When are vomiting males attractive? Sexual selection on condition-dependent nuptial feeding in Drosophila subobscura

Nuptial gifts are any nutritious items or inedible tokens transferred from the male to the female as a part of courtship or copulation. Although nuptial gift donation has been studied in a variety of taxa, this behavior has been largely overlooked in Drosophila. We studied nuptial feeding in Drosophila subobscura, where the gift is a regurgitated drop of liquid, in order to examine the importance of this behavior for male mating success and female fecundity. We varied male and female condition by dietary restriction to assess any condition dependence of male nuptial feeding ability and female feeding behavior and mate discrimination. Our results show that there was directional selection for males in good condition that produced a higher number of regurgitated gifts. Interestingly, the strength of selection was also dependent on female condition. Females in poor condition showed strongest preference for males in good condition. Such females could increase their fecundity to a level similar to that of females in good condition by feeding on regurgitated gifts from males in good condition. However, male exploitation of female gustatory response is also a plausible explanation for the courtship feeding response, as we did not find an effect of nuptial feeding on the fecundity of females in good condition. These findings suggest that, in this monandrous species, selection has favored males who invest in nuptial gifts, possibly as an example of paternal investment as well as mating effort, but that the strength of selection on nuptial feeding is strongly subject to environmental variation.