Abstract
Biased mutation spectra are pervasive, with widely varying direction and magnitude of mutational bias. Why are unbiased spectra rare, and how do such diverse biases evolve? We find that experimentally changing the mutation spectrum increases the beneficial mutation supply, because populations sample mutational classes that were poorly explored by the ancestor. Simulations show that selection does not oppose the evolution of a mutational bias in an unbiased ancestor; but it favours changing the direction of a long-term bias. Indeed, spectrum changes in the bacterial phylogeny are frequent, typically involving reversals of ancestral bias. Thus, shifts in mutation spectra evolve under selection, and may directly alter outcomes of adaptive evolution by facilitating access to beneficial mutations.
One Sentence Summary Altered mutational biases allow populations to sample poorly explored mutational space, with wide-ranging evolutionary consequences.
Competing Interest Statement
The authors have declared no competing interest.
