Fig. 3.

Genes that are targets of selection in the TEE often accumulated mutations later in the LTEE at 37 °C. For each TEE treatment, we calculated an RI equal to the percentage of mutations affecting single genes in those six genomes that also experienced mutations in clones from the same LTEE population that produced the TEE progenitor. We calculated RI values for comparisons to LTEE clones sampled at 5K, 10K, and 20K. The TEE began from a 2000-generation clone from this population, so these LTEE clones had evolved for 3,000, 8,000, and 18,000 additional generations at constant 37 °C. As expected, the 37 °C treatment had a significantly higher RI at 5K and 10K than the other four treatments combined (P < 0.05, one-tailed Fisher’s Exact Test). This difference was no longer significant at 20K. This convergence supports the hypothesis that many of the mutations that arose in the different temperature treatments, which all shared the same nutrient and other conditions with the LTEE, also improve fitness at 37 °C, although to a lesser degree, thus accounting for their later emergence at that ancestral temperature.