Reproductive costs of mating with a sibling male: sperm depletion and multiple mating in Cephalonomia hyalinipennis

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Polygynous parasitoid males may be limited by the amount of sperm they can transmit to females, which in turn may become sperm limited. In this study, I tested the effect of male mating history on copula duration, female fecundity, and offspring sex ratio, and the likelihood that females will have multiple mates, in the gregarious parasitoid Cephalonomia hyalinipennis Ashmead (Hymenoptera: Bethylidae: Epyrinae), a likely candidate for sperm depletion due to its local mate competition system. Males were eager to mate with the seven females presented in rapid succession. Copula duration did not differ with male mating history, but latency before a first mating was significantly longer than before consecutive matings. Male mating history had no bearing on female fecundity (number of offspring), but significantly influenced offspring sex ratio. The last female to mate with a given male produced significantly more male offspring than the first one, and eventually became sperm depleted. In contrast, the offspring sex ratio of first-mated females was female biased, denoting a high degree of sex allocation control. Once-mated females, whether sperm-depleted or not, accepted a second mating after a period of oviposition. Sperm-depleted females resumed production of fertilized eggs after a second mating. Young, recently mated females also accepted a second mating, but extended in-copula courtship was observed. Carrying out multiple matings in this species thus seems to reduce the cost of being constrained to produce only haploid males after accepting copulation with a sperm-depleted male. I discuss the reproductive fitness costs that females experience when mating solely with their sibling males and the reproductive fitness gain of males that persist in mating, even when almost sperm-depleted. Behavioural observations support the hypothesis that females monitor their sperm stock. It is concluded that C. eng

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