A consensus endocrine profile for chronically stressed wild animals does not exist

Effects of the combination of chronic unpredictable stress and environmental enrichment on anxiety-like behavior assessed using the elevated plus maze in Swiss male mice: Hypothalamus-Pituitary-Adrenal Axis-mediated mechanisms

Environmental enrichment (EE) is a paradigm that offers the animal a plethora of stimuli, including physical, cognitive, sensory, and social enrichment. Exposure to EE can modulate both anxiety responses and plasma corticosterone. In this study, our objective was to explore how chronic unpredictable stress (CUS) impacts anxiety-related behaviors in male Swiss mice raised in EE conditions. Additionally, we investigated corticosterone and adrenocorticotropic hormone (ACTH) levels to assess the involvement of the hypothalamic-pituitary-adrenal (HPA) axis in mediating these responses. Mice were housed under either EE or standard housing conditions for 21 days. Afterward, they were exposed to 11 days of CUS while still reared in their distinct housing conditions, with half of the mice receiving daily pretreatment with the vehicle and the other half receiving daily metyrapone (MET) injections, an inhibitor of steroid synthesis, 30 mins before CUS exposure. Blood samples were obtained to assess plasma corticosterone and ACTH levels. The 11-day CUS protocol induced anxiety-like phenotype and elevated ACTH levels in EE mice. Chronic MET pretreatment prevented anxiety-like behavior in the EE-CUS groups, by mechanisms involving increased plasma corticosterone levels and decreased ACTH. These results suggest a role of the HPA axis in the mechanism underlying the anxiogenic phenotype induced by CUS in EE mice and shed light on the complex interplay between environmental factors, stress, and the HPA axis in anxiety regulation.

Salivary analysis to unveil the paradigma of stress of domestic horses reared in the wild

Horse welfare is the product of multiple factors, including behavioral and physiological adjustments to cope with stressful situation regarding environment and housing condition. Collectively, it is supposed that a horse kept in the wild has a lower level of stress than other housing system, and the aim of the present study was to investigate the level of stress in domestic horses reared in the wild and then moved to human controlled housing, through saliva analysis. Twelve clinically healthy Catria (Italian local breed) mares, usually reared in the wild, were moved into collective paddocks for a folkloric event. Saliva samples were obtained before and after the change of housing condition to evaluate stress biomarkers including salivary cortisol, salivary alpha-amylase, and butyrylcholinesterase (BChol). The mares were also scored using the Welfare Aggregation and Guidance (WAG) Tool to highlight the presence of abnormal behaviors. Despite the absence of differences in behavioral scores between wild and paddocks, salivary cortisol and BChol were found to be higher in the wild and lower when mares were moved to paddocks. The highest concentrations in stress biomarkers like salivary cortisol and BChol in the wild was unexpected, but the need for managing hierarchical relationships, and the exposure to feral animals, predators, and weather changes, might explain these findings. The overall results of the present study may provide further knowledge toward stress response in domesticated horses living in the wild moved to human controlled housing system.

Long-term, medium-term and acute stress response of urban populations of Eurasian red squirrels affected by different levels of human disturbance

Animals in urban areas often encounter novel and potentially stressful conditions. It is important to understand how wildlife cope with anthropogenic disturbance. To investigate this specific adaptation we live-trapped squirrels in two study sites in Warsaw: a forest reserve and an urban park and we estimated stress responses at three levels: long-term and medium-term stress (the level of stress hormones, i.e. cortisol and cortisone concentrations, in hair and feces) and acute reaction to human-induced stress (measured during handling with the aid of the three indices: breath rate, struggle rate, and vocalization). According to GLMM models no difference in the stress hormones level was found between the two populations. The only differences in cortisol concentrations clearly depended on the season, i.e. being higher in autumn and winter comparying to other seasons. There was no influence of sex, or reproductive status on stress hormones. Forest squirrels had significantly higher breath rates, suggesting they were more stressed by handling. There was no difference in the struggle rate between study areas, this index was mostly affected by season (i.e. being highest in winter). First-trapped squirrels vocalized less than during the subsequent trappings. Assumingly, during the first, and more stressful trapping, squirrels used 'freezing' and/or little vocalization, while during next captures they used alarm calls to warn conspecifics. Overall, we showed that the two squirrel populations differed only in terms of their breath rate. This suggests that they did not differ in medium-term and long-term stress in general, but they can differ in acute response to handling. This also suggests that both populations were similarly affected by environmental factors. The lack of clear effects may also be due to population heterogeneity. Thus, in order to assess the effects of anthropogenic stressors a broader range of indicators and diverse analytical methods, including behavioral analyses, should be employed.

Feather corticosterone is lower in translocated and historical populations of the endangered Laysan duck (Anas laysanensis)

Identifying reliable bioindicators of population status is a central goal of conservation physiology. Physiological stress measures are often used as metrics of individual health and can assist in managing endangered species if linked to fitness traits. We analysed feather corticosterone, a cumulative physiological stress metric, of individuals from historical, translocated, and source populations of an endangered endemic Hawaiian bird, the Laysan duck (Anas laysanensis). We hypothesized that feather corticosterone would reflect the improved reproduction and survival rates observed in populations translocated to Midway and Kure Atolls from Laysan Island. We also predicted less physiological stress in historical Laysan birds collected before ecological conditions deteriorated and the population bottleneck. All hypotheses were supported: we found lower feather corticosterone in the translocated populations and historical samples than in those from recent Laysan samples. This suggests that current Laysan birds are experiencing greater physiological stress than historical Laysan and recently translocated birds. Our initial analysis suggests that feather corticosterone may be an indicator of population status and could be used as a non-invasive physiological monitoring tool for this species with further validation. Furthermore, these preliminary results, combined with published demographic data, suggest that current Laysan conditions may not be optimal for this species.

Investigating the effects of acute and chronic stress on DNA damage

A hallmark of the vertebrate stress response is a rapid increase in glucocorticoids and catecholamines; however, this does not mean that these mediators are the best, or should be the only, metric measured when studying stress. Instead, it is becoming increasingly clear that assaying a suite of downstream metrics is necessary in stress physiology. One component of this suite could be assessing double-stranded DNA damage (dsDNA damage), which has recently been shown to increase in blood with both acute and chronic stress in house sparrows (Passer domesticus). To further understand the relationship between stress and dsDNA damage, we designed two experiments to address the following questions: (1) how does dsDNA damage with chronic stress vary across tissues? (2) does the increase in dsDNA damage during acute stress come from one arm of the stress response or both? We found that (1) dsDNA damage affects tissues differently during chronic stress and (2) the hypothalamic-pituitary-adrenal axis influences dsDNA damage with acute stress, but the sympathetic-adreno-medullary system does not. Surprisingly, our data are not explained by studies on changes in hormone receptor levels with chronic stress, so the underlying mechanism remains unclear.

Experimentally elevated corticosterone does not affect bacteria killing ability of breeding female tree swallows (Tachycineta bicolor)

The immune system can be modulated when organisms are exposed to acute or chronic stressors. Glucocorticoids (GCs), the primary hormonal mediators of the physiological stress response, are suspected to play a crucial role in immune modulation. However, most evidence of stress-associated immunomodulation does not separate the effects of glucocorticoid-dependent pathways from those of glucocorticoid-independent mechanisms on immune function. In this study, we experimentally elevated circulating corticosterone, the main avian glucocorticoid, in free-living female tree swallows (Tachycineta bicolor) for one to two weeks to test its effects on immune modulation. Natural variation in bacteria killing ability (BKA), a measure of innate constitutive immunity, was predicted by the interaction between timing of breeding and corticosterone levels. However, experimental elevation of corticosterone had no effect on BKA. Therefore, even when BKA is correlated with natural variation in glucocorticoid levels, this relationship may not be causal. Experiments are necessary to uncover the causal mechanisms of immunomodulation and the consequences of acute and chronic stress on disease vulnerability. Findings in other species indicate that acute increases in GCs can suppress BKA; but our results support the hypothesis that this effect does not persist over longer timescales, during chronic elevations in GCs. Direct comparisons of the effects of acute vs. chronic elevation of GCs on BKA will be important for testing this hypothesis.

