Genomic mutation rates that neutralize adaptive evolution and natural selection

TL;DR

This paper derives simple mathematical expressions to identify mutation rates at which adaptive evolution and natural selection are neutralized in asexual populations, highlighting the detrimental effects of high mutation rates.

Contribution

It provides novel, parameter-free formulas for mutation rates that neutralize adaptation and natural selection in a standard asexual evolution model.

Findings

High mutation rates can reverse adaptation gains.

Excessive mutations can erode adaptive and compensatory mutations.

Derived expressions unify previous theoretical results.

Abstract

When mutation rates are low, natural selection remains effective, and increasing the mutation rate can give rise to an increase in adaptation rate. When mutation rates are high to begin with, however, increasing the mutation rate may have a detrimental effect because of the overwhelming presence of deleterious mutations. Indeed, if mutation rates are high enough: 1) adaptation rate can become negative despite the continued availability of adaptive and/or compensatory mutations, or 2) natural selection may be disabled because adaptive and/or compensatory mutations -- whether established or newly-arising -- are eroded by excessive mutation and decline in frequency. We apply these two criteria to a standard model of asexual adaptive evolution and derive mathematical expressions -- some new, some old in new guise -- delineating the mutation rates under which either adaptive evolution or natural selection is neutralized. The expressions are simple and require no \emph{a priori} knowledge of organism- and/or environment-specific parameters. Our discussion connects these results to each other and to previous theory, showing convergence or equivalence of the different results in most cases.