Relationships among size, development, and Batrachochytrium dendrobatidis infection in African tadpoles

School of Environmental Sciences and Development, North-West University, Private Bag x6001, Potchefstroom 2520, South Africa.
Diseases of Aquatic Organisms (Impact Factor: 1.59). 03/2007; 74(2):159-64. DOI: 10.3354/dao074159
Source: PubMed

ABSTRACT The fungal pathogen Batrachochytrium dendrobatidis contributes to the global decline of amphibians. Although mortality from B. dendrobatidis infections occurs primarily in postmetamorphic individuals, infected tadpoles may suffer reduced growth and developmental rates as a result of oral chytridiomycosis, possibly affecting adult fitness. We conducted a field study in which we examined South African tadpoles for oral chytridiomycosis and compared the body sizes of infected and uninfected individuals of 2 species, Heleophryne natalensis and Strongylopus hymenopus. Presence of B. dendrobatidis was determined by microscopic inspection of mouthparts. Infection prevalence was high in both species, 62.5 and 38.6%, respectively, and infected individuals were significantly larger in both species. The inclusion of developmental stage in the analysis of S. hymenopus body size eliminated the relationship between body size and infection status, suggesting that differences in body size were not due to differences in growth, but to differences in developmental stage of infected larvae. These results suggest that larvae at more advanced developmental stages are more likely to be infected with B. dendrobatidis and that infection in larval amphibians may be dependent on time or developmental status of larvae. Contrary to the results of past studies, there was no evidence that oral chytridiomycosis resulted in decreased growth of tadpoles, despite the occurrence of oral abnormalities in infected individuals of 1 species. Because tadpole performance can subsequently affect the health of anuran populations and because tadpoles can act as reservoirs of infection, the study of B. dendrobatidis in larval amphibians is important to understanding the effects of this emerging disease.

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    ABSTRACT: The amphibian pathogen Batrachochytrium dendrobatidis (Bd) is causing population declines and species extirpations worldwide. Montane amphibians in tropical and temperate regions are especially vulnerable to chytridiomycosis. High-elevation amphibian assemblages typically include few species, so that epizootics should be limited once high frog mortality hinders transmission of the pathogen. We hypothesized that tadpoles of a high-elevation frog in the Peruvian Andes, Telmatobius jelskii, could function as reservoir for Bd in Andean streams. We postulated that, for tadpoles to function as an efficient reservoir of Bd, they should inhabit streams over extended periods of time, and have high prevalence of Bd. We surveyed streams between 2400 and 4850 m in the wet and dry seasons of 2010, where we captured, swabbed and determined the developmental stage of 458 tadpoles. We found that cohorts of tadpoles overlap continuously in these streams, as a consequence of multiple breeding events throughout the year. Prevalence of Bd among tadpoles averaged 53.1% (95% confidence interval: 49.8–56.3%); 8 out of 13 streams inhabited by T. jelskii had a prevalence greater than 50%. Prevalence of Bd was also higher during the dry season and increased with the age of the tadpoles. Our results support the hypothesis that the year-long presence of infected tadpoles in streams makes high-Andean Telmatobius frogs especially vulnerable to chytridiomycosis. The genus is already extirpated in Ecuador, and has been observed to decline rapidly in Peru, Bolivia and Argentina. Conservation strategies to mitigate the impact of Bd on populations of Telmatobius should consider aquatic life-stages.
    Biological Conservation 03/2013; 159:413–421. DOI:10.1016/j.biocon.2012.11.023 · 4.04 Impact Factor
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    ABSTRACT: Batrachochytrium dendrobatidis (Bd), the fungus responsible for chytridiomycosis, grows on the keratinized parts of the body (i.e., the entire skin of juveniles and adults, and the oral disk of tadpoles).The fungus affects epidermal structures, generating an imbalance of the osmotic equilibrium through the skin that ultimately leads to death. Therefore, larvae are likely to be much more resistant compared with juveniles and adults, which may suffer high mortality. However, nothing is known about how susceptibility varies during the juvenile life stages (from the end of metamorphosis to sexual maturity). The coexistence of tolerant hosts (either tolerant species or unaffected developmental stages) with susceptible hosts is a major reason why chytridiomycosis has become an epidemic disease. The aim of this study was to analyze the interspecific and developmental variation in susceptibility to Bd in juveniles of three North American anurans. Leopard Frog (Lithobates pipiens) incurred no lethal effects at 104 Bd zoospores ml-1, regardless of the age at which they were exposed to the fungus. On the contrary, Bd infection was more severe for newly metamorphosed juveniles of American toads (Anaxyrus americanus) than for 4-week-old juveniles. When exposed to 104 Bd zoospores ml-1, newly metamorphosed juveniles of this species experienced mortality rates above 70%, whereas 4-week-old juveniles had mortality rates below 30%. Variations in structural characteristics of the skin or the antifungal efficiency of skin peptides are proposed as potential reasons to explain the observed developmental differences in susceptibility to Bd
    Journal of Herpetology 06/2013; 47(2):286-292. DOI:10.1670/11-134 · 0.84 Impact Factor

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