leopard frog 1Emerging and re-emerging infectious diseases are a major concern for the health of humans, domestic animals, and wildlife. Effective disease management requires an intimate understanding of how hosts resist and tolerate parasitism, including how these abilities are affected by their environment. Work in the Koprivnikar lab takes an integrative approach to such questions, incorporating behaviour, habitat, molecular analyses, and physiology that has applied value for disease ecology.

Ag&NonAg-3Environmental influences on parasitism

Abiotic and biotic factors may affect host susceptibility to parasitism, resulting pathology, and parasite prevalence and diversity. This is critical in understanding how environmental features, and any subsequent changes, may be expected to impact both disease and host populations. Various environmental perturbations can influence parasite reproduction, activity, longevity, and infectivity, altering host encounter rate and parasite prevalence/load. These same factors will also affect host resistance and tolerance to parasites. We tackle such questions with a combination of fieldwork, laboratory, and mesocosm approaches. Current areas of focus include biodiversity, contaminants, and landscape influences. For instance, road and forest density differ around agricultural vs. non-agricultural ponds, affecting the presence of generalist and specialist parasites (Koprivnikar & Redfern, 2012).

water dd-2Understanding the effects of parasitism

It is now widely recognized that multiple stressors can affect organisms in unexpected ways through interactive effects. This means that separate examinations do not accurately reflect most natural processes and can generate misleading conclusions. Because host-parasite interactions can also be strongly context-dependent, naturally-occurring infections may become harmful in the presence of additional stressors that are becoming more common owing to environmental changes and fewer available habitats. For example, we recently found that parasitized larval amphibians were not able to speed up their development in response to habitat drying (Koprivnikar et al. 2014). Consequently, we assess host susceptibility and tolerance, as well as effects on parasites themselves, under a number of environmental conditions, incorporating a variety of host and parasite taxa to examine the general occurrence and importance of such synergisms for disease dynamics. In addition, we study parasite influences on host interactions within ecosystems as these may play a significant role in the structure of natural communities. Conservation and management efforts will be enhanced by the integration of parasites into individual, population, community, and ecosystem-level processes.

tad choice-1Host defences against parasitism

Past studies of host resistance to parasites have largely focused on immunology, yet growing evidence suggests that behavioural defences often play an important complementary role. Notably, avoiding infections might be simpler and less costly than fighting invading parasites. Our lab continues to explore the extent and effectiveness of host anti-parasite behaviour, a relatively unknown area of study. If such behaviours are common and effective, environmentally-induced alterations of host behaviour may have important implications for disease dynamics. While many studies have examined the effects of predators on host behavioural choices, parasites likely represent an even greater universal natural enemy and their influences require far more study to truly understand the ecological forces shaping animal behaviours. As an example, we recently found that larval amphibians prefer to forage in the presence of cues indicating a risk of parasitism rather than a threat of predation (Koprivnikar & Penalva, 2015).