Habitat degradation increases stress-hormone levels during the breeding season,and decreases survival and reproduction in adult common lizards

The allostatic load model describes how individuals maintain homeostasis in challenging environment and posits that costs induced by a chronic perturbation (i.e., allostatic load) are correlated to the secretion of glucocorticoids, such as corticosterone. Habitat perturbations from anthropogenic activities are multiple and functional responses to those are still unclear. Here, we manipulated the habitat quality in 24 semi-natural populations of the common lizard during 1 year. We tested the predictions of the allostatic load model that habitat degradation should increase baseline corticosterone levels, and should induce concomitant physiological changes, such as lipid mobilization and lower immunocompetence, and demographic changes, such as lower body growth, survival and/or reproductive performances. Our results highlight stage-dependent effects of habitat degradation on physiological traits during the breeding season: adult lizards had higher baseline corticosterone levels and yearling lizards had a lower inflammatory response than adults, whereas juveniles had higher circulating lipid levels than yearlings and adults without concomitant change in corticosterone levels. In addition, habitat degradation reduced the performances of adults but not of juveniles: in low habitat quality populations, adult males had a lower survival and females had a smaller fecundity. These results are in accordance with the allostatic load model given that allostatic load was detected only during the season and in life stages of maximal energy expenditure. This underlines the importance to account for individual energy requirements to better understand demographic responses to habitat perturbation.     

Physiological dysregulation and somatic decline among elders: modeling, applying and re-interpreting allostatic load

Mortality rates continue to decline among post-reproductive individuals. This makes understanding long-term physiological responses to stress increasingly important. Allostatic load (AL) was developed to assess detrimental effects on the soma of responding to multiple stressors over a lifetime. AL arises from developmental experiences, genetic predispositions, environmental, psychosocial, life style and other stressors. In early life stress responsive systems are initiated that produce hormones that maintain the soma through continual allostatic responses. Later in life, systems designed to mitigate stressors may fail or be compromised, promoting unwanted somatic changes and dysregulation. This places a load on the regulatory system that impedes day-to-day stress responses, predisposing to cellular damage and degenerative diseases. Here we review 44 peer-reviewed 2005-2010 publications reportedly examining relationships between AL and risk factors, chronic diseases, morbidity and mortality in samples of elderly adults. The sum of results suggests that AL does assess aspects of physiological dysregulation and somatic decline, predicts detrimental age-related declines, and is associated with negative sociocultural attributes and psychological outcomes. Such consistent results and wide application of AL, while it is still being modeled and re-interpreted, suggest its perceived usefulness as a research and clinical tool. AL provides a possible biomarker of senescence, assessing it over the life span will aid in predicting future negative health outcomes.     

Allostasis,Allostatic Load,and the Aging Nervous System: Role of Excitatory Amino Acids and Excitotoxicity

The adaptive responses of the body to challenges, often known as "stressors", consists of active responses that maintain homeostasis. This process of adaptation is known as "allostasis", meaning "achieving stability through change". Many systems of the body show allostasis, including the autonomic nervous system and hypothalamo-pituitary-adrenal (HPA) axis and they help to re-establish or maintain homeostasis through adaptation. The brain also shows allostasis, involving the activation of nerve cell activity and the release of neurotransmitters. When the individual is challenged repeatedly or when the allostatic systems remain turned on when no longer needed, the mediators of allostasis can produce a wear and tear on the body that has been termed "allostatic load". Examples of allostatic load include the accumulation of abdominal fat, the loss of bone minerals and the atrophy of nerve cells in the hippocampus. Circulating stress hormones play a key role, and, in the hippocampus, excitatory amino acids and NMDA receptors are important mediators of neuronal atrophy. The aging brain seems to be more vulnerable to such effects, although there are considerable individual differences in vulnerability that can be developmentally determined. Yet, at the same time, excitatory amino acids and NMDA receptors mediate important types of plasticity in the hippocampus. Moreover, the brain retains considerable resilience in the face of stress, and estrogens appear to play a role in this resilience. This review discusses the current status of work on underlying mechanisms for these effects.     

Physiological seasonality in the symbiont and host of the northern star coral,Astrangia poculata

Coral Reefs - Assessing physiological responses that correspond to the normal range of seasonal variation can provide a better understanding of how environmental stressors may impact physiology....     