Asian elephant calf physiology and mahout perspectives during taming in Myanmar

A quarter of Asian elephants are captive, with greater than 90% of these tamed and cared for by handlers (mahouts) in Asia. Although taming is a much-discussed welfare issue, no studies to our knowledge have empirically assessed its impact on calves, and dialogue surrounding taming often lacks perspectives of those involved. Here, we interviewed mahouts involved in taming and monitored five physiological measures (faecal glucocorticoid metabolites (FGMs), serum cortisol, glucose, creatine kinase (CK) and heterophil:lymphocyte (H:L)) over the first 10 days of taming and following six months in 41 calves undergoing taming and 16 control individuals. These measures assess the duration and intensity of stress during taming. Interviews suggested mahouts had major concerns for their safety when discussing changing taming practices, an important consideration for future management. Calf physiological measures were elevated by 50-70% (FGMs/cortisol/glucose), 135% (H:L) and greater than 500% (CK) over the first few days of taming, indicative of elevated stress, not seen to the same extent in control adults. Some measures stabilized sooner (glucose/cortisol/CK/FGM: 7-10 days) than others (H:L: one-two months), indicating mostly acute stress. Our findings inform the welfare of approximately 15 000 captive elephants around the world. Future studies should compare taming in different populations and consider calf and mahout welfare.

Husbandry Protocols for Juvenile Loggerhead Sea Turtles (Caretta caretta) Based on Stress Response to Stocking Density and Dry-Dock Time

When necessary, sea turtles are held captive for veterinarian care and research purposes. Protocols and basic guidelines have been described for husbandry of sea turtles with veterinarian needs but not considering physiological indicators of animal welfare. Because all sea turtle are imperiled species, monitoring their welfare is important. The aim of this study was to standardize husbandry protocols for loggerhead (Caretta caretta) juveniles held under seminatural conditions, based on circulating concentration of plasma corticosterone (Cort) and behavior. Two experiments were performed to analyze physiological and behavioral responses of the animals facing changes in stocking density and different dry-docking times. Cort analyses suggested that the number of animals per tank can be modified occasionally, without affecting their health and welfare. However, dry-docking time should be < 30 min, as indicated by the significant elevation of circulating Cort at ≥ 30 min, rising from 1.51- ng/ml to 5.28-ng/ml. Protocols tested did not affect behavioral responses, except for the breaths per move, which increased while Cort increased, despite differences exhibited by experimental animals in behavioral responses according to daily times (morning vs afternoon) and the sex of the animals.

No additional stress of sublethal gas supersaturation in a landlocked population of Atlantic salmon (Salmo salar) exposed to environmental acidification

The landlocked Atlantic salmon population "bleke" faces extinction due to environmental acidification (EA) and hydropower expansion in the Norwegian river Otra. Despite of restoration, unexpected mortality has been reported for this population, possibly due to gas bubble trauma (GBT) from gas supersaturation (GSS) downstream of hydroelectric plants, or EA induced aluminum toxicity. In this study, we applied the allostasis concept to investigate interactions between EA and GBT. This concept comprises additive effects of stressors, which can lead to allostatic overload. Stress coping mechanisms become maladaptive in such situations, which can be indicated by an inability to mount a proper cortisol response in fish. Fish were exposed to sublethal levels of simulated EA (SEA), GSS (a total gas pressure; TGP; of 110%) or a combination of these stressors for six days. Effects on allostatic load were subsequently investigated by assessing the cortisol response to an acute stress test. SEA increased cortisol responsiveness and GSS induced clinical signs of GBT, but no interacting effects between GSS and SEA were observed. This suggests that that 110% TGP did not have an additive effect on the allostatic load imposed by SEA.

Quality of hematology and clinical chemistry results in laboratory and zoo nonhuman primates: Effects of the preanalytical phase. A review

Most errors in clinical pathology originate in the preanalytical phase, which includes all steps from the preparation of animals and equipment to the collection of the specimen and its management until analyzed. Blood is the most common specimen collected in nonhuman primates. Other specimens collected include urine, saliva, feces, and hair. The primary concern is the variability of blood hematology and biochemistry results due to sampling conditions with the effects of capture, restraint, and/or anesthesia. Housing and diet have fewer effects, with the exception of food restriction to reduce obesity. There has been less investigation regarding the impact of sampling conditions of nonblood specimens.

Corticosterone and immune responses to dehydration in squamate reptiles

Many environments present some degree of seasonal water limitations; organisms that live in such environments must be adapted to survive periods without permanent water access. Often this involves the ability to tolerate dehydration, which can have adverse physiological effects and is typically considered a physiological stressor. While having many functions, the hormone corticosterone (CORT) is often released in response to stressors, yet increasing plasma CORT while dehydrated could be considered maladaptive, especially for species that experience predictable bouts of dehydration and have related coping mechanisms. Elevating CORT could reduce immunocompetence and have other negative physiological effects. Thus, such species likely have CORT and immune responses adapted to experiencing seasonal droughts. We evaluated how dehydration affects CORT and immune function in eight squamate species that naturally experience varied water limitation. We tested whether hydric state affected plasma CORT concentrations and aspects of immunocompetence (lysis, agglutination, bacterial killing ability and white blood cell counts) differently among species based on how seasonally water limited they are and whether this is constrained by phylogeny. The species represented four familial pairs, with one species of each pair inhabiting environments with frequent access to water and one naturally experiencing extended periods (>30 days) with no access to standing water. The effects of dehydration on CORT and immunity varied among species. Increases in CORT were generally not associated with reduced immunocompetence, indicating CORT and immunity might be decoupled in some species. Interspecies variations in responses to dehydration were more clearly grouped by phylogeny than by habitat type.

The effects of early-life and intergenerational stress on the brain

Stress experienced during ontogeny can have profound effects on the adult phenotype. However, stress can also be experienced intergenerationally, where an offspring's phenotype can be moulded by stress experienced by the parents. Although early-life and intergenerational stress can alter anatomy, physiology, and behaviour, nothing is known about how these stress contexts interact to affect the neural phenotype. Here, we examined how early-life and intergenerational stress affect the brain in eastern fence lizards (Sceloporus undulatus). Some lizard populations co-occur with predatory fire ants, and stress from fire ant attacks exerts intergenerational physiological and behavioural changes in lizards. However, it is unclear if intergenerational stress, or the interaction between intergenerational and early-life stress, modulates the brain. To test this, we captured gravid females from fire ant invaded and uninvaded populations, and subjected offspring to three early-life stress treatments: (1) fire ant attack, (2) corticosterone, or (3) a control. Corticosterone and fire ant attack decreased some aspects of the neural phenotype while population of origin and the interaction of early-life stress and population had no effects on the brain. These results suggest that early-life stressors may better predict adult brain variation than intergenerational stress in this species.

Changes in Fecal Glucocorticoid Metabolites in Captive Coyotes (Canis latrans): Influence of Gender, Time, and Reproductive Status

Reproduction is considered an energetically and physiologically demanding time in the life of an animal. Changes in physiological stress are partly reflected in changes in glucocorticoid metabolites and can be measured from fecal samples. We examined levels of fecal glucocorticoid metabolites (fGCMs) in 24 captive coyotes (Canis latrans) to investigate responses to the demands of reproduction. Using 12 pairs of coyotes (five pairs produced pups, seven pairs did not), we analyzed 633 fecal samples covering 11 biological periods (e.g., breeding, gestation, and lactation). Levels of fGCMs showed high individual variability, with females having higher fGCM levels than males. The production of pups showed no statistical effect on fGCM levels among females or males. Among females, fGCM levels were highest during 4-6 weeks of gestation compared to other periods but were not significantly different between pregnant and nonpregnant females. Among males, the highest fGCM levels were during 1-3 weeks of gestation compared to other periods, but were not significantly different between males with a pregnant mate versus nonpregnant mate. Of females producing pups, litter size did not influence fGCM levels. Given that they were fed ample food throughout the year, we found that the demands of producing pups did not appear to statistically influence measures of fGCM concentrations in captive coyotes.

