Ecology directs host-parasite coevolutionary trajectories across Daphnia-microparasite populations

Host-parasite interactions often fuel coevolutionary change. However, parasitism is one of a myriad of possible ecological interactions in nature. Biotic (e.g., predation) and abiotic (e.g., temperature) variation can amplify or dilute parasitism as a selective force on hosts and parasites, driving population variation in (co)evolutionary trajectories. We dissected the relationships between wider ecology and coevolutionary trajectory using 16 ecologically complex Daphnia magna-Pasteuria ramosa ponds seeded with an identical starting host (Daphnia) and parasite (Pasteuria) population. We show, using a time-shift experiment and outdoor population data, how multivariate biotic and abiotic ecological differences between ponds caused coevolutionary divergence. Wider ecology drove variation in host evolution of resistance, but not parasite infectivity; parasites subsequently coevolved in response to the changing complement of host genotypes, such that parasites adapted to historically resista...