Wild Bee Pollen Usage and Microbial Communities Co-vary Across Landscapes.

Bees forage for pollen and nectar at flowers but simultaneously acquire pathogenic, commensal, and likely beneficial microbes from these same flowers. Characterizing pollen usage of wild bees is therefore crucial to their conservation yet remains a challenging task. To understand pollen usage across landscapes and how this affects microbial communities found in the pollen provisions collected from flowers, we studied the generalist small carpenter bee Ceratina australensis. We collected C. australensis nests from three different climatic zones across eastern and southern Australia. To characterize the plant, fungal, and bacterial composition of these pollen provisions, we used a metabarcoding and next-generation sequencing approach. We found that the species richness of plant types, fungi, and bacteria was highest in a subtropical zone compared to a temperate or a grassland zone. The composition of these communities also differentiated by zone, particularly in pollen composition and fungal communities. Moreover, pollen composition strongly correlated with fungal community composition, suggesting that variation in pollen usage across landscapes results in variation in microbial communities. While how these pollen usage and microbial community patterns affect bee health merits additional work, these data further our understanding of how flowering plant community composition affects not only the pollen usage of a generalist bee but also its associated microbial communities.