The evolution of life history trade-offs in viruses

- Life history trade-offs are experienced by both eukaryotic viruses and by phage.
- Experimental evolution is a powerful method to study viral trade-offs.
- Intracellular reproduction and extracellular survival can trade-off in viruses.
- Viral survival interacts with host range and organization of the viral genome.
- The 'curse of the pharaoh' (extreme survival and virulence) is unlikely for phage.

Viruses can suffer 'life-history' trade-offs that prevent simultaneous improvement in fitness traits, such as improved intrahost reproduction at the expense of reduced extrahost survival. Here we examine reproduction-survival trade-offs and other trait compromises, highlighting that experimental evolution can reveal trade-offs and their associated mechanisms. Whereas 'curse of the pharaoh' (high virulence with extreme stability) may generally apply for viruses of eukaryotes, we suggest phages are instead likely to suffer virulence/stability trade-offs. We examine how survival/reproduction trade-offs in viruses are affected by environmental stressors, proteins governing viral host range, and organization of the virus genome. Future studies incorporating comparative biology, experimental evolution, and structural biology, could thoroughly determine how viral trade-offs evolve, and whether they transiently or permanently constrain virus adaptation.