Queen-worker conflict over male production and the sex ratio in a facultatively polyandrous bumblebee, Bombus hypnorum: the consequences of nest usurpation

Evolutionary conflicts among social hymenopteran nestmates are theoreticall y likely to arise over the production of males and the sex ratio. Analysis of these conflicts has become an important focus of research into the role of kin selection in shaping social traits of hymenopteran colonies. We empl oy microsatellite analysis of nestmates of one social hymenopteran, the pri mitively eusocial and monogynous bumblebee Bombus hypnorum, to evaluate the se conflicts. In our 14 study colonies, B. hypnorum queens mated between on e and six times (arithmetic mean 2.5). One male generally predominated, fat hering most of the offspring, thus the effective number of matings was subs tantially lower (1-3.13; harmonic mean 1.26). In addition, microsatellite a nalysis allowed the detection of alien workers, those who could not have be en the offspring of the queen, in approximately half the colonies. Alien wo rkers within the same colony were probably sisters. Polyandry and alien wor kers resulted in high variation among colonies in their sociogenetic organi zation. Genetic data were consistent with the view that all males (n = 233 examined) were produced by a colony's queen. Male parentage was therefore i ndependent of the sociogenetic organization of the colony, suggesting that the queen, and not the workers, was in control of the laying of male-destin ed eggs. The population-wide sex ratio (fresh weight investment ratio) was weakly female biased. No evidence for colony-level adaptive sex ratio biasi ng could be detected.