The Influence of Deleterious Mutations on Adaptation in Asexual Populations

Xiaoqian Jiang,Shiheng Tao,Jingjing Li,Zhao Xu,Youyi Shi,Wenwu Wu,Henry Harpending

doi:10.1371/journal.pone.0027757

Abstract

We study the dynamics of adaptation in asexual populations that undergo both beneficial and deleterious mutations. In particular, how the deleterious mutations affect the fixation of beneficial mutations was investigated. Using extensive Monte Carlo simulations, we find that in the “strong-selection weak mutation (SSWM)” regime or in the “clonal interference (CI)” regime, deleterious mutations rarely influence the distribution of “selection coefficients of the fixed mutations (SCFM)”; while in the “multiple mutations” regime, the accumulation of deleterious mutations would lead to a decrease in fitness significantly. We conclude that the effects of deleterious mutations on adaptation depend largely on the supply of beneficial mutations. And interestingly, the lowest adaptation rate occurs for a moderate value of selection coefficient of deleterious mutations.

Highlights

The appearance of beneficial mutations as well as their subsequent spread determines the adaptive process of a population
Once multiple beneficial mutations are allowed, how deleterious mutations put impact on the fixation process of beneficial mutations? Under what kind of conditions deleterious mutations would accumulate in adaptive process? To address these problems, we focus our attention on the distribution of selection coefficients of the fixed mutations (SCFM) and the number of mutations accumulated in a single fixation event
We have presented a detailed study of the adaptive process in asexual populations by using extensive Monte Carlo simulation, where the population is subject to both beneficial and deleterious mutations

Summary

Introduction

The appearance of beneficial mutations as well as their subsequent spread determines the adaptive process of a population. A single beneficial mutation with small selection coefficient sb, has a fixation probability equal to approximately 2sb, where beneficial mutations are rare and get fixed independently [1–3]. A large supply of beneficial mutations does not result in a sequential fixation process in asexual populations [1,4,5]. There are two important processes affect the ability of asexual populations to accumulate beneficial mutations [6]. Multiple mutations that are fixed simultaneously cause the lineage with a single mutation of large effect to be outcompeted by the lineage with several moderate effects mutations [8]. The experiment on asexual budding yeast that evolves in glucose-limited media supports the theoretical analysis of multiple mutations, i.e., the adaptation is dominated by the accumulation of multiple mutations with moderate beneficial effects [16]

Methods

Results

Conclusion