Adrenocortical Stress Response Research Articles

Administering the maternal appeasing substance before slaughter to improve carcass characteristics of finishing cattle.

Two experiments evaluated carcass characteristics of finishing steers administered the maternal bovine appeasing substance (mBAS) prior to slaughter. In Exp. 1, 954 Angus-influenced finishing steers housed in 6 original pens were used. Each original pen was split into a pair of experimental pens 14.3 d ± 3 d prior to slaughter, in a manner that number of steers and average pen body weight (BW; 636 ± 4kg) were similar. An oiler containing mBAS (Ferappease Finish Cattle 5%; FERA Diagnostics and Biologicals; College Station, TX) was added to one of the experimental pens 7 d prior to slaughter (n = 6), whereas the other pen did not contain an oiler (CON; n = 6). The oiler delivered 120mL of mBAS/steer during a 7-d period. Steer BW was recorded 7 d prior to and during loading (final BW) to the packing plant. No treatment effects were detected (P ≥ 0.51) for BW gain, final BW, and proportion of carcasses that graded Choice or Prime. Carcass dressing percentage was greater (P = 0.02) in mBAS compared with CON steers (65.9% vs. 64.2%; SEM = 0.5), which was not sufficient to impact hot carcass weight (HCW; P = 0.29). Incidence of dark-cutting carcasses did not differ between treatments (P = 0.23). In Exp. 2, 80 Angus-influenced finishing steers housed in 16 pens (5 steers/pen; 600 ± 4kg of BW) were used. Pens were arranged in 4 rows of 4 pens/row, and rows were alternately assigned to receive an oiler containing mBAS (n = 8) or mineral oil (CON+; n = 8) 7 d prior to slaughter. Oilers were designed to deliver 120mL/steer of mBAS or mineral oil during the 7-d period. Steer BW was recorded as in Exp. 1, and a blood sample was collected during exsanguination. No treatment effects were detected (P ≥ 0.20) for BW parameters, carcass marbling score, backfat thickness, Longissimus muscle area, yield grade, and proportion of carcasses that graded Choice or Prime. Carcass dressing was greater (P = 0.02) in mBAS steers compared with CON + (60.6 vs. 59.6%; SEM = 0.3) but HCW did not differ (P = 0.47) between treatments. Plasma cortisol concentration was less (P < 0.01) in mBAS steers compared with CON + (11.7 vs. 20.8ng/mL; SEM = 1.6). Incidence of dark-cutting carcasses did not differ (P = 0.53) between treatments. In summary, mBAS administration to finishing cattle using oilers during the last 7 d on feed alleviated the adrenocortical stress response elicited by the process of slaughter, which likely resulted in increased carcass dressing.

Androgen Deprivation Modulates the Adrenocortical Stress Response

Androgen Deprivation Modulates the Adrenocortical Stress Response

Variation in feather corticosterone levels in Alpine swift nestlings provides support for the hypo-responsive hypothesis

In birds, feather corticosterone values (CORTf) are increasingly used as a retrospective and integrative proxy of an individual’s physiological state during the period of feather growth. Relatively high CORTf values are usually interpreted as an indicator of exposure to energy-demanding or stressful conditions during feather growth. However, in nestlings this interpretation might not always hold true. The reasons are that, firstly nestlings (especially altricial ones) still develop their hypothalamo-pituitary-adrenal (HPA) reactivity during the growth of their feathers. Hence, at a young age, nestlings might be unable to mount a substantial adrenocortical stress response. Secondly, some species are able to down-regulate their metabolism during food scarcity and therewith probably also their CORT release. Consequently, CORTf values may not unambiguously reflect whether nestlings have suffered from energy-demanding or stress situations. Relatively high CORTf values might indicate either energy-demanding or stressful conditions (‘stress responsive hypothesis’), or – conversely – favourable conditions during the period of feather growth (‘hypo-responsive hypothesis’). In the altricial Alpine swift (Tachymarptis melba), we tested which factors help to distinguish between the two hypotheses by considering factors which affect CORT release (brood size, weather) and factors which are affected by high CORT levels (nestling size and condition). We measured CORTf in 205 nestlings over 7 years and collected data on brood size, body size, body condition and prevailing weather. Nestling CORTf values were positively correlated with body condition and negatively with adverse weather, supporting the hypo-responsive hypothesis. Results from the Alpine swift study, supplemented with a survey of the literature, show that relatively easily collected parameters on brood size, nestling size and condition, and environmental factors can help to distinguish between the two hypotheses. A meaningful interpretation of nestling CORTf should only be made in the context of species-specific traits.

