Evolution of generalists by phenotypic plasticity

Adapting organisms face a tension between specializing their phenotypes for certain ecological tasks or developing generalist strategies which permit persistence in multiple environmental conditions. Understanding when and how generalists or specialists evolve is therefore an important question in evolutionary dynamics. Here we study the evolution of bacterial range expansions by selecting Escherichia coli for faster migration through porous media containing one of four different sugars supporting growth and chemotaxis. We find that selection in any one sugar drives the evolution of faster migration in all sugars relative to the ancestral strain. Measurements of growth and motility of all evolved lineages in all nutrient conditions reveal that the ubiquitous evolution of fast migration arises via phenotypic plasticity. Phenotypic plasticity permits evolved strains to exploit distinct phenotypic strategies to achieve fast migration in each environment irrespective of the environment in which they were evolved. Our work suggests that plasticity plays an important role in the evolution of generalist phenotypes.