On the feasibility of saltational evolution

TL;DR

This paper investigates whether evolutionary leaps via multiple simultaneous mutations are feasible and significant, finding they are generally rare but could be important under high mutation rates like stress-induced mutagenesis.

Contribution

The study provides an analytic model quantifying the probability of multi-mutation leaps and explores conditions under which they become evolutionarily relevant.

Findings

Multi-mutation leaps are generally rare under typical parameters.

Elevated mutation rates can increase the significance of leaps.

Sign epistasis can make leaps more impactful in evolution.

Abstract

Is evolution always gradual or can it make leaps? We examine a mathematical model of an evolutionary process on a fitness landscape and obtain analytic solutions for the probability of multi-mutation leaps, that is, several mutations occurring simultaneously, within a single generation in one genome, and being fixed all together in the evolving population. The results indicate that, for typical, empirically observed combinations of the parameters of the evolutionary process, namely, effective population size, mutation rate, and distribution of selection coefficients of mutations, the probability of a multi-mutation leap is low, and accordingly, the contribution of such leaps is minor at best. However, we show that, taking sign epistasis into account, leaps could become an important factor of evolution in cases of substantially elevated mutation rates, such as stress-induced mutagenesis in microbes. We hypothesize that stress-induced mutagenesis is an evolvable adaptive strategy.