Host life history and the evolution of parasite virulence

We present a general epidemiological model of host-parasite interactions th at includes various forms of superinfection. We use this model to study the effects of different host life-history traits on the evolution of parasite virulence. In particular, we analyze the effects of natural host death rat e on the evolutionarily stable parasite virulence. We show that, contrary t o classical predictions, an increase in the natural host death rate may sel ect for lower parasite virulence if some form of superinfection occurs. Thi s result is in agreement M with the experimental results and the verbal arg ument presented by Ebert and Mangin (1997). This experiment is discussed in the light of the present model. We also point out the importance of superi nfections for the effect of nonspecific immunity on the evolution of virule nce. In a broader perspective, this model demonstrates that the occurrence of multiple infections may qualitatively alter classical predictions concer ning the effects of various host life-history traits on the evolution of pa rasite virulence.