CAREER: A Metabolic Theory Approach to the Thermal Biology of Parasitism

Oakland University, Rochester MI

Investigators

Abstract

Recent changes in global temperature variability make it vital to develop better predictive models for how temperature fluctuations influence species interactions like parasitism. This is particularly pressing for amphibians, many of which are threatened by temperature-dependent emerging diseases. One challenge in predicting temperature effects on parasitism is that both host and parasite have independent responses to temperature, and these responses are difficult to disentangle with infection experiments. To help solve this problem, this project will test a new Metabolic Theory (MT) based approach to modeling parasite-host interactions in variable-temperature environments. MT postulates that metabolic rates govern all biological rates, leading to the prediction that all physiological processes within a given organism should respond to temperature in similar ways. This means it should be possible to estimate key model parameters for the temperature-dependence of parasite infectivity or host resistance to infection, by measuring the temperature-dependence of metabolic proxies like parasite growth in culture or host respiration. This approach could be especially valuable for predicting temperature effects on multi-host pathogens like the amphibian chytrid fungus, because it is impossible to conduct infection experiments for every species threatened by this disease. These funds will also help to support: (1) a new thermal-physiology classroom lab activity for use in Introductory Biology and Project Upward Bound's summer academy, (2) an annual summer workshop to train graduate teaching assistants and early-career faculty in modern teaching methods, and (3) at least four graduate students and over a dozen undergraduate student researchers. This project will test assumptions and predictions of a new Metabolic Theory (MT) based approach to modeling parasite-host interactions in variable-temperature environments, using chytrid fungus in amphibians as a model host-parasite system. Thermal performance curves for parasite infectivity and host resistance will be described using modified Sharpe-Schoolfield equations, and key model parameters (e.g., activation energies for parasite infectivity and host resistance) will be estimated by measuring the temperature dependence of host and parasite metabolic proxies. These separate thermal performance curves will then be combined into a predictive model for parasite growth rates on hosts, and maximum-likelihood statistics will be used to estimate remaining model parameters. To model thermal acclimation effects, key parameters will be allowed to vary as functions of host or parasite acclimation temperatures. The specific aims of this project are: (1) to test the core assumption that different organisms and physiological processes have similar values and thermal acclimation responses for key MT model parameters, (2) test the ability of MT based models to predict parasite transmission in variable-temperature environments, and (3) delve into the cellular and molecular mechanisms underlying thermal acclimation effects on host-parasite interactions. To achieve the third goal, we will measure effects of temperature and thermal acclimation on (5) cellular immune activity and (6) gene expression responses to chytridiomycosis infection. We will replicate experiments using arrays of custom-built experimental incubators and temperature-controlled outdoor mesocosms.