Assessing variation in faecal glucocorticoid concentrations in gray whales exposed to anthropogenic stressors

Understanding how individual animals respond to stressors behaviourally and physiologically is a critical step towards quantifying long-term population consequences and informing management efforts. Glucocorticoid (GC) metabolite accumulation in various matrices provides an integrated measure of adrenal activation in baleen whales and could thus be used to investigate physiological changes following exposure to stressors. In this study, we measured GC concentrations in faecal samples of Pacific Coast Feeding Group (PCFG) gray whales (Eschrichtius robustus) collected over seven consecutive years to assess the association between GC content and metrics of exposure to sound levels and vessel traffic at different temporal scales, while controlling for contextual variables such as sex, reproductive status, age, body condition, year, time of year and location. We develop a Bayesian Generalized Additive Modelling approach that accommodates the many complexities of these data, including non-linear variation in hormone concentrations, missing covariate values, repeated samples, sampling variability and some hormone concentrations below the limit of detection. Estimated relationships showed large variability, but emerging patterns indicate a strong context-dependency of physiological variation, depending on sex, body condition and proximity to a port. Our results highlight the need to control for baseline hormone variation related to context, which otherwise can obscure the functional relationship between faecal GCs and stressor exposure. Therefore, extensive data collection to determine sources of baseline variation in well-studied populations, such as PCFG gray whales, could shed light on cetacean stress physiology and be used to extend applicability to less-well-studied taxa. GC analyses may offer greatest utility when employed as part of a suite of markers that, in aggregate, provide a multivariate measure of physiological status, better informing estimates of individuals' health and ultimately the consequences of anthropogenic stressors on populations.

Birds living near airports do not show consistently higher levels of feather corticosterone

Noise represents a threat to human and wildlife health, triggering physiological and behavioral challenges to individuals living close to sources of extreme noise. Here, we considered airport environments as sources of potentially stressful stimuli for birds and tested if those living near airports are under higher physiological stress than birds living in quiet sites. We used measurements of CORT in feathers (CORTf) as a proxy of chronic stress. We evaluated 14 passerine and 1 non-passerine species, living near three Brazilian airports. We found that, across species, individuals with a better body condition had lower CORTf concentration. At the species level, we found that CORTf concentration was not consistently affected by airport noise. Comparing individuals living in quiet sites with those living near airports, we found that 2 species had higher and 2 had lower CORTf concentrations near airports, while 11 species presented no significant differences between sites. At the population level, model selection indicated that the direction and strength of these differences are weakly related to species' song frequency (peak frequency), as lower-frequency singers tended to present higher CORTf levels at airport-affected sites. In summary, we were unable to find a consistent response among species, probably due to species-specific differences in their response to anthropogenic disturbances. Instead, we found that species might be affected differently according to their singing spectral frequency and that individuals in good body condition show lower CORTf, suggesting that this measure is consistent with lower physiological stress.

A mathematical representation of the reactive scope model

Researchers have long sought to understand and predict an animal's response to stressful stimuli. Since the introduction of the concept of homeostasis, a variety of model frameworks have been proposed to describe what is necessary for an animal to remain within this stable physiological state and the ramifications of leaving it. Romero et al. (Horm Behav 55(3):375-389, 2009) introduced the reactive scope model to provide a novel conceptual framework for the stress response that assumes an animal's ability to tolerate a stressful stimulus may degrade over time in response to the stimulus. We provide a mathematical formulation for the reactive scope model using a system of ordinary differential equations and show that this model is capable of recreating existing experimental data. We also provide an experimental method that may be used to verify the model as well as several potential additions to the model. If future experimentation provides the necessary data to estimate the model's parameters, the model presented here may be used to make quantitative predictions about physiological mediator levels during a stress response and predict the onset of homeostatic overload.

Varying intensities of chronic stress induce inconsistent responses in weight and plasma metabolites in house sparrows (Passer domesticus)

One of the biggest unanswered questions in the field of stress physiology is whether variation in chronic stress intensity will produce proportional (a gradient or graded) physiological response. We were specifically interested in the timing of the entrance into homeostatic overload, or the start of chronic stress symptoms. To attempt to fill this knowledge gap we split 40 captive house sparrows (Passer domesticus) into four groups (high stress, medium stress, low stress, and a captivity-only control) and subjected them to six bouts of chronic stress over a 6-month period. We varied the number of stressors/day and the length of each individual bout with the goal of producing groups that would experience different magnitudes of wear-and-tear. To evaluate the impact of chronic stress, at the start and end of each stress bout we measured body weight and three plasma metabolites (glucose, ketones, and uric acid) in both a fasted and fed state. All metrics showed significant differences across treatment groups, with the high stress group most frequently showing the greatest changes. However, the changes did not produce a consistent profile that matched the different chronic stress intensities. We also took samples after a prolonged recovery period of 6 weeks after the chronic stressors ended. The only group difference that persisted after 6 weeks was weight-all differences across groups in metabolites recovered. The results indicate that common blood metabolites are sensitive to stressors and may show signs of wear-and-tear, but are not reliable indicators of the intensity of long-term chronic stress. Furthermore, regulatory mechanisms are robust enough to recover within 6 weeks post-stress.

Analytical Validation and Assessment of Baseline Fecal Glucocorticoid Metabolites in Northern Sea Otters (Enhydra lutris kenyoni) in Human Care

Fecal glucocorticoid metabolites (FGMs) have been used as a non-invasive and indirect measurement of the complex stress response in a variety of species. Animals in facilities under managed care allow for the longitudinal study of FGMs in a controlled environment. Animal histories often include environmental, husbandry, and medical notes that can be matched to FGM concentrations to aid in the physiological validation of adrenal stimulation and response. The goal of this study was to demonstrate analytical validations using two enzyme-linked immunosorbent assays (EIA) to measure FGMs from northern sea otters (Enhydra lutris kenyoni) under human care (Seattle Aquarium, Seattle, WA, USA) and to determine baseline and stress response spike levels for individual sea otters. Individual variation was found among the four subjects in the study with fecal baseline levels ranging from 20.2 to 83.7 ng/g for cortisol-immunoreactive metabolites and 52.3 to 102 ng/g for corticosterone-immunoreactive metabolites. As a retrospective study, 39 percent of hormone peaks were associated with notes and most FGM spikes were associated with veterinary procedures or days in which enrichment items were provided and produced an excitatory response. Monitoring baseline FGMs levels and events associated with hormone peak values may provide insight into effective husbandry management to improve the overall welfare of sea otters and other marine mammals.

Zoo Animal Welfare Assessment: Where Do We Stand?

Zoological institutions, such as zoos and aquariums, have made animal welfare a top priority, as it is not only a moral obligation but also crucial for fulfilling their roles in education and conservation. There is a need for science-based tools to assess and monitor animal welfare in these settings. However, assessing the welfare of zoo animals is challenging due to the diversity of species and lack of knowledge on their specific needs. This review aims to discuss the advantages and disadvantages of existing methodologies for assessing zoo animal welfare through: (1) A critical analysis of the main approaches to zoo animal welfare assessment; (2) A description of the most relevant animal-based welfare indicators for zoo animals with a particular focus on behavioural and physiological indicators; and (3) An identification of areas that require further research.

Feather corticosterone reveals that urban great tits experience lower corticosterone exposure than forest individuals during dominance-rank establishment

Although the consequences of urbanization for the physiological health of animals are the focus of much active research, an overlooked aspect is how physiology could be indirectly modulated by the urban environment via changes in intraspecific behavioural interactions, particularly among gregarious species. Both urbanization and the establishment, as well as maintenance, of hierarchical rank position are processes that could incur physiological stress. Measurements of glucocorticoids (GCs) in relation to urbanization, however, have yielded inconsistent results. In most cases, GCs have been measured in blood, offering only a 'snapshot' of an animal's current physiological state. Because circulating GCs are incorporated into growing feathers or hair, measurements of feather/hair GCs offer a longer term measure of stress exposure reflecting the whole period of feather/hair growth. During two calendar years, we collected tail feathers from 188 urban and forest great tits (P. major) across multiple sampling sites and analysed corticosterone (CORT-the main GC in birds) levels, reflecting CORT exposure during the extended period in late summer and early autumn when great tits moult and winter flocks are formed. Urban individuals exhibited consistently lower feather CORT (fCORT) levels than forest birds indicating lower overall exposure to CORT during this period. The lower fCORT levels in urban individuals could represent an adaptation to cope with the more challenging urban environment, physiological constraints on stress axis function or a trade-off between the ability to respond to stressors and predation risk during moult. Despite the expectation that CORT responses to urbanization are highly context-dependent, the spatial consistency of our results and agreement with a multi-population study of fCORT in European blackbirds (Turdus merula) suggests a generalization of the effect of urbanization on CORT exposure during post-breeding moult (i.e. not site- or species-specific).

