Towards the validation of endogenous steroid testing in wildlife hair

Validation of enzyme immunoassays for quantifying sex steroid hormones in tropical screech owls (Megascops choliba)

Androgens and estrogens are steroid hormones that regulate reproductive processes in both males and females. Monitoring plasma levels of these steroids or their metabolites present in feces, offers diagnostic support for assessing the reproductive status of animals. Immunoassays are commonly used methods for quantifying these hormones, but their protocols require species-specific validation to ensure reliability. The objective of this study was to perform analytically and biologically validation of enzyme immunoassay (EIA) kits for measuring testosterone (T), estradiol (E2), faecal androgen metabolites (fAM), and faecal estrogenic metabolites (fEM) in the tropical screech owl (Megascops choliba). Serum and fecal samples were collected from six adult females and six males both before and during breeding season, with males' gonadal activity assessed using electroejaculation (EE). The parallelism test confirmed the immunogenic similarity of the antigens in the estradiol and testosterone standards and the antigens in the serum samples and fecal extracts of M. choliba. Additionally, the EIA kits displayed nearly 100% recovery rates, and showed coefficients of variation ranging from 8% to 14% at the intra-assay level and from 10% to 16% at the inter-assay level, underscoring result reliability and consistency. In males, the highest serum T and fAM levels were recorded concurrently with the presence of spermatozoa in samples collected via EE. Although females did not exhibit oviposition events, significantly higher E2 and fEM levels were observed in August compared to May, suggesting potential seasonal variations in estrogenic hormone production. Fecal androgen and estrogen levels were significantly different between sexes in August, with males having higher fAM and females having higher fEM levels. Overall, the immunoassays validated in this study were found to be efficient in diagnosing reproductive activity in owls.

Tracking reproductive events: Hoof growth and steroid hormone concentrations in hair and hoof tissues in moose (Alces alces)

Measurements of reproductive and stress-related hormones in keratinous tissues (e.g. hair, claws, hooves, baleen) can provide a record of stress and reproductive response in wildlife. We evaluated a method to collect keratin tissue from hooves of immobilized moose (Alces alces) and validated enzyme immunoassays for measuring cortisol and progesterone in hooves and hair. We also measured the annual growth and wear rates of moose hooves. Progesterone (range: 1.0-43.7 pg/mg) and cortisol (range: 0.05-2.9 pg/mg) were measurable and showed variation among hoof samples and moose. Pregnant females had twice as high progesterone concentrations (18.00 ± 3.73 pg/mg) from hoof sample locations post breeding compared to non-pregnant moose (9.40 ± 0.25 pg/mg). Annual hoof growth differed between the front (5.58 ± 0.12 cm) and rear (4.73 ± 0.13 cm) hooves and varied by season with higher growth rates during summer which decreased into autumn and winter. Adult female hooves represented between 1.6 and 2.1 years of growth and included up to two reproductive cycles. We established a method to estimate hoof growth rate and applied this to postmortem samples and were able to detect previous pregnancies. Shoulder guard hairs grew between August and March including during late gestation; however, hair progesterone concentrations (range: 2-107.1 pg/mg) were not related to reproductive state. Hair cortisol concentrations in our study (range: 0.2-15.9 pg/mg) were within the range of values previously reported for cervids. Our study supports the use of hooves for longitudinal sampling and measuring reproductive and stress-related hormones, providing a new tool for tracking reproductive events and understanding what variables may contribute to population level changes in reproduction.

Stress in the city? Coyote hair cortisol varies with intrinsic and extrinsic factors within a heavily urbanized landscape

Wildlife living in proximity to people are exposed to both natural and anthropogenic factors that may influence cortisol production associated with stress response. While some species, including coyotes (Canis latrans), have become commonplace in developed areas throughout North America, urban individuals still must navigate ever-changing, novel environments and cope with frequent disturbance. Given that coyotes are relatively large predators compared to most other urban wildlife, they face unique pressures such as crossing roadways to use suitable habitat fragments and are at a greater risk of being detected and experiencing negative human interactions. To assess whether urbanization influences hypothalamic-pituitary-adrenal axis activity in free-ranging coyotes, we analyzed cortisol concentration in hair samples from 97 coyotes residing across the urbanization gradient within the Greater Chicago Metropolitan area. As the proportion of developed landcover within coyote home ranges increased, coyotes experienced more stress. Body condition and social status also had strong relationships with stress. Animals in poorer body condition experienced more stress and subordinate coyotes experienced less stress than alphas. We also found some evidence that stress varied seasonally and among different age classes. Understanding how intrinsic and extrinsic factors influence endocrine activity in urban carnivores is vital for predicting how hormone production and related behavioral patterns may change in future populations as more areas become developed.

Free-living gerbils with higher testosterone take fewer risks

Among the physiological differences between the sexes are circulating androgen levels. Testosterone (T) is an androgen that has been linked to aggression and risk-taking in male vertebrates, so that males with higher T are generally more aggressive and take more risks. In females, T is not often measured, and its relationship with behaviour has been less studied. The costs of elevated T are assumed to be higher for reproductive females, while the benefits higher for males. Here, we tested the association between endogenous T and risk-taking behaviours in both males and females under well-studied experimental settings in free-living Baluchistan gerbils (Gerbillus nanus; Gn). In addition, we experimentally elevated Gn T levels using implants and measured risk-taking behaviour. Surprisingly, we found that there were no differences in the association between T and risk-taking behaviours between males and females, and that in both sexes, Gn with higher T levels took fewer risks. We also found that Gn spent equal time foraging between risky (open habitat) and safe (under a bush) experimental food patches. We expected Gn, which are nocturnal, to take fewer risks during full moon nights, but found that Gn were more active during moon lit nights than during dark (new moon) nights. This study demonstrates that T has many functions, and that its effects are complex and often unpredictable. It also shows that hypotheses regarding the propensity to take risks under specific coverage and light regimes are not universal, and likely include variables such as species, environment, context, and predator-specific behavioural strategies.

