Sex Combs are Important for Male Mating Success in Drosophila melanogaster

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Abstract
The sex comb is one of the most rapidly evolving male-specific traits in Drosophila, making it an attractive model to study sexual selection and developmental evolution. Drosophila males use their sex combs to grasp the females’ abdomen and genitalia and to spread their wings prior to copulation. To test the role of this structure in male mating success in Drosophila melanogaster, we genetically ablated the sex comb by expressing the female-specific isoform of the sex determination gene transformer in the tarsal segments of male legs. This technique does not remove the sex comb entirely, but simply restores the morphology of its constituent bristles to the ancestral condition found in Drosophila species that lack sex combs. Direct observations and differences in long-term insemination rates show that the loss of the sex comb strongly reduces the ability of males to copulate with females. Detailed analysis of video recordings indicates that this effect is not due to changes in the males’ courtship behavior. Rapid evolution of sex comb morphology may be driven either by changes in female preferences, or by co-evolution between sex combs and female external genitalia.