A genetic model of copulatory wounding in Drosophila melanogaster.

In the animal kingdom, copulatory wounds occur due to aggressive behavior or injury from the female or male appendages in contact. Copulatory wounds are a source of sexual conflict as the injury can lead to death or infection. In the laboratory, Drosophila melanogaster does not ordinarily exhibit signs of injury during copulation, but here we find that it can be induced to do so by overexpression of the serine protease, Hayan, in either the male or female fruit fly. Melanin deposits mark sites of injury along the female ventral abdomen and occur following a single copulation event. The male fly's mid-legs are the source of injury as they rub against the ventral female abdomen. Surgical removal of the male mid-legs prevents melanization while still permitting mating to occur. Likewise, removal of the right or left mid-leg results in a corresponding loss of melanization on the female abdominal side that lacks the mid-leg contact. Thus, it appears that overexpression of Hayan alters the female and male anatomy to sensitize it to injury during copulation. We show that these copulatory wounds heal similar to a puncture wound via the generation of enlarged multinucleated, polyploid cells. However, the size of the injury dictates the mechanism of healing. The polyploid cells arise solely by cell fusion in response to small injuries (<1,000 μm2), whereas the endocycle is simultaneously stimulated by larger wounds (>3,000 μm2) to compensate for cell loss. Therefore, we speculate that wound-induced polyploidization may have evolved to repair similar injuries resulting from sexual conflict in nature.