Hair glucocorticoids are not a historical marker of stress - Exploring the time-scale of corticosterone incorporation into hairs in a rat model

Hair glucocorticoids are increasingly popular biomarkers, used across numerous research fields, and studied species, as a measure of stress. Although they are suggested to be a proxy of the average HPA axis activity spanning a period of weeks or months into the past, this theory has never been tested. In the present study, adrenalectomized rats with no endogenous (adrenal) glucocorticoid production were used to study how circulating glucocorticoid levels would be reflected in the glucocorticoid levels found in hair samples. By dosing the animals daily with high levels of corticosterone for seven days, while sampling hairs before, during, and after treatments, a timeline for glucocorticoid uptake into hairs was constructed. This kinetic profile was compared to two hypothetical models, and the theory that hair glucocorticoids are a record of historical stress had to be rejected. Corticosterone concentrations in hairs were found to increase within three hours of the first injection, the highest concentrations were found on the seventh day of treatments, and the decrease in concentrations post-treatment suggests rapid elimination. We speculate that hair glucocorticoid levels can only be used to characterize a stress-response for a few days following a postulated stressor. An updated model, where glucocorticoids diffuse into, along, and out of hairs needs to be adopted to reconcile the experimentally obtained data. The inescapable consequence of this updated model is that hair glucocorticoids become a marker of - and can only be used to study - recent, or ongoing, stress, as opposed to historical events, weeks or months in the past.

The interaction between cortisol and testosterone predicts leadership within rock hyrax social groups

Group movement leadership is associated with higher risks for those in the front. Leaders are the first to explore new areas and may be exposed to predation. Individual differences in risk-taking behavior may be related to hormonal differences. In challenging circumstances, such as risk-taking leadership that may pose a cost to the leader, cortisol is secreted both to increase the likelihood of survival by restoring homeostasis, and to mediate cooperative behavior. Testosterone too has a well-established role in risk-taking behavior, and the dual-hormone hypothesis posits that the interaction of testosterone and cortisol can predict social behavior. Based on the dual-hormone hypothesis, we investigated here whether the interaction between testosterone and cortisol can predict risk-taking leadership behavior in wild rock hyraxes (Procavia capensis). We used proximity loggers, observations, and playback trials to characterize hyrax leaders in three different leadership contexts that varied in their risk levels. In support of the dual-hormone hypothesis, we found that cortisol and testosterone interactions predict leadership that involves risk. Across different circumstances that involved low or high levels of risk, testosterone was positively related to leadership, but only in individuals (both males and females) with low levels of cortisol. We also found an interaction between these hormone levels and age at the low-risk scenarios. We suggest that the close social interactions and affiliative behavior among hyrax females within small egalitarian groups may make female leadership less risky, and therefore less stressful, and allow female leaders to influence group activities.

Are hair cortisol levels dependent on hair growth rate? A pilot study in rhesus macaques

Research incorporating the analysis of glucocorticoids, specifically cortisol, in hair samples has exploded over the past 10-15 years, yet factors contributing to the accumulation of cortisol in hair are not yet fully characterized. In particular, it is not clear whether cortisol accumulation in hair is dependent on hair growth rate, a possibility raised by prior rodent studies reporting glucocorticoid-mediated inhibition of hair growth. Using rhesus macaque monkeys (Macaca mulatta), an extensively studied nonhuman primate species, the present pilot study evaluated the hypothesis that hair cortisol accumulation is inversely related to hair growth rate (i.e., slower hair growth leading to elevated cortisol levels). Hair samples were collected from 19 adult female macaques and 17 infants (9 males) 3 months apart using a shave-reshave procedure from the same site below the posterior vertex of the scalp. The second hair samples were measured to the nearest millimeter (mm) for growth rate over the previous 3 months and assayed for hair cortisol concentrations (HCCs) using enzyme immunoassay. Because of the possibility of age-related differences in hair growth rate, correlational analyses were performed separately for adults and infants to determine whether HCC values were associated with growth rate in each age group. These analyses revealed that neither group displayed a significant correlation of HCCs with hair growth. The results additionally showed that overall, adults had a faster hair growth rate than infants and, as expected from previous studies, had lower HCCs than infants. Our results suggest that higher HCCs within the non-stress range do not result from cortisol-mediated inhibition of hair growth. Moreover, similarities between humans and macaque monkeys in both HPA axis regulation and hair growth rates argue that these findings are relevant for human hair cortisol studies. Extrapolation to other species in which the features of hair growth and the relevant regulatory mechanisms are less well understood should be done with caution.

Ultra-performance convergence chromatography tandem mass spectrometry analysis of adrenal and gonadal steroid hormones in southern white rhinoceros(Ceratotherium simum simum) faeces and serum

Steroid hormone analysis is routinely undertaken in the assessment of stress response and reproductive function in the management of both captive and free-ranging wildlife species. Faecal samples have become the preferred sample type for analysis as collection is non-invasive and easily assessable. These investigations are generally aimed at aiding successful translocations, enhanced survival outcomes in captivity and improvement of reproductive rate. Immunoassays are the most common approach in the analysis of hormones, particularly in the case of the southern white rhinoceros (Ceratotherium simum simum). Non-specificity, attributed to structural similarity of steroid metabolites impedes accurate evaluations which can be eliminated by chromatographic techniques which are more specific, selective and provide comprehensive analyses. This study developed and validated three methods using ultra-performance convergence chromatography tandem mass spectrometry for the assessment of classical androgens, progestogens and adrenal steroids, as well as the C11-oxy androgens and C11-oxy progestogens in serum and faeces from white rhinoceros. The limit of detection and quantification were determined for each steroid, parameters such as accuracy (<19.8 % RSD) and precision (<20.2 % RSD) were established with recovery, matrix effect, and process efficiency within acceptable limits. Subsequent analysis of serum and faecal samples from five white rhinoceros identified novel steroids for the first time in this species. In addition to the classical adrenal steroids, the following C11-oxy steroids were detected in faecal samples: 11α-hydroxydihydroprogesterone (168 ng/g), 11α-hydroxyprogesterone (125.9 ng/g), 11β-hydroxyprogesterone (210.2 ng/g) and 11-ketoandrostenedione (3.3-19.6 ng/g) with 11-deoxycortisol being the major glucocorticoid (24.2-67.3 ng/g) together with 21-deoxycortisone (40.7 ng/g) and deoxycorticosterone (7.6-14.6 ng/g). In serum samples 11β-hydroxyandrostenedione (0.35-2.34 ng/mL) and 11β-hydroxytestosterone (0.18-1.62 ng/mL) were the predominant androgens with cortisol (5.8-20.5 ng/mL), the predominant glucocorticoid, while corticosterone, 18-hydroxycorticosterone and aldosterone were also detected. These methods can be applied independently to assess either androgens, progestogens, or adrenal steroid panels or in combination to assess the cohort of gonadal and adrenal steroids in faeces and/or serum, in southern white rhinoceros as well as other wildlife species. Analysis would enable the accurate assessment of reproductive health and stress responses while also distinguishing between stress and distress thus contributing to the conservation of wildlife species.

