Why are RNA virus mutation rates so damn high?

Abstract

The high mutation rate of RNA viruses is credited with their evolvability and virulence. This Primer, however, discusses recent evidence that this is, in part, a byproduct of selection for faster genomic replication.

Fig 1. Biological mutation rates summarized from fastest to slowest: Viroid (RNA elements that cause some plant disease without encoding any genes), viruses (RNA shown as Ebola, single-stranded DNA shown as an icosohedron, and double-stranded DNA shown as a myophage), prokaryotes (rod-shaped bacteria), and eukaryotes (rodent).

Icons are roughly the size of the range of mutation rates and genome sizes of measured organisms within that group. Axes are log-transformed, data as in [3]. Images are in the public domain except viroid [4], single-stranded DNA virus (icon made by Pixel perfect, www.flaticon.com), and rodent (icon made by Freepik, www.flaticon.com).

Fig 2

A fitness landscape showing three genotypes on different places on the landscape (A, B, and C) and a schematic pie chart of the distribution of mutations available to each genotype. The genotype at A is not well adapted to the environment (far from a fitness peak) so has a larger fraction of mutations that would be beneficial. The genotype at B is more fit than A and is closer to a fitness peak, so it has a smaller fraction of beneficial mutations than that at A. The genotype at the fitness peak C does not have any way to become more fit on this landscape and thus has no beneficial mutations available to it. The allocations of mutations as beneficial, neutral, and deleterious is for representational purposes only (not based on actual data), and the proportion of neutral mutations was held constant for all three genotypes. Figure includes a fitness landscape from the public domain, originally created by C. Wilke.