Dynamics of plant responses to combinations of air pollutants

The focus of this review is on how plants respond to combinations of multiple air pollutants. Global pollution trends, plant physiological responses and ecological perspectives in natural and agricultural systems are all discussed. In particular, we highlight the importance of studying sequential or simultaneous exposure of plants to pollutants, rather than exposure to individual pollutants in isolation, and explore how these responses may interfere with the way plants interact with their biotic community. Air pollutants can alter the normal physiology and metabolic functioning of plants. Here we describe how the phenotypic and molecular changes in response to multiple pollutants can differ compared to those elicited by single pollutants, and how different responses have been observed between plants in the field and in controlled laboratory conditions and between trees and crop plants. From an ecological perspective, we discuss how air pollution can result in greater susceptibility to biotic stressors and in direct or indirect effects on interactions with organisms that occupy higher trophic levels. Finally, we provide an overview of the potential uses of plants to mitigate air pollution, exploring the feasibility for pollution removal via the processes of bio‐accumulation and phytoremediation. We conclude by proposing some new directions for future research in the field.     

Evaluation of physiological stress in free-ranging bears: current knowledge and future directions

Stress responses, which are mediated by the neurogenic system (NS) and hypothalamic–pituitary–adrenal (HPA) axis help vertebrates maintain physiological homeostasis. Fight-or-flight responses are activated by the NS, which releases norepinephrine/noradrenaline and epinephrine/adrenaline in response to immediate stressors, whilst the HPA axis releases glucocorticoid hormones (e.g. cortisol and corticosterone) to help mitigate allostatic load. There have been many studies on stress responses of captive animals, but they are not truly reflective of typical ranges or the types of stressors encountered by free-ranging wildlife, such as responses and adaptation to environmental change, which are particularly important from a conservation perspective. As stress can influence the composition of age and sex classes of free-ranging populations both directly and indirectly, ecological research must be prioritised towards more vulnerable taxa. Generally, large predators tend to be particularly at risk of anthropogenically driven population declines because they exhibit reduced behavioural plasticity required to adapt to changing landscapes and exist in reduced geographic ranges, have small population sizes, low fecundity rates, large spatial requirements and occupy high trophic positions. As a keystone species with a long history of coexistence with humans in highly anthropogenic landscapes, there has been growing concern about how humans influence bear behaviour and physiology, via numerous short- and long-term stressors. In this review, we synthesise research on the stress response in free-ranging bear populations and evaluate the effectiveness and limitations of current methodology in measuring stress in bears to identify the most effective metrics for future research. Particularly, we integrate research that utilised haematological variables, cardiac monitors and Global Positioning System (GPS) collars, serum/plasma and faecal glucocorticoid concentrations, hair cortisol levels, and morphological metrics (primarily skulls) to investigate the stress response in ursids in both short- and long-term contexts. We found that in free-ranging bears, food availability and consumption have the greatest influence on individual stress, with mixed responses to anthropogenic influences. Effects of sex and age on stress are also mixed, likely attributable to inconsistent methods. We recommend that methodology across all stress indicators used in free-ranging bears should be standardised to improve interpretation of results and that a wider range of species should be incorporated in future studies.     

Composite estimates of physiological stress, age, and diabetes in American Samoans

Composite estimates of physiological stress such as allostatic load (AL) were developed to help assess cumulative impacts of psychosocial and physical stressors on the body. Physiological responses to stress generally accelerate somatic wear-and-tear and chronic degenerative conditions (CDCs). Following McEwen (Neuropsychopharmacology 22 (1999) 108-124) and others, primary physiological mediators of somatic stress responses include glucocorticoids (cortisol), catecholamines (adrenaline and noradrenaline), and serum dihydroepiandosterone-sulfate (DHEA-S). Conversely, blood pressure (BP), serum HDL and total cholesterol, glycated hemoglobin (HbA1c), and waist/hip (w/h) ratio are modulated by such hormones, thereby acting as secondary mediators of stress response. When these risk factors are aggregated into a composite score, higher stress loads are associated with increased risks for days of school/work missed, functional losses, morbidity, and mortality in US samples. To examine stress loads in American Samoans, data on all 6 secondary mediators along with estimates of body habitus (i.e. height, weight, circumferences, skinfolds) and physiology (i.e. fasting insulin, LDLc, triglycerides, fasting glucose) were measured on 273 individuals residing on Tutuila Island in 1992. Four combinations of these physiological factors were used to determine composite estimates of stress. These were then assessed by sex for associations with age and the presence of diabetes. Composite estimates of stress load were higher in Samoan women than men. Associations with age tended to be low and negative in men, but positive in women, appearing to reflect cultural circumstances and population history. Stress load scores also were higher among those with diabetes than those without among both men and women. These results suggest that composite estimates of stress may be useful for assessing future risks of CDC's and the senescent processes that may underlie them in cross-cultural research.     

