Initial validation of blubber cortisol and progesterone as indicators of stress response and maturity in an otariid; the California sea lion (Zalophus californianus)

Social roles influence cortisol levels in captive Livingstone's fruit bats (Pteropus livingstonii)

A critical component of conserving and housing species ex situ is an explicit scientific understanding of the physiological underpinnings of their welfare. Cortisol has been repeatedly linked to stress, and therefore used as an indicator of welfare for many species. In order to measure cortisol in the Livingstone's fruit bat (Pteropus livingstonii; a critically endangered keystone species) without disturbing the captive population, we have developed and validated a non-invasive, novel hormone extraction procedure and faecal glucocorticoid assay. A total of 92 faecal samples, 73 from the P. livingstonii breeding colony at Jersey Zoo, Channel Islands and 19 samples from P. livingstonii housed at Bristol Zoological Gardens, UK, have been collected and analyzed. Mixed-effect modelling of the influence of physiological state variables on cortisol concentration revealed that lactating females had higher cortisol levels than non-lactating females, indicating that our assay is measuring biologically relevant hormone concentrations. Males and older bats also had higher cortisol than non-lactating females and younger individuals. Further analysis applied social network methodology to compare the cortisol levels of bats with different social roles. We found that individuals that linked social groups possessed higher than average cortisol levels and conversely, individuals with high-quality, positive relationships had lower cortisol levels. These results demonstrate, for the first time in a bat species, social mediation of stress hormones. Lastly, the frequency of vocalisation was found to positively correlate with cortisol concentration in males, suggesting that this behaviour may be used by animal management as a visual indicator of a bat's hormonal status. Hence, this research has provided unique insights and empirical scientific knowledge regarding the relationship between the physiology and social behaviour of P. livingstonii, therefore allowing for recommendations to be made to optimise bat welfare at the individual level.

Stress reactivity near birth affects nest building timing and offspring number and survival in the European rabbit (Oryctolagus cuniculus)

The physiological response to stressors has great importance, and its variance has an adaptive role in the survival of individuals. This study describes the effects of stress-axis activation on maternal behavior during the birthing process (parturition) in captive rabbits (Oryctolagus cuniculus). In this species, chances of survival are strongly influenced by nest quality. Thus, maternal care is initiated with nest preparation in late pregnancy, which itself is subject to strict and complex hormonal regulation. Among these hormones, progesterone is one of the most dominant in the process of nest construction. We have demonstrated that its level is altered by the level of cortisol elevation in the animal in question, potentially having an influence on the preparation of the nest for the newborn kittens. We found that does that had a constant and un-elevated level of cortisol metabolite while delivering their litters performed better than those individuals that showed an increased corticoid response around parturition. The latter group exhibited a perceptible delay in the building of their nests, and in addition, further losses were also experienced in their already smaller litters. As the quality of the nest itself proved to be was in no way inferior to those of the other group, this higher kitten-mortality rate may be attributed to impaired maternal behavior. Individual variances in cortisol levels may also result in subtle changes in hormonal regulation, potentially affecting the expression of maternal behavior. We have concluded that the higher level of cortisol detected in more-sensitive does effectively disrupts the natural hormonal regulation involved in their nest-building processes.

Steroid hormones in Pacific walrus bones collected over three millennia indicate physiological responses to changes in estimated population size and the environment

