Influence of body and genital morphology on relative male fertilization success in oriental beetle

Although the frequently large variance in relative male fertilizationsuccess when females are mated by more than 1 male has beenappreciated for some time, the factors that influence relativepaternity are still poorly understood. Recently, experimentalevidence that morphology of male genitalia influences fertilizationsuccess has been documented in 2 water striders, a dung beetle,and a leaf beetle. We explored the role of male genital morphologyin postcopulatory sexual selection in the oriental beetle. Wemated females to 2 males in succession and assessed relativepaternity by the sterile male technique. Morphology of the malegenitalia was found to strongly influence relative paternitybut only for the first male to mate. Male body size influencedrelative fertilization success as well, but again, only forthe first male; surprisingly, smaller males achieved higherpaternity when mating first. We also found suggestive evidencethat copula duration of both the first and second male to mateinfluenced paternity. Other factors, including female size anddegree of asymmetry of hind tibiae length of males had no effecton relative fertilization success. Our results for the orientalbeetle are novel among sperm precedence studies for 2 reasons:1) traits of the first male appear to be more important in influencingpaternity than those of the second, and 2) smaller, not larger,males achieved greater relative paternity. Our results alsocontribute to the growing body of empirical evidence in supportof the hypothesis that male genitalia evolve by postcopulatorysexual selection.