The role of the commensal microbiota in adaptive and maladaptive stressor-induced immunomodulation

Over the past decade, it has become increasingly evident that there are extensive bidirectional interactions between the body and its microbiota. These interactions are evident during stressful periods, where it is recognized that commensal microbiota community structure is significantly changed. Many different stressors, ranging from early life stressors to stressors administered during adulthood, lead to significant, community-wide differences in the microbiota. The mechanisms through which this occurs are not yet known, but it is known that commensal microbes can recognize, and respond to, mammalian hormones and neurotransmitters, including those that are involved with the physiological response to stressful stimuli. In addition, the physiological stress response also changes many aspects of gastrointestinal physiology that can impact microbial community composition. Thus, there are many routes through which microbial community composition might be disrupted during stressful periods. The implications of these disruptions in commensal microbial communities for host health are still not well understood, but the commensal microbiota have been linked to stressor-induced immunopotentiation. The role of the microbiota in stressor-induced immunopotentiation can be adaptive, such as when these microbes stimulate innate defenses against bacterial infection. However, the commensal microbiota can also lead to maladaptive immune responses during stressor-exposure. This is evident in animal models of colonic inflammation where stressor exposure increases the inflammation through mechanisms involving the microbiota. It is likely that during stressor exposure, immune cell functioning is regulated by combined effects of both neurotransmitters/hormones and commensal microbes. Defining this regulation should be a focus of future studies.     

The physiological response to anthropogenic stressors in marine elasmobranch fishes: a review with a focus on the secondary response

Elasmobranchs (sharks, rays, and skates) are currently facing substantial anthropogenic threats, which expose them to acute and chronic stressors that may exceed in severity and/or duration those typically imposed by natural events. To date, the number of directed studies on the response of elasmobranch fishes to acute and chronic stress are greatly exceeded by those related to teleosts. Of the limited number of studies conducted to date, most have centered on sharks; batoids are poorly represented. Like teleosts, sharks exhibit primary and secondary responses to stress that are manifested in their blood biochemistry. The former is characterized by immediate and profound increases in circulating catecholamines and corticosteroids, which are thought to mobilize energy reserves and maintain oxygen supply and osmotic balance. Mediated by these primary responses, the secondary effects of stress in elasmobranchs include hyperglycemia, acidemia resulting from metabolic and respiratory acidoses, and profound disturbances to ionic, osmotic, and fluid volume homeostasis. The nature and magnitude of these secondary effects are species-specific and may be tightly linked to metabolic scope and thermal physiology as well as the type and duration of the stressor. In fishes, acute and chronic stressors can incite a tertiary response, which involves physiological changes at the organismal level, thereby impacting growth rates, reproductive outputs or investments, and disease resistance. Virtually no studies to date have been conducted on the tertiary stress response in elasmobranchs. Given the diversity of elasmobranchs, additional studies that characterize the nature, magnitude, and consequences of physiological stress over a broad spectrum of stressors are essential for the development of conservation measures. Additional studies on the primary, secondary, and tertiary stress response in elasmobranchs are warranted, with particular emphasis on expanding the range of species and stressors examined. Future studies should move beyond simply studying the effects of known stressors and focus on the underlying physiological mechanisms. Such studies should include the coupling of stress indicators with quantifiable aspects of the stressor, which will allow researchers to test hypotheses on survivorship and, ultimately, derive models that effectively link physiology to mortality. Studies of this nature are essential for decision-making that will result in the effective management and conservation of these species.     

