Sexual conflict occurs when traits or behaviors that improve reproductive success for one sex impose evolutionary costs to the other. Copulatory wounding is an example of this conflict as injuries from mating can lead to infection or death of one partner.

A key organism for studying sexual conflict is the fruit fly Drosophila melanogaster, which boasts an extensive genetic toolkit and a fast life cycle, making it a prominent model system in biological research. Until recently, studies of injury in flies have largely relied on genetic cell ablation or artificial mechanical injury. Now, new research published in GENETICS introduces a genetic model to study copulatory wounds in Drosophila in a more behaviorally relevant setting.

The model emerged from an unexpected observation in Vicki Losick‘s lab at Boston College. While the team was studying the role of melanization in wound healing, they found that overexpressing Hayan, a protein involved in this process, caused female flies to produce melanin on the ventral abdomen. Male flies did not show this pattern. Because male flies grasp female flies with their foreleg during copulation, the sex-specific patterns led the researchers to think that mating-related contact was involved.

The team then tested their mating-related hypothesis by conducting all nine pairwise crosses between female and male flies that were wild type, overexpressed Hayan, or that overexpressed a defective form of Hayan. The researchers found that when either females or males overexpressed Hayan, melanization occurred. The effect was greater when female flies overexpressed Hayan.

Males overexpressing Hayan had longer bristles in a part of the male forelegs used in mating. The team noticed that the male mid-legs repeatedly contacted the ventral abdomen in female flies during mating, corresponding to the location of the melanin deposits. To test the correlation, the team removed the male mid-legs, which aren’t used for mating. After mating, none of the female flies overexpressing Hayan developed melanin deposits in their abdomen. Removing just one of the legs produced a side-specific result: females didn’t develop melanin on the side corresponding to the removed male leg.

Then, the researchers looked at how these wounds healed and found it to be similar to how a puncture wound would: small lesions heal with neighboring cells merging to become one large cell with multiple nuclei and larger lesions trigger the endocycle to create polypoid cells. This supports the idea that the melanin deposits mark true epithelial injuries repaired through established wound healing programs in Drosophila.

This new genetic system allows researchers to induce and visualize copulatory wounds that have been difficult to detect and manipulate before. Because the injury is an outcome of mating and not from needle puncture or artificial cell ablation, the model can help researchers study copulatory wounding and sexual conflict in a more realistic setting.

References

  • Jalkut SL, Bischoff LM, Pitsch MJ, and Losick VP. A genetic model of copulatory wounding in Drosophila melanogaster. GENETICS. 2026;iyag206, https://doi.org/10.1093/genetics/iyag206

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