Queen-controlled sex ratios and worker-reproduction in the bumble bee Bombus hypnorum, as revealed by microsatellites

Abstract

Social insect colonies provide model systems for the examination of conflicts among parties with different genetic interests. As such, they have provided the best tests of inclusive fitness theory. However, much remains unknown about in which party?s favour such conflicts are resolved, partly due to the only recent advent of the molecular tools needed to examine the outcome of these conflicts. Two key conflicts in social insect colonies are over control of the reproductive sex ratio and the production of male offspring. Most studies have examined only one of these conflicts, but in reality they occur in tandem and may influence each other. Using microsatellite analyses, we examined the outcome of conflict over sex ratios and male production in the bumble bee, Bombus hypnorum. We determined the genotypes of mother queens, their mates and males for each of ten colonies. In contrast to other reports of mating frequency in this species, all of the queens were singly-mated. The population sex ratio was consistent with queen control, suggesting that queens are winning this conflict. In contrast, workers produced over 20% of all males in queen-right colonies, suggesting that they are more effective in competing over male-production. Combining our results with previous work, we suggest that worker-reproduction is a labile trait that may well impose only small costs on queen fitness.