Differences in courtship, mating and postcopulatory behaviour between male morphs of the dung beetle Onthophagus binodis Thunberg (Coleoptera: Scarabaeidae)

Abstract

Large, horned males of the dung beetle Onthophagus binodis assisted their mates in gathering larval provisions and guarded their mates' burrows when vacated. The horned males' assistance is expected to increase their mates' reproductive success. In contrast, small, hornless males did not appear to help females during oviposition. Differences in courtship behaviour between the male morphs indicated that large, horned males may be assessing female size and employing precopulatory mate discrimination. Under laboratory conditions small, hornless males inseminated females on the first encounter more often than large, horned males and presumably exercise minimal mate discrimination. However, the mating frequencies of the male morphs may be different in the field as a result of either intrasexual selection or female choice. Features of mating in O. binodis were the male's (1) tactile stimulation of the female, and (2) upward jerks of the head and pronotum before, during and after copulation. This latter action would facilitate dissemination of pheromones from the exocrine glands on their forelegs.