I am a disease ecologist with an interest in the biotic and abiotic factors that influence a host's susceptibility to infectious disease. My Ph.D. research was under the supervision of Prof. Andrew Blaustein at Oregon State University, where I studied infectious diseases in amphibians. I am currently a postdoctoral fellow in the laboratory of Prof. Meghan Duffy at the University of Michigan where I am studying the disease ecology of freshwater zooplankton.
My postdoctoral research focuses on disease dynamics in freshwater crustaceans (Daphnia). This system is ideal for studying the intersection of ecology and evolution because Daphnia have relatively fast generation times and can reproduce clonally. One aspect of my research investigates how pathogens change as they switch between host types (species or genotypes). As a population of pathogens passes through one host type, the conditions within that host may alter the pathogen through maternal effects or rapid evolution (Figure 1). I am studying the effects of host switching in two multi-host pathogens of zooplankton; the bacterium, Pasteuria ramosa and the fungus, Metschnikowia bicuspidata. Another aspect of this research investigates the effects of Daphnia lumholtzi, a species invasive in North America, on disease dynamics of native Daphnia species. The pathogen, P. ramosa, has been found infecting D. lumholtzi in the southern regions of the United States and I am investigating how this invasive host is affecting infection in native Daphnia species.
I also study the community ecology of the emerging fungal pathogen, Batrachochytrium dendrobatidis (Bd), which has caused population declines and extinctions of amphibians around the world. To understand the interspecific dynamics of this multi-host pathogen, I have performed a number of studies to determine how species differ in their interactions with Bd and how those differences influence infection in host communities. I found large differences among species in rates of survival and pathogen loads when infected with Bd, even when species are exposed to the same number of zoospores (infectious particles). I've also demonstrated a dilution effect in the Bd system (a negative relationship between biodiversity and disease risk; Fig. 2). These studies highlight the complexity of the community ecology of Bd, where species identity and host diversity can influence infection dynamics.
While host and pathogen diversity has been shown to impact disease dynamics, non-host species can also affect host-pathogen interactions. One way this can occur is when a non-host species preys upon either the host or the pathogen. As part of my postdoctoral research, I am studying the ability of Daphnia to act as predators to the fungal pathogen, Bd. Daphnia are non-selective grazers of detritus and small aquatic organisms (e.g. bacteria, fungi and protists). Since Bd swims through water to infect its hosts, Daphnia may directly consume Bd, reducing infection in amphibians. I have found that high concentrations of Daphnia can sometimes reduce the amount of Bd detected in water and the severity of infection in tadpoles. Thus, Daphnia may help reduce Bd infection, but only in circumstances when Daphnia densities are high.
Hosts under stress may have impaired immune function and lack the ability to launch an effective immune response to a pathogen. Therefore, it is generally thought that environmental stressors will increase a host's susceptibility to infectious diseases. However, some stressors (such as extreme temperatures or habitat disturbance) can also directly affect pathogens, altering their ability to infect hosts. I have studied the effects of stress on susceptibility of amphibians to Bd by exposing amphibians to exogenous corticosterone (to isolate stress in larval hosts) or to ultraviolet-B radiation in outdoor mesocosms (stress for the host and pathogen). In both of these studies, I found direct effects of stress on the tadpole host, but no influence on infection. These studies indicate that stress may not play a role in altering Bd infection in tadpoles, but I am continuing to study the effects of stress on post-metamorphic infection.