Far from Home: Evolution of haploid and diploid populations reveals common, strong, and variable pleiotropic effects in non-home environments

Adaptation is the process by which organisms acquire mutations that result in them being better suited to their "home" environment. However, whether those mutations remain adaptive in other "non-home" environments has an important impact on an organism's evolution as the environment changes. We define a mutation's effect on an organism's change in frequency in a population, its fitness, in different environments as its pleiotropic effect. To determine the patterns of pleiotropy of adaptive mutations, we evolved haploid and diploid barcoded S. cerevisiae populations in 12 different environments. We then isolated barcoded lineages, identified their mutations, and then performed pooled fitness remeasurement experiments to estimate the fitness of each lineage in the various environments and compared those fitnesses to the lineage's home fitness. Consistent with prior work, we found that pleiotropic effects are unpredictable in both haploids and diploids. However, by measuring fitness for lineages with single adaptive mutations, we were also able to show that mutations in the same gene tend to result in similar pleiotropic effects.