Dataset Information

Host age alters amphibian susceptibility to Batrachochytrium dendrobatidis, an emerging infectious fungal pathogen.

ABSTRACT: Parasites and pathogens are often aggregated in a minority of susceptible hosts within a population, with a majority of individuals harboring low infection intensities. However, determining the relative importance of host traits to explain this heterogeneity is a challenge. One ecologically important pathogen is Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis and has been associated with many amphibian population declines worldwide. For many hosts, post-metamorphic stages are generally more susceptible than the larval stage. Yet, examination of the effects of Bd infection at different ages within a life stage, has received little attention. This study investigated the hypothesis that recently-post-metamorphic frogs were more sensitive to chytridiomycosis than older frogs, and that sensitivity to Bd infection decreased as frogs aged. We examined this relationship with Pacific treefrogs (Pseudacris regilla) and red legged frogs (Rana aurora). Age had a strong effect on susceptibility to infection, infection intensity, and survival-but not in the directions we had predicted. In both host species, an increase in age was associated with frogs becoming more susceptible to Bd infection, harboring larger infection intensities, and greater risk of mortality. This suggests that the timing of Bd exposure may influence amphibian population dynamics.

SUBMITTER: Bradley PW

PROVIDER: S-EPMC6730893 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Host age alters amphibian susceptibility to Batrachochytrium dendrobatidis, an emerging infectious fungal pathogen.

Bradley Paul W PW Snyder Paul W PW Blaustein Andrew R AR

PloS one 20190906 9

Parasites and pathogens are often aggregated in a minority of susceptible hosts within a population, with a majority of individuals harboring low infection intensities. However, determining the relative importance of host traits to explain this heterogeneity is a challenge. One ecologically important pathogen is Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis and has been associated with many amphibian population declines worldwide. For many hosts, post-metamorphic ...[more]

PMID: 31491016

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Project description:Projected changes in climate conditions are emerging as significant risk factors to numerous species, affecting habitat conditions and community interactions. Projections suggest species range shifts in response to climate change modifying environmental suitability and is supported by observational evidence. Both pathogens and their hosts can shift ranges with climate change. We consider how climate change may influence the distribution of the emerging infectious amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), a pathogen associated with worldwide amphibian population losses. Using an expanded global Bd database and a novel modeling approach, we examined a broad set of climate metrics to model the Bd-climate niche globally and regionally, then project how climate change may influence Bd distributions. Previous research showed that Bd distribution is dependent on climatic variables, in particular temperature. We trained a machine-learning model (random forest) with the most comprehensive global compilation of Bd sampling records (~5,000 site-level records, mid-2014 summary), including 13 climatic variables. We projected future Bd environmental suitability under IPCC scenarios. The learning model was trained with combined worldwide data (non-region specific) and also separately per region (region-specific). One goal of our study was to estimate of how Bd spatial risks may change under climate change based on the best available data. Our models supported differences in Bd-climate relationships among geographic regions. We projected that Bd ranges will shift into higher latitudes and altitudes due to increased environmental suitability in those regions under predicted climate change. Specifically, our model showed a broad expansion of areas environmentally suitable for establishment of Bd on amphibian hosts in the temperate zones of the Northern Hemisphere. Our projections are useful for the development of monitoring designs in these areas, especially for sensitive species and those vulnerable to multiple threats.

Project description:Host-associated microbial biofilms can provide protection against pathogen establishment. In many host-microbe symbioses (including, but not limited to humans, plants, insects, and amphibians), there is a correlation between host-associated microbial diversity and pathogen infection risk. Diversity may prevent infection by pathogens through sampling effects and niche complementarity, but an alternative hypothesis may be that microbial biomass is confounded with diversity and that host-associated biofilms are deterring pathogen establishment through space preemption. In this study, we use the amphibian system as a model for host-microbe-pathogen interactions to ask two questions: (i) is bacterial richness confounded with biofilm thickness or cell density, and (ii) to what extent do biofilm thickness, cell density, and bacterial richness each deter the establishment of the amphibian fungal pathogen Batrachochytrium dendrobatidis? To answer these questions, we built a custom biofilm microcosm that mimics the host-environment interface by allowing nutrients to diffuse out of a fine-pore biofilm scaffolding. This created a competitive environment in which bacteria and the fungal pathogen compete for colonization space. We then challenged bacterial biofilms ranging in community richness, biofilm thickness, bacterial cell density, and B. dendrobatidis (also known as Bd)-inhibitory metabolite production with live B. dendrobatidis zoospores to determine how B. dendrobatidis establishment success on membranes varies. We found that biofilm thickness and B. dendrobatidis-inhibitory isolate richness work in complement to reduce B. dendrobatidis establishment success. This work underscores that physical aspects of biofilm communities can play a large role in pathogen inhibition, and in many studies, these traits are not studied. IMPORTANCE Our finding highlights the fact that diversity, as measured through 16S rRNA gene sequencing, may obscure the true mechanisms behind microbe-mediated pathogen defense and that physical space occupation by biofilm-forming symbionts may significantly contribute to pathogen protection. These findings have implications across a wide range of host-microbe systems since 16S rRNA gene sequencing is a standard tool used across many microbial systems. Further, our results are potentially relevant to many host-pathogen systems since host-associated bacterial biofilms are ubiquitous.

Project description:Many pathogens infect more than one host species, and clarifying how these different hosts contribute to pathogen dynamics can facilitate the management of pathogens and can lend insight into the functioning of pathogens in ecosystems. In this study, we investigated a suite of native and non-native amphibian hosts of the pathogen Batrachochytrium dendrobatidis (Bd) across multiple scales to identify potential mechanisms that may drive infection patterns in the Colorado study system. Specifically, we aimed to determine if: 1) amphibian populations vary in Bd infection across the landscape, 2) amphibian community composition predicts infection (e.g., does the presence or abundance of any particular species influence infection in others?), 3) amphibian species vary in their ability to produce infectious zoospores in a laboratory infection, 4) heterogeneity in host ability observed in the laboratory scales to predict patterns of Bd prevalence in the landscape. We found that non-native North American bullfrogs (Lithobates catesbeianus) are widespread and have the highest prevalence of Bd infection relative to the other native species in the landscape. Additionally, infection in some native species appears to be related to the density of sympatric L. catesbeianus populations. At the smaller host scale, we found that L. catesbeianus produces more of the infective zoospore stage relative to some native species, but that this zoospore output does not scale to predict infection in sympatric wild populations of native species. Rather, landscape level infection relates most strongly to density of hosts at a wetland as well as abiotic factors. While non-native L. catesbeianus have high levels of Bd infection in the Colorado Front Range system, we also identified Bd infection in a number of native amphibian populations allopatric with L. catesbeianus, suggesting that multiple host species are important contributors to the dynamics of the Bd pathogen in this landscape.

Dataset Information

Host age alters amphibian susceptibility to Batrachochytrium dendrobatidis, an emerging infectious fungal pathogen.

Publications

Host age alters amphibian susceptibility to Batrachochytrium dendrobatidis, an emerging infectious fungal pathogen.

Similar Datasets

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