Complex life cycles and parasite-mediated trophic cascades drive species coexistence and the maintenance of genetic diversity

Ecological and evolutionary processes shape the dynamics of species interactions, yet the drivers of eco-evolutionary feedback remain elusive. Here, we developed an individual-based model of a coevolving predator-prey-parasite system, in which predators can be infected by trophically transmitted parasites. We combined host-parasite coevolution with prey-predator interactions at an individual level, hence integrating evolutionary and ecological processes. We show that species coexist more when parasite-mediated selection is weak on both the predator and the prey. Population size and genotypic diversity of the parasite are highest at intermediate parasite-mediated selection on the predator and no parasite-mediated selection on the prey. Interestingly, we show that the evolution of super-resistant genotypes, where host genotypes have resistant alleles in all loci, is driven by interspecific interactions rather than by the population size of the host species. Overall, host-parasite coevolution shapes the direction of interspecific ecological interactions which, in turn, determine species coexistence and community diversity in a complex system.