FIGURE 12.1 Phylogeny and nomenclature of the experimental lineages of E. coli used in this study. The ancestral organism (Anc) was obtained from a lineage that evolved under defined laboratory conditions at 37°C for 2,000 generations. A clone was sampled and cultured in six replicate populations that evolved in each of four thermal environments: 32°C, 37°C, or 42°C, or a daily alteration between 32°C and 42°C. After 2,000 generations, a clone was isolated from each lineage and propagated for another 2,000 generations at 20°C. Note that each of the 20°C selected lineages are equally related to Anc (separated by 4,000 generations) and are equally distant from each other (separated by 8,000 generations).