Ecology and evolution of host/parasite interactions

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The long term goal of my research program is to advance our knowledge of host-parasite interactions from an evolutionary ecology perspective because this approach is critical to establishing how and why disease spreads, evolves, and impacts hosts over space and time. In the field of evolutionary ecology, it is common to view parasites as agents of natural selection and focus on how parasites impact host biology. From the host perspective, parasites can alter individual host behaviors, regulate host populations, and constitute important components in food-webs. This one-sided perspective ignores parasite diversity and the potential implications it has for host biology. Not only is parasitism one of the most common forms of life, but parasites are also extremely diverse, meaning that there are many taxa that have independently evolved a parasitic lifestyle. Moreover, there is a diversity in life cycles, reproductive modes, host species, and ecosystems utilized by parasites. Yet, parasite biodiversity is underestimated and for many species very few aspects of their biology is known. My work over the next five years will integrate field and molecular data with ecological, phylogenetic, and population genetic analyses to reveal novel insights into parasite biodiversity, host specificity, and parasite-mediated selection on host immune response genes. My research on parasites will focus on discovering and characterizing parasite biodiversity in echinostomes trematodes. Echinostomes are a group of flatworm parasites that exemplify diversity in terms of species richness (>100 named species) and host species utilized (e.g. up to 29 used by one echinostome species). The variation exhibited by this group provides a great opportunity to study parasite evolution; however, efforts have been stymied by the taxonomic uncertainty as genetic evidence suggests that some individual species may in fact be complexes of several distinct species. My research addresses this problem by using molecular and morphological tools to identify and place echinostome species into a phylogenetic context, and then to recognize the hosts (vertebrates and invertebrates) which are responsible for maintaining and spreading disease. With these results, future studies can evaluate broad scale evolutionary or ecological topics such as speciation, hybridization, character evolution, and community trophic dynamics. In addition, the genetic database of echinostomes will prevent misidentification, and help determine which echinostome species play a significant role in wildlife disease, including amphibian decline. My research on hosts will investigate how parasites have influenced adaptively important regions of the host genome. I will focus on the major histocompatibility complex (MHC) because this region is a highly variable, genetic component of the vertebrate immune system that helps combat macroparasite infections (i.e. flatworms, nematodes, and arthropods). Relatively few studies have investigated, let alone differentiated between the mechanisms of parasite-mediated selection on MHC in natural populations. To do so, I will use a gecko-parasite system because large gecko sample sizes are obtainable and their parasites are easy to identify and quantify. By characterizing gecko MHC and then testing among the mechanisms of parasite-mediated selection, I will fill phylogenetic gaps in vertebrate MHC evolution, and clarify which mechanisms have most impacted natural populations. This knowledge will reveal how important genetic variation at the MHC is to the overall health of natural populations, which is thought to be critical to the long term survival and viability of natural populations.