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UBC Theses and Dissertations

Adaptation in Escherichia coli : ecological and genetic constraints on diversification Schick, Alana


There is growing evidence that disruptive selection generated by intraspecific resource competition may be a common mechanism for generating biological diversity. Adaptive dynamics models provide a framework describing how frequency dependent selection drives such diversification, but these models don’t consider the complexities that arise as a result of gene interactions. Here, we explore the relative effects of ecological and genetic constraints on diversification using an experimental system of Escherichia coli in which diversification is driven by frequency dependence based on resource use. Diversified populations consist of ecotypes that consume glucose and ac- etate at different rates, and a mutation in the arcA gene has been identified that has a large effect on this phenotype. By isolating clones of each eco- type from a previously diversified population, we find that the effect of the arcA mutation on rediversification depends on both the ecotype and the genetic background. While some of these observations are consistent with predictions made by adaptive dynamics models, others cannot be explained without also accounting for epistasis and genetic constraints, highlighting the importance of considering both ecological and genetic factors when pre- dicting diversification. Adaptation in this system also provides an example of an interaction between ecological and evolutionary processes, adding to a growing number of studies that exhibit a clear feedback between these two processes.

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