  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.
