Diet and foraging-related aspects of host-parasite dynamics in freshwater systems

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Emerging and re-emerging infectious diseases caused by parasites and pathogens are of major concern for the health of humans, domestic animals, and wildlife in Canada and globally. It is thus vital to understand how hosts can resist and tolerate parasitic infections. Diet may influence resistance or tolerance, but even the risk of parasitism can affect foraging behaviour in animals, with consequences for individuals and populations. In this way, parasites could have significant influences in nature without ever infecting an organism, and sometimes this occurs in surprising ways. For instance, it has recently been shown that various aquatic animals readily consume the free-swimming infectious stages of helminth parasites. In other words, parasites do not just potentially affect host diets, but can be a part of some diets. Building upon our previous work with freshwater organisms and their helminth parasites as a model system, we will use a suite of interdisciplinary tools and approaches to study diet-based interactions of hosts and parasites through three specific related themes as part of a long-term program in aquatic disease ecology. Given current and projected world-wide environmental changes that will alter aquatic habitats, including food availability and parasite abundance, this may have consequences for host diets and parasite consumption which merit consideration in order to better predict and manage infectious disease outcomes. 1) Importance of host diet for resistance and tolerance to parasite infection Focusing on dietary antioxidants and essential lipids available to animals in aquatic habitats by eating algae and plants, we will examine how these affect host-parasite dynamics. This has important implications for understanding the ability of animals to defend themselves if particular dietary compounds are available, but also for parasite transmission. 2) Consumption of parasite infectious stages If free-living infectious stages are consumed, this can reduce transmission to other hosts. Identifying key consumers and the range of infectious stages they will eat, along with quantifying such removal, is therefore essential for understanding the potential scope for reduced transmission in this way. If such consumption is common, and parasites contribute substantially to the diets of some aquatic animals, it is also important to determine how they meet consumer energetic and nutritional needs. 3) Alterations in foraging behaviour under the risk of parasitism Finding food is a critical activity that takes up a lot of time and energy for most animals. If the risk of becoming infected causes animals to change their foraging behaviour in sub-optimal ways, this could have significant consequences for their ability to meet their needs. We will examine the extent to which aquatic animals alter their foraging based on specific risk.