Seasonal variation in molecular and physiological stress markers in Asian elephants

Free-living species exhibit seasonal variation in various life history traits, including vital rates such as birth and death patterns. Different physiological mechanisms are thought to underlie the expression of life history traits that contribute to lifetime fitness. However, although the broad impacts of seasonality on life history traits and trade-offs is well established in many systems, the exact physiological mechanisms responsible for driving differences within and between individuals are poorly understood. Among them, molecular and physiological stress pathways, such as stress hypothalamic-pituitary-adrenal axis and oxidative stress, have potential to mediate relationships between individual survival, reproduction and environmental seasonality. Here, we determine how different physiological markers of stress including faecal cortisol metabolites (FCMs), heterophils/lymphocytes (H/L) ratio, two markers indicating oxidative balance including a marker of oxidative damage (reactive oxygen metabolites, ROM) and a marker of antioxidant defences (superoxide dismutase, SOD) and body weight vary in a large semi-captive population of Asian elephants (Elephas maximus) exposed to extreme seasonality (e.g. elevated temperatures). Individuals showed higher FCM levels and H/L ratios during cold season, indicating increased stress, and the lowest FCM levels during monsoon season and H/L ratios during hot and dry season, but we found no pattern in oxidative stress (ROM and SOD) levels. Hot season also associated with a decline in body weight. The present study shows how different physiological parameters (FCM levels and H/L ratio), molecular (oxidative stress) and body condition vary with seasonal changes, and how these parameters might allow individuals to adapt to such variations. Our results on an endangered long-lived species are crucial in indicating the most productive timing for conservation efforts, predicting how individuals cope with environmental changes, and allow for a more accurate representation of how animal physiology operates in nature.

Mothers of disabled infants had higher cortisol levels in a free-ranging group of Japanese macaques (Macaca fuscata)

Glucocorticoids (GCs) are hormones released in response to stressors and can provide insight into an organism's physiological well-being. Experiencing chronic challenges to homeostasis is associated with significant deviations from baseline fecal GCs (fGCs) in many species, providing a noninvasive biomarker for assessing stress. In the group of free-ranging Japanese macaques (Macaca fuscata) at the Awajishima Monkey Center in Japan, ~17% have congenital limb malformations. We collected 646 fecal samples from 27 females over three consecutive birth seasons (May-August) and analyzed them using enzyme immunoassay to extract fGCs. We explored the relationship between fGC levels and individual (physical impairment and reproductive status), social (dominance rank and availability of kin for social support), and ecological variables (exposure to potential predators, rainfall, and wild fruit availability). A disabled infant was associated significantly with higher fGC in the mother; however, physical impairment in adult females was not significantly related to fGC levels. Females with higher dominance rank had significantly lower fGC levels than lower ranking females. Other factors did not relate significantly to fGC. These results suggest that providing care that meets the support needs of disabled infants poses a physiological challenge for mothers and suggests that physically impaired adults are able to effectively compensate for their disabilities with behavioral plasticity. Once an individual with congenital limb malformations survives infancy through their mother's care, physical impairment does not appear to influence fGC values, while social variables like dominance rank significantly influenced cortisol values in free-ranging female Japanese macaques.

Invited review: Adrenocortical function in avian and non-avian reptiles: Insights from dispersed adrenocortical cells

Herein we review our work involving dispersed adrenocortical cells from several lizard species: the Eastern Fence Lizard (Sceloporus undulatus), Yarrow's Spiny Lizard (Sceloporus jarrovii), Striped Plateau Lizard (Sceloporus virgatus) and the Yucatán Banded Gecko (Coleonyx elegans). Early work demonstrated changes in steroidogenic function of adrenocortical cells derived from adult S. undulatus associated with seasonal interactions with sex. However, new information suggests that both sexes operate within the same steroidogenic budget over season. The observed sex effect was further explored in orchiectomized and ovariectomized lizards, some supported with exogenous testosterone. Overall, a suppressive effect of testosterone was evident, especially in cells from C. elegans. Life stage added to this complex picture of adrenal steroidogenic function. This was evident when sexually mature and immature Sceloporus lizards were subjected to a nutritional stressor, cricket restriction/deprivation. There were divergent patterns of corticosterone, aldosterone, and progesterone responses and associated sensitivities of each to corticotropin (ACTH). Finally, we provide strong evidence that there are multiple, labile subpopulations of adrenocortical cells. We conclude that the rapid (days) remodeling of adrenocortical steroidogenic function through fluctuating cell subpopulations drives the circulating corticosteroid profile of Sceloporus lizard species. Interestingly, progesterone and aldosterone may be more important with corticosterone serving as essential supportive background. In the wild, the flux in adrenocortical cell subpopulations may be adversely susceptible to climate-change related disruptions in food sources and to xenobiotic/endocrine-disrupting chemicals. We urge further studies using native lizard species as bioindicators of local pollutants and as models to examine the broader eco-exposome.

Unpredictable fasting transiently alters corticosterone and feeding behavior but not body mass or later HPA axis function in zebra finches (Taeniopygia guttata)

The hypothalamic-pituitary-adrenal (HPA) axis is commonly activated in response to unpredictable conditions, including unstable or inadequate food supply. Extended exposure to unpredictable food resources can alter HPA axis function, with the potential for negative fitness consequences. We addressed the interrelationships of unpredictable food resources, HPA axis activity, and food intake in adult and juvenile zebra finches (Taeniopygia guttata). Finches exposed to prolonged periods of unpredictable food elevate corticosterone (the primary avian glucocorticoid) when food is unavailable; however, whether they experience chronic elevation in baseline corticosterone during periods of unpredictability, even when food is available, is unclear. We subjected adults and juveniles to an extended period of temporally unpredictable food (consisting of a random daily fast) or predictable food supply. We investigated baseline corticosterone under fed conditions and in response to an acute fast (mimicking the daily fasting periods in the unpredictable treatment), and assessed differences in body mass, food intake, and corticosterone responses to restraint. Regardless of sex and age, individuals in both treatment groups elevated corticosterone when fasted, and baseline corticosterone under fed conditions was indistinguishable between groups. Thus, corticosterone levels were not persistently elevated in the unpredictably fed group. Treatment groups did not differ in body mass or corticosterone responses to restraint, but unpredictably fed birds consumed food more rapidly when food was available. Our findings suggest that the unpredictably fed birds experienced repeated, moderate elevations in corticosterone. Such elevations may aid birds in coping with unpredictable food sources, in part by activating compensatory changes in foraging behavior.

How chronic anthropogenic noise can affect wildlife communities

Anthropogenic noise is a major pollutant in terrestrial and aquatic ecosystems. Since the industrial revolution, human activities have become increasingly noisy, leading to both acute and chronic disturbance of a wide variety of animals. Chronic noise exposure can affect animals over their lifespan, leading to changes in species interactions and likely altering communities. However, the community-level impacts of chronic noise are not well-understood, which impairs our ability for effective mitigation. In this review, we address the effects of chronic noise exposure on communities and explore possible mechanisms underlying these effects. The limited studies on this topic suggest that noise can affect communities by changing the behavior and/or physiology of species in a community, which results in direct or knock-on consequences for other species in the ecosystem. Major knowledge gaps remain due to the logistically complex and financially expensive nature of the long-term studies needed to address these questions. By identifying these gaps and suggesting approaches to answer them, we provide a road map toward mitigating the effects of a noisy world.

