The evolution of queen‐rearing nepotism in social Hymenoptera: Effects of discrimination costs in swarming species

Abstract

AbstractPolyandry by social hymenopteran queens leads to a potential worker reproductive strategy of rearing full‐sister queens in preference to half‐sister queens. If there is no cost to discrimination, discriminatory queen rearing will be the ESS. However, if discrimination has a cost this conclusion is weakened. This study examines the effect of a “worker efficiency cost” (i.e. discriminatory, nepotistic workers are less effective than non‐nepotistic workers in working to increase total colony reproductive output) on the invasion of rare “nepotist” and “non‐nepotist” alleles in a population in which the other allele is near fixation. Efficiency costs are considered of special relevance to species with swarm founded colonies (e.g., army ants, honey bees).Two analyses are presented: 1) A general model exploring the effects of efficiency costs, the queen‐rearing‐biasing ability of nepotists, and queen mating frequency on invasion of nepotists and non‐nepotists; 2) a discriminatory removal model, in which the actual amount of biasing is dependent on recognition abilities and the discriminatory intensity of nepotists, queen mating frequency, and whether or not removed immature queens are replaced.The results of the removal model indicate that when queen mating frequency is close to one (i.e., because of double mating with unequal sperm use or mixed double and single mating) non‐nepotist is likely to be the ESS. At a higher mating frequency nepotist will become the ESS. At even higher mating frequencies, non‐nepotist may reinvade. This latter conclusion is robust across all models. In particular, non‐nepotists may reinvade at the high mating frequencies found in the honey bee (10–20) if their work efficiency is only a few percent higher than nepotists (the exact amount depends on recognition errors and the intensity of discrimination), resulting in a genetic polymorphism of both nepotists and non‐nepotists. Results of a recent study of patriline discrimination in honey bees (Page et al., 1989) are consistent with such a polymorphism.