Adaptation and irreversibility in microevolution

TL;DR

This paper investigates how asexual populations adapt under rapidly changing stochastic environments, revealing that adaptation occurs on fast time-scales but is balanced by fitness loss, with implications for experimental detection.

Contribution

It derives effective genotype and fitness dynamics under stochastic environmental changes and proposes an observable to detect rapid adaptation.

Findings

Populations adapt quickly despite environmental fluctuations.

Fast adaptation contributes positively to fitness but is balanced by fitness loss.

An experimental observable is proposed to detect rapid adaptation.

Abstract

Within the framework of population genetics we consider the evolution of an asexual haploid population under the effect of a rapidly varying natural selection (microevolution). We focus on the case in which the environment exerting selection changes stochastically. We derive the effective genotype and fitness dynamics on the slower time-scales at which the relevant genetic modifications take place. We find that, despite the fast environmental switches, the population manages to adapt on the fast time-scales yielding a finite positive contribution to the fitness. However, such contribution is balanced by the continuous loss in fitness due to the varying selection so that the statistics of the global fitness can be described neglecting the details of the fast environmental process. The occurrence of adaptation on fast time-scales would be undetectable if one were to consider only the effective genotype and fitness dynamics on the slow time-scales. We therefore propose an experimental observable to detect it.