Eco-Evolutionary Dynamics of Infection and Immunity in Experimentally Founded Lake Populations of Threespine...

AbstractHost-parasite interactions are likely to involve eco-evolutionary feedbacks. Parasites can impose strong selection on host immune traits. Evolution of these traits can suppress parasite abundance, which alters the strength of selection. Such eco-evo feedbacks can be hard to document in natural settings, where long-term interactions may have converged on relatively stable equilibria. However, when a species disperses into an unoccupied habitat, it can experience altered parasite abundance (e.g., enemy release) or encounter new parasite genotypes. These perturbations may be followed by observable eco-evolutionary dynamics as the newly assembled host-parasite communities interact and evolve. To test this hypothesis, we experimentally founded nine whole-lake populations of threespine stickleback and tracked changes in the prevalence of a parasite (Schistocephalus solidus) and a heritable host immune trait (fibrosis) for 7 years. In native source lakes, among-population differences in tapeworm prevalence and fibrosis were relatively stable across years, suggesting there are alternative eco-evolutionary equilibria. In contrast, the experimentally founded populations initially exhibited enemy release, followed by strong year-to-year fluctuations in infection and fibrosis. In lakes with high initial infection rates, fibrosis subsequently increased in severity, suppressing infections. Conversely, low fibrosis was followed by increased parasite prevalence. This temporal autocorrelation between parasite prevalence and immune traits weakened over time. These results are consistent with the existence of transient eco-evolutionary dynamics between host and parasite in newly founded populations.