Abstracts (first author)
Shifting fitness landscapes in response to altered environments
One of the most controversial questions in evolutionary biology is the role of adaptation in molecular evolution. Following decades of debate between selectionists and neutralists, new high-throughput methods are beginning to illuminate the full distribution of fitness effects of new mutations. Here, we shed light on the adaptive potential in Saccharomyces cerevisiae by presenting systematic high-throughput fitness measurements for 578 possible point mutations in a region of Hsp90 in each of six environmental conditions. Under elevated salinity, we observe numerous beneficial mutations with growth advantages up to 7% relative to the wild type. We thus demonstrate that an essential protein can harbor adaptive potential upon an environmental challenge, and report a remarkable fit of the data to Fisher's geometric model - which well predicts the observed costs of adaptation associated with environmentally specific beneficial mutations. Furthermore, we utilize a Bayesian MCMC modeling framework to evaluate the statistical significance of the results - showing a remarkable accuracy of the experimental approach, e.g., allowing for direct inference of the non-neutrality of certain synonymous substitutions.