This action funds an NSF Minority Postdoctoral Research Fellowship for FY 2010. The fellowship supports a research and training plan in a host laboratory for the Fellow who also presents a plan to broaden participation in biology. The title of the research and training plan for this fellowship to Quinn McFrederick is "Microbial communities associated with social and solitary sweat bees: implications for bee health." The host institution for this research is University of Texas at Austin, and the sponsoring scientist is Dr. Ulrich Mueller.
Wild and managed bee populations are in decline, threatening both natural and agricultural ecosystems that depend on their essential pollination services. Although no causal relationships have been established, links between pollinator declines and pathogens have been posited. This project uses next generation sequencing to screen microbial communities found in the nests of socially variable wild bees in the genus Megalopta. Two hypotheses are being tested: 1) microbial communities inside the enclosed ecosystem of a bee's brood chamber exhibit predictable patterns of community structure and 2) microbial communities in the nests of social bees are more diverse than communities in the nests of solitary bees. A major goal of the project is to determine how microbes affect bee health by identifying putative pathogens and mutualists and examining their interactions.
Training objectives include analysis and interpretation of the large amounts of data produced by next generation sequencing technology, and development of a research program that utilizes new tools to answer as yet unanswered questions of social evolution and pollinator health. This greater understanding of how microbes affect the health of pollinators is all the more important in the era of honey bee colony collapse disorder and wild pollinator decline. Broader impacts include substantial public outreach as well as educational outreach to students, especially those with disabilities.
Bees are responsible for one-third of our food and for pollinating the majority of wild flowering plants, yet bee populations are in decline in several parts of the world. The human microbiome project has shown how important bacteria are to human health, but we know little about the role microbes play in wild bee health. This research was the first to apply modern techniques to the study of microbes in wild bees. I had several questions I wanted to address in this research: (1) what microbes associate with wild bees and how are these bacteria transmitted? (2) Do microbial communities inside the enclosed ecosystem of a bee's brood chamber exhibit predictable patterns of community structure? (3) Are microbial communities in the nests of social bees more diverse than communities in the nests of solitary bees? (4) How do microbes affect bee health? At the beginning of my fellowship I collected nests from three species of bees and used modern DNA sequencing to investigate the bacterial communities associated with these nests. I found something completely new yet not surprising; wild bees associate with bacteria commonly found on flowers (McFrederick et al. Molecular Ecology 2012). Other researchers were finding something very different in honey bees and bumble bees; these bees associate with very host-specific bacteria that are not found in the environment. Both honey bees and bumble bees are social, and social transmission is thought to help them maintain their host specific gut bacteria. I decided to collaborate with some ant researchers to see if highly social ants also have host-specific bacteria, but we found that the ants we studied, like my sweat bees, associate with environmentally acquired instead of host-specific bacteria (McFrederick et al. Applied and Environmental Microbiology 2013). Bumble bees and honey bees are special, for reasons we still don't understand. I further studied how (question 2) host developmental stage and (question 3) social structure affects bacterial community structure in sweat bees that live in Central America. These bees (Megalopta genalis and Megalopta centralis) are special in that social and solitary nests occur in the same population of bees. I sampled both solitary and social bees across different developmental stages and used modern sequencing to investigate bacterial community structure. I found that the samples were generally dominated by a common flower associated bacteria (Lactobacillus kunkeei), and that bacterial communities did not differ between social and solitary nests. Sociality does not affect bacterial communities associated with these bees, but host developmental stage does. I found that larvae are dominated by L. kunkeei until they are mature and defecate (larval bees usually defecate only when they are ready to become pupae- when they are young their hind gut is not connected to the rest of their gut). Once they defecate, the bees lack most gut bacteria, as do pupae and young adults. But once the adults start to forage they can obtain L. kunkeei from flowers. So environmental transmission is more important than social transmission in these bees. As a first stab at determining how gut bacteria might affect bee health, I looked for interactions between bacteria and fungi in the guts of larvae of the Alfalfa Leafcutting Bee (ALCB), Megachile rotundata. The ALCB has a specialist fungal pathogen, Ascosphaera aggregata, which causes the larval disease chalkbrood. I wanted to see what happens to fungi when I got rid of bacteria, and vice-versa, in hopes that I would find bacteria that might suppress A. aggregata. I treated young larvae with antibacterials, antifungals, or A. aggregata spores. I also left some larvae untreated as a control group. I let the larvae develop, and then sequenced the fungal and bacterial communities in their guts. I found that when I knocked back A. aggregata new fungi showed up, indicating that A. aggregata may suppress the growth of other fungi. I also found that bacteria were less diverse when I knocked back A. aggregata, but I am not sure if that is due to interactions between fungi and bacteria or if the treatment directly affected bacteria. But I did not find that fungi were affected when I knocked back bacteria. This research has impacts on wild and agricultural ecosystems in that it draws us closer to understanding how wild bees obtain possibly beneficial bacteria. I am continuing with this research and hope to find ways to enrich these 'good' bacteria, perhaps by planting flowers that the bacteria thrive on. I also reached out to groups underrepresented in the sciences by taking my research to schools and talking to grade school classes. I will continue to do this kind of outreach, and hope to convince a diverse swath of humanity why they should be interested in understanding and conserving wild bee diversity!
