Out-of-equilibrium competitive dynamics of quasispecies

¹  Centro de Astrobiología, CSIC-INTA - Ctra. de Ajalvir km. 4, 28850 Torrejón de Ardoz, Madrid, Spain
²  Departamento de Ciencias de la Naturaleza y Física Aplicada, Universidad Rey Juan Carlos - c/ Tulipán s/n 28933 Móstoles, Madrid, Spain

Received: 28 July 2006
Accepted: 27 November 2006

Abstract

The composition of a quasispecies is completely characterized, in the large population and long time limit, by the matrix yielding the transition probabilities between different types in the population. Further, its asymptotic growth rate —i.e. the largest eigenvalue of the transition matrix— completely determines the winning population in an equilibrium competition. However, due to the intrinsically heterogeneous nature of quasispecies, out-of-equilibrium fluctuations in population size might change the expected fate of competition experiments. Using a simple model for a heterogeneous population we quantify the probability that, after a population bottleneck, the a priori weaker competitor wins in a competition with a population characterized by a larger asymptotic growth rate. We analyse the role played by different degrees of neutrality in the outcome of the process, and demonstrate that lower neutrality favours the weaker competitor in out-of-equilibrium situations. Our results might shed light on empirical observations in competition experiments with RNA viruses.