Frank Beach Award Winner: The centrality of the hypothalamic-pituitary-adrenal axis in dealing with environmental change across temporal scales

Understanding if and how individuals and populations cope with environmental change is an enduring question in evolutionary ecology that has renewed importance given the pace of change in the Anthropocene. Two evolutionary strategies of coping with environmental change may be particularly important in rapidly changing environments: adaptive phenotypic plasticity and/or bet hedging. Adaptive plasticity could enable individuals to match their phenotypes to the expected environment if there is an accurate cue predicting the selective environment. Diversifying bet hedging involves the production of seemingly random phenotypes in an unpredictable environment, some of which may be adaptive. Here, I review the central role of the hypothalamic-pituitary-adrenal (HPA) axis and glucocorticoids (GCs) in enabling vertebrates to cope with environmental change through adaptive plasticity and bet hedging. I first describe how the HPA axis mediates three types of adaptive plasticity to cope with environmental change (evasion, tolerance, recovery) over short timescales (e.g., 1-3 generations) before discussing how the implications of GCs on phenotype integration may depend upon the timescale under consideration. GCs can promote adaptive phenotypic integration, but their effects on phenotypic co-variation could also limit the dimensions of phenotypic space explored by animals over longer timescales. Finally, I discuss how organismal responses to environmental stressors can act as a bet hedging mechanism and therefore enhance evolvability by increasing genetic or phenotypic variability or reducing patterns of genetic and phenotypic co-variance. Together, this emphasizes the crucial role of the HPA axis in understanding fundamental questions in evolutionary ecology.

House sparrows prioritize skin repair over constitutive innate immunity during long-term chronic stress

The reactive scope model was created to address two major unanswered questions in stress physiology: how and when does the adaptive acute stress response turn into harmful chronic stress? Previous studies suggest that immunoenhancement should occur in reactive homeostasis (acute stress) and immunosuppression should occur in homeostatic overload (chronic stress). We used this dichotomy of immune function to further elucidate the transition from acute to chronic stress by treating house sparrows (Passer domesticus) with different intensities of chronic stress and then monitoring their immune function. By varying the number of stressors given per day and the length of chronic stress bouts over a period of 6 months, we produced four treatment groups: high, medium, and low stress, and captivity-only. We tracked immunity through the bacterial killing assay and monitored healing of a 4 mm skin biopsy punch. We hypothesized that higher-stress birds would repair their skin more slowly and have lower bacterial killing capacity. The opposite was true-high-stress birds initially repaired their skin fastest. Additionally, all birds dramatically reduced bacterial killing capacity after the biopsy and increased food-derived uric acid, suggesting increased energy acquisition and a shift in immune resources to a more immediate concern (healing). Once healing finished, only the high-stress birds were unable to recover circulating immune function, suggesting that the combination of high stress and an immune challenge pushed these birds into homeostatic overload. Prioritizing healing over other immunological processes might be the best defense for a bird in its natural habitat.

Immune and stress physiology of two captively-housed tortoise species

Ecoimmunology affords us the ability to better understand immunological processes through consideration of external factors, such as the thermal microenvironment. This consideration is imperative when examining the immunological processes of ectothermic organisms like reptiles. Reptiles uniquely rely heavily on their innate immune function but remain poorly understood in immunological studies. In this study, we examined innate immunity in two zoo-housed tortoise species, the Indian star tortoise (Geochelone elegans, Schoepff, 1795) and northern spider tortoise (Pyxis arachnoides brygooi, Vuillemin & Domergue, 1972). Bacterial killing assays (BKAs) were optimized and used to assess the monthly immunocompetence of these tortoises to three different bacteria: Escherichia coli, Salmonella enterica, and Staphylococcus aureus. We evaluated differences in blood biochemistry values (lactate and glucose) among months and species as well as fecal corticosterone (CORT) between species. Lastly, we examined the potential influences of individual thermal microenvironments on bactericidal ability. Both G. elegans and P. a. brygooi demonstrated immunocompetence against all bacterial challenges, but only bactericidal ability against E. coli varied over months. Optimal BKA serum dilutions, blood glucose levels, and fecal CORT concentrations differed between the two species. Finally, there was evidence that the thermal microenvironment influenced the tortoises' bactericidal ability against E. coli. Through use of nonmodel organisms, such as tortoises, we are given insight into the inner workings of innate immunity and a better understanding of the complexities of the vertebrate immune system.

Impact of alternating overnight housing conditions on welfare measures in a bachelor group of western lowland gorillas (Gorilla gorilla gorilla)

Spatial parameters and design of overnight housing spaces can have significant influences on both nocturnal and diurnal behaviors of western lowland gorillas (Gorilla gorilla gorilla) in captivity. This is especially true for bachelor groups, as adult males have demonstrated a greater tendency to separate from conspecifics overnight. Additionally, previous studies have suggested that the social needs of individuals in bachelor units may shift over time. The bachelor unit at the Detroit Zoo is managed in a unique hybrid strategy in which the group is housed socially for three nights (either indoors or indoors with outdoor access), then separately on the fourth. A 2016 study of this group (n = 3) suggested that individuals had better welfare following social overnight housing as compared to solitary overnight housing. We aimed to reassess how overnight housing conditions affect individual welfare several years later. We revised a previously developed qualitative behavioral assessment tool that included 13 behavioral items spanning both positive and negative indicators of welfare. Animal care staff completed the assessment and collected a fecal sample every day for each gorilla for a period of 3 months. We used Kruskal-Wallis tests to analyze variation in behavioral items and FGMs between conditions. We then used generalized linear mixed models to identify whether overnight housing condition or other potentially confounding variables were driving observed variation in welfare indicators. We found significant variation demonstrating significantly better welfare indicators after being housed separately as compared to being socially housed indoors overnight. Although separate housing appears to be the ideal condition for this group at this point in time, if seasonality permits, social housing with outdoor access may be a feasible alternative to consistent overnight separation for these gorillas.

VALIDATION OF ENZYME-LINKED IMMUNOSORBENT ASSAY TECHNIQUES TO MEASURE SERUM DEHYDROEPIANDROSTERONE (DHEA) AND DHEA-S IN NARWHALS (MONODON MONOCEROS)

Narwhals (Monodon monoceros) are increasingly exposed to anthropogenic disturbances that may increase their stress levels with unknown consequences for the overall population dynamics. The validation and measurement of chronic stress biomarkers could contribute toward improved understanding and conservation efforts for this species. Dehydroepiandrosterone (DHEA) and its sulfated metabolite DHEA-S are collectively referred to as DHEA(S). Serum DHEA(S) concentrations combined in ratios with cortisol [cortisol/DHEA(S)] have been shown to be promising indicators of chronic stress in humans, domestic animals, and wildlife. During field tagging in 2017 and 2018 in Baffin Bay, Nunavut, Canada, 14 wild narwhals were sampled at the beginning and end of the capture-tagging procedures. Serum DHEA(S) were measured with commercially available competitive enzyme-linked immunosorbent assays (ELISA) developed for humans. A partial validation of the ELISA assays was performed by the determination of the intra-assay coefficient of variation, confirmation of the DHEA(S) dilutional linearity, and the calculation of the percentage of recovery. Mean values (nanograms per milliliter ± standard error of the mean) of narwhal serum cortisol, DHEA(S), and cortisol/DHEA(S) ratios, at the beginning and at the end of handling, respectively, are reported (cortisol = 30.74 ± 4.87 and 41.83 ± 4.83; DHEA = 1.01 ± 0.52 and 0.99 ± 0.50; DHEA-S = 8.72 ± 1.68 and 7.70 ± 1.02; cortisol/DHEA = 75.43 ± 24.35 and 84.41 ± 11.76, and cortisol/DHEA-S = 4.16 ± 1.07 and 6.14 ± 1.00). Serum cortisol and cortisol/DHEA-S were statistically higher at the end of the capture (P= 0.024 and P= 0.035, respectively). Moreover, serum cortisol at the end of handling was positively correlated to total body length (P = 0.042) and tended to be higher in males (P = 0.086). These assays proved easy to perform, rapid, and suitable for measuring serum DHEA(S) of narwhals and that calculated cortisol/DHEA(S) are potential biomarkers for chronic stress in narwhals and possibly other cetaceans.

