Abstract
Although the use of fecal glucocorticoid metabolite (FGCM) measurements as non-invasive biomarkers for the stress response in mammals has increased, few studies have been conducted in odontocetes. We investigated if animal sex, age, pregnancy or contextual variations (season, sampling time, enrichment, social separation and presence of visitors) influenced the FGCM concentrations in presumably healthy, captive and endangered Yangtze finless porpoises (YFPs, N = 4) and bottlenose dolphins (BDs, N = 3). For YFPs, the FGCM concentrations were influenced by season (p = 0.01), diurnal variation (p = 0.01) and pregnancy (p = 0.005). Contextual variables that were associated with increases in FGCM concentrations included social separations (p = 0.003) and numbers of visitors (p = 0.0002). Concentrations of FGCMs were lower (p = 0.001) after exposure to environmental enrichment. For BDs, enrichment was associated with reduced concentrations of FGCMs (p < 0.0001). The presence of visitors also influenced this species’ FGCM concentrations (p = 0.006). These results demonstrate that changes in the FGCM concentrations in YFPs and BDs may occur in response to contextual and social changes. In combination with other behavioral and physiological assessments, measurements of FGCMs may be a useful tool for monitoring cetacean welfare. Such monitoring may help researchers identify and better understand situations that may be stressful for animals and, therefore, improve management and husbandry. Furthermore, results from our study and inferences of the FGCM concentrations in cetaceans, and their potential relationship to stress, may be extrapolated to studies of free-ranging animals, which may help detect possible environmental or anthropogenic stressors that could be affecting these populations.
Highlights
In mammals, physiological or psychological stress is defined as unpredictable and/or uncontrollable stimuli [1] that activates the hypothalamic–pituitary–adrenal axis (HPA)
It has been suggested that measurements of fecal steroid metabolites may reflect the cumulative secretion and subsequent elimination of these hormones through the intestine over several hours and, as a result, may be less influenced by circadian rhythms compared to circulating steroids [71]. Despite this hypothesis and similar to circulating GCs in other odontocetes, we found an influence of diurnal variation on fecal glucocorticoid metabolite (FGCM) concentrations in the YFP, with significantly increased concentrations during the morning, supporting the concept that the YFP, like other cetaceans, experiences diurnal secretory patterns of GCs and indicates that cetacean fecal samples that will be used for hormonal analysis should be collected at the same time every day or should be balanced between different sampling times to avoid this bias
We showed that reproductive status, physical, contextual and social variables may influence the FGCM concentrations in both YFPs and BDs
Summary
Physiological or psychological stress is defined as unpredictable and/or uncontrollable stimuli [1] that activates the hypothalamic–pituitary–adrenal axis (HPA). Such stress results in the release of multiple hormones designed to help regulate physiological allostasis, principally through increasing metabolic activity and energy availability [2,3,4]. Elevated GC concentrations in response to repeated, chronic or long-term stimulation (several hours per day for weeks, months or longer) has been described as homeostatic overload [3,8] This homeostatic overload can negatively impact multiple physiological systems (e.g., immunological, reproductive, circulatory), animal growth and cognitive and/or behavioral functions [9,10,11,12,13,14]
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