Co-evolution of host dispersal and parasite virulence in complex landscapes

Spatial network structure impacts the ecological and evolutionary dynamics of species interactions. Previous work on host-parasite systems has shown that parasite virulence is driven by dispersal rates and spatial structure, assuming that dispersal is an ecologically fixed parameter. However, dispersal is also a trait under selection and can evolve. In this context, we develop an individual-based eco-evolutionary model, in which both parasite virulence and host dispersal can evolve in representative terrestrial (random-geometric graphs; RGGs) and riverine aquatic (optimal channel networks; OCNs) landscapes. We find that in riverine aquatic landscapes, evolutionarily stable (ES) dispersal rates are lower and ES virulence is greater relative to terrestrial landscapes when dispersal mortality is low. When dispersal mortality is high, both dispersal and virulence evolve to lower values in both landscape types. Diverging co-evolutionary patterns between landscapes are explained by differences in network topology. Specifically, the highly heterogeneous degree distribution in riverine aquatic landscapes (1) leads to low parasite relatedness allowing for the evolution of greater virulence and (2) leads to spatial heterogeneity in host densities that constrains the evolution of dispersal to lower values. Our work highlights the importance of considering the concurrent and co-evolution of dispersal when studying trait evolution in complex landscapes.