Alternative ejaculate allocation tactics in relation to male mating history of the swallowtail butterfly, Papilio xuthus L. (Lepidoptera: Papilionidae)

Abstract

In polyandrous species, a male's fertilization success is strongly related to the number of sperm he carries and the mass of the ejaculate substance transferred to the female. However, because ejaculate production is costly and limited, males are expected to allocate their ejaculates adaptively among matings. In order to clarify the ejaculate allocation pattern in the polyandrous swallowtail butterfy, Papilio xuthus (Linnaeus, 1767), the spermatophore size and the number of sperm were counted just after the termination of the frst and second copulations. Virgin males slowly increased the size of their spermatophores with age after eclosion, while there was a negative correlation between the ratio of sperm transferred to the female and the number of sperm produced. Males seemed to keep some sperm for further matings. On the other hand, the spermatophore size rapidly increased in males that had mated once, and these males transferred most of the sperm in their sperm storage organs at their second mating, irrespective of the number of sperm stored. Therefore, males might use their own mating history to tailor their ejaculates, probably assessing the probability of additional matings.