|Correlates of urinary thyroid hormone and cortisol excretion in female Assamese macaques|
|Sonia Touitou1,2, Michael Heistermann3, Oliver Schülke1,2, Julia Ostner1,2. 1Dept. Behavioral Ecology, University of Göttingen , Göttingen, , Germany; 2Primate Social Evolution Group, German Primate Centre , Göttingen, , Germany; 3Endocrinology Laboratory, German Primate Centre, Göttingen, , Germany
Hormone metabolites offer a gateway to non-invasive assessment of energy status in wild species as they provide reliable cues on physiological adaptations when coping with energetic challenges. Here, we aim at investigating and comparing in wild female Assamese macaques the response of immunoreactive urinary triiodothyronine (iuT3, thyroid hormone regulating the basal metabolic rate) and urinary cortisol (iuC, main glucocorticoid involved in energy mobilization) to potential stressors. Combining physiological (382 urine samples) and behavioral (~3,000 focal hours of energy intake and expenditure) data on 42 adult females with climatic data, we validate both hormones as valuable markers of energy intake as low energy intake was associated with decreased iuT3 and increased iuC levels. Both iuT3 and iuC were affected by female reproductive status indicative of higher metabolic demands during late gestation. Neither hormone was affected by distance travelled, our measure of energy expenditure. Finally, iuC increased in colder temperatures, whereas uT3 did not. Our results add to the body of research on the role of different endocrine axes involved in energy allocation in wild mammals.