The possible influences of environmental stresses on the effects of mutations on fitness. Shown are schematic reaction norms of a wild-type strain (solid line) and three different mutants (dashed lines). The wild-type growth rates in favorable and stressful conditions are represented by νF and νS, respectively. The growth rates of each specific mutant in these environments is represented by μF and μS, respectively. The effects of mutations in favorable and stressful environments are illustrated; they are defined as αF ≡ log(νF/μF) and αS ≡ log(νS/μS), respectively. The effect of a specific mutation could be alleviated (αS < αF, green), unchanged (αS = αF, black) or aggravated (αS > αF, red) under stressful conditions. The average mutation effects under favorable and stressful conditions and , are calculated by averaging αF and αS over a set of random mutations. We define a stress as alleviating (or aggravating) mutation effects if the average mutation effect is decreased, < (or increased, >) by the stress.
Kishony and Leibler Journal of Biology 2003 2:14 doi:10.1186/1475-4924-2-14