The evolutionary ecology of model microbial communities

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Harcombe, William Russell

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The biological world is complex. Communities contain a multitude of interacting species, while populations contain extensive genetic variation. How much complexity must one consider to understand patterns and processes of interest? When are species interactions and community properties shaped by evolution? Conversely, when is evolution altered by community context? I test these questions in a series of experiments with simple microbial communities. The first data chapter investigates the impact of competition on the evolution of phage resistance in bacteria. This work demonstrates that community context can dramatically alter the evolution of resistance to phage. Next I tested the impact of evolution on assembly of a three species community. I demonstrate that evolution can influence the content of a microbial community by altering the process of assembly. Finally, I investigated the evolutionary origin and maintenance of cross-feeding mutualisms. This work suggests that species interactions can enable novel evolutionary pathways, and that evolution can significantly increase the productivity of cross-feeding communities. Jointly these experiments suggest that consideration of the interplay between ecological and evolutionary forces can provide insight into the complexity of the natural world.