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• 1. [Article] Ecology and applications of cutaneous mechanisms of resistance to amphibian chytridiomycosis

  Amphibian biodiversity is in rapid global decline, due in part to the fungal disease chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd). Susceptibility to Bd and chytridiomycosis varies between ...

  Citation × Citation Citation Abstract Copy Title: Ecology and applications of cutaneous mechanisms of resistance to amphibian chytridiomycosis Author: Nebergall, Emily E. Amphibian biodiversity is in rapid global decline, due in part to the fungal disease chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd). Susceptibility to Bd and chytridiomycosis varies between species and populations. Skin peptides and symbiotic skin bacteria appear to be important mechanisms of Bd resistance. However, not much is known about the ways in which these mechanisms vary between species and locations or about the relative importance of these mechanisms to different amphibian species. This thesis sought to explore the ecology and applications of mechanisms of resistance to Bd. In the second chapter, I use an information theoretic approach to investigate the source of intraspecies and interspecies variation in three measures of predicted resistance against chytridiomycosis: skin peptide inhibition of Bd, skin peptide quantity, and prevalence of Bd-inhibitory bacteria. I collected peptide and bacterial samples from three amphibian species in Mt. Rainier National Park, which is characterized by landscape heterogeneity and low connectivity and hence is likely to produce high variability between amphibian populations in different park regions. I found that skin peptide defenses may vary primarily by species, whereas anti-Bd skin bacteria may vary primarily by location. In the third chapter, I investigate the feasibility of using anti- Bd bacteria to bioaugment an endangered amphibian species, Rana chiricahuensis, against infection with Bd. I screened skin bacterial communities from wild R. chiricahuensis for anti- Bd bacteria and selected Pseudomonas fluorescens as an experimental bioaugmentation agent. I tested P. fluorescens alongside Janthinobacterium lividum in Bd challenges studies with wild adult R. chiricahuensis. Results of these studies do not indicate bioaugmentation with either of these two bacteria as a feasible Bd management strategy for R. chiricahuensis. Title: Ecology and applications of cutaneous mechanisms of resistance to amphibian chytridiomycosis Author: Nebergall, Emily E. Amphibian biodiversity is in rapid global decline, due in part to the fungal disease chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd). Susceptibility to Bd and chytridiomycosis varies between species and populations. Skin peptides and symbiotic skin bacteria appear to be important mechanisms of Bd resistance. However, not much is known about the ways in which these mechanisms vary between species and locations or about the relative importance of these mechanisms to different amphibian species. This thesis sought to explore the ecology and applications of mechanisms of resistance to Bd. In the second chapter, I use an information theoretic approach to investigate the source of intraspecies and interspecies variation in three measures of predicted resistance against chytridiomycosis: skin peptide inhibition of Bd, skin peptide quantity, and prevalence of Bd-inhibitory bacteria. I collected peptide and bacterial samples from three amphibian species in Mt. Rainier National Park, which is characterized by landscape heterogeneity and low connectivity and hence is likely to produce high variability between amphibian populations in different park regions. I found that skin peptide defenses may vary primarily by species, whereas anti-Bd skin bacteria may vary primarily by location. In the third chapter, I investigate the feasibility of using anti- Bd bacteria to bioaugment an endangered amphibian species, Rana chiricahuensis, against infection with Bd. I screened skin bacterial communities from wild R. chiricahuensis for anti- Bd bacteria and selected Pseudomonas fluorescens as an experimental bioaugmentation agent. I tested P. fluorescens alongside Janthinobacterium lividum in Bd challenges studies with wild adult R. chiricahuensis. Results of these studies do not indicate bioaugmentation with either of these two bacteria as a feasible Bd management strategy for R. chiricahuensis. Close

• 2. [Article] Emerging infectious disease in lentic environments : the ecology and biogeography of the amphibian chytrid fungus Batrachochytrium dendrobatidis, with perspectives on water quality, limnology, and chemical contaminants

  Biodiversity losses in terrestrial, freshwater, and marine systems are accelerating at a global scale and the most threatened vertebrate taxa are those associated with freshwater habitats. The causes of ...

