Validation of a radioimmunoassay-based fecal corticosteroid assay for Richardson’s ground squirrels Urocitellus richard-sonii and behavioural correlates of stress

Abstract

We validated a radioimmunoassay-based method quantifying fecal glucocorticoid metabolites (FGMs) from captive male and female Richardson’s ground squirrels Urocitellus richardsonii. Blood samples were drawn to explore the correlation between plasma cortisol and FGM concentrations. We also injected groups of squirrels with normal saline (CTL; control), adre-nocorticotropic hormone (ACTH; stimulating adrenal activity), or dexamethasone (DEX; suppressing adrenal activity). Potential correlations between stress and behaviour were explored through quantification of fecal pellet production and the intervention necessary to elicit defecation, as well as the behaviour of subjects in the context of handling. Changes in plasma cortisol concentration between capture (baseline), and following handling (stress-induced) were also quantified for free-living squirrels. While glucocorticoid concentrations recovered from feces during our captive-animal study were not well correlated with plasma cortisol concentrations, and uncorrelated with defecation or behaviour, FGM concentrations did reflect the activation of the hypothalamic-pituitary-adrenal (HPA) axis. FGM concentrations increased significantly during initial captivity, but declined to baseline level as individuals acclimated to the novel environment. Injection of subjects with ACTH increased FGMs above baseline, confirming activation of the HPA axis. Plasma cortisol concentrations increased significantly with induced stress, indicating that capture and handling activated the glucocorticoid stress response even among previously handled, free-living subjects. Our findings validate a non-invasive tool that will afford new insight into the physiological processes underlying social, reproductive and antipredator behaviour of Richardson’s ground squirrels.

HPLC‐QTOF method for quantifying 11‐ketoetiocholanolone, a cortisol metabolite, in ruminants' feces: Optimization and validation

“…Quantification of FGCM by either fluorescence immunoassays, EIA, or radioimmunoassays (RIA) has been traditionally used as a noninvasive method for monitoring responses of free‐living or captive animals to environmental and social stressors (Good, Khan, & Lynch, ; Hare et al., ; Palme et al., ; Yu et al., ). But all of these techniques have disadvantages.…”

“…Hare et al, 2014;Palme et al, 2005;Yu et al, 2011). But all of these techniques have disadvantages.The use of radioisotopes involves environmental risk, high costs, and the need for specific equipment and qualified personnel.…”

Shyness–Boldness, but not Exploration, Predicts Glucocorticoid Stress Response in Richardson's Ground Squirrels (Urocitellus richardsonii)

“…; Hare et al. ). Faecal samples were dried overnight at 60°C before approximately 0.2 g of the faeces was combined with 1.5 ml 95% ethanol.…”

“…Radioimmunoassay methods for the measurement of glucocorticoid metabolites from the faecal matter of Richardson's ground squirrels employed in the present study are validated in Hare et al. ().…”

“…) and are not as subject to potential biases owing to differential responsiveness to capture and handling as plasma‐derived glucocorticoid samples (Hare et al. ). All faecal samples were collected between 1200 and 1500 h CDT and stored in 20‐ml polycarbonate vials with a unique numeric label so that they could be cross‐referenced with the date, time of collection and animal identity from field notes.…”