The Pacific walrus (Odobenus rosmarus divergens) is an iconic Arctic marine mammal and an important resource to many Alaska Natives. A decrease in sea ice habitat and unknown population numbers has led to concern of the long-term future health of the walrus population. There is currently no clear understanding of how walrus physiology might be affected by a changing Arctic ecosystem. In this study, steroid hormone concentrations (progesterone, testosterone, cortisol and estradiol) were analysed in walrus bones collected during archaeological [3585-200 calendar years before present (BP)], historical [1880-2006 common era (CE)] and modern (2014-2016 CE) time periods, representing ~ 3651 years, to track changes in reproductive activity and cortisol concentrations (biomarker of stress) over time. Our results show that modern walrus samples have similar cortisol concentrations (median = 43.97 ± standard deviation 904.38 ng/g lipid) to archaeological walruses (38.94 ± 296.17 ng/g lipid, P = 0.75). Cortisol concentrations were weakly correlated with a 15-year average September Chukchi Sea ice cover (P = 0.002, 0.02, r 2 = 0.09, 0.04, for females and males, respectively), indicating a possible physiological resiliency to sea ice recession in the Arctic. All steroid hormones had significant negative correlations with mean walrus population estimates from 1960 to 2016 (P < 0.001). Progesterone in females and testosterone in males exhibited significant correlations with average September Chukchi Sea ice cover for years 1880-2016 (P < 0.001 for both, r2  = 0.34, 0.22, respectively). Modern walruses had significantly lower (P = < 0.001) reproductive hormone concentrations compared with historic walruses during times of rapid population increase, indicative of a population possibly at carrying capacity. This is the first study to apply bone as a tool to monitor long-term changes in hormones that may be associated with changes in walrus population size and sea ice cover.

Whiskers as a novel tissue for tracking reproductive and stress-related hormones in North Pacific otariid pinnipeds

Keratinized tissues, including whiskers, are ideal for acquiring a record of physiological parameters. Most tissues provide a snapshot of physiological status; however, whiskers may support longitudinal sampling for reproductive and stress-related hormones, if hormones are incorporated as whiskers grow and concentrations change with physiological state. Whiskers from female Steller sea lions (Eumetopias jubatus) and northern fur seals (Callorhinus ursinus) were serially sectioned and pulverized and steroid hormones were extracted. Standard methods were used to validate enzyme immunoassay kits for cortisol, progesterone, 17β-estradiol and testosterone. All hormones were measurable in whisker segments from both species with progesterone concentrations showing cyclical patterns, which appear to signify previous pregnancies or luteal phases. Yearly progesterone concentrations were greater in years a pup was produced compared with years when no pup was observed. Free-ranging female Steller sea lions had reproductive rates between 0 and 1.0 (0.53 ± 0.33, n = 12) using a yearly progesterone concentration of 30 pg/mg or greater to classify a reproductive year as producing a pup and below 30 pg/mg as non-reproductive. Cortisol concentrations were greater near the root and rapidly declined, lacking any obvious patterns, throughout the rest of the whisker. Progesterone and testosterone concentrations were able to help determine sex of unknown individuals. Immunohistochemistry revealed that steroid hormones most likely do not leach out of whiskers based on the deposition patterns of progesterone and cortisol being present throughout the whisker length. Overall, measuring steroid hormones in whiskers can reveal individual reproductive histories over multiple years in sea lions and fur seals. Cyclical patterns of δ¹⁵N were useful for identifying periods of up to ~10 years of growth within whiskers, and measuring both stable isotopes and hormones may be useful for differentiating periods of active gestation from diapause and potentially track multi-year reproductive histories of female otariids.

Detection of steroid and thyroid hormones in mammalian teeth

Endocrine tools can provide an avenue to better understand mammalian life histories and predict how individuals and populations may respond to environmental stressors; however, few options exist for studying long-term endocrine patterns in individual marine mammals. Here, we (i) determined whether hormones could be measured in teeth from four marine mammal species: narwhal (Monodon monoceros), beluga (Delphinapterus leucas), killer whale (Orcinus orca) and Atlantic walrus (Odobenus rosmarus rosmarus); (ii) validated commercially available enzyme immunoassay kits for use with tooth extracts; and (iii) conducted biological validations for each species to determine whether reproductive hormone concentrations in teeth correlated with age of sexual maturity. Tooth extracts from all species had measurable concentrations of progesterone, testosterone, 17β-estradiol, corticosterone, aldosterone and triiodothyronine (T3); however, cortisol was undetectable. Parallelism between the binding curves of assay kit standards and serially diluted pools of tooth extract for each species was observed for all measurable hormones. Slopes of accuracy tests ranged from 0.750 to 1.116, with r² values ranging from 0.977 to 1.000, indicating acceptable accuracy. Biological validations were inconsistent with predictions for each species, with the exception of female killer whales (n = 2), which assumed higher progesterone and testosterone concentrations in mature individuals than immature individuals. Instead, we observed a decline in progesterone and testosterone concentrations from infancy through adulthood in narwhal (n = 1) and walruses (n = 2) and higher reproductive hormone concentrations in immature individuals than mature individuals in belugas (n = 8 and 10, respectively) and male killer whales (n = 1 and 2, respectively). While unexpected, this pattern has been observed in other taxa; however, further analytical and biological validations are necessary before this technique can be used to assess individual mammalian endocrine patterns.