Zoo studies in primate physiology, health, and welfare

Researchers have been studying primates in zoos for more than half a century. There are numerous benefits to conducting research with zoo collections, such as access to a variety of species, ease of sample collection, and the potential to manipulate some research variables. While much of the primate research conducted in zoos is behavioral, there also is a tradition of research focused on reproduction and endocrinology, especially in North America. The contributions to this special issue exemplify how this tradition continues today through a collection of articles on basic and applied research on reproduction and using physiological measures of health and welfare that could be beneficial across primate taxa. As is the case for primatological research in zoos more broadly, the articles in this special issue reflect a taxonomic bias for great apes despite the high species diversity found across zoo collections. Given this bias as well as the threat of extinction faced by many species, there remains a pressing need to increase primatology in zoos through research dedicated to both conservation in the wild and wellbeing in human care.

Urbanization and maternal hormone transfer: Endocrine and morphological phenotypes across ontogenetic stages

The phenotypes observed in urban and rural environments are often distinct; however, it remains unclear how these novel urban phenotypes arise. Hormone-mediated maternal effects likely play a key role in shaping developmental trajectories of offspring in different environments. Thus, we measured corticosterone (Cort) and testosterone (T) concentrations in eggs across the laying sequence in addition to Cort concentrations in nestling and adult female house wrens (Troglodytes aedon) at one urban and one rural site. We found that egg T concentrations were not different between birds from urban and rural sites. However, across all life stages (egg, nestling, and adult female), Cort concentrations were higher at the urban site. Additionally, urban nestling Cort concentrations, but not rural, correlated with fine-scale urban density scores. Furthermore, rural egg volume increased over the laying sequence, but urban egg volume leveled off mid-sequence, suggesting either that urban mothers are resource limited or that they are employing a different brood development strategy than rural mothers. Our study is one of the first to show that egg hormone concentrations differ in an urban environment with differences persisting in chick development and adult life stages. We suggest that maternal endocrine programing may shape offspring phenotypes in urban environments and are an overlooked yet important aspect underlying mechanisms of urban evolution.

Assessment of lipids and adrenal hormones in the Florida manatee (Trichechus manatus latirostris) from different habitats

Florida manatees (Trichechus manatus latirostris), a federally protected species, are classified as threatened due to anthropogenic stressors. Manatees inhabit sites that are impacted by human activities that can negatively affect stress physiology and metabolism. Samples collected from healthy manatees (pregnant females, non-pregnant females, and males) at Crystal River and Indian River Lagoon in Florida, were assessed for adrenal hormones, proteins, glucose, and lipid content in plasma. The objective was to determine if healthy manatees sampled between 2010-2014 from the Indian River Lagoon exhibited evidence of stress compared to healthy manatees sampled between 2012-2019 from Crystal River. Plasma cortisol concentrations were not different in male and non-pregnant female manatees between sites but were elevated in pregnant manatees. Plasma aldosterone concentrations were elevated in Indian River Lagoon manatees relative to those at Crystal River, possibly due to differences in salinity and available freshwater between the two environments. Site differences were noted for plasma protein and glucose concentrations in manatees; additionally, differences between the sexes were also observed in glucose concentrations. Fifteen lipid subclasses, including oxidized lysophosphatidylcholines, oxidized phosphatidylcholines, oxidized triacylglycerols, were elevated in manatees from the Indian River Lagoon relative to manatees from Crystal River. Evidence of a stress response in healthy Indian River Lagoon manatees was lacking compared to Crystal River manatees. Differences in metabolites related to energy (glucose, protein, and lipids) may be related to site-specific variables, such as salinity and food availability/quality. This study generates novel data on plasma lipid profiles and provides cortisol, aldosterone, glucose, and protein values from healthy Florida manatees in two disparate sites that can be referenced in future studies. These data contribute to an improved understanding of manatee physiology to better inform population management.

Integrating Reference Intervals into Chimpanzee Welfare Research

Animal welfare researchers are committed to developing novel approaches to enhance the quality of life of chimpanzees living in professional care. To systematically monitor physical, mental, and emotional states, welfare scientists highlight the importance of integrating non-invasive, animal-based welfare indicators. This study aimed to create species-specific reference intervals for behavioral measures and physiological biomarkers. Specifically, we analyzed data from 40 adult chimpanzees (22 females, 18 males) residing at 16 zoological facilities to generate reference intervals for behavioral states and events, behavioral diversity, fecal glucocorticoid metabolites (GCMs), and fecal immunoglobulin-A (IgA). Comparisons of sex and age using linear regression models revealed significant differences for several behaviors. The proportion of time spent engaged in mutual/multiple social grooming significantly decreased as individuals aged. Furthermore, males spent a higher proportion of time performing aggressive contact behaviors and displaying to other chimpanzees when compared to females. Males also performed sexual examination behaviors at a higher rate than females. Behavioral diversity, fecal GCM, and fecal IgA did not vary by sex or age. In the future, values for individual chimpanzees can be compared to the ranges reported here for particular age/sex classes. Ultimately, animal care professionals can utilize reference intervals to make evidence-based decisions regarding management practices and environmental conditions.

Effects of corticosterone administration on the body condition and blood parameters of the house sparrow, Passer domesticus

Glucocorticoids are steroid hormones produced by the adrenal glands and released into the bloodstream in response to stressful situations. In birds, corticosterone (CORT) is the main glucocorticoid released under stress. Throughout their lives, animals in nature are continually exposed to noxious stimuli known as stressful events. Any alteration of homeostatic stability is a stressful situation and this alteration triggers physiological changes to restore homeostasis. Glucocorticoids are one of the components of the complex set of physiological and behavioral responses to stress. In this work, we use CORT supplied in drinking water to evaluate its effect in blood parameters and physiology in house sparrows (Passer domesticus). To accomplish this, P. domesticus were administered three different doses of CORT in drinking water for 72 h. Body mass, organ mass, pectoral muscle mass, leg muscle mass, and blood parameters (CORT, triglycerides, glucose and uric acid, heterophils/lymphocytes ratio, hematocrit, and serum protein profile) were determined before and after CORT treatment. A 15% decrease in body mass with a significant decrease in pectoral mass were observed after the higher CORT treatment, as well as a decrease in the plasma concentration of uric acid. Lastly, we found a reversal of the heterophils/lymphocytes ratio and a decrease in hematocrit. It was possible to establish first data for baseline and CORT-alteration values in serum protein profile for P. domesticus. Baseline and altered values of blood parameters and serum protein profile could be an important tool in field ecology because they provide important data to assess the physiological condition in wild birds.

Past and future: Urbanization and the avian endocrine system

Urban environments are evolutionarily novel and differ from natural environments in many respects including food and/or water availability, predation, noise, light, air quality, pathogens, biodiversity, and temperature. The success of organisms in urban environments requires physiological plasticity and adjustments that have been described extensively, including in birds residing in geographically and climatically diverse regions. These studies have revealed a few relatively consistent differences between urban and non-urban conspecifics. For example, seasonally breeding urban birds often develop their reproductive system earlier than non-urban birds, perhaps in response to more abundant trophic resources. In most instances, however, analyses of existing data indicate no general pattern distinguishing urban and non-urban birds. It is, for instance, often hypothesized that urban environments are stressful, yet the activity of the hypothalamus-pituitary-adrenal axis does not differ consistently between urban and non-urban birds. A similar conclusion is reached by comparing blood indices of metabolism. The origin of these disparities remains poorly understood, partly because many studies are correlative rather than aiming at establishing causality, which effectively limits our ability to formulate specific hypotheses regarding the impacts of urbanization on wildlife. We suggest that future research will benefit from prioritizing mechanistic approaches to identify environmental factors that shape the phenotypic responses of organisms to urbanization and the neuroendocrine and metabolic bases of these responses. Further, it will be critical to elucidate whether factors affect these responses (a) cumulatively or synergistically; and (b) differentially as a function of age, sex, reproductive status, season, and mobility within the urban environment. Research to date has used various taxa that differ greatly not only phylogenetically, but also with regard to ecological requirements, social systems, propensity to consume anthropogenic food, and behavioral responses to human presence. Researchers may instead benefit from standardizing approaches to examine a small number of representative models with wide geographic distribution and that occupy diverse urban ecosystems.