  Citation × Citation Citation Abstract Copy Title: Emerging infectious disease in lentic environments : the ecology and biogeography of the amphibian chytrid fungus Batrachochytrium dendrobatidis, with perspectives on water quality, limnology, and chemical contaminants Author: Chestnut, Tara Biodiversity losses in terrestrial, freshwater, and marine systems are accelerating at a global scale and the most threatened vertebrate taxa are those associated with freshwater habitats. The causes of biodiversity losses are often complex and include synergistic effects of natural and human-induced stressors, such as habitat loss and fragmentation, urbanization, invasive species, contaminants, global climate change, and emerging infectious diseases. In the last 35 years, the amphibian extinction rate has been estimated to exceed 105 times the baseline expected rate for all species and in the USA, the number of occupied amphibian sites has been reported to be declining by 3.7% per year. Among the many threats to amphibians, the role of disease in population declines has been recognized increasingly over the last two decades. Numerous amphibian diseases have been identified and attributed to mass mortality events. Chytridiomycosis, the emerging infectious disease caused by the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), is implicated as a causal agent in many recent global amphibian population declines and extinctions. To understand the pathology and conservation implications of Bd, a greater understanding of its ecology, life history, and distribution in the wild is of paramount importance. Although it has an impact on the persistence of selected amphibian populations around the world, the full scope of the effects of chytridiomycosis on global amphibian population declines are not well understood. Most Bd research efforts have focused on Bd in amphibian hosts per se, with little attention to understand the environmental associations and dynamics of free-living Bd outside of the amphibian host. In particular, information on Bd responses to climatic variation outside of hosts is a research gap. Furthermore, as a microorganism within an aquatic environment, studies are lacking of potential water quality associations, how Bd may interact with other members of their biological communities, and how Bd responses to chemical contaminants found in aquatic environments. My research begins to fill these gaps by studying the basic ecology of free-living Bd in field settings, and investigating factors that may influence its distribution at a landscape scale, occurrence at a regional scale, and detection at a site scale. Herein, I describe spatial and temporal patterns in the detection and density of free-living Bd in aquatic habitats in two different geographic regions of the United States, Alaska (Chapter 2) and Oregon (Chapter 3). The Alaska work examines Bd ecology at the northernmost extent of amphibian occurrence in North America, where climate associations may be particularly relevant and where Bd occurrence may be representative of one of the most novel pathogen-host systems in the world. I also describe (Chapter 2) experimental results of Bd and amphibian response to extreme cold temperatures they may experience in continental settings, at high elevations, and at high latitudes. My Oregon studies (Chapter 3) focus on multivariate associations of free-living Bd occurrences with a suite of aquatic environmental factors, both abiotic and biotic in nature. In Chapter 4, I describe how amphibians and Bd respond to agricultural chemicals (fungicides) that they may be exposed to in field settings. These results are specific to Bd, but might also warrant consideration as fungicidal treatments for a newly described chytrid affecting salamanders; both of these amphibian chytrids have been detected in captive animals and solutions to treat trade animals for the pathogen are gaining relevancy. Finally, in Chapter 5, I reflect upon the journey of conservation biologists and herpetologists for 25 years of amphibian decline research, with global losses becoming widely recognized in 1989. In this context, my research significantly advances understanding of the geographic distribution and ecology of one potential threat factor to amphibian populations on Earth, Batrachochytrium dendrobatidis. The factors that I report to both promote or limit free-living Bd distribution and abundance will further inform pathogen dynamics research. Title: Emerging infectious disease in lentic environments : the ecology and biogeography of the amphibian chytrid fungus Batrachochytrium dendrobatidis, with perspectives on water quality, limnology, and chemical contaminants Author: Chestnut, Tara Biodiversity losses in terrestrial, freshwater, and marine systems are accelerating at a global scale and the most threatened vertebrate taxa are those associated with freshwater habitats. The causes of biodiversity losses are often complex and include synergistic effects of natural and human-induced stressors, such as habitat loss and fragmentation, urbanization, invasive species, contaminants, global climate change, and emerging infectious diseases. In the last 35 years, the amphibian extinction rate has been estimated to exceed 105 times the baseline expected rate for all species and in the USA, the number of occupied amphibian sites has been reported to be declining by 3.7% per year. Among the many threats to amphibians, the role of disease in population declines has been recognized increasingly over the last two decades. Numerous amphibian diseases have been identified and attributed to mass mortality events. Chytridiomycosis, the emerging infectious disease caused by the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), is implicated as a causal agent in many recent global amphibian population declines and extinctions. To understand the pathology and conservation implications of Bd, a greater understanding of its ecology, life history, and distribution in the wild is of paramount importance. Although it has an impact on the persistence of selected amphibian populations around the world, the full scope of the effects of chytridiomycosis on global amphibian population declines are not well understood. Most Bd research efforts have focused on Bd in amphibian hosts per se, with little attention to understand the environmental associations and dynamics of free-living Bd outside of the amphibian host. In particular, information on Bd responses to climatic variation outside of hosts is a research gap. Furthermore, as a microorganism within an aquatic environment, studies are lacking of potential water quality associations, how Bd may interact with other members of their biological communities, and how Bd responses to chemical contaminants found in aquatic environments. My research begins to fill these gaps by studying the basic ecology of free-living Bd in field settings, and investigating factors that may influence its distribution at a landscape scale, occurrence at a regional scale, and detection at a site scale. Herein, I describe spatial and temporal patterns in the detection and density of free-living Bd in aquatic habitats in two different geographic regions of the United States, Alaska (Chapter 2) and Oregon (Chapter 3). The Alaska work examines Bd ecology at the northernmost extent of amphibian occurrence in North America, where climate associations may be particularly relevant and where Bd occurrence may be representative of one of the most novel pathogen-host systems in the world. I also describe (Chapter 2) experimental results of Bd and amphibian response to extreme cold temperatures they may experience in continental settings, at high elevations, and at high latitudes. My Oregon studies (Chapter 3) focus on multivariate associations of free-living Bd occurrences with a suite of aquatic environmental factors, both abiotic and biotic in nature. In Chapter 4, I describe how amphibians and Bd respond to agricultural chemicals (fungicides) that they may be exposed to in field settings. These results are specific to Bd, but might also warrant consideration as fungicidal treatments for a newly described chytrid affecting salamanders; both of these amphibian chytrids have been detected in captive animals and solutions to treat trade animals for the pathogen are gaining relevancy. Finally, in Chapter 5, I reflect upon the journey of conservation biologists and herpetologists for 25 years of amphibian decline research, with global losses becoming widely recognized in 1989. In this context, my research significantly advances understanding of the geographic distribution and ecology of one potential threat factor to amphibian populations on Earth, Batrachochytrium dendrobatidis. The factors that I report to both promote or limit free-living Bd distribution and abundance will further inform pathogen dynamics research. Close