Determining pregnancy status in harbour seals using progesterone concentrations in blood and blubber

Pregnancy status in harbour seals can be estimated from concentrations of progesterone in blubber as well as in blood samples, which are significantly higher in pregnant than non-pregnant animals. This study investigated the accuracy of estimating pregnancy rates using samples from live-captured and released harbour seals from three regions around Scotland, coupled with observed pregnancy outcomes. Concentrations of progesterone in blood (plasma) and blubber were obtained during the capture of animals early in the year (February to May). Individual animals were identified from the unique markings on their pelage, with a proportion (n = 51) of females re-sighted during the subsequent breeding season and the reproductive outcomes determined (pregnant or possibly non-pregnant) during observations from long-term photo-identification studies. Generalised linear models with a binomial link function were fitted to training (60% of the data) and test datasets (40% of the data) to estimate pregnancy status from progesterone concentrations in blubber, plasma or both, and a received operating curves (ROC) approach was used to evaluate the performance of each classifier. The accuracy for the plasma concentrations was 85% with a high classification performance (as estimated from an area under the curve (AUC) of 0.82). The Youden method to determine the cut-point (threshold) and bootstrapping the training dataset resulted in a cut-point of 58 ng ml^-1 (95th percentiles, 25-102 ng ml^-1). For blubber, the accuracy was 77% (AUC = 0.86) with an optimal cut-point of 56 ng g^-1 (95th percentiles, 26-223 ng g^-1). In the combined analysis (both blubber and plasma), the accuracy was 87.5% (AUC 0.81) with the cut-points of 72 ng ml^-1 (95th percentiles, 25-103 ng ml^-1) in plasma and 56 ng g^-1 (95th percentiles, 26-223 ng g^-1) in blubber. These thresholds were then used to estimate the pregnancy proportions among adult females at the three study sites, including those that were not included in the photo-id studies. Proportions were high at all sites, (63%-100%) regardless of which matrices were used and were not statistically significantly different from each other but suggested that analysing concentrations in both sample matrices would minimise the uncertainty.

Blubber cortisol levels in humpback whales (Megaptera novaeangliae): A measure of physiological stress without effects from sampling

Baleen whales are vulnerable to environmental impacts due to low fecundity, capital breeding strategies, and their reliance on a large amount of prey resources over large spatial scales. There has been growing interest in monitoring health and physiological stress in these species but, to date, few measures have been validated. The purpose of this study was to examine whether blubber cortisol could be used as a measure of physiological stress in humpback whales. Cortisol concentrations were initially compared between live, presumably 'healthy' whales (n = 187) and deceased whales (n = 35), which had died after stranding or entanglement, or washed ashore as a carcass. Deceased whales were found to have significantly higher cortisol levels (mean ± SD; 5.47 ± 4.52 ng/g) than live whales (0.51 ± 0.14 ng/g; p < 0.001), particularly for those animals that had experienced prolonged trauma (e.g. stranding) prior to death. Blubber cortisol levels in live whales were then examined for evidence of life history-related, seasonal, or sampling-related effects. Life history group and sampling-related factors, such as encounter time and the number of biopsy sampling attempts per animal, were found to be poor predictors of blubber cortisol levels in live whales. In contrast, blubber cortisol levels varied seasonally, with whales migrating north towards the breeding grounds in winter having significantly higher levels (0.54 ± 0.21 ng/g, p = 0.016) than those migrating south towards the feeding grounds in spring (0.48 ± 1.23 ng/g). These differences could be due to additional socio-physiological stress experienced by whales during peaks in breeding activity. Overall, blubber cortisol appears to be a suitable measure of chronic physiological stress in humpback whales.

