Large spermatophores reduce female receptivity and increase male paternity success in the almond moth, Cadra cautella

Abstract

The size of a male's reproductive investment may have profound consequences for female mating frequency and male fitness. Male ejaculate size may affect female fecundity and fertility, while large ejaculates may confer an advantage for males in both avoiding and engaging in sperm competition. We explored experimentally the effect of male ejaculate size on female receptivity and male fertilization success, in the largely monandrous almond moth. Females received either a large or small first spermatophore, and were then given the opportunity to remate with another male that also provided a large or small ejaculate. We examined the effect of spermatophore size on female postmating receptivity, likelihood of remating and reproductive output. For males, we examined the effect that spermatophore size and mating order had on subsequent paternity success. Females that received a small first ejaculate were both more likely to remate (with mated males) and remated sooner than females that received a large first ejaculate. Furthermore, females that remated were also more likely to commence calling behaviour following their first mating, but there were no effects of spermatophore size on female reproductive output. For a male, however, if his female remated, the size of the spermatophore he transferred had important fitness consequences. Second-mating males suffered a paternity cost when competing against a rival that provided a large spermatophore. We propose that the enlarged spermatophore transferred by virgin males explains the low remating rate in this species, and may suggest a more polyandrous past for the almond moth, potentially shaped by sexual conflict.