MIP: Addressing the Role of Community Ecological Interactions in Population Niche Evolution along Hot Spring Thermal Gradients

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Developing an understanding of the factors that determine the origins and distribution of biological diversity on the planet is a fundamental goal of ecology and evolution. Whereas the potential distribution of a group of organisms is determined solely by its evolved limits of environmental tolerance, its actual realized distribution also depends upon the outcome of its interactions with other community members. A grant has been awarded to Dr. Scott R. Miller of The University of Montana to investigate how interactions among competing photosynthetic microorganisms (cyanobacteria and green non-sulfur bacteria) have shaped their realized distribution patterns along two well-characterized hot spring environmental gradients (White Creek, Rabbit Creek) in Yellowstone NP. Project 1 integrates environmental gene expression analyses with laboratory physiology experiments to address the central tenet of evolutionary theory that competing species evolve to reduce competition by testing whether green non-sulfur bacteria exhibit a genetically-programmed shift in resource utilization in regions of strong distribution overlap with competing cyanobacteria. Project 2 combines genetic and physiological approaches to address why the different springs differ in the abundance of the cyanobacterium Synechococcus B: the realized distribution of this cyanobacterium is twice as broad at Rabbit Creek compared with White Creek. It will be determined whether these differences in realized distribution are the result of different amounts of genetically-determined variation in temperature performance among Synechococcus B between springs, and whether either limitations in the ability of organisms to migrate between springs or exclusion by competitors contribute to these differences.The questions of how ecological variation is distributed within and between communities, and how ecological interactions themselves contribute to the evolved traits of competing organisms, are longstanding in ecology and evolution, but progress on these questions has been historically hampered for microorganisms by technological limitations. Addressing them has major implications for our understanding of how microbial communities are assembled and function, and of how they may respond to environmental change. Together, these projects promise fresh insights into these questions from a novel microbial perspective. The research plan thereby addresses key program goals of integrating microbial physiology and genomic diversity with environmental processes to determine the mechanistic basis of biotic interactions within communities and to reveal the patterns of microbial distribution in time and space. The award enables the integration of research and education through support for both graduate and undergraduate student training, as well as through the PI?s Biology of Yellowstone Hot Springs course, a sophomore-level offering which uses these hot springs as a natural teaching laboratory to provide a hands-on microbiological research experience. Outreach components include a continued focus on these microbial communities in the PI?s annual field-based course for college and high school instructors on the biology of Yellowstone hot springs through the NSF National Chautauqua Workshop summer program.