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

Although the frequently large variance in relative male fertilization success when females are mated by more than 1 male has been appreciated for some time, the factors that influence relative paternity are still poorly understood. Recently, experimental evidence that morphology of male genitalia influences fertilization success has been documented in 2 water striders, a dung beetle, and a leaf beetle. We explored the role of male genital morphology in postcopulatory sexual selection in the oriental beetle. We mated females to 2 males in succession and assessed relative paternity by the sterile male technique. Morphology of the male genitalia was found to strongly influence relative paternity but only for the first male to mate. Male body size influenced relative fertilization success as well, but again, only for the first male; surprisingly, smaller males achieved higher paternity when mating first. We also found suggestive evidence that copula duration of both the first and second male to mate influenced paternity. Other factors, including female size and degree of asymmetry of hind tibiae length of males had no effect on relative fertilization success. Our results for the oriental beetle are novel among sperm precedence studies for 2 reasons: 1) traits of the first male appear to be more important in influencing paternity than those of the second, and 2) smaller, not larger, males achieved greater relative paternity. Our results also contribute to the growing body of empirical evidence in support of the hypothesis that male genitalia evolve by postcopulatory sexual selection.