Fig. 4.

Temperature specificity of beneficial mutations from two TEE populations. Two mutations that evolved during the TEE were moved into the ancestral genetic background. The resulting constructed strains then competed against a neutrally marked variant of the ancestor in each of five thermal regimes. Temperatures used for these competitions differed slightly from those used in the TEE (Materials and Methods). Error bars show 95% confidence intervals estimated from a one-way ANOVA. For treatments marked with one or two asterisks, the relative fitness of the strain with the evolved mutation was greater than one at P < 0.05 or P < 0.01, respectively (one-tailed t tests). (A) Results for the nadR mutation from the clone designated 32+3 (REL2042), which is a 2-bp deletion that causes a frameshift in the protein-coding sequence at amino acid 105. (B) Results for the aceB mutation from clone Sw−1 (REL2052), which is an A→C base change that causes a glutamate to alanine substitution at amino acid 69. This aceB mutation is expected to have an effect on cellular metabolism similar to that of the iclR mutations that were common in the 42 °C and Switch treatments (see Gene Targets That Contribute to Evolved Thermal Specificity).