Polyandry in grain beetles, Tenebrio molitor, leads to greater reproductive success: material or genetic benefits?

Abstract

Females that mate with more than one male may derive both material and genetic benefits, and differentiating between the two benefits is often difficult. We tested for both material and genetic effects associated with multiple mating in the highly promiscuous yellow mealworm beetle, Tenebrio molitor. Females that mated four times to the same male laid more eggs and produced more larvae than females that mated only once. Whether copulations occurred on the same day or over several days, the result was an immediate increase in the production of eggs by females. Some females were kept on a restricted diet to test whether nutrients in the spermatophore disproportionately benefitted food-deprived females. Although females on poor diets produced fewer and smaller offspring, diet did not significantly affect the proportional benefit of mating treatment on female fecundity. By controlling for male mating history, we were able to separate the effects of mating with different males from the effects of receiving multiple spermatophores from the same male. Females that mated with four different males achieved substantial gains in numbers of eggs produced (32% increase) beyond those of females that mated an identical number of times with the same male. We found no evidence that males allocate fewer sperm to previous mates. Egg hatchability was unaffected by mating behavior, suggesting that genetic incompatibility at that stage is not responsible for the low reproductive success of females mated with a single male. These results suggest that females may delay or reduce oviposition or may be incapable of achieving maximal fecundity until they have gained the material and/or genetic benefits of mating with multiple males.