I am a disease ecologist with an interest in the effects of host diversity on infectious disease. I study how host diversity influences infection rates, and how host diversity can affect pathogens on short and long time scales (i.e. plasticity and evolution). Through these studies, I aim to understand how altered host diversity, from factors such as biodiversity loss or invasive species, can affect disease dynamics.
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 environmental effects or rapid evolution (Figure 1). I study 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. Native pathogens have been found infecting D. lumholtzi and I am investigating how infectious diseases will invasion invasion success of this 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 when infected with Bd, even when species are exposed to the same number of zoospores (infectious particles). Additionally, amphibian hosts can shed infection during development, but the ability to do this depends on community context. I have also demonstrated a dilution effect in the Bd system (a negative relationship between biodiversity and disease risk; Fig. 2) indicating that preserving biodiversity may help reduce infection. These studies highlight the complexity of the community ecology of Bd, where species identity and host diversity can influence infection dynamics.
Non-host species can also impact disease dynamics through predation upon hosts or pathogens. I am studying the ability of potential Bd predators (Daphnia) to reduce infection in amphibian hosts. 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 Daphnia can reduce Bd levels in water and infection in tadpoles, but these effects vary with species, algal concentration and Daphnia density. Thus, the effects of Daphnia on Bd are context-dependent.
Hosts under stress may have impaired immune function and lack the ability to launch an effective immune response to a pathogen. However, some environmental stressors can also directly affect pathogens, altering their ability to infect hosts. One aspect of my research has investigated the effects of stress on susceptibility of amphibians to Bd. I have exposed amphibian hosts to stressors such as exogenous corticosterone and to ultraviolet-B radiation, while exposing them to Bd. In these studies, I found direct effects of stress on the host, but no influence on infection. Therefore, stress may not play a role in altering Bd infection in amphibians, indicating that global increases in Bd prevalence are likely due to other factors.