Evolution of fast mutating replicators: RNA viruses and the RNA world

Population dynamics studies often assume that the individuals of a population are, with rare exceptions, identical with respect to a given character. This holds whenever the mutation rate in the reproduction of individuals is sufficiently low. However, the RNA molecule is exceptional in that it does not benefit from correction mechanisms able to maintain a high fidelity of copy. As a consequence, any large population of RNA molecules will be necessarily heterogeneous. The best example of such systems are RNA viruses, which form quasispecies of related though phenotypically different individuals. Heterogeneity in sequence, structure, and function, confers a high degree of plasticity to quasispecies and permits rapid adaptation in a relatively small number of generations.

In this talk we will present an overview of in vitro experiments carried out with RNA viruses aimed at determining the dynamical evolutionary properties of heterogeneous populations. It will be shown how a number of theoretical expectations could be falsified and how our understanding of evolution at the molecular level has advanced. Further, there are a number of computational models that help disentangle the complex collective properties of heterogeneous populations. Another scenario where these studies are of relevance is that of a hypothetical, prebiotic RNA world --where RNA molecules would store information and perform catalytic activity simultaneously--, where replication would be unavoidably affected by high mutation rates.