Genital spines of D. ananassae promote mating success

What is it about?

Using a laser ablation device to cut off precise increments of the genital spines of male fruit flies (D. ananassae), we were able to show that these genital spines/claws function to grasp onto females' genitalia to initiate copulation (i.e. this genital trait functions to promote mating success). The reduction in mating success exhibited by males with surgically reduced genital spines is more pronounced when they compete with control males over access to an individual female. Behavioral analyses show that the mechanism underlying this effect is male-male competition, not female choice, since females did not behave differently toward cut vs. control males.

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Why is it important?

One of the most consistent findings in biology is that animal genitalia evolve faster than any other morphological traits. They are at the very front of evolutionary diversification. Often two closely related species that are otherwise morphologically identical can only be distinguished by inspecting the difference in their genital morphology. Decades of research has show that sexual selection is driving much of this rapid evolutionary diversification, but this is predominantly post-copulatory sexual selection (sperm competition and cryptic female choice), which makes sense, since genitalia typically function after copulation has begun. Here, we demonstrate, among only a few other researchers, that genitalia can function prior to copulation, opening the window for more traditional forms of sexual selection (mating competition and female choice) to also be playing a role in the rapid evolutionary diversification animal genitalia, and hence, the very beginnings a of species diverging into two or more.