Abstract:
In mammals, glucocorticoid (i.e. GC) levels have been associated with specific life-history
stages and transitions, reproductive strategies, and a plethora of behaviors. Assessment of
adrenocortical activity via measurement of glucocorticoid metabolites in feces (FGCM) has
greatly facilitated data collection from wild animals, due to its non-invasive nature, and thus
has become an established tool in behavioral ecology and conservation biology. The aim of
our study was to validate a fecal glucocorticoid assay for assessing adrenocortical activity
in meerkats (Suricata suricatta), by comparing the suitability of three GC enzyme immunoassays
(corticosterone, 11β-hydroxyetiocholanolone and 11oxo-etiocholanolone) in detecting
FGCM increases in adult males and females following a pharmacological challenge with
adrenocorticotropic hormone (ACTH) and biological stimuli. In addition, we investigated the
time course characterizing FGCM excretion, the effect of age, sex and time of day on
FGCM levels and assessed the potential effects of soil contamination (sand) on FGCM patterns.
Our results show that the group specific 11β-hydroxyetiocholanolone assay was
most sensitive to FGCM alterations, detecting significant and most distinctive elevations in
FGCM levels around 25 h after ACTH administration. We found no age and sex differences
in basal FGCM or on peak response levels to ACTH, but a marked diurnal pattern, with
FGCM levels being substantially higher in the morning than later during the day. Soil contamination
did not significantly affect FGCM patterns. Our results emphasize the importance
of conducting assay validations to characterize species-specific endocrine excretion patterns,
a crucial step to all animal endocrinology studies using a non-invasive approach.
Description:
SUPPORTING INFORMATION : S1 FILE. Group FGCM response (median ± SE, μg/g) to a natural attack on a group member
(ZIM005) that resulted in its permanent eviction. The victim showed the greatest FGCM
response to the event. Group FGCM levels returned to baseline levels after the male was
removed from the colony. “Within 48 h” represent FGCM levels measured within 2 days after
the attack on M5 took place. = p < 0.01 (Fig A). Average (median ± SE) baseline FGCM levels
(μg/g) in fecal samples deposited in the morning (AM), at midday (MD) and late afternoon (PM), as measured with the 11β-hydroxyetiocholanolone assay. N = 128 fecal samples from 13
individuals. = p < 0.05 (Fig B).
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