Environmental and social influences of foraging behaviour and maternal investment with a note on the mating frequency of the eastern carpenter bee, Xylocopa virginica

Abstract

This thesis studies how weather and sociality influence the foraging effort input costs of brood production, and that multiple mating contributes to low-group relatedness and non-kin sociality in the Eastern carpenter bee, Xylocopa virginica. In Chapter 2, using a natural experiment which included a drought and three normal weather years, we found that mothers foraged more in a drought but had smaller offspring than most normal weather years. Droughts conditions lead to fewer flowers, and it follows that less abundant food resources should lead to a trade-off of more work for fewer resources. Indeed, we found that during the drought, the size of pollen loads that mothers carried were smaller than in every other normal year showcasing the impact of the drought. In Chapter 3, I assess the foraging effort in both solitary and social foundresses showing that the foraging input costs are much higher for social primary foundresses than for solitary foundresses. That foraging costs are higher for social foundresses is atypical compared to most literature, which usually suggests that solitary behaviour is more costly than social behaviour. Lower social costs implies that social behaviour should become the more predominant phenotype in the population, however, in our Niagara population there was always a mix of solitary and social phenotypes. A mix of solitary and social phenotypes suggests balanced selection for both phenotypes. That the social phenotype is more costly is interesting and we suggest that social primary foundresses must feed their nestmates throughout the foraging period. Nestmate feeding has been documented in this bee before, so it seems like the most plausible explanation. In Chapter 4, we assessed the mating frequency of female carpenter bees using behavioural observations and microsatellite markers. We found using both sets of data that X. virginica mates multiply. Multiple mating has direct implications on the genetic relatedness of already low relatedness in non-kin social groups. Non-kin sociality is understudied, and we hope that these findings spur additional studies.