Physical Injuries and Hair Corticosterone Concentration in Rabbit Kits from Single- and Group-Housed Does Kept on a Commercial Farm

In intense breeding programs, rabbits are exposed to numerous stress factors which could affect their welfare and health. It has been suggested that group housing is more comfortable for does and similar to the living conditions of European wild rabbits. In this study, we compared three different housing systems—single housing; housing in pairs; and housing in groups of three does—to test whether there is a measurable impact on skin lesions, health, and hair corticosterone concentration (HCC) of their kits. The number of kits with lesions increased with the number of does kept together. The probability of kits getting injured was higher in groups of three does than in pens of single-housed does (p = 0.041). When does were pair-housed, kits seemed to have fewer disease symptoms compared to the other treatments. Concerning HCC of kits, there was no significant difference between the housing systems (p > 0.05). The mean HCC of kits was 2.94 pg/mg, while pair housing had the lowest HCC (2.59 pg/mg). This study focused on the welfare of kits from group-housed does. From this perspective, pair housing of does may be appropriate to allow social interaction between does without unduly affecting the welfare of their kits.

Preliminary Investigation into Developing the Use of Swabs for Skin Cortisol Analysis for the Ocean Sunfish (Mola mola)

Simple Summary

Zoos and aquaria play an important role in preventing the mass extinction of wildlife through public awareness of conservation issues and providing a safe haven for wildlife populations. Because aquatic populations face many challenges due to pollution and global warming, it is important to develop an understanding of how species can cope with their environment whether it be in the wild or under human care. Here, we were interested in developing non-invasive methods to study fish stress physiology. We use the unique ocean sunfish (Mola mola) to develop the use of skin swabs to measure the stress hormone, cortisol. We used known times of stress including when a mola was injured or ill and during acclimation to the Monterey Bay Aquarium. We found that cortisol increased initially within the first month of being admitted to the aquarium, but returned to normal values afterward. Molas also had elevated cortisol when being treated for an injury or illness. This is the first step in the development of the use of skin swabs to collect samples for stress analysis in the mola. Additional biochemical analysis is needed to confirm these results and allow this method to be applied to other species of fish.

Abstract

The ocean sunfish (mola; Mola mola) is the heaviest bony fish in the world. This slow-moving fish often is injured by fishing boats that use drift gillnets attributing to its listing as Vulnerable by the IUCN. The Monterey Bay Aquarium (Monterey, CA, USA) has a program that brings in smaller molas from the ocean and acclimates them for an exhibit. When they grow too large for the million-gallon Open Seas exhibit, they are returned to Monterey Bay through a “reverse” acclimatization. Our overall goal was to use skin swabs to evaluate mola stress physiology to better understand the effects of this program. Our objectives were to validate this non-invasive method by taking opportunistic swabs throughout acclimatization and during stressful events. We swabbed each individual (n = 12) in three different body locations. Swabs were analyzed using a cortisol enzyme immunoassay. We averaged the three swabs and examined the absolute change of cortisol from the first taken upon handling to during treatments and the different acclimation stages. We considered elevated cortisol concentrations to be ≥1.5-fold higher than the first sample. Overall, mean (±SEM) cortisol varied among individuals (564.2 ± 191.5 pg/mL swab (range, 18.3–7012.0 pg/mL swab). The majority (four of six) of molas swabbed within the first week or month had elevated skin cortisol compared to their first sample. All seven molas that were being treated for an injury or illness had elevated skin cortisol (range, 1.7- to 127.6-fold higher) compared to their post-acclimation sample. This is the first step in validating the use of non-invasive skin swabs for glucocorticoid analysis in the mola. Further biochemical analysis is needed to determine the specific steroids that are being measured.

Can spines tell a story? Investigation of echidna spines as a novel sample type for hormone analysis in monotremes

The short-beaked echidna (Tachyglossus aculeatus) is a monotreme endemic to Australia and New Guinea, and is the most widespread native mammal in Australia. Despite its abundance, there are considerable gaps in our understanding of echidna life history such as reproductive cycles in both sexes, patterns of stress physiology, and possible seasonal changes in metabolism. Slow-growing integumentary sample types comprised of keratin (hair, claw, etc.) have been used in other wildlife to assess these questions via analysis of longitudinal patterns in steroid and thyroid hormones that are deposited in these tissues as they grow. Hairs and spines comprise the pelage of echidnas, the spines being keratinized structures homologous to hair. Thus, echidna spines could be a viable sample type for hormone analysis contributing to a better understanding of the biology of echidnas. The aim of this work was to determine whether steroid hormones are detectable in echidna spines, to perform assay validations, and to establish a protocol for extracting and quantifying hormones in echidna spines using commercially available assay kits. We also inspected cross-sectioned spines using light and electron microscopy for any evidence of annual growth markers that might enable inferences about spine growth rate. Corticosterone, progesterone, estradiol, and testosterone were detectable in all samples, and echidna spine extract passed standard assay validations (parallelism and accuracy), indicating that commercially available assay kits can quantify hormones accurately in this sample type. No visible growth marks were identified in the spines and thus spine growth rate is currently unknown. Echidna spines show promise as a novel matrix from which hormones can be quantified; next steps should involve determination of spine annual growth rate, possible seasonal changes in growth rate, and persistence of spines over time in order to perform physiological validations, i.e., relationship between physiological status and hormone concentrations in spines.

