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Mol Biol Evol. 2014 Dec;31(12):3314-23. doi: 10.1093/molbev/msu262. Epub 2014 Sep 16.

Testing the role of genetic background in parallel evolution using the comparative experimental evolution of antibiotic resistance.

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Department of Zoology, University of Oxford, Oxford, United Kingdom
CNRS, Aix-Marseille Université, Laboratoire de Bioénergétique et Ingénierie des Protéines, UMR 7281, IMM, Marseille, France.
Department of Zoology, University of Oxford, Oxford, United Kingdom.


Parallel evolution is the independent evolution of the same phenotype or genotype in response to the same selection pressure. There are examples of parallel molecular evolution across divergent genetic backgrounds, suggesting that genetic background may not play an important role in determining the outcome of adaptation. Here, we measure the influence of genetic background on phenotypic and molecular adaptation by combining experimental evolution with comparative analysis. We selected for resistance to the antibiotic rifampicin in eight strains of bacteria from the genus Pseudomonas using a short term selection experiment. Adaptation occurred by 47 mutations at conserved sites in rpoB, the target of rifampicin, and due to the high diversity of possible mutations the probability of within-strain parallel evolution was low. The probability of between-strain parallel evolution was only marginally lower, because different strains substituted similar rpoB mutations. In contrast, we found that more than 30% of the phenotypic variation in the growth rate of evolved clones was attributable to among-strain differences. Parallel molecular evolution across strains resulted in divergent phenotypic evolution because rpoB mutations had different effects on growth rate in different strains. This study shows that genetic divergence between strains constrains parallel phenotypic evolution, but had little detectable impact on the molecular basis of adaptation in this system.


Pseudomonas; adaptation; antibiotic resistance; comparative biology; experimental evolution; selection experiment

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