Diet breadth affects bacterial identity but not diversity in the pollen provisions of closely related polylectic and oligolectic bees

Authors: ROTHMAN, JASON - University Of California; Cox-Foster, Diana; ANDRIKOPOULOS, COREY - Utah State University; MCFREDERICK, QUINN - University Of California

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2020
Publication Date: 7/20/2020
Citation: Rothman, J.A., Cox-Foster, D.L., Andrikopoulos, C., McFrederick, Q.S. 2020. Diet breadth affects bacterial identity but not diversity in the pollen provisions of closely related polylectic and oligolectic bees. Insects. 11(9). Article 645. https://doi.org/10.3390/insects11090645.
DOI: https://doi.org/10.3390/insects11090645

Interpretive Summary: Microbes found in the pollen provisions of wild and solitary bees may be important in larval bee development and play a role in larval nutrition or as a pathogen. Since microbes in the pollen provisions of solitary bees come from the environment via the flowers, the flowers a bee visits may affect the diversity and identity of the microbes in the pollen provision and availability to the larva. This study tested the hypothesis that the diversity in flowers visited by the female bee affected the types and diversity of the microbes found in her pollen provisions. Pollen provisions were collected from nests at four sites from Osmia lignaria and Osmia ribifloris. Osmia lignaria is polylectic and visits many different flower species; whereas, Osmia ribifloris is oligolectic and visits a small number of closely-related flowers species related to blueberries. High throughput sequencing of the bacterial 16S rRNA gene was used to characterize the bacteria found in these provisions. Minimal overlap in the microbe types was found in the pollen provisions from the two bee species, even when the bees were foraging from the same flowers in a cage. Similarly, there was minimal overlap in microbes in the provisions from different sites, even within the same bee species. Together, these findings highlight the importance of environmental transmission and how diet breadth of bees determines the microbes found in pollen provisions. Future studies addressing the functional consequences of this filtering will provide rich insights into the microbial ecology of solitary bees.

Technical Abstract: Mounting evidence suggests that microbes found in the pollen provisions of wild and solitary bees are important drivers of larval development. As these microbes are also known to be transmitted via the environment, most likely from flowers, the diet breadth of a bee may affect the diversity and identity of the microbes that occur in its pollen provisions. Here we tested the hypothesis that, due to the importance of floral transmission of microbes, diet breadth affects pollen provision microbial community composition. We collected pollen provisions at four sites from the polylectic bee Osmia lignaria and the oligolectic bee Osmia ribifloris. We used high throughput sequencing of the bacterial 16S rRNA gene to characterize the bacteria found in these provisions. We found minimal overlap in the specific bacterial variants in pollen provisions across the host species, even when the bees were constrained to foraging from the same flowers in cages at one site. Similarly, there was minimal overlap in the specific bacterial variants across sites, even within the same host species. Together, these findings highlight the importance of environmental transmission and host specific sorting influenced by diet breadth for microbes found in pollen provisions. Future studies addressing the functional consequences of this filtering will provide rich insights into the microbial ecology of solitary bees.