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.
The Sable Island Sweat Bee (Lasioglossum (Dialictus) sablense Gibbs, 2010) is endemic to Sable Island, an isolated sandbar located about 160 km east of Nova Scotia. L. sablense is classified as Threatened due to its restricted geographic distribution, so promoting its conservation requires detailed information about nesting phenology and behaviour. We combined measurements and dissections of adult females collected in 2016 and 2017 with behavioural observations of nests and foragers on the grounds of the Sable Island Station in 2019 and 2022, to compile the first description of flight phenology and social status. Like many members of its subgenus, L. sablense exhibits a diphasic life history. Phase 1 begins when large adult females emerge from hibernation, begin burrow and brood cell construction, and forage to provision Brood 1, which comprises both daughters and sons. Most, but not all, nests initiated during Phase 1, reactivate during Phase 2, as adult Brood 1 daughters emerge from their nests and initiate foraging to provision Brood 2. This suggests a mix of univoltine (single generation) and bivoltine (two generation) reproductive strategies. Behavioural observations at nest entrances demonstrated that during Phase 2, reactivated nests sometimes contained multiple adult females, suggesting the potential for colonies to become social. Comparisons of body size and ovarian status of Phase 1 and 2 females collected from flowers, showed Phase 2 foragers were significantly smaller than Phase 1 foragers and had somewhat lower levels of ovarian development, as expected if Phase 2 females were workers from eusocial nests. However, five large females collected during Phase 2 , which had high levels of wear, likely were Phase 1 foundresses that resumed foraging during Phase 2. Taken together, these observations suggest a mix of phenological and social strategies, including both univoltine and bivoltine life histories, and a mix of solitary and social behaviour among reactivated colonies in Phase 2.
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