Allostatic load, social status and stress hormones: the costs of social status matter

Cooperation and social support are the major advantages of living in social groups. However, there are also disadvantages arising from social conflict and competition. Social conflicts may increase allostatic load, which is reflected in increased concentrations of glucocorticoids. We applied the emerging concept of allostasis to investigate the relation between social status and glucocorticoid concentrations. Animals in a society experience different levels of allostatic load and these differences may predict relative glucocorticoid concentrations of dominant and subordinate individuals. We reviewed the available data from free-ranging animals and generated, for each sex separately, phylogenetic independent contrasts of allostatic load and relative glucocorticoid concentrations. Our results suggest that the relative allostatic load of social status predicts whether dominants or subordinates express higher or lower concentrations of glucocorticoids. There was a significant correlation between allostatic load of dominance and relative glucocorticoid concentrations in both females and males. When allostatic load was higher in dominants than in subordinates, dominants expressed higher levels of glucocorticoids; when allostatic load was similar in dominants and subordinates, there were only minor differences in glucocorticoid concentrations; and when allostatic load was lower in dominants than in subordinates, subordinates expressed higher levels of glucocorticoids than dominants. To our knowledge, this is the first model that consistently explains rank differences in glucocorticoid concentrations of different species and sexes. The heuristic concept of allostasis thus provides a testable framework for future studies of how social status is reflected in glucocorticoid concentrations.     

Integrating animal behaviour into research on multiple environmental stressors: a conceptual framework

While a large body of research has focused on the physiological effects of multiple environmental stressors, how behavioural and life-history plasticity mediate multiple-stressor effects remains underexplored. Behavioural plasticity can not only drive organism-level responses to stressors directly but can also mediate physiological responses. Here, we provide a conceptual framework incorporating four fundamental trade-offs that explicitly link animal behaviour to life-history-based pathways for energy allocation, shaping the impact of multiple stressors on fitness. We first address how small-scale behavioural changes can either mediate or drive conflicts between the effects of multiple stressors and alternative physiological responses. We then discuss how animal behaviour gives rise to three additional understudied and interrelated trade-offs: balancing the benefits and risks of obtaining the energy needed to cope with stressors, allocation of energy between life-history traits and stressor responses, and larger-scale escape from stressors in space or time via large-scale movement or dormancy. Finally, we outline how these trade-offs interactively affect fitness and qualitative ecological outcomes resulting from multiple stressors. Our framework suggests that explicitly considering animal behaviour should enrich our mechanistic understanding of stressor effects, help explain extensive context dependence observed in these effects, and highlight promising avenues for future empirical and theoretical research.     

Conservation physiology for applied management of marine fish: an overview with perspectives on the role and value of telemetry

Physiological studies focus on the responses of cells, tissues and individuals to stressors, usually in laboratory situations. Conservation and management, on the other hand, focus on populations. The field of conservation physiology addresses the question of how abiotic drivers of physiological responses at the level of the individual alter requirements for successful conservation and management of populations. To achieve this, impacts of physiological effects at the individual level need to be scaled to impacts on population dynamics, which requires consideration of ecology. Successfully realizing the potential of conservation physiology requires interdisciplinary studies incorporating physiology and ecology, and requires that a constructive dialogue develops between these traditionally disparate fields. To encourage this dialogue, we consider the increasingly explicit incorporation of physiology into ecological models applied to marine fish conservation and management. Conservation physiology is further challenged as the physiology of an individual revealed under laboratory conditions is unlikely to reflect realized responses to the complex variable stressors to which it is exposed in the wild. Telemetry technology offers the capability to record an animal's behaviour while simultaneously recording environmental variables to which it is exposed. We consider how the emerging insights from telemetry can strengthen the incorporation of physiology into ecology.     

Iron deficiency stress induced morphological and physiological changes in root tips of sunflower

Typical morphological and physiological changes were observed in iron deficient sunflower ( Helianthus annuus L. cv. Sobrid) roots. These changes, or so-called iron stress reactions, are exclusively confined to the root tips. Typical morphological changes included additional cell division in the rhizodermis layer and enhanced formation of root hairs, leading to an increase in root diameter ("swollen root tips"). These morphological changes were correlated with physiological changes such as increased release of protons, accumulation of phenols in the rhizodermis, and an increased ability of the roots to reduce iron-III compounds ("reducing capacity"). A marked increase in ability of the root tips to take up and translocate iron occurred simultaneously with these changes. There is good evidence that these morphological and physiological changes are reflections of an effective regulatory mechanism for enhanced mobilization of sparingly soluble iron-III compounds in the rhizosphere and for iron uptake by sunflower plants.     

