Collaborative Research: The effects of parasitism: from host consequences to ecosystem processes

Parasites certainly have strong effects on their hosts, but potentially also have important consequences for host populations, communities, and even ecosystem processes. However, it has been difficult to accurately scale the impact of parasitic infections from the community to the ecosystem level. Thus, parasites may be the “dark matter” of ecosystems: hard to detect, often unmeasured, but critically important to the way they work. This project develops and tests predictions about how parasites influence ecosystems. Freshwater zooplankton are the focus of the study because these organisms are key members of lake food chains: they eat algae and in turn are a main food source for young fish. Working with four distinct parasites of zooplankton, the project measures how infections affect host growth, reproduction, and lifespan. Predictions are also tested in freshwater lakes through tracking disease and measuring its effects on the food web. This project provides benefits through developing classroom teaching materials, conducting outreach to the public, and strengthening the national STEM workforce by providing training and professional advancement opportunities for early career scientists and teachers. Infectious diseases are exhibiting unprecedented changes, with pathogen emergence, disease invasion, and parasite extinction playing out across terrestrial and aquatic ecosystems alike. To understand these changes, empirical data from different systems are needed, including strong quantification of disease-driven effects up to the level of the ecosystem. This project tests how parasites of an ecologically important freshwater invertebrate grazer (Daphnia) affect primary productivity and secondary consumers in lakes. Three different approaches are used. Data from (i) infection assays quantify parasite impacts on hosts, including growth, survival, reproduction, foraging rate, nutrient cycling, and nutritional quality. Impacts are then scaled up in (ii) mesocosm experiments that unite density and trait effects of infection to examine their effects on primary producers and secondary consumers. Finally, predictions are tested in a (iii) multi-year multi-lake limnological survey that tracks parasite dynamics and disease outcomes for individuals, populations, communities, and ecosystems. Results are compared among four parasites that vary in transmission, energy use, and fitness impacts. The goal is to develop general theory about which parasite types are likely to have strong ecosystem effects. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.