Plasma Biochemistry and Hematologic Values of Cold-Stunned Loggerhead Sea Turtles (Caretta caretta)

Cold-stunned loggerhead sea turtles (Caretta caretta) strand annually in the northeastern United States and are admitted to rehabilitation facilities when rescued alive. Hematologic and plasma biochemical data were retrospectively evaluated from 133 cold-stunned loggerhead turtles that were admitted for rehabilitation between 2008 and 2016. Convalescent data were compared with initial data for 24 turtles for which paired data were available. Convalescent values for white blood cell count, heterophil count creatine kinase, lactate dehydrogenase, glucose, and uric acid were significantly lower than initial values, whereas convalescent eosinophil count, alanine aminotransferase, aspartate aminotransferase, albumin, gamma-glutamyl transferase, total protein, globulin, blood urea nitrogen, calcium, phosphorus, chloride, and potassium were significantly higher. Results indicate that cold-stunned loggerhead turtles may be affected by dehydration, reduced renal function, cellular injury, deranged metabolic status, and activation of the adrenocortical stress response. Specific derangements associated with mortality could not be statistically characterized because only four turtles died.

Developmental programming of the adrenocortical stress response by yolk testosterone depends on sex and life history stage.

Developmental exposure of embryos to maternal hormones such as testosterone in the avian egg influences the expression of multiple traits, with certain effects being sex specific and lasting into adulthood. This pleiotropy, sex dependency and persistency may be the consequence of developmental programming of basic systemic processes such as adrenocortical activity or metabolic rate. We investigated whether experimentally increased in ovo exposure to testosterone influenced hypothalamus-pituitary-adrenal function, i.e. baseline and stress-induced corticosterone secretion, and resting metabolic rate (RMR) of adult male and female house sparrows (Passer domesticus). In previous experiments with this passerine bird we demonstrated effects of embryonic testosterone exposure on adult agonistic and sexual behavior and survival. Here we report that baseline corticosterone levels and the stress secretion profile of corticosterone are modified by in ovo testosterone in a sex-specific and life history stage-dependent manner. Compared with controls, males from testosterone-treated eggs had higher baseline corticosterone levels, whereas females from testosterone-treated eggs showed prolonged stress-induced corticosterone secretion during the reproductive but not the non-reproductive phase. Adult RMR was unaffected by in ovo testosterone treatment but correlated with integrated corticosterone stress secretion levels. We conclude that exposure of the embryo to testosterone programs the hypothalamus-pituitary-adrenal axis in a sex-specific manner that in females depends, in expression, on reproductive state. The modified baseline corticosterone levels in males and stress-induced corticosterone levels in females may explain some of the long-lasting effects of maternal testosterone in the egg on behavior and could be linked to previously observed reduced mortality of testosterone-treated females.

Dexamethasone treatment supports age‐related maturation of the stress response in altricial nestling birds