Liquid chromatography tandem mass spectrometry for the quantification of steroid hormone profiles in blubber from stranded humpback whales (Megaptera novaeangliae)

Marine mammal blubber is known to have quantifiable concentrations of steroid hormones and is increasingly chosen as a matrix for the detection of these reproductive and stress biomarkers. Steroid hormones act through complex cascades, often in concert, yet studies conducted on cetaceans have rarely measured more than two steroids simultaneously. Due to the role of steroid hormones in multiple physiological processes, and variability in concentration among individuals, data on single compounds are often difficult to interpret. Here a liquid chromatography tandem mass spectrometry method for the simultaneous analyses of multiple steroid hormones in cetacean blubber was validated and applied to samples from 10 stranded humpback whales (Megaptera novaeangliae). Progesterone, 17α-hydroxyprogesterone, testosterone, androstenedione, oestrone, oestradiol, cortisone, cortisol, corticosterone and 11-deoxycorticosterone were reliably (relative standard deviation on six replicates <15%) and accurately (recovery of an amended sample between 70% and 120%) quantified, but not 11-deoxycortisol. With the exception of progesterone, testosterone, oestradiol and cortisol, these compounds were quantified for the first time in humpback whales. Given that blubber is frequently collected from free-swimming cetaceans in ongoing research programs, the technique developed here could substantially strengthen understanding and monitoring of the physiological condition of these species.

Examining the relationships between blubber steroid hormones and persistent organic pollutants in common bottlenose dolphins

Odontocete cetaceans bioaccumulate high concentrations of endocrine disrupting persistent organic pollutants (POPs), including dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyltrichloroethylene (DDE), and dichlorodiphenyldichloroethane (DDD) - collectively DDTs - but few studies have explored DDTs-mediated endocrine disruption in cetaceans. Herein, we use remotely collected blubber biopsies from common bottlenose dolphins (Tursiops truncatus) inhabiting a site with high localized DDTs contamination to study the relationships between DDTs exposure and steroid hormone homeostasis in cetaceans. We quantified blubber steroid hormone concentrations by liquid chromatography-tandem mass spectrometry and blubber POP concentrations by gas chromatography-mass spectrometry. We detected six steroid hormones in blubber, including progesterone (P₄), 17-hydroxyprogesterone (17OHP₄), androstenedione (AE), testosterone (T), cortisol (F), and cortisone (E). Sampled dolphins (n = 62) exhibited exposure to DDT, DDE, DDD, chlordanes (CHLDs), mirex, dieldrin, hexachlorobenzene, polychlorinated biphenyls (PCBs), and brominated diphenyl ethers (BDEs). Using principal components analysis (PCA), we determined that blubber DDTs primarily loaded to the first principal component (PC1) explaining 81.6% of the total variance in POP exposure, while the remaining POPs primarily loaded to the PC2 (10.4% of variance). PC1 scores were negatively correlated with blubber T in males and blubber F in females, suggesting that exposure to DDTs impacted androgen and corticosteroid homeostasis. These conclusions were further supported by observed negative correlations between T and o,p'-DDE, o,p'-DDD, and p,p'-DDD in males sampled in the fall, and between F and the six individual DDTs and ∑₆DDTs in females. Overall, these results suggest that POP-mediated endocrine disruption may have occurred in this stock of dolphins, which could negatively impact their health and fitness. However, this study relied on uncontrolled incidental exposures, making it impossible to establish a causal relationship between DDTs exposure and endocrine effects. Importantly, this study demonstrates that remotely collected blubber biopsies are a useful matrix for studying endocrine disruption in marine mammals.