Evaluating the use of hair as a non-invasive indicator of trace mineral status in woodland caribou (Rangifer tarandus caribou)

Trace mineral imbalances can have significant effects on animal health, reproductive success, and survival. Monitoring their status in wildlife populations is, therefore, important for management and conservation. Typically, livers and kidneys are sampled to measure mineral status, but biopsies and lethal-sampling are not always possible, particularly for Species at Risk. We aimed to: 1) determine baseline mineral levels in Northern Mountain caribou (Rangifer tarandus caribou; Gmelin, 1788) in northwestern British Columbia, Canada, and 2) determine if hair can be used as an effective indicator of caribou mineral status by evaluating associations between hair and organ mineral concentrations. Hair, liver, and kidney samples from adult male caribou (n_Hair = 31; n_Liver, n_Kidney = 43) were collected by guide-outfitters in 2016–2018 hunting seasons. Trace minerals and heavy metals were quantified using inductively-coupled plasma mass spectrometry, and organ and hair concentrations of same individuals were compared. Some organ mineral concentrations differed from other caribou populations, though no clinical deficiency or toxicity symptoms were reported in our population. Significant correlations were found between liver and hair selenium (rho = 0.66, p<0.05), kidney and hair cobalt (rho = 0.51, p<0.05), and liver and hair molybdenum (rho = 0.37, p<0.10). These findings suggest that hair trace mineral assessment may be used as a non-invasive and easily-accessible way to monitor caribou selenium, cobalt, and molybdenum status, and may be a valuable tool to help assess overall caribou health.

Hair cortisol concentration reflects the life cycle and management of grey wolves across four European populations

The grey wolf (Canis lupus) persists in a variety of human-dominated landscapes and is subjected to various legal management regimes throughout Europe. Our aim was to assess the effects of intrinsic and methodological determinants on the hair cortisol concentration (HCC) of wolves from four European populations under different legal management. We determined HCC by an enzyme-linked immune assay in 259 hair samples of 133 wolves from the Iberian, Alpine, Dinaric-Balkan, and Scandinavian populations. The HCC showed significant differences between body regions. Mean HCC in lumbar guard hair was 11.6 ± 9.7 pg/mg (range 1.6–108.8 pg/mg). Wolves from the Dinaric-Balkan and Scandinavian populations showed significantly higher HCC than Iberian wolves, suggesting that harvest policies could reflected in the level of chronic stress. A significant negative relationship with body size was found. The seasonal, sex and age patterns are consistent with other studies, supporting HCC as a biomarker of chronic stress in wolves for a retrospective time frame of several weeks. Our results highlight the need for standardization of sampling and analytical techniques to ensure the value of HCC in informing management at a continental scale.

Steroid hormones in hair and fresh wounds reveal sex specific costs of reproductive engagement and reproductive success in wild house mice (Mus musculus domesticus)

Not only males but also females compete over reproduction. In a population of free-living house mice (Mus musculus domesticus), we analyzed how (metabolic) costs of aggressive interactions (reflected in fresh wounds and long-term corticosterone concentrations in hair) are predicted by individual reproductive physiology and reproductive success in males and females. Over eight years, we studied wounds and reproduction of more than 2800 adults under naturally varying environmental conditions and analyzed steroid hormones from more than 1000 hair samples. Hair corticosterone were higher and wounds more frequent in males than females. In males, wound occurrence increased with increasing breeding activity in the population, without affecting hair corticosterone levels. Unexpectedly, individual male reproductive success did not predict wounds, while hair corticosterone increased with increasing levels of hair testosterone and reproductive success. High corticosterone in hair of males might therefore reflect metabolic costs of fighting over reproduction. In females, hair corticosterone was generally lower than in males and high levels did not impede pregnancy. Reproductive investment (reflected in hair progesterone) was dissociated from reproductive success. Occasional wounds in females indicated individuals without recent reproductive success and revealed reproductive competition, presumably driven by instability in the social environment. In both sexes, corticosterone increased with age, but there was no evidence that received overt aggression, as indicated by wounds or elevated corticosterone, suppressed reproductive physiology. Our results diverge from laboratory findings and emphasize the need to also study animals in their natural environment in order to understand the complexity of their behavioral physiology.

Validation and utility of hair cortisol analysis as a measure of long-term physiological stress in the Pallas's squirrel Callosciurus erythraeus

In various mammalian species, there has been an increase in the use of hair cortisol analysis to evaluate long-term stress. This trend is because of some advantages relative to the standard tools, such as hormone analysis using blood, urine, or feces. Here, I carried out assay validation and adrenocorticotrophic hormone (ACTH) challenge to measure long-term stress in Pallas's squirrel Callosciurus erythraeus. In addition, I investigated the effects of sex, body condition, season, and reproductive conditions on hair cortisol concentrations (HCC) in free-living individuals. The assay validation was reported in this study. Hair cortisol concentrations in squirrels given repeated ACTH injections were significantly higher than those that received a single-ACTH injection and a saline injection. I found a negative effect of body condition on adult HCC. In contrast, body condition had a positive effect on HCC in juveniles. I found no effects of other factors in either adult or juvenile squirrels. Furthermore, although I investigated whether reproductive conditions, such as pregnancy, lactation, and non-breeding in females or testis size in males, affected HCC, I found that there were no effects of reproductive conditions. This study validated the assay and utility of hair cortisol analysis to assess long-term stress, and continuous investigation of the relationship between HCC and fitness is important for determining whether hair cortisol analysis is a reliable method for estimating population health in Pallas's squirrels.

Do boars compensate for hunting with higher reproductive hormones?

