Properties of male ejaculates do not generate geographical variation in female mating tactics in a butterfly Pieris napi

Abstract

Polyandry brings about benefits for females but, from the males' perspective, if there is a possibility of females mating with multiple partners, male characteristics that prevent or delay remating of females are favoured, which may result in antagonistic coevolution between the sexes. The green-veined white butterfly, Pieris napi, is a predominantly polyandrous species with male nutrient donation transferred within the ejaculate at mating. Male ejaculates that are exaggerated in size or content can be interpreted as a means to reduce female remating. We explored whether geographical variation in the degree of polyandry among P. napi populations results from variation in the male's ability to manipulate females to mate at a suboptimal rate. Females that mated with a larger male capable of delivering a large spermatophore remated later than those that mated with a smaller male. However, we found no spatial variation in sexual size dimorphism or relative ejaculate size. Moreover, the mating frequency of females was not affected by the origin of males with which they mated. We argue that even if large male ejaculates evolved to ensure paternity of a given male with negative side-effects on female fitness, female counteradaptations conceal possible implications of antagonistic coevolution. Geographical variation in female mating frequency is probably maintained by selection acting upon female life history traits associated with the degree of polyandry.