Glucocorticoids in relation to behavior, morphology, and physiology as proxy indicators for the assessment of animal welfare. A systematic mapping review

Translating theoretical concepts of animal welfare into quantitative assessment protocols is an ongoing challenge. Glucocorticoids (GCs) are frequently used as physiological measure in welfare assessment. The interpretation of levels of GCs and especially their relation to welfare, however, is not as straightforward, questioning the informative power of GCs. The aim of this systematic mapping review was therefore to provide an overview of the relevant literature to identify global patterns in studies using GCs as proxy for the assessment of welfare of vertebrate species. Following a systematic protocol and a-priory inclusion criteria, 509 studies with 517 experiments were selected for data extraction. The outcome of the experiments was categorized based on whether the intervention significantly affected levels of GCs, and whether these effects were accompanied by changes in behavior, morphology and physiology. Additional information, such as animal species, type of intervention, experimental set up and sample type used for GC determination was extracted, as well. Given the broad scope and large variation in included experiments, meta-analyses were not performed, but outcomes are presented to encourage further, in-depth analyses of the data set. The interventions did not consistently lead to changes in GCs with respect to the original authors hypothesis. Changes in GCs were not consistently paralleled by changes in additional assessment parameter on behavior, morphology and physiology. The minority of experiment quantified GCs in less invasive sample matrices compared to blood. Interventions showed a large variability, and species such as fish were underrepresented, especially in the assessment of behavior. The inconclusive effects on GCs and additional assessment parameter urges for further validation of techniques and welfare proxies. Several conceptual and technical challenges need to be met to create standardized and robust welfare assessment protocols and to determine the role of GCs herein.

The Effect of Unpredictable Chronic Stress on Rare Minnow (Gobiocypris rarus): Growth, Behaviour and Physiology

Fishes often adjust their behaviour patterns and physiological responses to cope with changing environments, and different life experiences affect them differently. Fishes might adapt to short-term stress, whereas long-term unpredictable stress may lead to various adverse effects. Although some studies have constructed unpredictable stress models of fish, the effect of unpredictable chronic stress (UCS) in the laboratory is poorly understood in fishes. In the current study, we exposed adult rare minnow to an unpredictable chronic stress protocol over 7 and 14 days and measured their response in terms of growth performance, cortisol, neurotransmitter levels (DA, 5-HT, and related metabolites), and behaviour patterns to comprehensively assess the effects of UCS on laboratory rare minnow. We discovered that specific growth rates were significantly decreased, and cortisol levels were lowered in both 7-days and 14-days stress groups. In the behaviour test, the activity level of the 14-days stress group increased, but there was no significant difference in the number of crossings to the center areas, time spent in the center areas, or the speed. In addition, the levels of DA and 5-HT did not change in the stress groups, but the DOPAC and 5-HIAA levels in the 14 days stress group were significantly higher than those in the control group. These results suggested that UCS influences rare minnow growth performance, behaviour patterns, and cortisol levels, and similar stress should be minimised in the laboratory.

Effects of methylmercury and food stress on migratory activity in song sparrows, Melospiza melodia

Avian migration is a challenging life stage susceptible to the adverse effects of stressors, including contaminants like methylmercury (MeHg). Although birds often experience stressors and contaminants concurrently in the wild, no study to date has investigated how simultaneous exposure to MeHg and food stress affects migratory behavior. Our objectives were to determine if MeHg or food stress exposure during summer, alone or combined, has carry-over effects on autumn migratory activity, and if hormone levels (corticosterone, thyroxine) and body condition were related to these effects. We tested how exposure to dietary MeHg and/or food stress (unpredictable temporary food removal) affected migratory behavior in captive song sparrows, Melospiza melodia. Nocturnal activity was influenced by a 3-way interaction between MeHg × stress × nights of the study, indicating that activity changed over time in different ways depending on prior treatments. Thyroxine was not affected by treatment or sampling date. During the migratory season, fecal corticosterone metabolite concentrations increased in birds co-exposed to MeHg and food stress compared to controls, suggesting an additive carry-over effect. As well, during the period of behavioral recording, body condition increased with time in unstressed birds, but not in stressed birds. Fecal corticosterone metabolite concentrations were positively correlated to duration of nocturnal activity, but thyroxine levels and body condition were not. The differences in nocturnal activity between groups suggest that food stress and MeHg exposure on breeding grounds could have direct and indirect carry-over effects that have the potential to affect the fall migration journey.

Expanding the frame around social dynamics and glucocorticoids: From hierarchies within the nest to competitive interactions among species

The effect of the social environment on individual state or condition has largely focused on glucocorticoid levels (GCs). As metabolic hormones whose production can be influenced by nutritional, physical, or psychosocial stressors, GCs are a valuable (though singular) measure that may reflect the degree of "stress" experienced by an individual. Most work to date has focused on how social rank influences GCs in group-living species or how predation risk influences GCs in prey. This work has been revealing, but a more comprehensive assessment of the social environment is needed to fully understand how different features of the social environment influence GCs in both group living and non-group living species and across life history stages. Just as there can be intense within-group competition among adult conspecifics, it bears appreciating there can also be competition among siblings from the same brood, among adult conspecifics that do not live in groups, or among heterospecifics. In these situations, dominance hierarchies typically emerge, albeit, do dominants or subordinate individuals or species have higher GCs? We examine the degree of support for hypotheses derived from group-living species about whether differential GCs between dominants and subordinates reflect the "stress of subordination" or "costs of dominance" in these other social contexts. By doing so, we aim to test the generality of these two hypotheses and propose new research directions to broaden the lens that focuses on social hierarchies and GCs.

Orphaning stunts growth in wild African elephants

Orphans of several species suffer social and physiological consequences such as receiving more aggression from conspecifics and lower survival. One physiological consequence of orphaning, stunted growth, has been identified in both humans and chimpanzees, but has not been assessed in a non-primate species. Here, we tested whether wild African elephant orphans show evidence of stunted growth. We measured individually known female elephants in the Samburu and Buffalo Springs National Reserves of Kenya, with a rangefinder capable of calculating height, to estimate a von Bertalanffy growth curve for female elephants of the study population. We then compared measurements of known orphans and non-orphans of various ages, using a Bayesian analysis to assess variation around the derived growth curve. We found that orphans are shorter for their age than non-orphans. However, results suggest orphans may partially compensate for stunting through later growth, as orphans who had spent a longer time without their mother had heights more similar to non-orphans. More age mates in an individual's family were associated with taller height, suggesting social support from peers may contribute to increased growth. Conversely, more adult females in an individual's family were associated with shorter height, suggesting within-group competition for resources with older individuals may reduce juvenile growth. Finally, we found a counterintuitive result that less rainfall in the first 6 years of life was correlated with taller height, potentially reflecting the unavoidable bias of measuring individuals who were fit enough to survive conditions of low rainfall as young calves. Reduced growth of individuals has been shown to reduce survival and reproduction in other species. As such, stunting in wildlife orphans may negatively affect fitness and represents an indirect effect of ivory poaching on African elephants.

Social support correlates with glucocorticoid concentrations in wild African elephant orphans

Social relationships have physiological impacts. Here, we investigate whether loss of the mother/offspring relationship has lasting effects on fecal glucocorticoid metabolite (fGCM) concentrations in wild African elephant orphans several years following their mothers’ deaths. We find no difference in fGCM concentrations between orphans and nonorphans, but find lower fGCM concentrations in elephants with more age mates in their family. We also unexpectedly identify lower concentrations in orphans without their natal family versus nonorphans and natal orphans, which we speculate may be due to the development of hypocortisolism following a prolonged period without familial support. An index of plant productivity (i.e. food) shows the largest correlation with fGCM concentrations. Our findings indicate no lasting differences in glucocorticoid concentrations of surviving orphan elephants who are with their family, suggest the presence of age mates may reduce glucocorticoid concentrations in elephants, and emphasize that basic survival needs are the primary regulators of the stress response.

Remaining with the family group may reduce long-term stress effects in orphaned African elephants.

