perturbation", similar to that which can impact natural populations. The final replicate was integrated into the main LTEE experiment, becoming the thirteenth population, Ara-7. Various interpretations of the findings Other researchers have experimented on evolving aerobic citrate-utilizing E. coli. Dustin Van Hofwegen et al. were able to isolate 46 independent citrate-utilizing mutants of E. coli in just 12 to 100 generations using highly prolonged selection under starvation, during which the bacteria would sample more mutations more rapidly. In their research, the genomic DNA sequencing revealed an amplification of the citT and dctA loci, and rearrangement of DNA were the same class of mutations identified in the experiment by Richard Lenski and his team. They concluded that the rarity of the citrate-utilizing mutant in Lenski's research was likely a result of the selective experimental conditions used by his team rather than being a unique evolutionary speciation event. John Roth and Sophie Maisnier-Patin reviewed the approaches in both the Lenski team's delayed mutations and the Van Hofwegen team's rapid mutations on E. coli. They argue that both teams observed the same sequence of potentiation, actualization, and refinement leading up to similar Cit+ variants. According to them, Lenski's period of less than a day during which citrate usage would be under selection, followed by 100-fold dilution, and a period of growth on glucose that would not select for citrate use; ultimately lowered the probability of E. coli being able to accumulate early adaptive mutations from one period of selection to the next. In contrast, Van Hofwegen's team allowed for a continuous selection period of 7 days, which yielded a more rapid development of citrate-using E. coli. Roth and Maisnier-Patin suggest that the serial dilution of E. coli and short period of selection for citrate-use under the conditions of the LTEE perpetually impeded each generation of E. coli from reaching the next stages of aerobic citrate utilization. Lenski argues that the problem is not with the experiments or the data, but with the interpretations made by Van Hofwegen et al. and Maisnier-Patin and Roth. According to him, the rapid evolution of Cit+ was not necessarily unexpected since his team was also able to produce multiple Cit+ mutants in a few weeks during the replay experiments. He argues that the LTEE was not designed to isolate citrate-using mutants or to deal with speciation, which is a process, not an event. Furthermore, he argued that the