Levels of Selection in Positive Strand Virus Dynamics

Conflicting selection pressures occurring over the life cycle of an organism constitute serious challenges to the robustness of replication. Viruses present a credible model system for analysing problems that arise through evolutionary conflicts of interest. We present a multilevel selection model for the life cycle of positive strand RNA viruses. The model combines within-cell replication kinetics and protein synthesis, and between-cell population dynamics of virion production and transmission. We explore how these two levels of within-host selection interact to produce tradeoffs in the life history strategy of a virus. We observe intermediate optimum values for virus encapsidation rates. These can be interpreted as selection for intermediate host virulence without any consideration of host mortality. We report a critical persistence threshold arising from the tradeoff between genome replication and gene translation within the cell. We find counterintuitive relationships among genome decay rates, the rates of encapsidation and the abundance of virus-encoded proteins.