Research | Dave's Research Site

Main Research Themes

A brief presentation of my work, made for the Institute of Public Health at Washington University of St. Louis. March, 2020.

Movement and Infection Risk: The COVID-19 pandemic made brutally clear how movement can facilitate the spread of harmful pathogens. It also highlights how much of our normal lives is spent on the move. Whether to buy food or to meet friends, a lot of our time is spent in transit from one location to another. Wildlife are no different. Wildlife move farther and more frequently than once thought, and their movement patterns are shifting with globalization and climate change. With emergence of novel pathogens on the rise, more complete characterization of wildlife movement and its impact on disease risk can address outstanding threats to biodiversity and global health.

I study this topic in amphibians and the devastating fungal pathogen, Batrachochytrium dendrobatidis (Bd). Key findings include:

Radio-tracking of toads revealed that hosts cleared Bd infections during migration, indicating that host movements can reduce infection risk.
Laboratory experiments with newts (see photo of setup below, right) showed that (a) hosts sought upland habitats when they contracted Bd infections and (b) use of upland habitats expedited recovery from Bd infections, suggesting a behavioural mechanism for infection clearance. Patterns of infection observed in the experiments reflected those we saw in natural populations.
A spatial disease model introduced a transient phase covering the period of host travel, which enabled explicit modelling of infection dynamics in moving hosts. Doing so allowed modellers to consider often neglected biological realities my empirical work had demonstrated: wildlife movement can both aid and inhibit parasites, depending on the environmental context and how hosts respond to infection.

Wildlife Movement

The community context of parasitism

Real communities feature multiple interacting species. This includes parasites and their hosts. Most parasites infect multiple species and most hosts harbour multiple co-infecting parasites. For a long time, this complexity was overlooked, but multi-host, multi-parasite dynamics has become a prominent focus of disease ecology research. My collaborators in the UK and I execute studies combining mesocosm experiments with statistical and dynamical modelling to how parasites circulate and persist in multi-host and multi-parasite communities. Key findings include:

Host species that differed in Bd susceptibility and infectiousness played similar functional roles in community-level transmission of Bd, challenging the notion that host species identity is always a crucial factor in parasite circulation in multi-host communities.
Bd exposure increased prevalence of viral infections, especially in mixed-species host communities, indicating that the level of community-level stress imposed by parasites depends on both the presence of other co-circulating parasites and the wider host community context.

Endangered species conservation

My research at UCLA is investigating the extent to which Bd acts as a stressor in threatened Yosemite toads (Anaxyrus canorus) in Yosemite National Park. In coordination with the Yosemite Aquatic Resources Team, I am quantifying risk in toads to inform planned re-introductions. Infection data from systematic Bd surveillance indicate that (a) infection risk varies across toad life stages; juveniles are the most susceptible, and (b) significant Bd transmission occurs during toad hibernation. This research is informing an NPS recovery plan for Yosemite toads and a grant proposal for test mechanisms of Bd transmission during hibernation.

Structural equation modelling on data from mesocosm experiments showed that Bd infections circulated between frogs and toads but not in salamanders. Scaling these patterns to community-level Bd dynamics indicated that frogs and toads kept Bd thriving in communities, and the two species functioned identically in terms of Bd transmission.

Adult female Yosemite toad (Anaxyrus canorus).