Dawson K J
Laboratoire Génome et Populations CNRS UPR 9060, Université de Montpellier II, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France.
J Theor Biol. 1998 Sep 7;194(1):143-57. doi: 10.1006/jtbi.1998.0752.
I investigate the hypothesis that mutation rates in natural populations are determined by a balance between: (1) selection against deleterious mutations favouring lower mutation rates, and (2) selection opposing further reduction of the mutation rate, resulting from the costs incurred by more stringent proof-reading and repair (for example, a reduction in the rate of DNA replication). The influence of advantageous mutations is assumed to be negligible. In a previous paper, I analysed the dynamics of a modifier of the mutation rate in a large sexual population, where (infinitesimally rare) deleterious alleles segregate at an infinite number of unlinked loci with symmetric multiplicative fitness effects. A simple condition was obtained for a modifier allele to increase in frequency. Remarkably, this condition does not depend on the allele frequencies at the modifier locus. Here, I show that (as a consequence), given any set of possible values of the mutation rate (any set of possible modifier alleles), there always exists a single globally stable value of the mutation rate. This is an unusually strong form of "evolutionary stability" for a sexual population. Less surprisingly the optimum mutation rate in an asexual population has similar stability properties. Furthermore, in the case of an asexual population, it is not necessary to make any special assumptions about the selection acting against deleterious mutations, except that a deterministic mutation-selection equilibrium exists. I present a simple method for identifying the evolutionarily stable value of the mutation rate, given the function alpha(U) relating the value of the mutation rate to the fitness cost of maintaining this rate. I also argue that if there is a highly conserved relationship between the rate of replication per base, and the rate of mutation per base, and if this relationship has the form of a power law, then the remarkable uniformity of the per genome mutation rate in DNA based microbes can be explained.
自然种群中的突变率是由以下两者之间的平衡所决定的：（1）对有害突变的选择，倾向于较低的突变率；（2）由于更严格的校对和修复所产生的成本（例如，DNA复制速率的降低）而导致的对突变率进一步降低的选择。有利突变的影响被假定为可忽略不计。在之前的一篇论文中，我分析了一个大型有性种群中突变率修饰因子的动态变化，其中（极其罕见的）有害等位基因在无限多个不连锁的位点上分离，具有对称的乘法适合度效应。得到了一个修饰等位基因频率增加的简单条件。值得注意的是，这个条件并不取决于修饰位点的等位基因频率。在这里，我表明（结果是），给定任何一组可能的突变率值（任何一组可能的修饰等位基因），总是存在一个单一的全局稳定的突变率值。这是有性种群中一种异常强大的“进化稳定性”形式。不太令人惊讶的是，无性种群中的最优突变率具有类似的稳定性特性。此外，在无性种群的情况下，除了存在确定性的突变 - 选择平衡之外，无需对针对有害突变的选择做出任何特殊假设。我提出了一种简单的方法，在给定将突变率值与维持该速率的适合度成本相关联的函数α(U)的情况下，确定突变率的进化稳定值。我还认为，如果每个碱基的复制速率与每个碱基的突变速率之间存在高度保守的关系，并且如果这种关系具有幂律形式，那么基于DNA的微生物中每个基因组突变率的显著一致性就可以得到解释。
