Adaptive and pleiotropic effects of evolution in synonymous sugar environments

Abstract

AbstractAdaptation to an environment is enabled by the accumulation of beneficial mutations. When adapted populations are shifted to other environments, the byproduct or pleiotropic fitness effects of these mutations can be wide-ranged. Since there exists no molecular framework to quantify relatedness of environments, predicting pleiotropic effects based on adaptation has been challenging. In this work, we ask if evolution in highly similar environments elicits correlated adaptive and pleiotropic responses. We evolve replicate populations ofEscherichia coliin non-stressful environments that contain either a mixture of glucose and galactose, lactose, or melibiose as the source of carbon. We term these similar sugars as “synonymous”, since lactose and melibiose are disaccharides made up of glucose and galactose. Therefore, the evolution environments differed only in the way carbon was presented to the bacterial population. After 300 generations of evolution, we see that the adaptive responses of these populations are not predictable. We investigate the pleiotropic effects of adaptation in a range of non-synonymous environments, and show that despite uncorrelated adaptive changes, the nature of pleiotropic effects is largely predictable based on the fitness of the ancestor in the non-home environments. Overall, our results highlight how subtle changes in the environment can alter adaptation, but despite sequence-level variations, pleiotropy is qualitatively predictable.