Figure 1. Proportions of beneficial and deleterious mutations vary with strain growth rate.

Filled and empty triangles show the proportions of beneficial and deleterious mutations in each background strain as a function of its growth rate, respectively. Lines are the best-fit linear regressions; all are statistically significant ($P<0.05$, t-test) except for beneficial mutations in 37°C pH 3.0 and 37°C pH 5.0.