Quasi-social parasitoid sex ratios under multi-foundress local mate competition with reproductive dominance.

Social Sclerodermus parasitoids in the aculeate family Bethylidae form female multi-foundress groups on large, paralysed hosts and then cooperatively care for large broods of offspring throughout their development. The sex ratios of offspring produced by multi-foundress groups are more female biased than predicted by standard Local Mate Competition (LMC) theory. Using microsatellite markers to identify maternity shows that nearly every foundress produces offspring and overall reproductive skew is mild. However, males are more often the progeny of the largest or earliest-ovipositing foundress, and many foundresses do not produce any male offspring at all. Skew in male production suggests that larger females are able to dominate the production, or the survival, of males. We incorporate reproductive dominance and/or the infanticide of developing males into LMC theory, predicting both the sex ratios of individual foundresses and those of foundress groups. The predicited group sex ratios broadly match empirical observations and thus provide feasible explanation for the extremely female-biased sex ratios produced by multi-foundress groups and more generally expand the scope of LMC theory to consider reproductive dominance.