Originally published as Genetics Published Articles Ahead of Print on May 6, 2005.

Genetics, Vol. 170, 1001-1008, July 2005, Copyright © 2005
doi:10.1534/genetics.105.040741

Epistasis and the Adaptability of an RNA Virus

Rafael Sanjuán^*, José M. Cuevas^*,, Andrés Moya^* and Santiago F. Elena^,1

^* Institut Cavanilles de Biodiversitat i Biologia Evolutiva and Departament de Genètica, Universitat de València, 46071 València, Spain
Department of Zoology, University of Oxford, Oxford OX1 3PS, United Kingdom
Instituto de Biología Molecular y Celular de Plantas, CSIC-UPV, 46022 València, Spain

¹ Corresponding author: Instituto de Biología Molecular y Celular de Plantas, CSIC-UPV, Avenida de los naranjos s/n, 46022 València, Spain.
E-mail: sfelena{at}ibmcp.upv.es

We have explored the patterns of fitness recovery in the vesicular stomatitis RNA virus. We show that, in our experimental setting, reversions to the wild-type genotype were rare and fitness recovery was at least partially driven by compensatory mutations. We compared compensatory adaptation for genotypes carrying (1) mutations with varying deleterious fitness effects, (2) one or two deleterious mutations, and (3) pairs of mutations showing differences in the strength and sign of epistasis. In all cases, we found that the rate of fitness recovery and the proportion of reversions were positively affected by population size. Additionally, we observed that mutations with large fitness effect were always compensated faster than mutations with small fitness effect. Similarly, compensatory evolution was faster for genotypes carrying a single deleterious mutation than for those carrying pairs of mutations. Finally, for genotypes carrying two deleterious mutations, we found evidence of a negative correlation between the epistastic effect and the rate of compensatory evolution.

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