A novel method to measure steroid hormone concentrations in walrus bone from archaeological, historical, and modern time periods using liquid chromatography/tandem mass spectrometry

RATIONALE

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was validated and utilized to measure and analyze four steroid hormones related to stress and reproduction in individual samples from a novel tissue, Pacific walrus (Odobenus rosmarus divergens, herein walrus) bone. This method determines steroid hormone concentrations in the remote walrus population over millennia from archaeological (>200 bp), historical (200-20 bp), and modern (2014-2016) time periods.

METHODS

Lipids were extracted from walrus bone collected from these periods using methanol before LC/MS/MS analysis. Isotopically labeled internal standards for each target hormone were added to every sample. Analytical and physiological validations were performed. Additionally, a tissue comparison was done among paired walrus bone, serum, and blubber samples. A rapid resolution liquid chromatography system coupled to a QqQ mass spectrometer was used to analyze all samples after derivatization for progesterone, testosterone, cortisol, and estradiol concentrations. Multiple reaction monitoring was used for MS analysis and data were acquired in positive electrospray ionization mode.

RESULTS

Progesterone, testosterone, cortisol, and estradiol were linear along their respective standard calibration curves based on their R² values (all > 0.99). Accuracy ranged from 93-111% for all hormones. The recovery of extraction, recovery of hormones without matrix effect, was 92-101%. The overall process efficiency of our method for measuring hormones in walrus bone was 93-112%. Progesterone and testosterone concentrations were not affected by reproductive status among adult females and males, respectively. However, estradiol was different among pregnant and non-pregnant adult females. Overall, steroid hormones reflect a long-term reservoir in cortical bone. This method was also successfully applied to walrus bone as old as 3585 bp.

CONCLUSIONS

LC/MS/MS analysis of bone tissue (0.2-0.3 g) provides stress and reproductive data from elusive walruses that were alive thousands of years ago. Based on physiological validations, tissue comparison, and published literature, steroid hormone concentrations measured in walrus cortical bone could represent an accumulated average around a 10-20-year time span. By investigating how stress and reproductive physiology may have changed over the past ~3000 years based on bone steroid hormone concentrations, this method will help answer how physiologically resilient walruses are to climate change in the Arctic.

Physiological and behavioural responses to acid and osmotic stress and effects of Mucuna extract in Guppies

Variation in pH (acidification) and salinity conditions have severe impact at different levels of biological organization in fish. Present study focused to assess the effects of acidification and salinity changes on physiological stress responses at three different levels of function: i) hormonal and oxidative response, ii) osmoregulation and iii) reproduction, in order to identify relevant biomarkers. Second objective of the study was to evaluate the efficacy of plant (Mucuna pruriens) extract for alleviating pH and salinity related stress. Guppies (Poecilia reticulata) were exposed to different pH (6.0, 5.5, 5.0) and salinity (1.5, 3.0, 4.5 ppt) for 7, 14 and 21 days. Following exposure to stress for respective duration, fish were fed diet containing methanol extract of Mucuna seeds (dose 0.80 gm/kg feed) for 7, 14 and 21 days to measure their possible recovery response. Stress hormone (cortisol), hepatic oxidative stress parameters [superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GRd), glutathione peroxidise (GPx), glutathione S-transferase (GST), malondialdehyde (MDA), glutathione (GSH)], gill osmoregulatory response (Na⁺-K⁺ATPase activity), sex steroid profiles and mating behaviours (gonopodial thrust and gestation period) were estimated. Cortisol and MDA levels increased with dose and duration of acid and salinity stress, and cortisol levels were higher in males than in females. Effect on Na⁺-K⁺ATPase activity was more intense by salinity stress rather than pH induced stress. Both acid and salinity stress reduced sex steroid levels, and mating response was highly affected by both stresses in a dose- and duration-dependent manner. Mucuna treatment reduced stress-induced alteration of cortisol, MDA, Na⁺-K⁺ATPase activity and reproductive parameters. Dietary administration of Mucuna seed extract decreased the intensity of environmental stressors at all three functional levels. Mucuna treatment was more effective against salinity stress than acid stress. Thus, cortisol, oxidative stress marker MDA and Na⁺-K⁺ATPase could be effective indicators for acid and salinity stress in wild and domestic fish populations. Dietary administration of Mucuna extract may limit the detrimental effects of acidification and salinity variations that are the inevitable outcomes expected under global climate change conditions.

