A central goal of evolutionary biology is understanding how ecological diversity arises and is maintained in natural populations. White Creek, in Yellowstone National Park, is home to a population of the cyanobacterium, Mastigocladus laminosus, which grows along a thermal gradient of 37 to 55ºC. While genetically identical for much of the genome, the population has members that have specialized and adapted to live at different temperature zones along creek. This study takes an innovative approach using genomic data to identify strong candidates for genes responsible for natural variation within the population and that are temperature associated. Genes thus identified can shed light on the type, function, and number of genes involved in thermal adaptation.

Fundamental questions regarding how ecological niches develop in populations are: 1) what kind of genes are involved, regulatory or protein encoding? 2) What do the genes encode? and 3) How many genes are involved? This study's unique focus on a natural population facing a well defined environmental gradient, allows a robust analysis of associations between genetic makeup and the environmental variable. Undergraduate researchers in the University of Montana's Introductory Multicultural Summer Undergraduate Research Experience and the HHMI supported Montana Integrative Learning Experience for Students have had and will continue to have opportunities to work in the lab on this study. An educational module on microbiology and evolution will be developed from this study for use by Ecology Project International, which draws high school students from all over the U.S. and Latin America to Yellowstone NP.

Project Report

A central goal of evolutionary biology is to understand how biological diversity arises and is maintained in natural populations. This research addressed the genetic variation associated with ecological differences observed for a population of a thermophilic cyanobacterium (Mastigocladus laminosus) that lives across a range of temperatures along White Creek, a hot spring in Yellowstone National Park. Members of this population exhibit dramatic differences in their tolerances of high and low temperatures, respectively. Using genome data acquired as a part of this project for upstream and downstream members of the White Creek population which are known to vary in temperature tolerance, we have identified a small number of genetic factors that are tightly associated with these functional differences. These include genes that are involved in the regulation of development, pattern formation and structure of the heterocyst, a specialized cell for the conversion of atmospheric nitrogen gas to a biologically useful form (a process called nitrogen fixation). Heterocysts are essential for the survival and growth of these organisms in their natural environment at White Creek. More broadly, this structure contributes enormous quantities of usable, life-sustaining nitrogen to natural and agricultural systems each year, but its capacity for an evolutionary response in the face of environmental change such as increasing temperature is poorly understood. These results will guide future studies to reveal how naturally-occurring variation in the development architecture of the heterocyst impacts the temperature dependence of its function. By linking genetic variation with its functional consequences, the results of this project advance our understanding of fundamental and longstanding questions in evolutionary biology regarding the genetic basis of adaptation as well as have practical implications for our understanding of the effects of temperature on a microbial process of ecological importance and potential economic interest. Because the heterocyst is currently the best model for producing hydrogen (a byproduct of nitrogen fixation) from only sunlight, atmospheric gas, water and minerals, this work has implications for how to engineer a reliable and affordable source of alternative energy. The award supported the dissertation research of a graduate student as well as the development of educational outreach modules for high school students.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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George W. Gilchrist
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University of Montana
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