Distribution and Pathogenicity of Batrachochytrium dendrobatidis in Boreal Toads from the Grand Teton Area of Western Wyoming

Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007, USA.
EcoHealth (Impact Factor: 2.45). 06/2009; 6(1):109-20. DOI: 10.1007/s10393-009-0230-4
Source: PubMed


The pathogen Batrachochytrium dendrobatidis (Bd), which causes the skin disease chytridiomycosis, has been linked to amphibian population declines and extinctions worldwide. Bd has been implicated in recent declines of boreal toads, Bufo boreas boreas, in Colorado but populations of boreal toads in western Wyoming have high prevalence of Bd without suffering catastrophic mortality. In a field and laboratory study, we investigated the prevalence of Bd in boreal toads from the Grand Teton ecosystem (GRTE) in Wyoming and tested the pathogenicity of Bd to these toads in several environments. The pathogen was present in breeding adults at all 10 sites sampled, with a mean prevalence of 67%. In an experiment with juvenile toadlets housed individually in wet environments, 10(6) zoospores of Bd isolated from GRTE caused lethal disease in all Wyoming and Colorado animals within 35 days. Survival time was longer in toadlets from Wyoming than Colorado and in toadlets spending more time in dry sites. In a second trial involving Colorado toadlets exposed to 35% fewer Bd zoospores, infection peaked and subsided over 68 days with no lethal chytridiomycosis in any treatment. However, compared with drier aquaria with dry refuges, Bd infection intensity was 41% higher in more humid aquaria and 81% higher without dry refuges available. Our findings suggest that although widely infected in nature, Wyoming toads may escape chytridiomycosis due to a slight advantage in innate resistance or because their native habitat hinders Bd growth or provides more opportunities to reduce pathogen loads behaviorally than in Colorado.

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Available from: Charles Russell Peterson, Feb 15, 2014
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    • "Genetically divergent populations within a species may differ in immune response and therefore respond differently to infections of chytridiomycosis (Goebel et al. 2009; Murphy et al. 2009). Craugastor fitzingeri's phylogeography demonstrates high rates of gene flow across its distribution, and there are no significant clade differences across environments (Crawford et al. 2007). "
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    ABSTRACT: Population declines and extinctions of numerous species of amphibians, especially stream-breeding frogs, have been linked to the emerging infectious disease chytridiomycosis, caused by the chytrid fungus, Batrachochytrium dendrobatidis. In Central America, most of the 34 species of the Craugastor punctariolus species group have disappeared in recent years in high- and low-elevation rainforests. Distribution models for B. dendrobatidis and the continuous presence of the extirpated stream-dwelling species, Craugastor ranoides, in the driest site of Costa Rica (Santa Elena Peninsula), suggest that environmental conditions might restrict the growth and development of B. dendrobatidis, existing as a refuge from chytridiomycosis-driven extinction. We conducted field surveys to detect and quantify the pathogen using Real-time PCR in samples from 15 species of frogs in two locations of tropical dry forest. In Santa Elena Peninsula, we swabbed 310 frogs, and only one sample of the species, C. ranoides, tested positive for B. dendrobatidis (prevalence <0.1%). In Santa Rosa Station, we swabbed 100 frogs, and nine samples from three species tested positive (prevalence = 9.0%). We failed to detect signs of chytridiomycosis in any of the 410 sampled frogs, and low quantities of genetic equivalents (between 0 and 1073) were obtained from the ten positive samples. The difference in the prevalence between locations might be due not only to the hotter and drier conditions of Santa Elena Peninsula but also to the different compositions of species in both locations. Our results suggest that B. dendrobatidis is at the edge of its distribution in these dry and hot environments of tropical dry forest. This study supports the existence of climatic refuges from chytridiomycosis and highlights the importance of tropical dry forest conservation for amphibians in the face of epidemic disease.
    EcoHealth 09/2014; 11(4). DOI:10.1007/s10393-014-0967-2 · 2.45 Impact Factor
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    • "Bd has been detected in lowland forests [10], [13], [19]–[22]; however, in low elevation sites there is little evidence of population declines associated with Bd [20]. One of the possible reasons for the absence of dramatic declines in the lowlands is that environmental conditions, such as temperature and moisture, are not optimal for Bd growth and successful colonization [23], [24], [25]. In addition, it is possible that lowland species are less susceptible to infection because of physiological and ecological traits, such as differential immune response, production of antimicrobial peptides, presence of symbiotic beneficial bacterial, behavioral patterns and habitat associations [19], [26]–[29]. "
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    ABSTRACT: The fungal disease chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), is one of the main causes of amphibian population declines and extinctions all over the world. In the Neotropics, this fungal disease has caused catastrophic declines in the highlands as it has spread throughout Central America down to Panamá. In this study, we determined the prevalence and intensity of Bd infection in three species of frogs in one highland and four lowland tropical forests, including two lowland regions in eastern Panamá in which the pathogen had not been detected previously. Bd was present in all the sites sampled with a prevalence ranging from 15-34%, similar to other Neotropical lowland sites. The intensity of Bd infection on individual frogs was low, ranging from average values of 0.11-24 zoospore equivalents per site. Our work indicates that Bd is present in anuran communities in lowland Panamá, including the Darién province, and that the intensity of the infection may vary among species from different habitats and with different life histories. The population-level consequences of Bd infection in amphibian communities from the lowlands remain to be determined. Detailed studies of amphibian species from the lowlands will be essential to determine the reason why these species are persisting despite the presence of the pathogen.
    PLoS ONE 04/2014; 9(4):e95484. DOI:10.1371/journal.pone.0095484 · 3.23 Impact Factor
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    • "Despite the frequent reporting of mortality associated with this pathogen, there are populations of animals infected with B. dendrobatidis that appear to co-exist with the fungus.2,12–14 For example, B. dendrobatidis has been identified on boreal toads, Anaxyrus (Bufo) boreas boreas, in Grand Teton National Park (GTNP) in Wyoming, USA and no acute mass mortalities have been observed in this region.15,16 In contrast, in Colorado the same species of toad has experienced mortality from this pathogen.17 "
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    ABSTRACT: The chytrid fungus Batrachochytrium dendrobatidis is a significant cause of the worldwide decline in amphibian populations; however, various amphibian species are capable of coexisting with B. dendrobatidis. Among them are boreal toads (Anaxyrus (Bufo) boreas boreas) located in Grand Teton National Park (GTNP) in Wyoming, USA. The purpose of this study was to identify cultivable bacterial isolates from the skin microbiota of boreal toads from GTNP and determine if they were capable of inhibiting B. dendrobatidis in vitro, and therefore might be a factor in the toad's coexistence with this pathogen. Isolates from 6 of 21 genera tested were found to inhibit the growth of B. dendrobatidis. These bacteria represent diverse lineages such as the Gammaproteobacteria, the Betaproteobacteria, and the Bacteroidetes/Chlorobium groups. We propose that these bacteria compete via microbial antagonism with B. dendrobatidis.
    Microbiology Insights 02/2014; 7:1-8. DOI:10.4137/MBI.S13639
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