Module 4.1: Do Mutation Rates Evolve?

 I do think mutation rates evolve; the rate of mutation is central to evolution. Mutation rates have traditionally been thought of as the result of adaptability. As an organism becomes more adapted to its environment, its chances to adapt further are reduced significantly, a possible benefit of mutations. As an organism adapts to an unchanging environment, mutation in general becomes almost exclusively disadvantageous to the organism, and natural selection should then be expected to favor a decrease in mutation rate. According to the general reduction principle, where it is physiologically possible, the mutation rate would evolve to zero in an unchanging environment. On the other hand, in an environment that changes over time, there is endless room for improvement due to the continuous supply of potentially beneficial mutations. In a changing environment, therefore, it is easy to see how a certain amount of mutation might be beneficial even vital. An example is RNA viruses that readily adapt to changing environmental conditions. The high mutation rate of RNA viruses compared with DNA organisms is responsible for their enormous adaptive capacity. RNA viruses mutate at the maximum error rate compatible with maintaining the reliability of genetic information because this would allow them to quickly find the beneficial mutations needed for adaptation. RNA virus populations exist as groups of mutant genotypes which shows the lack of exonuclease proofreading activity of the virus-encoded RNA polymerases. A necessary condition for natural selection to optimize the mutation rate is that genetic variability exists in RNA viruses. Therefore, a decrease in mutation rate could come about with little or no loss of adaptive capacity but would benefit the population by slowing the accumulation of deleterious mutations. In conclusion, population mutation rates rise when cells experience stress and decline again once cells are adapted. Cellular mortality the leads to the rapid evolution of mutation rates helps explain the prevalence of hypermutation in various settings, from the development of antibiotic resistance in microbes to cancer relapses upon chemotherapy.  

Sources

Mutation rates among RNA viruses | PNAS