Mutation: Difference between revisions

{{cquote| There is almost certainly no physiological barrier to such an effect in most organisms: the genomic mutation rate in organisms from viruses to eukaryotes is a quantitative trait affected by many mutations whose effects can readily cumulate to intolerable levels of error. In what follows, we show that there need not be a selective barrier to this process either: because the full fitness effect of increased deleterious mutation takes some time to accumulate after a higher mutation rate has evolved, it is theoretically possible for a population to evolve a critically high mutation rate and subsequently go extinct.  

Our theoretical findings indicate that mutator hitchhiking can set in motion a self-reinforcing loss of replication fidelity, but the question of how a process as robust as natural selection could allow this to happen remains. The key fact is that natural selection, although eminently robust, is a short-sighted process that favors traits with immediate fitness benefits. The fitness cost of mutator hitchhiking is generally not anticipated because of the slow accumulation of deleterious load. When a mutator hitchhikes with a new beneficial mutation, a simple model shows that the increased deleterious load due to the mutator is in fact suppressed during the spread of the beneficial mutation. Indeed, the full fitness cost of the mutator is only realized well after the beneficial mutation has stopped spreading (SI Text). A mutator may therefore enjoy the immediate benefit of producing a new beneficial mutation without anticipating the eventual increase in deleterious load. Because of this delay in the accumulation of deleterious load, natural selection can drive mutation rate up to the point of no return, where fMmM becomes the dominant term (Fig. 4A); even if the increase in deleterious load is lethal, it is not anticipated (Fig. 4B). At the population level, this failure to anticipate the establishment of a lethal deleterious load is partly due to the sharpness of the threshold separating lethal from viable mutation rates (22, 24), such that there is no slow fitness decrease to "warn" of impending extinction. [http://www.pnas.org/cgi/content/full/104/15/6266] }}