Effects of Climate on Host-pathogen Interactions in Chytridiomycosis
Dr. Corinne Richards-Zawacki | University of Pittsburgh
Clarifying the links between climate and host-pathogen interactions will provide valuable insight into the dynamics, ecology, and evolution of infectious diseases and provide direction for effective management of threatened populations. Chytridiomycosis, a disease caused by the Batrachochytrium fungi, has recently caused declines and extinctions of amphibian populations on several continents. The central objective of the proposed research is to develop predictive models of chytridiomycosis, based on a clear understanding of how current and future climate may impact the ecology and dynamics of this host-pathogen interaction, and use the models to investigate the potential of alternative disease management tactics. Given the potential impact of climate change on disease, studies of this nature will be critical in developing strategies to promote the long-term health of threatened amphibians and other wildlife on Department of Defense (DoD) lands.
To investigate how climate impacts the ecology of chytridiomycosis (Objective 1), we will sample amphibian communities for Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal). At each of the field sites, which will include DoD installations in four climatically distinct regions of the United States, seasonal patterns of pathogen prevalence and load will be assessed in all amphibians present, as well as anti-Batrachochytrium immune defenses in our cross-region focal group: leopard frogs (Rana pipiens complex). To determine if variation among pathogen strains affects host-pathogen dynamics, research will examine the thermotolerance, life cycle, and expression of virulence traits in Batrachochytrium strains isolated from the study sites.
To investigate the impacts of current and future climates on amphibian-Batrachochytrium dynamics (Objective 2), a combination of experimental approaches will be used to evaluate whether hotter and more variable weather, as is predicted under global climate change, will increase the potential for transmission and disease development. The following will be conducted: (1) mesocosm experiments to evaluate whether the development and expression of host anti-fungal defenses, including innate, adaptive, and microbial skin defenses, are affected by changes in climate and hydroperiod; (2) in vitro thermotolerance and experimental evolution studies to ask how climate affects Batrachochytrium virulence, transmission potential, and the potential for pathogen niche evolution; and (3) mesocosm experiments to investigate how community structure, including shifts in host niches/ranges in future climates, might affect the dynamics and spread of chytridiomycosis.
To predict the risk that chytridiomycosis poses to the health of amphibian communities on DoD lands (Objective 3), process-based (mechanistic) models will be developed that use empirically derived relationships between climate variables and vital rates for amphibian hosts and Batrachochytrium pathogens to evaluate: (1) how climate affects the host/pathogen interaction, including the growth rate of Batrachochytrium on hosts and the transmission potential of infected hosts; (2) where and when chytridiomycosis outbreaks are likely to threaten amphibians on DoD installations (under both current and future climate scenarios); and (3) the effectiveness of alternative management strategies for sustaining threatened amphibian populations through times of increased disease risk.
Fungal pathogens are strongly temperature sensitive and increasingly recognized as drivers of wildlife declines and extinctions. Recent examples of emerging wildlife diseases caused by fungal pathogens underscore the need to understand the mechanisms by which current and future climates may affect virulence. This project aims to develop a clear understanding of the mechanisms that link climate to patterns of chytridiomycosis, a recently emerged and globally important wildlife pathogen. Studies like this one will be critical in this time of climate change, and this project could serve as a model for similar studies in other host-pathogen systems. The tools developed will aid the DoD in its mission to effectively steward the long-term health of ecosystems on its lands by generating predictions of the timing, distribution, and severity of chytridiomycosis outbreaks, as well as the potential impact of alternative management strategies on at-risk amphibian communities.