Mostly Biomathematics Lunchtime Seminar

How microscopic epistasis and clonal interference shape the fitness trajectory in a spin glass model of microbial long-term evolution

Speaker: Nicholas Boffi, NYU

Location: Warren Weaver Hall 1314

Date: Tuesday, March 28, 2023, 12:45 p.m.


Microscopic epistasis (interactions between the fitness effects of mutations at different genetic sites) and clonal interference (the presence of several competing microbial strains in a given culture) have both been widely observed experimentally in evolving laboratory microbial populations. Yet, for analytical tractability, many approaches in evolutionary theory neglect these effects, opting instead to make use of macroscopic models and to operate within a mutation regime that ensures the population consists of a single dominant strain at all times. Here, we introduce a computational approach that enables us to resolve the full microscopic complexity of an evolving population under standard laboratory conditions, and we apply the method to study the impact of both epistasis and clonal interference on the mean fitness trajectory of the population. By systematically varying its strength, we find that microscopic epistasis generically slows the fitness trajectory with or without clonal interference, as measured by power law fits to the resulting data. By contrast, we show that clonal interference has a more subtle effect. In the absence of epistasis, clonal interference accelerates the trajectory, while in the presence of sufficiently strong epistasis, varying the magnitude of clonal interference leaves the power law trajectory invariant. We rationalize this result in the context of past predictions made within a macroscopic formalism, where we arrive at a surprising conclusion: macroscopic models of microscopic evolutionary processes must be tuned to the level of clonal interference, which dynamically filters the distribution of available fitness effects.