Abstract
Hair cortisol concentration (HCC) provides a long-term retrospective measure of hypothalamic–pituitary–adrenal axis activity, and is increasingly used to assess the life history, health and ecology of wild mammals. Given that sex, age, season and pregnancy influence HCC, and that it may indicate ongoing stress, we examined HCC in common marmosets (Callithrix jacchus) naturally inhabiting a hot and dry semi-desert like habitat, Caatinga, in northeastern Brazil. We trapped, measured, weighed, marked and collected shaved hair from the back of the neck of 61 wild marmosets during the wet and dry seasons. Using enzyme immunoassay, we found that HCC was higher in the dry season compared with the wet season among all age/sex classes. Females had significantly higher HCC than males, juveniles had higher HCC than adults, and reproductively active adult females and non-pregnant/non lactating adult females did not differ in HCC. There were no interaction effects of sex, age, group, or season on HCC. The magnitude of the effect of this extremely hot and dry environment (average yearly rainfall was only 271 mm) on HCC in common marmosets is difficult to ascertain as these animals are also experiencing a variety of other stressors. However, the elevated HCC seen in common marmosets during the 5–8 month dry season, suggests these primates face an extended period of heat, water and possibly nutritional stress, which appears to result in a high rate of juvenile mortality.
Highlights
Glucocorticoid hormones, of which cortisol is the most prominent in primates, are involved in multiple physiological processes, including the conversion of sugar, fat and protein stores into usable energy, and as an anti-inflammatory preventing tissue and nerve damage (Katsu & Iguchi, 2016)
Given that the CAT represents an extreme environment characterized by high heat and water stress and reduced plant productivity, especially during the extended dry season, we examined and compared Hair cortisol concentration (HCC), an indicator of overall health and hypothalamic–pituitary– adrenal (HPA) axis activity, among breeding female, non-breeding adult female, adult male and juvenile CAT common marmosets
Our most important findings were that across all age and sex classes, HCC was higher in the dry season compared with the wet season, female reproductive condition did not predict HCC, adult females had higher HCC than adult males, and juveniles had higher HCC than adults
Summary
Glucocorticoid hormones, of which cortisol is the most prominent in primates, are involved in multiple physiological processes, including the conversion of sugar, fat and protein stores into usable energy, and as an anti-inflammatory preventing tissue and nerve damage (Katsu & Iguchi, 2016). Cortisol is regulated by the hypothalamic–pituitary– adrenal (HPA) axis and its production is increased during periods of stress and elevated blood glucose levels Environmental stressors such as habitat fragmentation (Seltmann et al, 2017), climate extremes (Bechshoft et al, 2013; Fardi et al, 2018), reduced food availability and anthropogenic disturbances (Carlitz et al, 2016; Strasser & Heath, 2013) impact HPA-axis activity. If individuals encounter environmental, nutritional, or social stressors that persist for an extended period, HCC can provide useful information about physiological response and physiological condition
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