Simultaneous investigation of pollen and bacterial communities in brood provisions of a small carpenter bee

Transmission of bacteria from mother to offspring is commonplace, but how a mother’s foraging decisions influence her offspring’s microbiome remains an open question. To address this gap, we studied a bee that forages for pollen from multiple species of plants and may therefore acquire diverse bacteria from different plants. We tested the hypothesis that pollen diversity correlates with bacterial diversity by simultaneously characterizing these two communities in bee brood provisions for the first time. We used deep sequencing of the plant RBCL gene and the bacterial 16S rRNA gene to characterize pollen and bacterial diversity. We then tested for associations between plant and bacterial species richness and community composition, as well as co-occurrence of specific bacteria and plants. We found that both plant and bacterial communities were extremely diverse, indicating that mother bees visit a wide variety of flowers for pollen and nectar and subsequently bring a diversity of microbes back into their nests. Pollen and bacterial species richness and community composition, however, were not correlated. Certain plants significantly co-occurred with the most proportionally abundant bacteria, indicating that these plants may serve as reservoirs for these bacteria. Even so, the overall diversity of these communities appears to mask these associations at a broader scale. Further study of these plant and bacteria associations will be important for understanding the complicated associations between bacteria and wild bees.