Ecophysiology of a host-parasite interaction that causes metabolic disease

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The causes and rates at which humans and other mammals develop metabolic diseases such as diabetes and obesity are complex. Biomedical research has traditionally focused on how shifts in diet and physical activity affect metabolism in mammalian model organisms such as rats and mice. While these two factors are known to be significant, there is very little information on other conditions that can cause or contribute to metabolic disease. The range of animal species that can develop metabolic disease is also unknown. The investigators recently demonstrated that diabetes and obesity are not unique to mammals and occur in natural populations of dragonflies as a consequence of gut infection by a protozoan parasite. Preliminary data indicate that the level of acidity in water bodies that dragonflies inhabit is a strong predictor of rates of infection and therefore, metabolic disease in the dragonfly species. The role of infection in the development of metabolic disease is poorly understood in any animal system. This project represents a unique opportunity to provide new ecological and physiological insights and will allow in-depth studies on this problem. This integrative project will experimentally link natural variation in water acidity, dragonfly gut microbiome composition and parasitic infection susceptibility to dragonfly metabolic and other performance phenotypes. This work will underline the importance of environmental factors to metabolic disease. This project also has broad relevance given the growing prevalence of natural insect-protozoan parasite interactions that cause disease in humans (e.g. malaria, toxoplasmosis) and in species of economic importance (e.g. honey bees, bumblebees) to humans. The causative role of infection in the development of metabolic disease such as obesity is poorly understood in any animal system. The project proposes to conduct experiments that will extend previous work on this dragonfly host-parasite interaction and provide novel insights into the ecophysiology of infection-related metabolic disease in an insect. Based on new ecological and physiological data from this system, these studies will examine the hypotheses that both environmental pH and chemical interactions of parasite and gut microbiota are important drivers of susceptibility to infection, and its escalation into metabolic disease and reduced fitness in the dragonfly host. The investigator will 1) use full factorial treatment designs to examine effects of environmental (water) pH and exposure to infectious spores on larval and host gut microbiome composition and parasite load, 2) determine infection effects on flight muscle performance and fuel use during high intensity flight behavior (field high speed videography, in situ work loop and respiratory quotient assays), and 3) assess the extent of host manipulation by the parasite through examination of systemic immunity in healthy and infected adults, in response to parasite excretory/secretory products and to heat-inactivated bacterial cultures.