Assessing Stress in Zoo-Housed Western Lowland Gorillas (<Emphasis Type="Italic">Gorilla gorilla gorilla</Emphasis>) Using Allostatic Load

Stress contributes to the development of chronic degenerative diseases in primates. Allostatic load is an estimate of stress-induced physiological dysregulation based on an index of multiple biomarkers. It has been applied to humans to measure effects of stress and predict health outcomes. Assessing allostatic load in nonhuman primates may aid in understanding factors promoting compromised health and longevity in captive populations, as well as risk assessment among wild populations following human activities. We applied an allostatic load index to gorillas housed at the Columbus Zoo and Aquarium (N = 27, 1956–2014) using data from medical records and biomarkers from banked serum. We estimated allostatic load using seven biomarkers (albumin, cortisol, corticotropin-releasing hormone, dehydroepiandrosterone sulfate, glucose, interleukin-6, and tumor necrosis factor alpha) and then examined this index for associations with age, sex, number of stressful events, parturition, physiological health measures, and age at death. Stressful events were defined as agonistic interactions with wounding, translocations, and anesthetizations. Allostatic load positively associated with age and total number of lifetime stressful events. Allostatic load was significantly higher in females than in males. Allostatic load was not associated with number of pregnancies and was not different between nulliparous and parous females. Allostatic load associated positively with serum creatinine and triglyceride levels, showed a nonsignificant negative association with cholesterol, and did not associate significantly with age at death. These results demonstrate the potential utility of allostatic load for exploring long-term stress and health risks, as well as for evaluating environmental stressors for gorillas and other nonhuman primates in captivity and in the wild.     

Causes and consequences of stress

Stress involves real or perceived changes within an organismin the environment that activate an organism's attempts to copeby means of evolutionarily ancient neural and endocrine mechanisms.Responses to acute stressors involve catecholamines releasedin varying proportion at different sites in the sympatheticand central nervous systems. These responses may interact withand be complemented by intrinsic rythms and responses to chronicor intermittent stressors involving the hypothalamic-pituitary-adrenalaxis. Varying patterns of responses to stressors are also affectedby an animal's assessment of their prospects for successfulcoping. Subsequent central and systemic consequences of thestress response include apparent changes in affect, motivation,and cognition that can result in an altered relationship toenvironmental and social stimuli. This review will summarizerecent developments in our understanding of the causes and consequencesof stress. Special problems that need to be explored involvethe manner in which ensembles of adaptive responses are assembled,how autonomic and neurohormonal reflexes of the stress responsecome under the influence of environmental stimuli, and how somespecific aspects of the stress response may be integrated intothe life history of a species.     

Stressors and tasks: how and when should stressors be introduced during training for task performance in stressful situations?

Studies on the training of individuals for task performance in stressful situations have typically evaluated procedures that simultaneously expose trainees to tasks and to stressors. Such procedures might create a mutual interference of the stressor with task acquisition, or conversely, of preoccupation with task acquisition with familiarization with the stressors. Using a sample of 180 males, the present study compared a procedure that temporally separates task acquisition from exposure to stressors ("phased training") with the more typical approach which combines the two ("combined training"). The comparison was carried out under varying degrees of stressor-fidelity representation in the course of training, and under two degrees of contingency between quality of task performance and the possibility of avoiding stress. The main result indicates that phased and combined training are equally effective under conditions of noncontingency. In a contingent condition, on the other hand, phased training proves to be significantly superior.     

The concept of allostasis in biology and biomedicine

Living organisms have regular patterns and routines that involve obtaining food and carrying out life history stages such as breeding, migrating, molting, and hibernating. The acquisition, utilization, and storage of energy reserves (and other resources) are critical to lifetime reproductive success. There are also responses to predictable changes, e.g., seasonal, and unpredictable challenges, i.e., storms and natural disasters. Social organization in many populations provides advantages through cooperation in providing basic necessities and beneficial social support. But there are disadvantages owing to conflict in social hierarchies and competition for resources. Here we discuss the concept of allostasis, maintaining stability through change, as a fundamental process through which organisms actively adjust to both predictable and unpredictable events. Allostatic load refers to the cumulative cost to the body of allostasis, with allostatic overload being a state in which serious pathophysiology can occur. Using the balance between energy input and expenditure as the basis for applying the concept of allostasis, we propose two types of allostatic overload. Type 1 allostatic overload occurs when energy demand exceeds supply, resulting in activation of the emergency life history stage. This serves to direct the animal away from normal life history stages into a survival mode that decreases allostatic load and regains positive energy balance. The normal life cycle can be resumed when the perturbation passes. Type 2 allostatic overload begins when there is sufficient or even excess energy consumption accompanied by social conflict and other types of social dysfunction. The latter is the case in human society and certain situations affecting animals in captivity. In all cases, secretion of glucocorticosteroids and activity of other mediators of allostasis such as the autonomic nervous system, CNS neurotransmitters, and inflammatory cytokines wax and wane with allostatic load. If allostatic load is chronically high, then pathologies develop. Type 2 allostatic overload does not trigger an escape response, and can only be counteracted through learning and changes in the social structure.     

