Quantification of faecal glucocorticoid metabolites as a measure of stress in rock hyraxSubmitted by editor on 7 February 2022. Get the paper!
By Elisabetta Carlin
Although rock hyrax (Procavia capensis) is an abundant species in urban areas of South Africa, very little is known about levels of stress experienced when exposed to human activities. Previous endocrine studies investigating stress hormone levels related to social factors, utilized hair as hormone matrix. As hormone metabolite concentrations tend to accumulate over time in hair, such an approach presumably offers only insights into longer-term endocrine patterns. Thus, in this study we used faeces as a substitute hormone matrix for non-invasive monitoring, as this can be a suitable alternative way to investigate species-specific hormone fluctuation over a short-term period.
The aim of this research was to establish an enzyme-immunoassay (EIA) for reliably quantifying faecal glucocorticoid metabolites (fGCM) in hyrax faeces, by performing an adrenocorticotropic hormone stimulation test (ACTH challenge test) on captive individuals housed at the SANBI Mokopane Biodiversity Conservation Centre (South Africa). After identifying the most appropriate EIA for monitoring fGCM concentrations in the studied species, we analysed faecal samples from free ranging individuals at the National Botanical Garden (PBG) of Pretoria (South Africa). At the PBG, three areas (Section 1, 2 and 3) with differing levels of anthropogenic presence were chosen (high, medium and low). Seasonal differences in fGCM concentrations of different hyrax colonies living in these areas were examined, and the possible relationship between anthropogenic presence and fGCM concentrations were investigated.
Additionally, during two monitoring periods at the PBG (winter and late spring 2019), species’ habituation to human presence was examined by calculating the flight initiation distance (FID) in meters with a laser range finder, while camera traps were used to estimate anthropogenic presence.
Results from the ACTH challenge test demonstrated a variation over 3-fold within 15-30 min post ACTH administration. The maximum rises of fGCM concentrations were found 15-24 h post-injection. Out of five enzyme-immunoassays (EIA) tested, a 11β-hydroxyaetiocholanolone EIA was the most suitable to monitor alterations in fGCM concentrations in rock hyraxes, with respective fGCM concentrations remaining stable for up to 8 h post-defecation. Thus, we observed that faecal material should be collected within 8 h post-defecation to address adrenocortical activity analysis reliably.
Results for the animals living at the PBG showed an overall higher fGCM concentrations in late spring compared to winter. The fGCM concentrations, although not significantly different but possibly biologically relevant, in the section with the lowest anthropogenic disturbance were ~10% higher compared to those in the section with medium disturbance, and ~20% higher compared to those in the section with the highest human presence. Animal FID varied between animals of different sections, with a decreasing trend with increasing number of people, which indicates different levels of habituation across the rock hyrax population at the PBG. The non-invasive approach established in this study provides a foundation for assessing and managing rock hyrax wellbeing. It can contribute to better understand how, and at what extent, anthropogenic presence is perceived as a stressor in this species.