Environmental variation induced by both abiotic and biotic factors drives adaptation, and in some cases, selects for the evolution of phenotypic plasticity. There are many examples of plasticity in response to abiotic variation and predation, but we know little about how other biotic interactions influence the evolution of plasticity. We examined how evolution in an obligate pairwise nutritional mutualism can shape phenotypic plasticity. We used a synthetic mutualism based on brewer’s yeast strains that cross feed one another for an amino acid. One partner overproduces adenine but cannot produce lysine, and the other partner overproduces lysine but cannot produce adenine. We let the mutualistic pairs evolve for 15 weeks then assayed the reaction norms of growth rate in differing adenine environments as well as the reaction norms of adenine production of the adenine overproducer in the different adenine environments. We hypothesized that the selective environment created by the mutualism would lead to decreased plasticity due to a stable, but low nutrient supply of adenine. Similarly, we also hypothesized that overproduction should become less plastic.
Results/Conclusions
Our results demonstrate that both partners evolved differences in growth rate and plasticity to different adenine concentrations as compared to ancestral lines. As expected, the lysine overproducers had reduced growth plasticity after evolution in a mutualistic community as compared to their ancestors. In contrast, growth plasticity of the adenine overproducers was unchanged. Adenine overproduction plasticity did not show a consistent pattern across replicates. Some replicates evolved increased adenine overproduction plasticity whereas others had reduced plasticity. Together, these results suggest that mutualistic interactions can indeed drive evolutionary change in phenotypic plasticity.