Evidence for multiple mating by female eastern carpenter bees, Xylocopa virginica (Hymenoptera: Apidae)

Abstract

Abstract Relatedness within groups is influenced by the mating patterns of founders: the more parents that contribute to a group, the lower the relatedness of their offspring. Xylocopa virginica (Hymenoptera: Apidae) is a facultatively social bee in which low relatedness is influenced by sequential maternity. We investigated whether multiple paternity, which would occur if egg-laying females mate multiple times, might also contribute to low relatedness among female nestmates. We used two approaches to investigate how frequently females mate polyandrously. First, we used visual observations of mating behaviour to estimate mating frequencies and to evaluate evidence for temporal variation in female receptivity to mates. Second, we used a data set of microsatellite genotypes to evaluate evidence for multiple paternity based on inferred proportions of full and half sisters. Based on visual observations, we inferred a female mating frequency of 1.1 (harmonic mean). Females were more receptive early in their first nestmate provisioning phase and less receptive in their second brood provisioning phase. Based on microsatellite genotypes analysed with COLONY software, we inferred that 5–44% of female sibships included maternal half sisters, implying female mating frequencies between 1.13 and 1.41 (harmonic means). Thus, multiple mating contributes to the low group relatedness found in Xylocopa virginica.