Adaptation and irreversibility in microevolution

¹ Physics Department and INFN, University of Turin - via P. Giuria 1, I-10125, Turin, Italy
² The Abdus Salam International Centre for Theoretical Physics (ICTP) - Strada Costiera 11, I-34014, Trieste, Italy

Received: 20 August 2014
Accepted: 2 December 2014

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 timescales at which the relevant genetic modifications take place. We find that, despite the fast environmental switches, the population manages to adapt on the fast timescales 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 timescales would be undetectable if one were to consider only the effective genotype and fitness dynamics on the slow timescales. We therefore propose an experimental observable to detect it.