Impact of fluctuating environments on the fitness and robustness of evolving laboratory and industrial Saccharomyces cerevisiae strains.
Adaptation occurs through the selection of beneficial mutations enhancing fitness in a specific environment. However, since environments vary across time and space, mutations that are positively selected in one environment may be less beneficial or detrimental in others. Here we investigate the evolution of microbial robustness (i.e. a consistent fitness across many diverse environments), through the adaptive evolution of two genetically distinct Saccharomyces cerevisiae populations in fluctuating conditions, followed by fitness assays and whole-genome sequencing. Our results indicate that the haploid laboratory strain S288C achieved higher average fitness than its parental strain, particularly when evolved in fluctuating environments compared to constant environments, but did not show increased robustness. In contrast, populations of the industrial diploid strain Ethanol Red failed to achieve significant fitness improvement under both fluctuating and constant evolution regimes but became more robust. Populations that adapted to fluctuating conditions acquired mutations in genes involved with cell morphology and protein degradation. Overall, our results emphasize the importance of parental traits in shaping fitness and robustness during adaptive laboratory evolution.