One size does not fit all: Monitoring faecal glucocorticoid metabolites in marsupials
Fanson, KV, Best, EC, Bunce, A, Fanson, BG, Hogan, LA, Keeley, T, Narayan, EJ, Palme, R, Parrott, ML, Sharp, TM, Skogvold, K, Tuthill, L, Webster, KN & Bashaw, M 2017, General and Comparative Endocrinology, vol. 244, no. 1, pp. 146-156.
A comparison of five assays for monitoring adrenocortical activity in response to stress in thirteen marsupial species, including the koala, has shown that the suitability of assays varies greatly among species. This finding indicates that an effective assay for this purpose must be identified for each marsupial species individually.
Glucocorticoids (GCs) are hormones secreted by the adrenal glands that play a variety of important physiological roles, including regulating the body’s response to stress. As an indicator of physiological stress, changes in adrenocortical activity can be monitored by measuring faecal glucocorticoid metabolites (FGM). The purpose of this investigation was to compare the effectiveness of five different enzyme immunoassays (EIAs) for measuring FGM across thirteen species of marsupial, including the koala. As EIAs are not universally applicable to all species, the goal of the study was to determine how suitable each EIA was for each marsupial. To assess each animal’s adrenal stress response, marsupials were subjected to either a biological stressor, such as transport or exposure to a new environment, or pharmacological stimulation via an adrenocorticotropic hormone (ACTH) injection. Koalas were one of the marsupial species for which FGM response was monitored after an ACTH challenge. The effectiveness of each EIA for each species was assessed based on its robustness at detecting FGM peaks across individuals between 0.125 and 4.5 days after the stressor event, and its sensitivity as indicated by the strength of the measured FGM response relative to baseline variability. Using these criteria, two of the five EIAs were successful for koalas. These two EIAs both detected FGM peaks within 50% of koalas but differed in their biological sensitivity. For ten of the thirteen marsupials, at least one EIA was successful. Importantly, however, the EIAs that were successful varied considerably among marsupials, even between closely related species. This was likely due to the EIAs detecting different metabolites. Across all combinations of species and EIA type, FGM peaks were detected in only 35% of animals. Of those animals, 55% of peaks were detected in only a single faecal sample.
Monitoring adrenocortical activity is valuable for conservation research as it provides information about an animal’s physiological response to stressors. Such information could be used to examine an animal’s wellbeing in response to a threat or, conversely, a conservation action. While blood samples were previously required to monitor adrenocortical activity, the measurement of GC metabolites in faeces allows GC levels to be measured in free-ranging animals with no need for capture or invasive procedures.
Previously, little research had been conducted into the suitability of assays for monitoring FGM in marsupials. The findings of this report show that the effectiveness of EIAs varies greatly across marsupials. Thus, it should not be assumed that suitability of an EIA for one species indicates similar suitability for another. Further, as most FGM peaks detected were observed in only a single faecal sample, the authors stress the importance of intensive sampling for reliably monitoring adrenocortical activity.
Summarised by Joanna Horsfall
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