REL1206 and REL1207 are the Ara- and Ara+ ancestors, respectively, for the Bennett & Lenski temperature project. REL1206 is a clone sampled from population A-1 at generation 2,000 of the main long-term experiment. REL1206 and REL1207 are isogenic, with the exception of a spontaneous mutation to Ara+ in REL1207. Six populations were propagated under each of five thermal regimes. In each group, three were founded with each ancestor. The following strains are all from generation 2,000 of the temperature evolution. For example, REL2052 refers to the isolate from replicate A-1 in the switch regime that alternated between 32°C and 42°C each day.