Evolution of diversity

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The origin of diversity is the mystery of mysteries according to Darwin. Millions of species exist today, but the detailed mechanisms generating this diversity are still unclear. The traditional model of speciation is based on geographical isolation: if subpopulations of an ancestral lineage become geographically subdivided (e.g. through fragmentation due to climatic changes), they embark on different evolutionary trajectories, and hence diversify. Here the initial process of splitting the gene pool is not adaptive. In contrast, in the process of adaptive speciation, the splitting of the gene pool is itself an adaptation. The past decade has seen growing interest in such adaptive diversification, because both empirical and theoretical studies have documented its feasibility. The paradigmatic theory of evolutionary branching has popularized the notion that diversification can be driven by ecological interactions such as competition for resources. Using the bacterium E. coli, I have developed a microbial model system to test the theory of adaptive diversification due to evolutionary branching. E. coli offers many advantages, including the possibility of evolving it for thousands of generations and creating a fossil record by freezing intermediate stages. Our evolving E. coli populations have undergone diversification due to competition for carbon resources. Based on molecular, physiological and ecological experiments, my research aims at fully analyzing all aspects of the process of adaptive diversification in this model system, documenting the evolutionary changes prior, during and after the diversification event. We are also studying the origins of diversity in a different microbial system, in which diversification occurs in the context of the general problem of cooperation, leading to coexistence of cooperators and cheaters in the production of a beneficial substance. Another main focus of our research is the mathematical modeling of our experimental model systems based on "reaction kinetics" of individuals, describing individual growth, reproduction and survival using the knowledge gained from our experiments. Finally, we plan to investigate how predation affects diversification in both the experimental and the mathematical model systems.