While often studied in isolation, host-parasite interactions are typically embedded within complex communities in which parasite transmission is dependent not just on the host species, but non-host species such as predators. Recent research has focused on the ability of predators to limit the exposure of hosts to their pathogens by controlling population density of hosts and vectors. An additional mechanism by which predators could lower the risk of disease is by directly consuming parasite free-living infective stages. Preliminary evidence suggests that this mechanism may be common in aquatic ecosystems where various predator species consume free-living stages of parasites, including macroparasites such as trematodes. The central goal of this project is to determine how assemblages of predators affect parasitic infection of amphibians in nature, and whether loss of predator species would cause significant changes to disease dynamics. This research extends initial laboratory findings by testing hypotheses of predation on parasites in the field through extensive surveys of aquatic diversity and precise examination of host infection and disease on the landscape level. This research combines mathematical modeling, laboratory experiments, and field surveys linking observations of natural patterns to functional mechanisms.
Since trematodes are common pathogens of humans, domestic animals, and wildlife this study will advance understanding of how loss of biodiversity in general and predators in particular may be a factor in the recent emergence of some diseases. Development of the transmission models, evaluations of aquatic predator community structure in the field, and calculations of disease risk will be of practical application to management of wildlife and human diseases. This project will provide extensive outreach through after school programs for a local elementary school having many students from groups underrepresented in science, and through environmental science programs conducted by Boulder County 4-H. Undergraduate and high school students will be involved in the research and receive mentoring on science careers.
Around the world biodiversity is being lost at alarming rates. At the same time scientists are becoming more aware of the role of biodiversity in the function of ecosystems. One of the important functions that biodiversity may have is mediating transmission of parasites and pathogens, which can then affect the intensity of infection and severity of disease. One critical component of biodiversity is predators. Predators may influence disease dynamics by preying on hosts, but also by preying directly on parasite infective stages. Our research investigated the role of predator diversity on the transmission of a trematode parasite Ribeiroia ondatrae that causes severe limb malformations in amphibian hosts. Beginning with mathematical models and small-scale laboratory studies, we showed that transmission of the infective stages of the parasites to tadpoles depended on the abundance of these stages in the environment. Additional laboratory studies examined the interaction between predators and the parasite infective stages showing that predators not only consumed large numbers of infective stages, but that this predation resulted in lower transmission to the amphibians. The next step was to investigate whether communities of predators of parasite infective stages could affect infection and pathology in amphibians in nature. We conducted a large-scale field survey in California, a region with high prevalence of the parasite and among the highest reported incidence of amphibian malformations. Wetland surveys sampled aquatic invertebrate predators, and snails and amphibians that serve as hosts to parasites. By selectively sampling wetlands along a gradient of predator diversity we will address how the diversity of predators, the abundance of all predators, or the specific role of a particular group of predators can influence the intensity of infection (number of parasites in an individual host) and pathology, including malformed limbs. This research also helps place parasites into aquatic food webs and provides valuable information on the role of biodiversity in protecting vulnerable amphibians, a group of conservation concern, from pathogenic parasites. Since other trematode parasites are common pathogens of humans, domestic animals, and other wildlife this study will advance understanding of how loss of biodiversity in general and predators in particular may be one factor involved in recent disease emergence. By exploring how community changes influence disease this research will supply reliable information on the levels of biodiversity to maintain to mediate a parasite that is detrimental to amphibians. Furthermore, this research has formed the basis of efforts to educate the general public about parasites in general and the role of predators on parasites in food webs in particular. Specifically this research has been presented to a wide variety of ages from children to adults at the University of Colorado Natural History Museum Family Day event, K-12 teachers at science teaching workshops, and to undergraduate students through the use of original, interactive case studies. Finally, this work provided undergraduate researchers first hand experience in the field and laboratory.
