Figure 3.

Accumulation of spontaneous mutations in the germline and somatic genomes of T. thermophila over 1000 generations. Gradual accumulation of deleterious mutations in the germline genome causes mean fitness to decrease (A) and among-line variance in fitness to increase (C). In contrast, neither the mean nor the among-line variance in somatic fitness change significantly over the course of the experiment (B and D). Means and among-line variance components were estimated through linear mixed models. Error bars are 95% credible intervals (CIs), based on the posterior distribution of the mixed model. In A and C, the CIs for t = 800 generations are truncated to improve visualization (the wide CIs are caused by the large variance among a small number of lines; Figure 2). Solid lines are weighted least-squares regression fits where the mean or among-line variance at each time was weighted by the inverse of the variance of the posterior distribution; the dotted lines show the 95% CIs on the fits calculated from the posterior distribution.