Validating the use of dermal secretion as a matrix for monitoring glucocorticoid concentrations in African amphibian species.

Juan Scheun,Andre Ganswindt,Katarina Medger,Dominique Greeff,Kathleen Hunt

doi:10.1093/conphys/coz022

Juan Scheun, Andre Ganswindt + Show 3 more

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https://doi.org/10.1093/conphys/coz022

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Abstract

The complex interaction between factors leading to amphibian declines is responsible for the inability to develop robust, standardized conservation action plans. Monitoring physiological stress responses in amphibians may provide an ideal tool to assist conservationists in this regard. This study aimed to validate dermal secretions as a robust matrix for monitoring glucocorticoid alterations in an African amphibian, the edible bullfrog (Pyxicephalus edulis). Both a biological (handling) and physiological (ACTH challenge) validation were conducted to determine which of five available enzyme immunoassays (EIAs) tested is most suited for monitoring alterations in dermal glucocorticoid (dGC) concentrations. Additionally, the most optimal body region for monitoring dGC concentrations in P. edulis was identified. To confirm the activation of the hypothalamic-pituitary-interrenal (HPI) axis following ACTH administration, urinary glucocorticoid metabolites (uGCM) were also quantified. The tested corticosterone EIA was the only assay able to monitor alterations in dGC concentrations following the handling event in P. edulis. Further validation during the ACTH challenge supported the corticosterone EIA in this regard. Dermal secretions collected from both the ventral and dorsal regions were suitable for monitoring dGC concentrations in both sexes. A considerable increase in uGCM concentrations following ACTH administration was found, suggesting that the dGC concentrations observed were derived from the HPI axis. This study offers further support for the use of dermal secretions as an important matrix for monitoring physiological stress, and thus general health, in amphibian species.

Highlights

This study offers further support for the use of dermal secretions as an important matrix for monitoring physiological stress, and general health, in amphibian species
In 2004, a global amphibian assessment indicated that 32% of global amphibian species are threatened with extinction, with a further 22.5% of amphibian species listed as data deficient and likely to be added to this list (Stuart et al, 2004)
A number of factors have been reported as important drivers of such decline, Blaustein and Kiesecker (2002) argued that the decline in amphibian populations within a specific habitat is not the result of a single factor, but rather the different biotic and abiotic factors acting in a context-specific manner, which could lead to amphibian declines that vary temporally and spatially

Summary

Introduction

In 2004, a global amphibian assessment indicated that 32% of global amphibian species are threatened with extinction, with a further 22.5% of amphibian species listed as data deficient and likely to be added to this list (Stuart et al, 2004). Despite the benefits of GC secretion in an organism, which include the necessary adjustments in metabolism, energy availability, enhancing cardiovascular activity and altering behaviour, all in order to restore homeostasis (Moberg, 2000; Romero, 2002), chronic secretion of GCs can have a number of deleterious effects. These include the suppression of the immune and reproductive systems, muscle atrophy, growth suppression and a shortened lifespan (Möstl and Palme, 2002; Sapolsky, 2002; Charmandari et al, 2005; Cohen et al, 2007). As such, monitoring GC patterns within endangered amphibians could offer important insight into amphibian health and wellbeing

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