Validation of an Enzyme Immunoassay to Measure Faecal Glucocorticoid Metabolites in Common Brushtail Possums (Trichosurus vulpecula) to Evaluate Responses to Rehabilitation

Simple Summary

Little is known about how exposure to novel stimuli during rescue and rehabilitation could affect the physiology of native wildlife. We investigated this question in a species commonly rescued for rehabilitation, the common brushtail possum (Trichosurus vulpecula). Glucocorticoids (major hormones involved in stress responses) are metabolised in the body and excreted in the form of faecal glucocorticoid metabolites, which can be measured as a way of evaluating the response of animals to potential stressors. Comparing five enzyme immunoassay options, we found that the 11-oxoaetiocholanolone (abbreviation: 72a) EIA was the most suitable for measuring these metabolites in brushtail possums. This assay was then used to measure faecal glucocorticoid metabolite concentrations in 20 possums during rehabilitation. The probability of a physiological “stress” response occurring within five days of a potentially stressful event was about 50%, regardless of the type of event. There was a high level of variation in hormone profiles between possums. Our study has demonstrated that injured and orphaned possums show detectable changes in faecal glucocorticoid metabolites during captivity and rehabilitation, and has identified events that can induce a physiological response in some individuals. This is the first step toward understanding the relationship between these responses during rehabilitation and survival.

Abstract

Volunteer wildlife rehabilitators rescue and rehabilitate thousands of native animals every year in Australia. However, there is little known about how exposure to novel stimuli during rehabilitation could affect the physiology of wildlife. We investigated this question in a species that commonly enters rehabilitation, the common brushtail possum (Trichosurus vulpecula). We evaluated five enzyme immunoassays (EIA) to determine the most suitable for measuring faecal glucocorticoid metabolites (FGM) as a proxy for evaluating the response of brushtail possums to potential stressors during rehabilitation. An adrenocorticotrophin hormone (ACTH) challenge was conducted on wild-caught possums to determine the best-performing EIA based on the successful detection of FGM peaks in at least two of three possums. While a number of assays met these criteria, the 11-oxoaetiocholanolone (abbreviation: 72a) EIA was selected as it had the largest amplitude of change in response to the ACTH challenge. This assay was then used to measure FGM concentrations in 20 possums during rehabilitation. There was high variation in baseline FGM concentrations and response to captivity between possums. Significant changes in FGM levels were detected in most possums during captivity, but were not reliably associated with potentially stressful events that were identified by rehabilitators. The probability of an FGM peak occurring within five days of a potentially stressful event was about 50%, regardless of the type of event. Our study has demonstrated that injured and orphaned possums show changes in FGMs during captivity and rehabilitation and has identified events that can induce a physiological response in some individuals. We recommend that research now focus on the relationship between these responses during rehabilitation and pre- and post-release survival.

Glucocorticoids in a warming world: Do they help birds to cope with high environmental temperatures?

Climate change is threatening biodiversity world-wide. One of its most prominent manifestations are rising global temperatures and higher frequencies of heat waves. High environmental temperatures may be particularly challenging for endotherms, which expend considerable parts of their energy budget and water resources on thermoregulation. Thermoregulation involves phenotypic plasticity in behavioral and physiological traits. Information on causal mechanisms that support plastic thermoregulatory strategies is key to understand how environmental information is transmitted and whether they impose trade-offs or constraints that determine how endotherms cope with climate warming. In this review, we focus on glucocorticoids, metabolic hormones that orchestrate plastic responses to various environmental stimuli including temperature. To evaluate how they may mediate behavioral and physiological responses to high environmental temperatures, we 1) briefly review the major thermoregulatory strategies in birds; 2) summarize the functions of baseline and stress-induced glucocorticoid concentrations; 3) synthesize the current knowledge of the relationship between circulating glucocorticoids and high environmental temperatures in birds; 4) generate hypotheses for how glucocorticoids may support plastic thermoregulatory responses to high environmental temperatures that occur over different time-frames (i.e., acute, short- and longer-term); and 5) discuss open questions on how glucocorticoids, and their relationship with thermoregulation, may evolve. Throughout this review we highlight that our knowledge, particularly on free-living populations, is really limited and outline promising avenues for future research. As evolutionary endocrinologists we now need to step up and identify the costs, benefits, and evolution of glucocorticoid plasticity to elucidate how they may help birds cope with a warming world.

The social transmission of stress in animal collectives

The stress systems are powerful mediators between the organism's systemic dynamic equilibrium and changes in its environment beyond the level of anticipated fluctuations. Over- or under-activation of the stress systems' responses can impact an animal's health, survival and reproductive success. While physiological stress responses and their influence on behaviour and performance are well understood at the individual level, it remains largely unknown whether-and how-stressed individuals can affect the stress systems of other group members, and consequently their collective behaviour. Stressed individuals could directly signal the presence of a stressor (e.g. via an alarm call or pheromones), or an acute or chronic activation of the stress systems could be perceived by others (as an indirect cue) and spread via social contagion. Such social transmission of stress responses could then amplify the effects of stressors by impacting social interactions, social dynamics and the collective performance of groups. As the neuroendocrine pathways of the stress response are highly conserved among vertebrates, transmission of physiological stress states could be more widespread among non-human animals than previously thought. We therefore suggest that identifying the extent to which stress transmission modulates animal collectives represents an important research avenue.

Physiological effects of capture and short-term captivity in an invasive snake species, the Burmese python (Python bivittatus) in Florida

It is important to evaluate the role of captivity as a potential stressor. An understanding of stress responses to capture and transition to captivity may inform the limitations of laboratory studies on wild animals, aid in understanding the consequences of introducing animals into captive environments, and help predict which species may be successful invasives. We investigated physiological effects of captivity by comparing at-capture blood variables in wild Burmese pythons (Python bivittatus) in Florida to pythons recently brought into captivity (1-109 days). We conducted an acute restraint test by collecting samples at baseline (immediately at handling) and one hour post-restraint across wild field-sampled (n = 19) and recently-captive (n = 33) pythons to evaluate fluctuations in plasma corticosterone, bacterial killing ability, antibody response, leukogram, and serpentovirus infection. We observed higher baseline plasma corticosterone and monocytes in recently captive compared to wild snakes, which both subsided in snakes held for a longer time in captivity, and a mild decrease in lymphocytes in the middle of the captivity period. Functional immunity and viral infection were not affected by captivity, and pythons maintained restraint-induced responses in corticosterone, heterophil to lymphocyte ratio, and monocyte counts throughout captivity. Prevalence for serpentovirus was 50%, though infection status was related to sampling date rather than captivity, indicating that viral infection may be seasonal. The history of Burmese python as a common captive animal for research and pet trade, as well as its general resilience to effects of capture and short-term captivity, may contribute to its invasion success in Florida.

Identification of Metabolomic Biomarkers of Long-Term Stress Using NMR Spectroscopy in a Diving Duck

Human-induced environmental changes that act as long-term stressors pose significant impacts on wildlife health. Energy required for maintenance or other functions may be re-routed towards coping with stressors, ultimately resulting in fluctuations in metabolite levels associated with energy metabolism. While metabolomics approaches are used increasingly to study environmental stressors, its use in studying stress in birds is in its infancy. We implanted captive lesser scaup (Aythya affinis) with either a biodegradable corticosterone (CORT) pellet to mimic the effects of a prolonged stressor or a placebo pellet. 1D ¹H nuclear magnetic resonance (NMR) spectroscopy was performed on serum samples collected over 20 days after implant surgery. We hypothesized that CORT pellet-induced physiological stress would alter energy metabolism and result in distinct metabolite profiles in ducks compared with placebo (control). Quantitative targeted metabolite analysis revealed that metabolites related to energy metabolism: glucose, formate, lactate, glutamine, 3-hydroxybutyrate, ethanolamine, indole-3- acetate, and threonine differentiated ducks with higher circulatory CORT from controls on day 2. These metabolites function as substrates or intermediates in metabolic pathways related to energy production affected by elevated serum CORT. The use of metabolomics shows promise as a novel tool to identify and characterize physiological responses to stressors in wild birds.