The predation-stress hypothesis has been proposed as a general mechanism to explain the negative effect of predation risk on reproduction, through a chronic activation of the stress response. However, in some cases, stress appears to augment the reproductive potential of mammals. Wild boar (Sus scrofa) populations are on a rise worldwide, despite the high hunting pressure that they are exposed to. This hunting pressure instigates, among other effects, earlier sexual maturity in juvenile females, leading to the shortening of wild boars' generation time. The mechanism that underlies this earlier sexual maturity under high hunting pressure has not been examined to date. To explore the physiological effects that hunting has on the reproductive system and whether the stress response is involved, we examined steroid hormone levels in the hair of female wild boars in northern Israel, comparing populations exposed to high and low hunting pressure. Furthermore, we compared steroid levels in the hair of female wild boars that were roaming alone or as a part of a group. We found no hormonal signs of stress in the hunted boars. Cortisol levels were low in both the high and low hunting-pressure groups. Yet, progesterone levels were higher in females that were exposed to high hunting pressure. Females roaming in a group also had higher progesterone levels compared to females that were alone, with no distinguishable differences in cortisol levels. These elevations in reproductive hormones that were associated with hunting may lead to a higher reproductive potential in female wild boars. They further show that high hunting pressure does not necessarily lead to chronic stress that impairs the reproductive potential of female wild boars. This data suggests that a reproductive hormonal response may be one of the factors leading to the rapid wild boars population growth worldwide, despite the high hunting pressure.

Analysis of hair steroid hormones in polar bears (Ursus maritimus) via liquid chromatography-tandem mass spectrometry: comparison with two immunoassays and application for longitudinal monitoring in zoos

Analysis of hair cortisol concentrations (HCCs) is a promising method for monitoring long-term stress in mammals. However, previous measurements of HCCs in polar bears (Ursus maritimus) have yielded highly variable results, which are likely due to different methodological approaches. In this study, hair samples of zoo-housed polar bears were analyzed for cortisol with two independent immunoassays [an enzyme-linked immunoassay (EIA) and a chemiluminescence assay (CLIA)] and liquid chromatography-tandem mass spectrometry (LC-MS/MS). HCC measurements depended significantly on assay type applied, sample processing (cutting vs. powdering hair) and their interaction. Best agreement was observed between LC-MS/MS and CLIA (R² = 0.81 for powdered hair) and sample processing had a minor, albeit significant, effect on obtained HCC measurements in these assays (R² > 0.9). EIA measurements were consistently higher than with the other assays. HCC measurement was validated biologically for CLIA and LC-MS/MS in one male polar bear that experienced considerable stress for a prolonged period of time (> 18 weeks). Subsequently, by using the validated LC-MS/MS the measurement of cortisol could be complemented by the analysis of other steroids including cortisone, testosterone and progesterone levels from hair samples collected over a 9-month period (5-13 months) from six zoo-housed polar bears (five males, one female). No seasonal steroid variation was observed except in male progesterone levels. For all steroids except cortisone, a strong body region effect (neck or paw) was observed. Cortisol and cortisone, as well as progesterone and testosterone, concentrations were positively correlated. We show that hair steroid concentrations can be used to longitudinally measure stress and reproductive hormone axes in polar bears. The data established herein provide important basic information regarding methodology and study design for assessing hair steroid hormones.

Landscape of stress: Tree mortality influences physiological stress and survival in a native mesocarnivore

Climate change and anthropogenic modifications to the landscape can have both positive and negative effects on an animal. Linking landscape change to physiological stress and fitness of an animal is a fundamental tenet to be examined in applied ecology. Cortisol is a glucocorticoid hormone that can be used to indicate an animal's physiological stress response. In the Sierra Nevada Mountains of California, fishers (Pekania pennanti) are a threatened mesocarnivore that have been subjected to rapid landscape changes due to anthropogenic modifications and tree mortality related to a 4-year drought. We measured cortisol concentrations in the hair of 64 fishers (41 females, 23 males) captured and radio-collared in the Sierra National Forest, California. We addressed two main questions: (1) Is the physiological stress response of fishers influenced by anthropogenic factors, habitat type, canopy cover, and tree mortality due to drought in their home range? (2) Does the physiological stress response influence survival, reproduction, or body condition? We examined these factors within a fisher home range at 3 scales (30, 60, 95% isopleths). Using model selection, we found that tree mortality was the principle driver influencing stress levels among individual fishers with female and male fishers having increasing cortisol levels in home ranges with increasing tree mortality. Most importantly, we also found a link between physiological stress and demography where female fishers with low cortisol levels had the highest annual survival rate (0.94), whereas females with medium and high cortisol had lower annual survival rates, 0.78 and 0.81, respectively. We found no significant relationships between cortisol levels and body condition, male survival, or litter size. We concluded that tree mortality related to a 4-year drought has created a "landscape of stress" for this small, isolated fisher population.

Qiviut cortisol reflects hypothalamic-pituitary-adrenal axis activity in muskoxen (Ovibos moschatus)

Muskoxen (Ovibos moschatus) are increasingly exposed to a broad diversity of stressors in their rapidly changing Arctic environment. There is an urgent need to develop validated tools to monitor the impact of these stressors on the hypothalamic-pituitary-adrenal (HPA) axis activity of muskoxen to help inform conservation actions. Here, we evaluated whether muskox qiviut (dense wooly undercoat) cortisol accurately reflects changes in HPA axis activity. Two repeated pharmacological challenges, involving weekly administrations of saline (control group) or adrenocorticotropic hormone (ACTH) during five consecutive weeks, were done on captive muskoxen, in winter (no hair growth) and summer (maximum hair growth). Pre-challenge qiviut cortisol levels were significantly higher in the shoulder than in the neck, but neither differed from rump concentrations. Qiviut cortisol levels significantly increased (p < 0.001) in response to the administration of ACTH during the hair growth phase, but not in the absence of growth (p = 0.84). Cortisol levels in the qiviut segment grown during the summer challenge increased significantly over a six-month period in the ACTH-injected muskoxen with a similar trend occurring in the control animals. Finally, cortisol levels in shed qiviut were significantly higher and not correlated to those of fully grown qiviut shaved three months earlier. Our results show that cortisol is deposited in qiviut during its growth and that qiviut cortisol can thus be used as an integrated measure of HPA axis activity over the period of the hair's growth. Differences in qiviut cortisol across body regions, significant differences in qiviut segments over time, and differences between shed qiviut versus unshed qiviut, highlight the importance of consistent design and methodology for sample collection and analyses in order to account for sources of variation when using qiviut cortisol as a biomarker of HPA axis activity in muskoxen.

