Modeling host-parasite coevolution: a nested approach based on mechanistic models.

In this study we introduce a mechanistic framework for modeling host-parasite coevolution using a nested modeling approach. The first step in this approach is to construct a mechanistic model of the parasite population dynamics within a host. The second step is to define an epidemiological model which is used to derive the fitness functions for both the host and the parasite. The within-host model is then nested within the epidemiological model by linking the epidemiological parameters such as the transmission rate of the infection or the additional host mortality rate to the dynamics of the within-host model. Nesting the within-host model into an epidemiological model allows us to evaluate the fitness functions for each interactor which in turn allows us to determine the coevolutionary dynamics of the system. This nested approach has the advantage over other approaches in that mechanistic descriptions of the host-parasite biology are used to derive, rather than impose, life-history trade-offs. We illustrate this framework by analysing a simple host-parasite system. In this particular system we find that the coevolutionary equilibrium is always stable and that host survivorship and parasite fitness vary greatly with the cost of the immune response and parasite growth.