Untapped potential of physiology,behaviour and immune markers to predict range dynamics and marginality

Linking environmental conditions to the modulators of individual fitness is necessary to predict long‐term population dynamics, viability, and resilience. Functional physiological, behavioral, and reproductive markers can provide this mechanistic insight into how individuals perceive physiological, psychological, chemical, and physical environmental challenges through physiological and behavioral responses that are fitness proxies. We propose a Functional Marginality framework where relative changes in allostatic load, reproductive health, and behavior can be scaled up to evidence and establish causation of macroecological processes such as local extirpation, colonization, population dynamics, and range dynamics. To fully exploit functional traits, we need to move beyond single biomarker studies to develop an integrative approach that models the interactions between extrinsic challenges, physiological, and behavioral pathways and their modulators. In addition to providing mechanistic markers of range dynamics, this approach can also serve as a valuable conservation tool for evaluating individual‐ and population‐level health, predicting responses to future environmental change and measuring the impact of interventions. We highlight specific studies that have used complementary biomarkers to link extrinsic challenges to population performance. These frameworks of integrated biomarkers have untapped potential to identify causes of decline, predict future changes, and mitigate against future biodiversity loss.     

Stress in fishes: a diversity of responses with particular reference to changes in circulating corticosteroids

Physical, chemical and perceived stressors can all evoke non-specificresponses in fish, which are considered adaptive to enable thefish to cope with the disturbance and maintain its homeostaticstate. If the stressor is overly severe or long-lasting to thepoint that the fish is not capable of regaining homeostasis,then the responses themselves may become maladaptive and threatenthe fish's health and well-being. Physiological responses tostress are grouped as primary, which include endocrine changessuch as in measurable levels of circulating catecholamines andcorticosteroids, and secondary, which include changes in featuresrelated to metabolism, hydromineral balance, and cardiovascular,respiratory and immune functions. In some instances, the endocrineresponses are directly responsible for these secondary responsesresulting in changes in concentration of blood constituents,including metabolites and major ions, and, at the cellular level,the expression of heat-shock or stress proteins. Tertiary orwhole-animal changes in performance, such as in growth, diseaseresistance and behavior, can result from the primary and secondaryresponses and possibly affect survivorship. Fishes display a wide variation in their physiological responsesto stress, which is clearly evident in the plasma corticosteroidchanges, chiefly cortisol in actinopterygian fishes, that occurfollowing a stressful event. The characteristic elevation incirculating cortisol during the first hour after an acute disturbancecan vary by more than two orders of magnitude among speciesand genetic history appears to account for much of this interspecificvariation. An appreciation of the factors that affect the magnitude,duration and recovery of cortisol and other physiological changescaused by stress in fishes is important for proper interpretationof experimental data and design of effective biological monitoringprograms.     

Stress hormone dynamics: an adaptation to migration?

The hormone corticosterone (CORT) is an important component of a bird’s response to environmental stress, but it can also have negative effects. Therefore, birds on migration are hypothesized to have repressed stress responses (migration-modulation hypothesis). In contrast to earlier studies on long-distance migrants, we evaluate this hypothesis in a population containing both migratory and resident individuals. We use a population of partially migratory blue tits (Cyanistes caeruleus) in southern Sweden as a model species. Migrants had higher CORT levels at the time of capture than residents, indicating migratory preparations, adaptation to stressors, higher allostatic load or possibly low social status. Migrants and residents had the same stress response, thus contradicting the migration-modulation hypothesis. We suggest that migrants travelling short distances are more benefited than harmed by retaining the ability to respond to stress.