Adaptive dynamics during experimental evolution of RNA viruses

Abstract

One of the most astonishing observations about RNA viruses is their tremendous evolutionary potential. Their great adaptability is thought to be consequence of a high per generation genomic mutation rate (> 1) caused by error-prone RNA polymerases (Drake and Holland 1999) and of the very large population sizes that can be reached during infections. The combination of these two factors makes feasible to explore, quickly and efficiently, the vast genotypic space associated with the genome length characteristic of most RNA viruses. So far, the theories of population genetics and evolutionary ecology have been extensively used as theoretical framework for the study of viral evolution. Concepts such as Fisher's fundamental theorem, the mutation-selection balance, host-range specificity, evolution of virulence, Red Queen dynamics, competitive exclusion and, frequency- or density-dependent selection have been successfully applied to explain the origin, maintenance and fate of the high levels of genetic diversity that characterize viral populations (reviewed in Elena et al. 2003). However, the applicability of the classical theory and the necessity of a new theoretical framework, represented by the quasispecies theory, have recently been the target of a hot debate (Holmes and Moya 2002, Domingo 2002). The term quasispecies was first coined by Eigen (1971) in the context of his work on early replicons and the origin of primitive biochemical networks and refers to a dynamic entity constituted by a cloud of mutants centered around a so-called "master" sequence