Deleterious passengers in adapting populations

TL;DR

This paper investigates how beneficial mutations in adapting populations can hinder the removal of linked deleterious mutations, affecting evolutionary dynamics and the rate of adaptation.

Contribution

It provides analytical models describing the interaction between beneficial and deleterious mutations during adaptation, revealing their dependence on mutation rates and population size.

Findings

Deleterious mutation fixation probability varies with beneficial mutation rate.

Genetic load from passengers reduces beneficial substitution rate.

The impact of deleterious mutations depends non-monotonically on population size.

Abstract

Most new mutations are deleterious and are eventually eliminated by natural selection. But in an adapting population, the rapid amplification of beneficial mutations can hinder the removal of deleterious variants in nearby regions of the genome, altering the patterns of sequence evolution. Here, we analyze the interactions between beneficial "driver" mutations and linked deleterious "passengers" during the course of adaptation. We derive analytical expressions for the substitution rate of a deleterious mutation as a function of its fitness cost, as well as the reduction in the beneficial substitution rate due to the genetic load of the passengers. We find that the fate of each deleterious mutation varies dramatically with the rate and spectrum of beneficial mutations, with a non-monotonic dependence on both the population size and the rate of adaptation. By quantifying this dependence, our results allow us to estimate which deleterious mutations will be likely to fix, and how many of these mutations must arise before the progress of adaptation is significantly reduced.