Data and code for: Previous assessments of faecal glucocorticoid metabolites in Cape Mountain zebra (Equus zebra zebra) were flawed
Creators: name: Britnell, Jake
name: Palme, Rupert
name: Kerley, Graham
name: Jackson, John
name: Shultz, Susanne
Publisher: name: Zenodo
Year: 2024
Subjects: Equus zebra zebra
glucocorticoid
biological validation

description: Steroid hormones, especially glucocorticoids (GCs), are widely used to assess physiological responses to stressors. As steroid hormones are heavily metabolised prior to excretion, it is essential to validate enzyme immunoassays (EIAs) for measuring faecal glucocorticoid metabolites (fGCMs). Although problems with unvalidated assays have been raised repeatedly, their use persists widely. Lea et al. (2017) used an unvalidated corticosterone assay (CJM006) to relate fGCM concentrations to habitat quality, demography, and population performance in the Cape mountain zebra (Equus zebra zebra). Here, we revisit their findings and evaluate the validity of their conclusions using a validated EIA. First, we evaluate the biological sensitivity of six EIAs (three group-specific metabolite assays and three corticosterone assays, including CJM006) through a biological validation experiment (translocation) for two sub-species of mountain zebra, Cape mountain and Hartmann's mountain zebra (E. z. hartmannae). Second, we reanalyse the faecal extracts from Lea et al. (2017) using a validated EIA. fGCM concentrations consistently increased following translocation, when using two 11-oxoaetiocholanolone (lab codes: 72T and 72a) and an 11ß-hydroxyaetiocholanolone (69a) EIA, but did not with three different corticosterone EIAs. All corticosterone EIAs (including CJM006) failed to detect an increase in fGCMs within the critical 48–72-hour period post translocation. Therefore, the CJM006 EIA utilised in Lea et al. (2017) does not sensitively measure hypothalamic-pituitary-adrenal (HPA) axis activity in CMZ faeces.

Using a validated assay (72T), fGCM concentrations were no longer associated with adult sex ratio or habitat quality (measured by grassiness) and these variables were dropped from predictive models. fGCM concentrations now varied between seasons and were negatively associated with female fecundity (foal:mare ratio).  Consequently, we can conclude that the results of the previous study are unreliable. We introduce the terms "insensitive" and "sub-optimal" to categorise assays that are tested but fail validation, and assays that are comparatively poor at detecting relevant hormone changes, respectively. We discuss how both "insensitive" and "sub-optimal" assays could lead to incorrect inferences about population stressors and counterproductive conservation recommendations.

In this dataset, we provide all R code scripts, raw data and data to reproducible all results and figures in Previous assessments of faecal glucocorticoid metabolites in Cape Mountain zebra (Equus zebra zebra) were flawed. We have structured the project as an internally consistent directory with files corresponding to code, data, raw lab_ouputs, and figures.
description: Funding provided by: Natural Environment Research CouncilROR ID: https://ror.org/02b5d8509Award Number: NE/L002469/1
Funding provided by: Royal SocietyROR ID: https://ror.org/03wnrjx87Award Number: UF110641
description: The faecal samples were collected from Cape Mountain zebra (Equus zebra zebra) Hartmann's Mountain zebra (Equus zebra hartmannae) in South Africa and from European zoos respectively. We calculated faecal metabolite concentrations using 6 different glucocorticoid assays. All raw data generated is available as laboratory outputs as supplementary files. We used a mixed of custom and my assay software to convert raw optimal density estimates to metabolite concentration. All data files have been provided and all processing steps can be seen in the laboratory outputs supplementary xlsx files.