Research

All known life on Earth originated from a single ancestor, but as life evolved, it has diversified, with organisms occupying distinct ecological niches. I use experimental evolution to study the origin and ongoing evolution of ecological interactions. I am interested in how initially identical organisms are able to differentiate ecologically, such that multiple ecotypes are able to stably coexist. I am also interested in how this diversity is maintained and the evolutionary barriers to one ecotype invading the ecological niche of the other.

As a Ph.D. student in Richard Lenski's lab, I worked with the long-term evolution experiment with E. coli (LTEE) in which twelve populations founded from the same ancestor have been evolving under identical conditions for more than 60,000 generations. In one of those populations, a clade in the population evolved the ability to consume citrate, a molecule which is present in the media, but normally inaccessible to E. coli under aerobic conditions. These citrate consumers, rather than taking over the whole population, coexisted for more than 10,000 generations with another clade which could not consume citrate. I studied the basis of this coexistence and the eventual extinction of the clade which could not consume citrate. Surprisingly, this extinction was not due to exclusion by the citrate consumers, but rather due to chance laboratory variation.

Now, as a NASA post-doctoral fellow in Vaughn Cooper's lab at the University of Pittsburgh, I am studying the evolution of synergistic interactions. Under selection for biofilm formation, multiple coexisting ecotypes of the bacterial pathogen Burkholderia cenocepacia evolve. Intriguingly, these ecotypes exhibit synergistic interactions where their productivity is higher when grown together than expected based on their productivity when grown separately. I am studying the factors which promote the evolution of synergistic versus competitive interactions.

I also study evolutionary changes in the stoichiometry of organisms. All living organisms are made up of elements in varying proportions. These proportions are broadly similar across all organisms, with more carbon atoms than phosphorus and more phosphorus than manganese, for example. However, the precise ratios between elements can vary between organisms and that variation has ecological effects from population to ecosystem levels. Working with the long-term evolution experiment, I found that over the course of 50,000 generations, E. coli propagated under carbon-limited, batch-transfer conditions evolved lower carbon to phosphorus and carbon to nitrogen ratios.