Extent of adaptation is not limited by unpredictability of the environment in laboratory populations of Escherichia coli

Abstract

Environmental variability is on the rise in different parts of the earth and the survival of many species depend on how well they cope with these fluctuations. Our current understanding of how organisms adapt to unpredictably fluctuating environments is almost entirely based on studies that investigate fluctuations among different values of a single environmental stressor like temperature or pH. However, in nature multiple stresses often exist simultaneously. How would unpredictability in environmental fluctuations affect adaptation under such a scenario? To answer this question, we subjected laboratory populations of Escherichia coli to selection over ~260 generations. The populations faced predictable and unpredictable environmental fluctuations across qualitatively different selection environments, namely, salt and acidic pH. We show that predictability of environmental fluctuations does not play a role in determining the extent of adaptation. Interestingly, the extent of ancestral adaptation, to the chosen selection environments, is of key importance. Integrating the insights from two previous studies, our results suggest that it is the simultaneous presence of multiple environmental factors that poses a bigger constraint on extent of adaptation, rather than unpredictability of the fluctuations.