Intraspecific variation across interaction types in pollinating insects

Gordon Smith, Neurobiology and Behavior, Cornell University, Ithaca, NY, Hamutahl Cohen, University of Oregon, OR, S Hollis Woodard, UC Riverside, Quinn McFrederick, Entomology, Univ California Riverside, Riverside, CA and Lauren Ponisio, Biology, University of Oregon, Eugene, OR

Background/Question/Methods
Individuals vary extensively in their morphology and behavior, and this variation can have large impacts on species interactions. While this variation has the potential to affect a species’ interactions with all their partners (e.g., competitors, prey, predators), the interactions of a species with each of these communities are generally examined separately. Thus, how similar intraspecifc variation is across contexts and how it affects interactions with different types of partners is unknown. To examine whether species vary more in some of their interactions than others, we used DNA metabarcoding to identify the gut microbes and pollen species carried by 1488 bees captured in California sunflower fields. Using this dataset, we compared the variability of bee individuals in their plant and microbe interactions. Given that flowers act as transmission hubs for bee pathogens and bacteria, we predicted that 1) variability in pollen interactions would be positively correlated with variability in microbe interactions. As many bacteria face large barriers to transmission and recruitment, we predicted 2) that pollen interactions would be more variable than microbe interactions. Finally, we predicted 3) that variability in microbial interactions would be lower when the plant-bee interaction networks were dominated by a few highly visited flower “hubs”.
Results/Conclusions
Contrary to predictions, 1) intraspecific variation in a bee species’ pollen interactions did not predict variability in their microbe interactions, and 2) pollen interactions were significantly less variable than microbe interactions. These results suggest that many bee gut microbes are not picked up at flowers, but rather during non-foraging activities. These patterns, however, differed when analyses were restricted to only “core” microbial families that have previously been reported as important in bee guts. Intraspecific variation in pollen interactions was positively correlated with variation among core microbes, and bees were similarly variable between pollen and core microbe interactions. This discrepancy may be due to many of the microbial species encountered away from flowers being transient in the bee guts rather than resident. Furthermore, plant-pollinator network architecture did affect intraspecific variation in microbial interactions: consistent with prediction 3), microbe variation within bee species was lower in networks that were more nested and which had frequently visited plant “hubs”. We conclude that shared flowers serve as transmission hubs within and across bee species for many bee-associated microbes, and call for future work investigating the role of transient microbes in these communities.