Ecology of host/parasite interactions

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All parasites must solve the problem of transmitting infective stages into new hosts. Not surprisingly, transmission rate' is a fundamental parameter in epidemiological models that describe parasite population dynamics, including for problem parasites of humans, domestic animals, and wildlife. The long-term goal of my research program is to understand the factors that determine variation in transmission rates for parasites of wild animals. Many parasites have complex life-cycles, the completion of which requires the transmission of infective stages between a sequence of obligate hosts. Some solutions to solving the problem of transmission between hosts are spectacular in their expression. Ants infected with larvae of the fluke, Dicrocoelium, are chauffeured from their nests to adjacent flowers, onto which they remain attached with their mandibles during the evening hours. When temperature warms the next day, they detach and return to their nests. Attachment facilitates transmission of the larvae into grazing mammals. This cycle of attachment/detachment continues for weeks at our study sites in Cypress Hills Park, Alberta where the fluke has been introduced. In this proposal, my students and I combine genomics tools, imaging tools, and behaviour assays to determine if zombie-ism requires physical manipulation of structures in the brain that control mandibular muscles, or the secretion of gene products that lead to neuromodulation, or both. One possibility is that attachment/detachment behaviours are associated with the upregulation of particular gene products that are temperature-dependent. Understanding the mechanisms leading to the cycle of attachment/detachment in infected ants is a key step towards understanding the pervasive phenomenon of host phenotype alteration by parasites, which extends to humans infected with Toxoplasma, and wildlife/pets infected with rabies virus. In a second model system, we manipulate infection dose to test hypotheses regarding the factors underlying variation in rates of parasite transmission. My students and I will evaluate how rates of transmission are influenced by the diversity and structure of host communities. In our current age of ever-increasing changes in animal biodiversity, there is an increased recognition that features such as biodiversity loss and gain have strong effects on rates of transmission, including for diseases of humans. But the host biodiversity vs. transmission association is contentious because so few systems are amenable to the manipulation of both exposure dose and biodiversity. In our model minnow/snail/trematode interaction, we will combine exposure trials into experimental communities of fish and snails in lab and mesocosm settings to test whether introductions of non-native snails and fish can explain the marked changes in rates of transmission we have observed in local waterbodies in southern Alberta.