Abstract
Non-invasive stress and nutritional hormone analysis in relation to ecological and other biological indices have tremendous potential to address environmental disturbance impacts on wildlife health. To this end, we examined the relation between glucocorticoid (GC) and thyroid (T3) hormone indices of disturbance and nutritional stress in response to ACTH and TSH challenges in captive tigers, as well as how reproductive hormones vary by sex and reproductive condition. Glucocorticoid, thyroid, progesterone and androgen assays conducted on high-performance liquid chromatography separated fractions of biologically relevant fecal extracts revealed high cross-reactivity of these assays for their respective biologically relevant fecal hormone metabolites. Both adrenal and thyroid hormone metabolites were elevated in response to ACTH and TSH challenges. However, the adrenal and thyroid hormone responses to ACTH challenge were concurrent, whereas the adrenal response to TSH challenge was delayed relative to thyroid hormone elevation in both males and females. The concurrently elevated T3 in response to ACTH may serve to raise metabolic rate to maximize use of GC-mobilized glucose, whereas the relatively delayed GC rise following TSH challenge may be a response to glucose depletion due to increased metabolic rate associated with elevated T3. Progesterone, testosterone and androstenedione hormone metabolites were significantly elevated during gestation compared to lactation in a female monitored from conception through early lactation. Results suggest that the glucocorticoid, thyroid and reproductive hormone assays we tested can accurately measure the stress, nutrition and reproductive response from tiger feces, providing useful non-invasive tools to assess physiological responses to environmental stressors and their reproductive consequences in the wild.
Highlights
Fecal hormone analysis has become an increasingly valuable method for studying physiology of free-ranging animals
We examined the relation between glucocorticoid (GC) and thyroid (T3) hormone indices of disturbance and nutritional stress in response to adrenocorticotrophic hormone (ACTH) and thyroidstimulating hormone (TSH) challenges in captive tigers, as well as how reproductive hormones vary by sex and reproductive condition
The adrenal and thyroid hormone responses to ACTH challenge were concurrent, whereas the adrenal response to TSH challenge was delayed relative to thyroid hormone elevation in both males and females
Summary
Fecal hormone analysis has become an increasingly valuable method for studying physiology of free-ranging animals. The power of this approach stems from the accessibility of fecal samples and the variety of reproductive, stress and nutrition hormones that can be measured in fecal samples (Wasser et al, 1996, 2004, 2010, 2011, 2017; Creel et al, 2002; Hunt and Wasser, 2003; Keay et al, 2006; Gobush et al, 2008; Hayward et al, 2011). Temporal and spatial sample collection in relation to changes in environmental pressures can be used to partition impacts of psychological vs nutritional stress in relation to human disturbance (Wasser et al, 2017) as well as the effect they have on reproductive success such as pregnancy occurrence, health and failure (Gobush et al, 2008; Strasser and Heath, 2013). This study validates a number of fecal hormone measurements in captive tigers for eventual application to the wild, simultaneously examining the relation between GC and T3 secretion in response to both adrenocorticotrophic hormone (ACTH) and thyroidstimulating hormone (TSH) challenges
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