Noninvasive Monitoring of Fecal Cortisol Metabolites in the Eastern Chipmunk (Tamias striatus): Validation and Comparison of Two Enzyme Immunoassays

Abstract

Monitoring fecal glucocorticoid metabolites in wild animals, using enzyme immunoassays, enables the study of endocrinological patterns relevant to ecology and evolution. While some researchers use antibodies against the parent hormone (which is typically absent from fecal samples), others advocate the use of antibodies designed to detect glucocorticoid metabolites. We validated two assays to monitor fecal cortisol metabolites in the eastern chipmunk (Tamias striatus). We compared an antibody produced against cortisol and one produced against 5α-pregnane-3β, 11β, 21-triol-20-one using a radiometabolism study and an injection with adrenocorticotropic hormone (ACTH). Most cortisol metabolites were excreted in the urine (∼83%). Peak excretion in the feces occurred 8 h after injection. Both assays detected an increase in fecal cortisol metabolite levels after injection of ACTH. Males, but not females, exhibited a circadian variation in metabolite levels. The sexes did not exhibit any difference over the time course and route of excretion or the relative increase in fecal cortisol metabolite levels after ACTH injection. The cortisol assay displayed higher reactivity to ACTH injection relative to baseline than did the metabolite assay. While both antibodies gave comparable results, the cortisol antibody was more sensitive to changes in plasma cortisol levels in eastern chipmunks.

Intra-individual variability in fecal cortisol metabolites varies with lifetime exploration and reproductive life history in eastern chipmunks (Tamias striatus)

“…In brief, the assay detects a cortisol response to a standardized ACTH challenge test, as well as circadian variations in fecal cortisol metabolite levels in eastern chipmunks. Our validation also showed that fecal samples collected in this species represent an integrated measure of the cortisol produced over a period of 8 h preceding defecation (Montiglio et al 2012b). We collected fecal samples from the traps during each capture in 2009 (286 samples from 30 females, 9.57 samples/female, range=2-26; 161 samples from 27 males, 5.96 samples/male, range=1-19).…”

“…We previously validated an assay to quantify individual fecal cortisol (see Montiglio et al 2012b for details). In brief, the assay detects a cortisol response to a standardized ACTH challenge test, as well as circadian variations in fecal cortisol metabolite levels in eastern chipmunks.…”

“…Individuals expressed patterns ranging from slow, characterized by an intermediate but constant exploration level throughout the test, to fast, characterized by a high exploration level at the beginning of the test followed by a steep decline over the following seconds. The activity pattern in the open-field displays a repeatability of~30 % (estimated using a linear mixed model, Montiglio et al 2012b). Open-field tests predict the propensity of individuals to be captured or respond to handling over their entire life (see Montiglio et al 2012b for a full details and analysis).…”

“…The activity pattern in the open-field displays a repeatability of~30 % (estimated using a linear mixed model, Montiglio et al 2012b). Open-field tests predict the propensity of individuals to be captured or respond to handling over their entire life (see Montiglio et al 2012b for a full details and analysis). We built a model accounting for the effects of date, age, sex, year, and trial order on exploration levels.…”

Sex‐specific variation in the onset of reproduction and reproductive trade‐offs in a boreal small mammal

“…Also sex, age, time of the day and even diet may affect the metabolism , Dantzer et al 2011a. Another important matter is the excretion route of the hormone or its metabolites, which can vary significantly between species (Bahr et al 2000, Bamberg et al 2001, Montiglio et al 2012. For some species the main excretion route is feces while some other may excrete the majority of particular hormone metabolites via urine .…”