The mating status of mothers and offspring sex affect clutch size in a polyembryonic parasitoid wasp

Mothers can modify the phenotype of their offspring both genetically and epigenetically, in response to the environment they experience. The role of maternal experience in affecting offspring clutch size is often difficult to measure, because parent–offspring conflict over this trait is common. In polyembryonic parasitoids, where each egg proliferates to form a clone of genetically identical siblings, the conflict is minimized. Therefore, they are good models for studying maternal effects on clutch size. In the haplodiploid parasitoid wasp Copidosoma koehleri, female clones contain more individuals than male clones. This may result from differences in genome size or in optimal body size between the sexes. Alternatively, maternal mating may mediate epigenetic physiological changes in eggs, leading to increased proliferation. We evaluated these hypotheses by comparing the body size and number of clone mates produced by mated versus virgin females. Sons of mated females were significantly smaller and formed larger clones than sons of virgins. Daughters formed the largest clones, but resembled sons of mated females in body size. Clone sizes of parents and offspring were not correlated. These findings suggest that both offspring sex and maternal experience (mating status) affect clone size, and that this trait’s heritability is low. The increased proliferation by offspring of mated females may enhance paternal fitness by producing extra daughters, or benefit the offspring under conditions where the associated decrease in body size does not greatly reduce fitness. We estimated the contribution of large body size to male reproductive success through a mate choice assay.