The effect of pollen diet diversity on gut microbiome composition in two bee species

Background/Question/Methods

Loss of biodiversity at one trophic level can affect diversity at other levels, and in turn shape ecosystem services. We investigated the potential consequences of reduced floral diversity by asking how pollen diet diversity impacts gut microbial diversity and host performance in two ecologically and economically important generalist bee pollinators. Corbiculate bees host a relatively simple and consistent gut microbial community, while solitary bee gut microbiomes are typically more diverse, suggesting that different bee species may have different responses to changes in diet breadth. We experimentally tested the effect of one-, two-, or three-species diets on gut microbial communities in the solitary leafcutter bee (Megachile rotundata) and social bumble bee (Bombus impatiens). Pollen diets included dandelion (Taraxacum officinale), hawthorn (Crataegus sp.), or staghorn sumac (Rhus typhina) alone, each pair-wise combination, and a mix of all three species. All pollens were honey bee collected and sterilized by ethylene oxide before the experiment. We sequenced 16S rRNA genes to identify how diet treatment and bee species affected gut bacterial communities. Given the importance of gut bacteria for health and performance in many taxa including bees, understanding how diet diversity affects gut microbial communities will shed light on processes with large-scale ecological consequences.

Results/Conclusions

Neither pollen diet diversity nor composition affected bee survival within each species. Bombus impatiens pollen consumption did not differ across diet treatments, while M. rotundata consumed dandelion pollen less than other pollen types. We hypothesize that gut microbiome diversity will increase with diet diversity in both species, but that B. impatiens will exhibit more consistency between diet treatments (maintaining its core taxa) than M. rotundata. Based on survival rates (~95% for both species), neither species suffered obvious negative effects from any diet; however, analyzing changes in gut microbiome composition will provide insight into how these species would fare in the face of additional stressors. Interactions between pathogens, pesticides, and low-quality diets are implicated in pollinator declines and studies on social bees suggest that the gut microbiome can mediate effects of some of these stressors, such as by metabolizing toxins or protecting against pathogens. Extending this research to solitary bee species is paramount, given their abundance, diversity, and importance as pollinators. This research expands our understanding of consequences of biodiversity by testing theory in elusive diversity-driven interactions which may have broad ecosystem consequences and help identify species that are most threatened by landscape simplification.