Katherine E. Wynne-Edwards

In full-term elective caesarian sections, fetal flow of adrenal substrate steroids to products differs by sex, with males (M) in molar equilibrium whereas females (F) add net molarity and synthesize more cortisol. Using the same sampling design, paired, full-term, arterial, and venous umbilical cord samples and intrapartum chart records were obtained at the time of vaginal delivery (N = 167, 85 male) or emergency C-section (N = 38, 22 male). Eight steroids were quantified by liquid chromatography coupled to tandem mass spectrometry (adrenal glucocorticoids [cortisol, corticosterone], sequential cortisol precursor steroids [17-hydroxyprogesterone, 11-deoxycortisol], cortisol and corticosterone metabolites [cortisone and 11-dehydrocorticosterone], and gonadal steroids [androstenedione, testosterone]). Fetal sex was not significant in any analytic models. Going through both phase 1 and phase 2 labor increased fetal adrenal steroidogenesis and decreased male testosterone relative to emergency C-sections that do not reach stage 2 of labor (ie, head compressions) and elective C-sections with no labor. Sum adrenal steroid molarity arriving in venous serum was almost double the equivalent metric for deliveries without labor. No effects of operative vaginal delivery were noted. Maternal regional anesthetic suppressed venous concentrations, and fetal synthesis replaced that steroid. Approximate molar equivalence between substrate pool depletion and net glucocorticoid synthesis was seen. Paired venous and arterial umbilical cord serum has the potential to identify sex differences that underlie antenatal programming of hypothalamic-pituitary-adrenal axis function in later life. However, stage 2 labor before the collection of serum, and regional anesthetic for the mother, mask those sex differences.

Measuring corticosterone in feathers has become an informative tool in avian ecology, enabling researchers to investigate carry‐over effects and responses to environmental variability. Few studies have, however, explored whether corticosterone is the only hormone expressed in feathers and is the most indicative of environmental stress. Essential questions remain as to how to compare hormone concentrations across different types of feathers and whether preening adds steroids, applied after feather growth. We used liquid chromatography coupled to tandem mass spectrometry to quantify a suite of 11 steroid hormones in back, breast, tail, and primary feathers naturally grown at overlapping time intervals by rhinoceros auklet Cerorhinca monocerata captive‐reared fledglings and wild‐caught juveniles. The captive‐reared birds were raised on either a restricted or control diet. Measured steroids included intermediates in the adrenal steroidogenesis pathway to glucocorticoids and the sex steroids pathway to androgens and estrogens. Corticosterone was detected in the majority of feathers of each type. We also detected cortisone in back feathers, androstenedione in breast feathers, and testosterone in primary feathers. Captive fledglings raised on a restricted diet had higher concentrations of corticosterone in all four feather types than captive fledglings raised on a control diet. Corticosterone concentrations were reliably repeatable across feather types when standardized for feather mass, but not for feather length. Of the seven hormones looked for in uropygial gland secretions, only corticosterone was detected in one out of 23 samples. We conclude that corticosterone is the best feather‐steroid biomarker for detection of developmental nutritional stress, as it was the only hormone to manifest a signal of nutritional stress, and that exposure to stress can be compared among different feather types when corticosterone concentrations are standardized by feather mass.

Hair analysis is emerging as a popular tool to examine stress and reproduction hormone levels in wild mammals. The reliability of this approach, however, depends on an understanding of steroid hormone incorporation into hair as well as appropriate validations. We reviewed studies that have examined steroid hormones in wildlife hair with the goal of summarizing the analytical, physiological, and biological evidence that this approach is meaningful. Accordingly, we differentiated among validations aimed at evaluating the reliability of the analytical method versus those designed to assess whether hormone levels in hair reflect physiologically meaningful processes in the target species. Our literature survey revealed that endogenous steroids have been examined in hair from 40 species of nonhuman animals across seven mammalian classes. Although the majority (85%) of 72 studies reported analytical validations of the method, physiological validations have only been reported for five species. Moreover, results of physiological validations were inconsistent among studies. This highlights the need for further research, carefully designed to differentiate between the multiple purported models of steroid incorporation into hair in species with different types of hair and different hair growth patterns. To complement our review of published studies, we present new data supporting a positive relationship between levels of the steroid, cortisol, in hair and blood across eight mammalian species. In addition, we present novel results from a laboratory‐based study showing variable hair growth in genetically identical laboratory mice that were kept under controlled conditions. Synthesis and applications. Collectively, this Review reveals substantial progress towards the validation of stress hormone assays in hair from a variety of wildlife species. Further validations of reproductive steroids, combined with appropriate physiological validations, would expand the potential applications of hair analyses in wildlife research. As a key example, physiological data can provide mechanistic insights into species’ responses to change and may therefore contribute to conservation planning.