Multiple adaptive substitutions during evolution in novel environments

TL;DR

This study analyzes how asexual populations adapt in rugged fitness landscapes starting from low fitness, revealing that adaptation steps depend on genome length and fitness correlations, with analytical results for specific fitness distributions.

Contribution

It provides an analytical framework for understanding adaptation dynamics from low fitness in rugged landscapes, extending previous models that assumed high initial fitness.

Findings

Average steps to local optimum grow logarithmically with genome length.

Higher fitness correlations increase adaptation steps.

Derived fitness and walk length distributions for exponential and uniform fitness models.

Abstract

We consider an asexual population under strong selection-weak mutation conditions evolving on rugged fitness landscapes with many local fitness peaks. Unlike the previous studies in which the initial fitness of the population is assumed to be high, here we start the adaptation process with a low fitness corresponding to a population in a stressful novel environment. For generic fitness distributions, using an analytic argument we find that the average number of steps to a local optimum varies logarithmically with the genotype sequence length and increases as the correlations amongst genotypic fitnesses increase. When the fitnesses are exponentially or uniformly distributed, using an evolution equation for the distribution of population fitness, we analytically calculate the fitness distribution of fixed beneficial mutations and the walk length distribution.