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.
