Developmental changes in the microbial community of the ground-nesting bee Anthophora bomboides

Solitary bees make up the majority of bee species and are important pollinators in both natural and agricultural ecosystems. Microbial communities are detected in solitary bee brood food but whether and how the composition and role of these communities changes over time, particularly with bee development, is unclear. Anthophora bomboides is a solitary, gregarious, ground nesting bee found along the west coast of North America. We collected natural A. bomboides brood cells at each stage of the year long bee life cycle (egg, larvae, prepupae, pupae, adult) as well as samples from the surrounding flowers, soil, and water. We then used amplicon sequencing and quantitative PCR to examine bacterial and fungal composition and abundance through development. We found that A. bomboides brood cells have a core set of microbial taxa present in almost all brood cell samples, a consistent community profile within each stage, and significant shifts in the proportions of major taxa at both of the overwintering prepupae timepoints. Bacterial abundance increased from egg to overwintering prepupae stage, approximately June-December. The consistency within stages and shifts between developmental stages is surprising and may suggest an important role of the microbiome during bee development. Our results suggest that, unlike previously studied solitary bees which often host variable microbial communities, Anthophora hosts consistent microbial communities among nests that converge on a core set of taxa and increase in abundance through development. Future work will characterize the core taxa and examine their function in bee health and development.