Reproductive skew in quasi-social parasitoids

Primitively social Sclerodermus parasitoids form female multi-foundress groups on large, paralysed hosts and then cooperatively care for large broods of offspring throughout their development. We identified offspring with microsatellite markers and found that nearly every foundress produced offspring, implying that overall reproductive skew was thus not extreme. We expected that kinship may influence skew if, for instance, relatives within a group collectively suppress the reproduction of a non-relative or if non-relatives selfishly over-exploit group reproductive optima. We found slight skew, in favour of the non-sibling, when two full-sibling foundresses brooded with one non-sibling foundress but no skew when three sibs brooded with one non-sibling. All foundresses made similar contributions to the sexual composition of broods, which were highly female biased. We expected body size differences might promote skew via physical domination of some foundresses by others or via intrinsicall...