Collaborative Research: Physical Limnology for the Parasite Ecologist

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How infectious diseases influence population dynamics and community interactions is an understudied aspect of aquatic ecology. This work focuses on the ecological interaction between a common microparasitic fungus and its Daphnia host species, and the consequences to coexisting zooplankton and their phytoplankton prey. The PIs are merging three disciplines (community ecology, physical limnology and epidemiological modeling) to explain spatial and temporal patterns of host-parasite dynamics. Comparative and manipulative experiments are being conducted in parallel with modeling to couple physical mixing with host-parasite population dynamics in a broad set of lakes. The coupling of ecological and physical-mixing processes is a generally important goal since most aquatic microparasites, unlike their animal hosts, do not swim. Hence, sinking and resuspension of parasite spores from the sediment may limit horizontal transmission and spread of diseases in lakes and oceans. This work is motivated by the seasonal timing of disease outbreaks in natural populations of Daphnia and the substantial variability in the severity of epidemics among lakes differing in morphometry and potential for wind mixing. The PIs are examining both the temporal dynamics of host-parasite interactions within single lakes and broader scale physical-biological processes that govern host-parasite outcome among multiple lakes. Laboratory and field studies are being used to parameterize a standard host-parasite model and derive predictions, especially of threshold effects, and tested in whole water-column manipulative experiments. Measurements of lake thermal structure, bottom shear stresses and turbulent velocity scales, in conjunction with changes in spore concentration, are enabling model development to predict spore suspension and resuspension from lake sediments. Output from the physical mixing model are coupled to the model to predict the likelihood of epidemic outbreaks. Multi-generational dynamics of host and parasite are being explored in large enclosures to examine the indirect effects of infection within one Daphnia population on competitive interactions with congeners, and their phytoplankton prey. Broader impacts: Using this multiple-lake, Daphnia-parasite system, this collaborative research is addressing the general phenomenon of natural variation in disease prevalence and its impact on the structure of food webs. This research brings together junior and senior faculty with combined expertise in population and community ecology, physical limnology and modeling. Second, the PIs are a poorly studied area of aquatic ecology, the role of pathogens. Disease ecology is an emerging area of concern, but despite substantial evidence for pathogens as important components of food web, freshwater ecologists have largely ignored them. Third, the study of disease ecology at multiple temporal and spatial scales is being approached with a combination of descriptive, comparative and manipulative experiments with modeling. The project emphasizes training of undergraduates, graduates and a postdoc at the interface of physical limnology, population modeling, and community ecology. Finally, the work on physical limnology and parasitism is enhancing the knowledge base for the lakes around KBS (a field station) and directly benefit the research programs of aquatic ecologists from multiple institutions who conduct their work in these systems. It is contributing to the K-12 teacher partnership project at KBS and to other outreach activities.