Originally published as Genetics Published Articles Ahead of Print on November 19, 2005.

Genetics, Vol. 172, 751-757, February 2006, Copyright © 2006
doi:10.1534/genetics.105.051136

Pleiotropic Costs of Niche Expansion in the RNA Bacteriophage 6

Siobain Duffy^*,,1, Paul E. Turner^* and Christina L. Burch

^* Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520-8106 and Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599-3280

¹ Corresponding author: Yale University, 165 Prospect St., New Haven, CT 06520-8106.
E-mail: siobain.duffy{at}yale.edu

Natural and experimental systems have failed to universally demonstrate a trade-off between generalism and specialism. When a trade-off does occur it is difficult to attribute its cause to antagonistic pleiotropy without dissecting the genetic basis of adaptation, and few previous experiments provide these genetic data. Here we investigate the evolution of expanded host range (generalism) in the RNA virus 6, an experimental model system allowing adaptive mutations to be readily identified. We isolated 10 spontaneous host range mutants on each of three novel Pseudomonas hosts and determined whether these mutations imposed fitness costs on the standard laboratory host. Sequencing revealed that each mutant had one of nine nonsynonymous mutations in the 6 gene P3, important in host attachment. Seven of these nine mutations were costly on the original host, confirming the existence of antagonistic pleiotropy. In addition to this genetically imposed cost, we identified an epigenetic cost of generalism that occurs when phage transition between host types. Our results confirm the existence in 6 of two costs of generalism, genetic and environmental, but they also indicate that the cost is not always large. The possibility for cost-free niche expansion implies that varied ecological conditions may favor host shifts in RNA viruses.

This article has been cited by other articles:

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