Current Areas of Research
The emergence of infectious diseases is one of the largest threats to human and wildlife health. Disease outbreaks are challenging to predict because many pathogens interact with multiple species (hosts and vectors) and host-pathogen interactions occur across multiple levels of biological organization (within-host and between-host). My research program integrates physiological and ecological research techniques to study fundamental and applied questions related to host-pathogen interactions. My students and I study infectious diseases at different ecological scales, including the organism (e.g., stress physiology, metabolic ecology, and nutrition), populations (e.g., the distribution and abundance of parasites within different environments), and communities (e.g., pathogen-infected hosts and their effects on the structure and function of communities). We typically conduct research using two different model systems: (1) amphibians and the fungal pathogen Batrachochytrium dendrobatidis (Bd) and (2) ticks, small mammals, and Borrelia burgdorferi (Bb). Bd causes the emerging infectious disease Chytridiomycosis and it is one of the factors associated with global amphibian population declines. Bb causes Lyme Disease, the most common vector-borne disease in the United States
community ecology of host-parasite interactions
Amphibians & Bd
Bd can affect tadpole traits and also cause tadpole mortality. This allows us to evaluate whether trait- and density-mediated effects of Bd influence the top-down effects that tadpoles have on pond communities. We conduct replicated experiments in semi-realistic ponds to evaluate hypotheses related to community structure and organization.
In these experiments, we characterize the degree that tadpole mouthparts become damaged (image at top left; a common pathology from Bd infections) and test how that disease-induced trait might change algal and zooplankton communities in replicated mesocosms (image at bottom left).
Ticks & Lyme Disease
We recently received funding to start a collaborative research project (with the Tick Research Lab of PA) to study mice, ticks, and Lyme Disease in Crawford and Mercer Counties in PA. Our first field season started in April 2023 and we set up replicate plots in 18 different sites (N=9/county). We visit each site during the Spring, Summer, and Fall season to conduct a mark-recapture study on mice, collect ticks from the environment using drag cloths, and to quantify tree density and other vegetation variables. This work is new and ongoing, so check back for updates!
Stress and Disease Interactions
One way to assess a host's response to parasite infection is by examining resistance and tolerance to parasitic organisms (Raberg et al., 2009). Host resistance directly reduces pathogen colonization/proliferation at a cost of increased host pathology (mortality, impeded growth and development). Host tolerance, in contrast, limits the harm done by the infecting parasite to offset fitness consequences to hosts. It is important to decouple measures of resistance and tolerance because they can impose different selection pressures on pathogens. For example, resistance should have direct adverse effect on pathogens whereas but tolerance should have neutral effects. Emphasis in animal disease literature, however, is biased towards understanding traits that confer resistance (e.g., antimicrobial peptides in amphibians). Recent evidence suggests that tolerance to pathogens, such as Bd, might be more common than previously considered (e.g., Savage et al., 2011, Biol Cons).
In a laboratory experiment, we showed that adding exogenous CORT can increase host resistance to Bd, a finding opposite much of the literature on stress and disease. Contrary to predictions, CORT does not appear to affect tolerance to infection (data not shown).
Energetic costs of Bd resistance
My students and I have been working with plethodontid salamanders since my arrival at Allegheny. One of the more interesting patterns that we found is that individuals of Plethodon cinereus (the Eastern red-backed salamander) are highly resistant to Bd. In fact, they normally resist exposures of over 1 million zoospores and frequently clear their infections within 3-4 weeks following exposure to over 3 million zoospores (see left figure).
We are currently testing various hypotheses related to the energetic costs of this resistance by measuring host behavioral, physiological, and immunological traits that might allow them to rapidly limit and clear their infections. We've shown that that Bd-infected salamanders increase their feeding activity compared to non-infected salamanders, possibly in response to an increase in metabolic demands associated with Bd-resistance. We have ongoing experiments using both closed-system and flow-through respirometry to further test hypotheses related to energetics of Bd resistance.
Field patterns of disease in PA
I have a number of students who have been sampling natural areas in PA for the presence of various amphibian parasites (e.g., Bd, trematodes, leeches, etc.). After we get a better idea of the parasite communities in this region, we will begin to test for associations between host traits, biotic variables (e.g., amphibian biodiversity, predators), aboitic variables (e.g., pond hydrology) to get a better understanding of patterns of parasite diversity within ponds and individual host species.
This pond not only has the most abundant newt (Notophthalmus viridescens) newt population that I've ever encountered, it contains a number of micro- and macro-parasites. We are beginning to characterize the parasite diversity at this location.
This is a new field site for us this year and it is part of our expanded efforts to better understand the distribution and prevalence of Bd in the region.
This is one of our terrestrial field sites from which we collect the Eastern Redbacked Salamander (Plethodon cinereus). My lab has been working extensively with this species in an attempt to understand costs associated with Bd resistance.