CAREER: Tempo, Contingency, and Gene Flow in the Coevolution of a Model Microbial Mutualism

Mutualisms - beneficial interactions between two organisms - are common in nature and have profoundly shaped life on our planet. Mutualistic microbes are important to human health because of the importance of microbes that live in and on our bodies. They impact human welfare, for example because of the role of microbes associated with high-yielding crop plants. These examples demonstrate the fundamental importance of microbial mutualisms to human flourishing. Surprisingly, very little is understood about how such mutualisms are born, or the conditions that are important in their formation. This project will investigate how mutualistic relationships form and become established at the genetic level. It will explore how environmental factors impact the evolution and stability of these new mutualisms. Insights from this work may be relevant for biodiversity conservation efforts and for the management of invasive species in light of environmental change. This project will also facilitate the growth and development of initiatives aimed at improving STEM education practices and STEM preparedness of graduate, undergraduate, high school, and community college transfer students, that build upon the Principal Investigator's existing efforts to improve the STEM success landscape in Mississippi.<br/><br/>The Principal Investigator created a new mutualism based on carbon and nitrogen exchange between two model microbes, the budding yeast Saccharomyces cerevisiae and the green alga Chlamydomonas reinhardtii, a system with an unprecedented degree of experimental and genetic tractability. Using this system, this project will elucidate how nascent mutualistic relationships are consolidated at the genetic level and investigate the impact of (1) carbon and nitrogen nutrient availability, (2) historical contingency (i.e., prior evolutionary history), and (3) gene flow/migration (between communities adapted to different local environmental conditions) on the coevolution of mutualism. This work will experimentally test ideas underlying Thompson's Geographic Mosaic Theory of Coevolution, and address several questions, including: (i) how do environmental conditions and/or the degree of interspecies dependency (obligate or facultative) influence coevolutionary trajectories and the distribution of adaptive genetic changes among partners? (ii) To what degree does prior mutualistic evolutionary history canalize or limit the possibilities for subsequent evolutionary adaptation? (iii) How does genetic mixing of partners that have evolved under different sets of conditions influence subsequent coevolutionary outcomes compared to cases where there is no gene flow? An integral part of this project includes efforts to: (1) enhance undergraduate and graduate education in evolution and genomics, (2) improve academic preparedness and success of community college transfer students, and (3) catalyze STEM interest and college readiness among low-income high school students, notably from the Mississippi Delta.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.