Impact of population size on early adaptation in rugged fitness landscapes

TL;DR

This paper investigates how population size influences early adaptation in rugged fitness landscapes, revealing that smaller populations can sometimes adapt more efficiently than larger ones due to peak accessibility and stochastic effects.

Contribution

It demonstrates that the height of the first fitness peak encountered depends on population size and landscape accessibility, highlighting optimal sizes for early adaptation.

Findings

Finite population size can maximize early peak height.

Accessibility of fitness peaks influences adaptation dynamics.

Small populations may outperform large ones in early adaptation.

Abstract

Due to stochastic fluctuations arising from finite population size, known as genetic drift, the ability of a population to explore a rugged fitness landscape depends on its size. In the weak mutation regime, while the mean steady-state fitness increases with population size, we find that the height of the first fitness peak encountered when starting from a random genotype displays various behaviors versus population size, even among small and simple rugged landscapes. We show that the accessibility of the different fitness peaks is key to determining whether this height overall increases or decreases with population size. Furthermore, there is often a finite population size that maximizes the height of the first fitness peak encountered when starting from a random genotype. This holds across various classes of model rugged landscapes with sparse peaks, and in some experimental and experimentally-inspired ones. Thus, early adaptation in rugged fitness landscapes can be more efficient and predictable for relatively small population sizes than in the large-size limit.