sites, which suggests that mechanical stimulation during copulation might be involved in directing female oviposition amounts. Interestingly, the neurons attached to these bristles express fruitless, an important effector of male courtship behavior in Drosophila. Adult expression of fruitless in the female genitalia bristles suggests that this gene could be important for reproductive processes in females post mating.
