Factors affecting, and importance of, host species range in parasitic organisms: tests of hypotheses for causes and consequences.

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Parasites and pathogens of wildlife and humans, from viruses and bacteria to endoparasitic worms, are in news headlines around the world every day. What is acknowledged, even by the media seeking sound bytes, is that it is extremely difficult to predict the impact of such parasites and pathogens on host individuals and host populations (many of which are environmentally or economically important). Yet, our understanding of how these problem species act as enemies has strong implications for management of wildlife, production of domestic species, and protection of human health. In many instances, we expect parasites to have the upper hand over their hosts because of important asymmetries in their antagonistic interactions. Asymmetries arise because not all host individuals within a population are parasitized by individuals of a given parasite species. In comparison, all parasites must find and exploit a host(s) to be successful. Also in many parasite-host associations, the evolutionary rates of parasites, based on generation times and numbers of offspring, is much faster than that of their hosts. Other asymmetries likely exist such as whether it is the hosts or the parasites that have higher dispersal rates (which brings novel genetic variation into populations). One largely unexplored factor, likely as important as the asymmetries above, is the extent to which parasite species exploit more than one host species. We currently have little understanding of why some parasite species are generalists and others specialists. My Discovery Grant research, with students and collaborators over the next 5 years, will focus on factors affecting host species range in parasitic organisms, using model organisms. We will test hypotheses for causes and consequences of broad host species use. We will deploy observational, theoretical, and experimental approaches to ascertain which factors favor exploitation of particular host species and to predict impacts on those species. We will use such understanding to develop a general theory of antagonistic interactions between parasites species and their few to many host species.