Virulence evolution and the timing of disease life-history events

Recent research is directed towards testing the idea that parasite virulence evolution is constrained by a tradeoff between parasite transmission and parasite-induced host mortality (i.e. virulence). Such parasite fitness components are natural analogs of organismal life-history characters, and here I highlight the role that the timing of such disease life-history events can have in virulence evolution. I use reasoning from theory about the evolution of senescence, to suggest that differences in the relative timing of transmission and virulence can generate strong selective forces that shape virulence evolution. A consideration of such timing effects also suggests novel approaches for testing the tradeoff hypothesis, as well as alternative tradeoff interpretations of examples of virulence evolution that have previously been explained by other hypotheses.