Cortisol levels in blood and hair of unanesthetized grizzly bears (Ursus arctos) following intravenous cosyntropin injection

Hair cortisol concentration (HCC) is being used increasingly to evaluate long‐term stress in many mammalian species. Most of the cortisol is assumed to passively diffuse from circulating blood into hair follicles and gradually accumulate in growing hair. However, our research with free‐ranging grizzly bears (Ursus arctos) suggests HCC increases significantly within several hours following capture, a time too brief to be explained by this mechanism alone. In this study with captive grizzly bears, we sought to determine if a brief spike in blood cortisol concentration, thus mimicking a single stressful event, would cause an increase in HCC over a 7‐day period. To do this, we administered a single intravenous dose (5 μg/kg) of cosyntropin to three captive unanaesthetised adult female grizzly bears on two occasions, during April when hair growth was arrested and during August when hair was growing. In both trials, the cosyntropin caused a two‐fold or greater increase in serum cortisol levels within 1 hr but did not appear to influence HCC at 1, 48, and 168 hr following cosyntropin administration. We conclude the cosyntropin‐induced cortisol spike was likely insignificant when compared to the adrenocortical response that occurs in free‐ranging bears when captured. We suggest further study with a larger sample of captive bears to evaluate the combined effects of anaesthesia and multiple doses of cosyntropin administered over several hours would better simulate the adrenocortical response of free‐ranging grizzly bears during capture.

Using hair cortisol analysis to understand the biological factors that affect black-footed ferret (Mustela nigripes) stress physiology

The black-footed ferret (Mustela nigripes) was driven to near extinction due to habitat loss and an introduced disease, sylvatic plague (Yersinia pestis). After 35 years of breeding in ex situ facilities, the black-footed ferret has been experiencing infertility with seminal traits declining in males and only about a third of breeding-aged females are whelping. Our goal was to use hair cortisol analysis to determine if the ex situ population was experiencing chronic stress that was affecting reproduction by comparing captive ferrets to wild individuals. Our specific objectives were to (i) compare hair cortisol concentrations (HCCs) between age classes (juveniles versus adults), (ii) compare the HCCs of in situ and across different ex situ facilities and (iii) determine the relationship between HCCs and reproductive success. Overall, wild juveniles had higher HCC than wild adults. Our generalized linear mixed model determined that the parameters that best predict HCC for adults were the interactions among sex, in situ versus ex situ facilities and season. During both seasons, wild females had higher HCCs compared to the ex situ females. During the breeding season, male HCCs across breeding facilities varied and males at the breeding facility with the largest ferret habitats had HCCs similar to wild males. At one breeding facility, HCC was higher in males that sired compared to those that did not sire. In conclusion, ex situ ferrets do not have higher HCC than wild individuals when controlling for season and ex situ habitat size, and ex situ males with higher HCC tended to sire. This suggests that HCC may be metabolically driven and/or that low HCC may be an indication of hypothalamus-pituitary-adrenal axis dysregulation and warrants further investigation both for laboratory validation and biological relevance.

Small mammal glucocorticoid concentrations vary with forest fragment size, trap type, and mammal taxa in the Interior Atlantic Forest

Species that live in degraded habitats often show signs of physiological stress. Glucocorticoid hormones (e.g., corticosterone and cortisol) are often assessed as a proxy of the extent of physiological stress an animal has experienced. Our goal was to quantify glucocorticoids in free-ranging small mammals in fragments of Interior Atlantic Forest. We extracted glucocorticoids from fur samples of 106 small mammals (rodent genera Akodon and Oligoryzomys, and marsupial genera Gracilinanus and Marmosa) from six forest fragments (2–1200 ha) in the Reserva Natural Tapytá, Caazapá Department, Paraguay. To our knowledge, this is the first publication of corticosterone and cortisol levels for three of the four sampled genera (Akodon, Oligoryzomys, and Marmosa) in this forest system. We discovered three notable results. First, as predicted, glucocorticoid levels were higher in individuals living withing small forest fragments. Second, animals captured live using restraint trapping methods (Sherman traps) had higher glucocorticoid levels than those animals captured using kill traps (Victor traps), suggesting that hair glucocorticoid measures can reflect acute stress levels in addition to long-term glucocorticoid incorporation. These acute levels are likely due to urinary steroids diffusing into the hair shaft. This finding raises a concern about the use of certain trapping techniques in association with fur hormone analysis. Finally, as expected, we also detected genus-specific differences in glucocorticoid levels, as well as cortisol/corticosterone ratios.

Exploring the Utility of Hair Endocannabinoids for Monitoring Homeostasis in Bonobos

AbstractQuantifying physiological challenges has gained increasing importance in evolutionary biology, behavioral physiology, and conservation. One matrix that is particularly useful for obtaining long-term records of physiological changes in mammals is hair. Potential markers are components of the endocannabinoid (EC) system, which regulates homeostasis of the brain as well as the endocrine and immune systems. Here, we present results from the first study to measure ECs (anandamide [AEA], 2-archidonyl glycerol [2-AG]) and EC-like compounds (N-palmitoylethanolamine [PEA], N-oleoylethanolamine [OEA], N-stearoylethanolamine [SEA]) in the hair of a nonhuman primate. We found that AEA, SEA, PEA, and OEA can be reliably measured in hair samples. When comparing the measurements of hair from different body parts, we found that variations of some analytes suggest that hair location is likely to affect results. For changes in health status, measurements of ECs and EC-like compounds reflected differences at both intra- and interindividual levels. We concluded that the EC system potentially provides novel tools to assess well-being, health status, and metabolic stress-not only in the hair of humans but also in that of domestic and wild animals. Measuring changes in ECs and EC-like compounds may improve the long-term monitoring of health status in captive and wild primates and may serve as a useful measure in animal welfare programs.

