Heterogeneity of mortality rates among the 12 evolved lines under the repeated freeze-thaw regime. The height of each bar shows the mean mortality rate per day for one of the evolved lines, measured over ten daily freeze-thaw cycles, calculated from three assays for each line. The x-axis value (34%) is the estimated mortality rate of the ancestor; the dashed line shows the average mortality rate for the 12 evolved lines. Error bars are 95% confidence intervals calculated using the replicate assays for each line. See Table 1 for the statistical analysis testing for variation among the evolved lines.