The Molecular Diversity of Adaptive Convergence
The Article The authors of this article wanted to find out how the mutational background of adaptation looks like. Specifically, they asked if identical populations adapted to a fixed environment, would adaptation occur via identical mutations or via various alternative pathways. To answer this question they experimentally evolved 115 populations of Escherichia coli to 42.2° Celsius for 2000 generations (6.64 generations of binary fission daily) and sequenced one clone each of every population, what they call “strain” or “line” throughout the paper. All populations originated from the same E. coli B REL1206 ancestral clone. Their system fulfills all of the requirements needed to answer the question: (i) a large number of replicatesfor statistical power, (ii) complete genome sequencing, so that mutations can be identified unambiguously, and (iii) a complex biological system, to ensure that the number of potential adaptive solutions is not trivial. As the experimental environmental change they chose temperature, a rather complex environmental variable since it affects different biological reactions such as respiration, growth and reproduction. Performance of the different strains was measured as fitness and yield. Fitness was defined as the density after competition of each of the evolved lines against a newly-derived Ara+ mutant of REL1206 …
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