Age-based female preference in the fruit fly Drosophila pseudoobscura

With respect to mate choice, females of many species discriminate between males on the basis of age. The adaptive significance of age-based mate choice is unclear, with various hypotheses making conflicting predictions. We examined the possibility of female preference in the fruit fly Drosophila pseudoobscura, a species where females gain no significant nutritional benefits from mating. Females were shown to prefer to mate with old males in two-male choice experiments and accepted old males faster than young males in single-male tests. Females mated to old males had a higher fecundity, possibly related to a transfer of more sperm and/or a larger volume of accessory gland proteins during the longer copulation durations experienced with old males, although these possibilities were not directly tested. Hence, females appear to derive direct benefits from preferring to mate with older males. In contrast, there was no evidence of mate preference for the sons of either old or young males when matched for age, indicating that the mating advantage of old males is not passed to their sons. These sets of experiments suggest that in D. pseudoobscura the benefit of age-based preference to females is increased fecundity due to greater investment per mating by older males.