Presented by Ariel Amir, School of Engineering and Applied Sciences, Harvard

Abstract: I will talk about some recent theoretical work inspired by the Lenski lab long-term-evolution experiment - running for over 31 years - where the bacterium E. coli is grown and diluted into fresh media daily. Surprisingly, the fitness of the evolved strains (measured against the original ancestor) does not plateau but continues to increase continuously over time. Concurrently, cells get bigger over time. I will discuss models coupling cell physiology to the evolutionary dynamics, informing us which cellular traits should be under selection. The results suggest that cell size is a "spandrel" in the evolutionary sense, and that fitness can be defined in terms of other cellular traits. I will also discuss a theoretical model which includes interaction between genes (epistasis) and show how this can dramatically slow down the rate of evolutionary dynamics.