Spatial patterns of the exposure-response relationship between mercury and cortisol in the fur of river otter (Lontra canadensis)

Fur has been validated as a useful biomarker medium for chemical exposures and biological responses in wildlife. Mercury (Hg) is known to act as an endocrine disruptor by altering brain neurochemistry. In this study, we investigated the spatial patterns of relationships between total Hg (THg) and cortisol in the fur of river otter (Lontra canadensis). Geotagged fur samples were obtained from a wildlife biomonitoring program (n = 72) and the North American Fur Auction (n = 37) between 2014 and 2017. Fur THg was measured using direct thermal decomposition and fur cortisol was measured using an enzyme-linked immunosorbent assay (ELISA). The average fur THg concentration was 11.50 ± 12.40 μg/g fur weight (f.w.), and the fur cortisol concentration was 5.71 ± 8.24 pg/mg. Results from the global ordinary least squares regression show no relationship between THg and fur cortisol concentrations. However, both Hg and cortisol were heterogeneously distributed across the landscape. When a localized geographically weighted regression (GWR) was used, a geographically distinct bi-phasic relationship was observed. We suggest this bi-phasic relationship is associated with a threshold THg concentration, beyond which, there was a negative association with measured fur cortisol. Results of a break-point analysis, with one break, indicate that the threshold is 16 ± 1.27 μg/g f. w of THg in fur. This research highlights the need to use appropriate spatial methods when assessing exposure-response relationships in wildlife across large geographical areas. The identified threshold can be used for regulatory purposes.

Methodological Considerations for Using Fecal Glucocorticoid Metabolite Concentrations as an Indicator of Physiological Stress in the Brown Bear (Ursus arctos)

Reliable methods to measure stress-related glucocorticoid responses in free-ranging animals are important for wildlife management and conservation. Such methods are also paramount for our ability to improve our knowledge of the ecological consequences of physiological processes. The brown bear (Ursus arctos) is a large carnivore of ecological and cultural importance and is important for management. Here, we provide a physiological validation for an enzyme immunoassay (EIA) to quantify glucocorticoid metabolites in brown bear feces. We also provide an evaluation of the effects of sample exposure to ambient temperature on measured fecal glucocorticoid metabolite (fGCM) concentrations. We evaluated three EIA systems: a cortisol assay, an 11-oxoetiocholanolone assay, and an 11β-hydroxyetiocholanolone assay. Of these, the cortisol assay provided the best discrimination between peak fGCM concentrations detected 1-4 d after injections of synthetic adrenocorticotrophic hormone and preinjection baseline concentrations in four individual brown bears. The time of exposure to ambient temperature had substantial but variable effects on measured fGCM concentrations, including variation both between samples from the same individual and among samples from different bears. We propose that the validated EIA system for measuring fGCM concentrations in the brown bear could be a useful noninvasive method to monitor stress in this species. However, we highlight that this method requires that fecal samples be frozen immediately after defecation, which could be a limitation in many field situations.

Sex steroids and glucocorticoid ratios in Iberian lynx hair

Knowledge on species' reproductive biology is a fundamental pre-requisite of every conservation effort, but is often lacking. Sex steroids can provide valuable information for the assessment of reproductive success, whereas glucocorticoids are used to assess adrenocortical activity and stress-related bodily adaption. However, due to their perilous condition, access to animals is often difficult, which makes hormone measurement in non-invasively collected hair samples an attractive option. We determined cortisol, cortisone, corticosterone, testosterone and progesterone in Iberian lynx hair using enzyme immunoassay (EIA). Cross-validation was performed with high-performance liquid chromatography (HPLC) and high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS). Finally, we statistically evaluated the variations of sex steroids and glucocorticoids according to age, sex, origin, behavior and management. All steroids except corticosterone were detectable in Iberian lynx hair. Hair progesterone measured by EIA was overestimated by cross-reaction with 5α-dihydroprogesterone, a biologically active gestagene, and was highly correlated with HPLC-MS/MS results. Progesterone was higher in adult females compared to all other age-sex groups. Cortisol measured by EIA was overestimated due to antibody cross-reactivity with cortisone and was correlated to the sum of HPLC-MS/MS measurements for cortisol and cortisone. Cortisol was higher in females than in males measured by HPLC-MS/MS, but the EIA results were confounded by the lack of specificity. When using cortisol-cortisone and cortisol-dihydroepiandrosterone ratios, differences were noted between wild-caught and captive-bred lynxes. Additionally, longitudinal EIA measurements of an Iberian lynx after a wildfire showed an inversion of the cortisol-cortisone ratio that later subsided. These results validate the use of hair progesterone measurement for Iberian lynx reproductive monitoring and add to the growing evidence supporting the need for a more comprehensive approach to hair steroid measurement that accounts for local interconversion and co-regulation mechanisms.

Physiological Stress Reactions in Red Deer Induced by Hunting Activities

Hunting activity is usually seen as a factor capable of causing an intense stress response in wildlife that may lead to short but also long-term stress. In the Lousã Mountain, Portugal, the population of red deer (Cervus elaphus) is the target of intensive seasonal hunting. We collected and measured cortisol (and its metabolites) in three tissues types (blood, feces and hair) from red deer hunted during two hunting seasons to evaluate the stress levels at different time windows. We also assessed the immunological and physical condition of the animals. We predicted that the hunting activity would act as a stressor inducing increased short and long-term stress levels in the population. Results showed an increase in hair cortisol levels during the months of harvesting. Surprisingly, the tendency for plasma cortisol levels was to decrease during the hunting season, which could be interpreted as habituation to hunting activity, or due to the hunting duration. Contrary to our predictions, fecal cortisol metabolites did not show any clear patterns across the months. Overall, our results suggest an influence of hunting activities on the physiological stress in red deer. In addition, hair seems to be useful to measure physiological stress, although more studies are required to fully understand its suitability as an indicator of long-term stress. Methodologically, our approach highlights the importance of simultaneously using different methods to assess short and long-term effects in studies on physiological stress reactions.

