Evolution of cross-tolerance to metals in yeast

Studying tolerance and cross-tolerance to stressful environmental conditions as traits of organisms become increasingly important in a changing world. To unravel the potential for cross-tolerance, we evolved Saccharomyces cerevisiae in lethal concentrations of single metals in a short-term evolution experiment. We matched each evolved line's mutation with the amount of cross-tolerance by testing each evolved line in every metal. We found trade-offs evolved and that cross-tolerance is not reciprocal on average for pairs of environments. Many different fitness profiles evolved in any one environment, with the exception of copper-evolved lines showing remarkable parallelism. We learned that within the realm of stressful environments, generalist mutation arise in low quality environments and specialist mutations in highly receptive environments. Genes under selection involved in ion transport in the plasma membrane were significantly over-represented, however, many different genes influence the amount of cross-tolerance for metals. We hypothesized that the similarity in the environment would predict the amount of cross-tolerance, but the idiosyncratic nature of cross-tolerance to metals poses a challenge to predicting whether populations are likely to adapt or die when facing environmental stressors.