Relationship 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: 1.75). 03/2007; 74(2):159-64. DOI: 10.3354/dao074159
Source: PubMed


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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    • "Bd infects keratinized tissues, such as anuran larval mouthparts, reducing their foraging capabilities [18]–[20]. While Bd does not generally cause mortality in larvae (as it does in adults), the fungus often impairs growth and developmental rates [21]–[24]. Venesky et al. [20] found that Bd altered larval mouthparts, resulting in Hyla chrysoscelis (Cope’s treefrog) larvae foraging less efficiently than uninfected individuals. Additionally, Hanlon et al. (unpublished data) found that infected Hyla versicolor (gray treefrog) larvae spent significantly more time foraging than uninfected individuals. "
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    ABSTRACT: Amphibians are often exposed to a wide variety of perturbations. Two of these, pesticides and pathogens, are linked to declines in both amphibian health and population viability. Many studies have examined the separate effects of such perturbations; however, few have examined the effects of simultaneous exposure of both to amphibians. In this study, we exposed larval southern leopard frog tadpoles (Lithobates sphenocephalus) to the chytrid fungus Batrachochytrium dendrobatidis and the fungicide thiophanate-methyl (TM) at 0.6 mg/L under laboratory conditions. The experiment was continued until all larvae completed metamorphosis or died. Overall, TM facilitated increases in tadpole mass and length. Additionally, individuals exposed to both TM and Bd were heavier and larger, compared to all other treatments. TM also cleared Bd in infected larvae. We conclude that TM affects larval anurans to facilitate growth and development while clearing Bd infection. Our findings highlight the need for more research into multiple perturbations, specifically pesticides and disease, to further promote amphibian heath.
    PLoS ONE 08/2012; 7(8):e43573. DOI:10.1371/journal.pone.0043573 · 3.23 Impact Factor
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    • "Larger animals may acquire greater amounts of Bd, but may also be healthier and better able to resist infection (Carey et al. 1999), which could lead to longer survival. In previous studies with different species than the ones we studied here, both positive and negative relations have been found between body size and Bd infection (Kriger et al. 2007; Smith et al. 2007; Symonds et al. 2007). We found a positive correlation "
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    Conservation Biology 07/2011; 25(5):965-74. DOI:10.1111/j.1523-1739.2011.01708.x · 4.17 Impact Factor
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    • "In other species, the effects of Bd on anuran larvae have varied. Smith et al (2007) found no evidence of decreased growth in Heleophryne natalensis and Strongylopus hymenopus larvae infected with Bd. However, Parris and Cornelius (2004) showed that infections in larval stages cause increases in developmental instability of Bufo fowleri and Hyla chrysoselis metamorphs. "
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    ABSTRACT: Bullfrogs (Rana catesbeiana) are widely believed to be nonclinical carriers of Batrachochytrium dendrobatidis (Bd), the fungal pathogen that invades keratinized tissues of amphibians and causes the disease, chytridiomycosis. Although most research on this disease focuses on adults, larval anurans are also susceptible to infections in their keratinized mouthparts, and this allows for visual diagnosis of the disease via the degree of mouthpart depigmentation. When an unplanned outbreak of chytridiomycosis occurred in a set of captive bullfrog tadpoles in our lab, we conducted the current investigation into its effects on the nonspecific immune system (i.e., the leukocyte populations) of the tadpoles. We compared leukocyte counts from blood smears of 27 tadpoles that had contracted the disease (evidenced by severe mouthpart depigmentation and confirmed by histology) to those of 21 tadpoles that had little depigmentation (i.e., with little evidence of the disease). Tadpoles with severe depigmentation had significantly more neutrophils and less eosinophils than those with little depigmentation, while numbers of lymphocytes, basophils, and monocytes were not statistically different. That there was any effect at all on circulating leukocyte numbers is surprising since leukocytes are usually not seen migrating to sites of infection in tissue sections of amphibians infected with Bd, and since most research points to this disease having little outward effect on bullfrogs. Since monocyte numbers were unchanged, the leukocyte alterations were likely not due to a simple inflammation response. It is possible that Bd infections elicit increases in glucocorticoid hormones, which can cause increased numbers of circulating neutrophils and lower numbers of eosinophils, although this is often accompanied by a reduction in lymphocyte numbers, which we did not see. Further research is warranted to clarify if this effect is limited to this species.
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