Tradeoffs between microbial growth phases lead to frequency-dependent and non-transitive selection

TL;DR

This paper presents a microbial growth model revealing how tradeoffs between growth phases lead to complex evolutionary dynamics like coexistence, bistability, and non-transitive interactions, emphasizing the importance of multiple traits in selection.

Contribution

It introduces a theoretical framework analyzing how tradeoffs between growth, lag, and yield influence microbial evolution, predicting diverse population behaviors.

Findings

Multiple strains can coexist due to frequency-dependent selection.

Bistability can occur from tradeoffs between growth phases.

Non-transitive interactions like rock-paper-scissors emerge under certain conditions.

Abstract

Mutations in a microbial population can increase the frequency of a genotype not only by increasing its exponential growth rate, but also by decreasing its lag time or adjusting the yield (resource efficiency). The contribution of multiple life-history traits to selection is a critical question for evolutionary biology as we seek to predict the evolutionary fates of mutations. Here we use a model of microbial growth to show there are two distinct components of selection corresponding to the growth and lag phases, while the yield modulates their relative importance. The model predicts rich population dynamics when there are tradeoffs between phases: multiple strains can coexist or exhibit bistability due to frequency-dependent selection, and strains can engage in rock-paper-scissors interactions due to non-transitive selection. We characterize the environmental conditions and patterns of traits necessary to realize these phenomena, which we show to be readily accessible to experiments. Our results provide a theoretical framework for analyzing high-throughput measurements of microbial growth traits, especially interpreting the pleiotropy and correlations between traits across mutants. This work also highlights the need for more comprehensive measurements of selection in simple microbial systems, where the concept of an ordinary fitness landscape breaks down.