Evolution is a tricky game between exploration and fixation, we said. True, if you do not need to win the evolutionary arms race against your opponent (predator/parasite).
Yomo and Kashiwagi report about the phenotypic and genomic changes in experimental coevolution of RNA bacteriophage Qβ and Escherichia coli. They observed how the phenotypes and genotypes of coevolving parasite-host pairs change through the arms race. Copropagation experiments with Escherichia coli and the lytic RNA bacteriophage Qβ in a spatially unstructured environment revealed continuous adaptation and counter-adaptation: “E. coli first adapted by developing partial resistance to infection and later increasing specific growth rate. The phage counter-adapted by improving release efficiency with a change in host specificity and decrease in virulence. Whole-genome analysis indicated that the phage accumulated 7.5 mutations, mainly in the A2 gene, 3.4-fold faster than in Qβ propagated alone. E. coli showed fixation of two mutations (in traQ and csdA) faster than in sole E. coli experimental evolution.”
Kashiwagi A, Yomo T.
Ongoing phenotypic and genomic changes in experimental coevolution of RNA bacteriophage Qβ and Escherichia coli.
PLoS Genet. 2011 Aug;7(8):e1002188. Epub 2011 Aug 4.