Comprehensive endocrine response to acute stress in the bottlenose dolphin from serum, blubber, and feces

Several hormones are potential indicators of stress in free-ranging animals and provide information on animal health in managed-care settings. In response to stress, glucocorticoids (GC, e.g. cortisol) first appear in circulation but are later incorporated into other tissues (e.g. adipose) or excreted in feces or urine. These alternative matrices can be sampled remotely, or by less invasive means, than required for blood collection and are especially valuable in highly mobile species, like marine mammals. We characterized the timing and magnitude of several hormones in response to a stressor in bottlenose dolphins (Tursiops truncatus) and the subsequent incorporation of cortisol into blubber, and its metabolites excreted in feces. We evaluated the endocrine response to an acute stressor in bottlenose dolphins under managed care. We used a standardized stress protocol where dolphins voluntarily beached onto a padded platform and remained out of water for two hours; during the stress test blood samples were collected every 15 min and blubber biopsies were collected every hour (0, 60, and 120 min). Each subject was studied over five days: voluntary blood samples were collected on each of two days prior to the stress test; 1 and 2 h after the conclusion of the out-of-water stress test; and on the following two days after the stress test. Fecal samples were collected daily, each afternoon. The acute stressor resulted in increases in circulating ACTH, cortisol, and aldosterone during the stress test, and each returned to baseline levels within 2 h of the dolphin's return to water. Both cortisol and aldosterone concentrations were correlated with ACTH, suggesting both corticosteroids are at least partly regulated by ACTH. Thyroid hormone concentrations were generally unaffected by the acute stressor. Blubber cortisol increased during the stress test, and fecal GC excretion was elevated on the day of the stress test. We found that GCs in bottlenose dolphins can recover within hours of acute stress, and that cortisol release can be detected in alternate matrices within a few hours-within 2 h in blubber, and 3.5-5 h in fecal samples.

Repeated adrenocorticotropic hormone administration alters adrenal and thyroid hormones in free-ranging elephant seals

Understanding the physiological response of marine mammals to anthropogenic stressors can inform marine ecosystem conservation strategies. Stress stimulates the activation of the hypothalamic-pituitary-adrenal (HPA) axis and synthesis of glucocorticoid (GC) hormones, which increase energy substrate availability while suppressing energy-intensive processes. Exposure to repeated stressors can potentially affect an animal's ability to respond to and recover from subsequent challenges. To mimic repeated activation of the HPA axis by environmental stressors (or challenges), we administered adrenocorticotropic hormone (ACTH) to free-ranging juvenile northern elephant seals (Mirounga angustirostris; n = 7) once daily for 4 days. ACTH administration induced significant elevation in circulating cortisol and aldosterone levels. The cortisol responses did not vary in magnitude between the first ACTH administration on Day 1 and the last administration on Day 4. In contrast, aldosterone levels remained elevated above baseline for at least 24 h after each ACTH injection, and responses were greater on Day 4 than Day 1. Total triiodothyronine (tT3) levels were decreased on Day 4 relative to Day 1, while reverse triiodothyronine (rT3) concentrations increased relative to baseline on Days 1 and 4 in response to ACTH, indicating a suppression of thyroid hormone production. There was no effect of ACTH on the sex steroid dehydroepiandrosterone. These data suggest that elephant seals are able to mount adrenal responses to multiple ACTH administrations. However, repeated ACTH administration resulted in facilitation of aldosterone secretion and suppression of tT3, which may impact osmoregulation and metabolism, respectively. We propose that aldosterone and tT3 are informative additional indicators of repeated stress in marine mammals.