Hair Cortisol Concentration and Body Mass in Moose (Alces alces) Infested with Deer Keds (Lipoptena cervi)

The deer ked (Lipoptena cervi), a hematophagous ectoparasite of cervids, is currently spreading in Scandinavia, and the moose (Alces alces) is its main host. However, little is known about the impact of deer keds on moose. We analyzed the hair cortisol concentration (HCC) from 262 moose harvested in the fall in relation to age class, sex, body mass (BM), and deer ked infestation intensity, and BM in relation to age class, sex, and infestation intensity. We found that HCC decreased with increasing deer ked intensity at low ked intensities, but for the higher levels of ked intensities, there was a positive relationship between HCC and ked intensity. The HCC was higher in males than in females and lower in yearlings than in calves and adults. Our failure to find any association between BM and deer ked intensity suggested a negligible impact of deer ked infestation on moose foraging and metabolism at the level of infestation observed early in the infestation, but did not exclude an effect later in winter. Our findings suggested that moose generally tolerated moderate parasitism by keds. However, the increase in HCC at higher ked intensities suggested that the tolerance strategy could be disrupted with further increases in intensities and consequently may negatively affect animal health and welfare.

Do follicles matter? Testing the effect of follicles on hair cortisol levels

Cortisol concentrations in hair are used increasingly as a biomarker of long-term stress in free-ranging wildlife. Cortisol is believed to be integrated into hair primarily during its active growth phase, typically occurring over weeks to months or longer periods, depending on latitude. Cortisol concentrations in hair thus reflect the activity of the hypothalamic-pituitary-adrenal axis over this time. However, local, independent cortisol secretion within the skin, which includes hair follicles, may also contribute to cortisol levels in growing hair. Methodological differences between studies include the measurement of cortisol in only the hair shaft (i.e. follicle absent, as with shaved hair) versus the whole hair (i.e. follicle present, as with plucked hair). If the concentration of cortisol in the follicle is high enough to influence the overall hair cortisol concentration (HCC), this could confound comparisons between studies using different types of hair samples (hair shafts vs. whole hair) and collection methods. Here, we test the hypothesis that cortisol present in follicles influences HCC. We compared HCC in paired subsamples of hair with and without follicles from 30 free-ranging Scandinavian brown bears (Ursus arctos) and observed significantly greater HCC in samples with follicles present. The effect of follicles remained significant also with sex and age of sampled bears taken into account in a linear mixed model. Finally, we provide an overview of collection methods and types of hair samples used for HCC analysis in 77 studies dealing with stress in wild mammal species. Our findings highlight the need to unify methods of hair collection and preparation to allow for valid comparisons, and to optimize labour input in ecophysiological studies.

Validation of a novel method to create temporal records of hormone concentrations from the claws of ringed and bearded seals

Ringed (Pusa hispida) and bearded seals (Erignathus barbatus) inhabit vast and often remote areas in the Arctic, making it difficult to obtain long-term physiological information concerning health and reproduction. These seals are experiencing climate-driven changes in their habitat that could result in physiological stress. Chronic physiological stress can lead to immunosuppression, decreased reproduction and decreased growth. Recently, keratin has become a popular matrix to measure steroid hormones, such as stress-related cortisol and reproduction-related progesterone. We developed and validated methods to extract cortisol and progesterone from the claws of adult female ringed (n = 20) and bearded (n = 3) seals using enzyme immunosorbent assays. As ringed and bearded seal claws grow, a pair of dark- and light-colored bands of keratin is deposited annually providing a guide for sampling. Two processing methods were evaluated, removal of claw material with a grinding bit or grinding followed by mechanical pulverization (102 paired samples from six claws, two each from three seals). Adding the mechanical pulverization step resulted in a 1.5-fold increase in hormone extraction. Progesterone from the proximal claw band was evaluated to biologically validate claw material as a measure of pregnancy in ringed seals (n = 14). Claws from pregnant seals had significantly higher claw progesterone concentrations than from non-pregnant seals. This suggests that the elevated progesterone associated with gestation was reflected in the claws, and that the most proximal claw band was indicative of pregnancy status at time of death. Thus, although the sample size was low and the collection dates unbalanced, this study demonstrates the potential to use claws to examine an extended time series (up to 12 yrs) of cortisol and progesterone concentrations in ringed and bearded seal claws.

Steroid hormones in hair reveal sexual maturity and competition in wild house mice (Mus musculus domesticus)

Endocrine data from wild populations provide important insight into social systems. However, obtaining samples for traditional methods involves capture and restraint of animals, and/or pain, which can influence the animal’s stress level, and thereby undesirable release of hormones. Here, we measured corticosterone, testosterone and progesterone in the hair of 482 wild-derived house mice that experienced sexual competition while living under semi-natural conditions. We tested whether sex, age, weight and indicators of sexual maturity, reproduction and social conflicts predict hormone concentrations measured in hair (sampling at endpoint). We show that body weight, sex and age significantly predict cumulative testosterone and progesterone levels, allowing the differentiation between subadults and adults in both sexes. Corticosterone was only slightly elevated in older males compared to older females and increased with the level of visible injuries or scars. Testosterone in males positively correlated with body weight, age, testes size, and sperm number. Progesterone in females significantly increased with age, body weight, and the number of embryos implanted throughout life, but not with the number of litters when controlled for age and weight. Our results highlight the biological validity of hair steroid measurements and provide important insight into reproductive competition in wild house mice.

Of 11 candidate steroids, corticosterone concentration standardized for mass is the most reliable steroid biomarker of nutritional stress across different feather types

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.