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PLoS Biol. 2007 Sep;5(9):e225.

Recombination speeds adaptation by reducing competition between beneficial mutations in populations of Escherichia coli.

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School of Biological Sciences, University of Auckland, Auckland, New Zealand.


Identification of the selective forces contributing to the origin and maintenance of sex is a fundamental problem in biology. The Fisher-Muller model proposes that sex is advantageous because it allows beneficial mutations that arise in different lineages to recombine, thereby reducing clonal interference and speeding adaptation. I used the F plasmid to mediate recombination in the bacterium Escherichia coli and measured its effect on adaptation at high and low mutation rates. Recombination increased the rate of adaptation approximately 3-fold more in the high mutation rate treatment, where beneficial mutations had to compete for fixation. Sequencing of candidate loci revealed the presence of a beneficial mutation in six high mutation rate lines. In the absence of recombination, this mutation took longer to fix and, over the course of its substitution, conferred a reduced competitive advantage, indicating interference between competing beneficial mutations. Together, these results provide experimental support for the Fisher-Muller model and demonstrate that plasmid-mediated gene transfer can accelerate bacterial adaptation.

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