There is considerable variation in the level of infectivity of parasites and the degree of resistance of hosts. However, we lack a clear understanding of the processes that generate and maintain this trait diversity. We examine theoretically how epidemiological feedbacks and the characteristics of the interaction between host types and parasites strains determine the coevolution of host-parasite diversity. The interactions include continuous characterisations of the key phenotypic features of classic gene-for-gene and matching allele models. We show how costs to resistance in hosts and infectivity in parasites combine with the different infection interactions between hosts and parasites to produce static trait diversity.

co-evolution; host-parasite diversity; infectivity; resistance