In birds, the magnitude of the adrenocortical stress response can be down‐regulated during specific life‐history stages. Such modulation likely occurs when the effects of mounting robust corticosterone (Cort) elevations interfere with the normal progression of critical lifecycle activities (e.g. development, molt, migration, reproduction). The developmental hypothesis posits that altricial birds should display a ‘stress hyporesponsive period’ during the early post‐natal life stages, characterized by reduced adrenocortical stress responses compared to adult birds and a gradual age‐related increase. Such modulation would allow avoiding the potential deleterious effects that long‐term elevations of circulating Cort might exert on growth and development, when the physiological and behavioral abilities to cope with disturbance are limited. Two proximate hypotheses have been proposed to explain this age‐dependent pattern of Cort secretion. The ‘maturation hypothesis’ proposes a progressive age‐related growth, maturation and enhanced sensitivity to sensory input of the Hypothalamic‐Pituitary‐Adrenal (HPA) axis tissues, whereas the ‘negative feedback attenuation hypothesis’ proposes a gradual attenuation in the intensity of the negative feedback in the HPA axis. Here we tested these hypotheses by experimentally inducing negative feedback on the HPA axis via dexamethasone (DEX) treatment in nestling white storks Ciconia ciconia. Nestling age positively affected stress‐induced plasma Cort (STRESS‐Cort) levels during experimental handling and restraint, thus supporting the developmental hypothesis. DEX treatment significantly reduced STRESS‐Cort levels compared to saline (SAL) treatment, thus eliciting the expected negative feedback on the HPA axis. However, inter‐ and intra‐individual comparisons indicated no age effects on the intensity of the negative feedback exerted by DEX. Our results do not support the negative feedback attenuation hypothesis and suggest that progressive maturation of the HPA axis tissues is the proximate mechanism responsible for age‐related changes in the stress response during avian post‐natal development. We encourage further tests of the proposed proximate mechanisms during migration, breeding and molt.

Pre‐basic molt, feather quality, and modulation of the adrenocortical response to stress in two populations of rufous‐collared sparrows Zonotrichia capensis

Molt is an energetically expensive process in which birds may allocate 25% or more of their body protein mass to the production of new feathers. Stressful events can interfere with feather growth via the adrenal hormone corticosterone, which is released in response to environmental stress. Corticosterone release, in turn, regulates gluconeogenesis which could directly inhibit protein synthesis and deposition during molt when feathers are growing, which potentially could reduce feather quality dramatically. Thus, many species suppress the adrenocortical stress response, and therefore maintain lower corticosterone levels during molt. In this study we assessed the relationship between plasma corticosterone levels and feather quality in rufous‐collared sparrow inhabiting the valleys of the Atacama Desert – one of the most stable and aseasonal environments in the world, and in the semiarid and seasonal Fray Jorge National Park in the north of Chile. We tested two hypotheses; 1) feather quality is positively related to the amount of corticosterone suppression during molt, relative to corticosterone levels during other life history stages; and, 2) feather quality is negatively related to the absolute levels of corticosterone. We found negative associations between corticosterone levels and feather quality. However, these effects were stronger in the Atacama Desert where birds showed minimal corticosterone suppression and overall low feather quality. Although we found better feather quality in Fray Jorge, corticosterone suppression in these birds was relatively low in comparison with other species inhabiting higher latitudes. It is possible that birds in a highly variable environment face a stronger trade‐off between feather quality and the stress‐response. Our results suggest that the strength of the trade‐off between feather quality and corticosterone levels could be dependent on energetic demands, seasonality, and unpredictable events.

Seasonal modulation of the adrenocortical stress responses in Chilean populations of Zonotrichia capensis

To persist in a landscape, organisms are often faced with evolutionary tradeoffs between individual survival and reproduction. In environments where breeding opportunities are brief, it has been hypothesized that individuals will decrease investments in self-preservation in favor of reproductive success. Many avian species in the Northern Hemisphere have been shown to diminish their physiological response to perturbations of the environment by decreasing the adrenocortical response to acute stress during the parental care phase of reproduction. We present results from three populations of Rufous-collared Sparrow (Zonotrichia capensis) in the Southern Hemisphere in which we compared the dynamics of changes in plasma levels of corticosterone after capture, handling and restraint in pre-breeding and nesting phases. The results suggest that the degree of seasonal reduction of the adrenocortical stress response in parental birds is different from that of congeners in the Northern Hemisphere. Males of all three populations of Z. capensis in our study attenuated the adrenocortical stress response equally between the early breeding and parental sub-phases of nesting despite breeding at very different altitudes and latitudes. In contrast, females from all three populations showed no seasonal attenuation of the adrenocortical stress response over the seasons examined in this study. These findings suggest that further comparative investigations are needed to compare Northern Hemisphere-based endocrine patterns in different, global contexts.

Neurotransmitter diversity in pre-synaptic terminals located in the parvicellular neuroendocrine paraventricular nucleus of the rat and mouse hypothalamus.

Virtually all rodent neuroendocrine corticotropin-releasing-hormone (CRH) neurons are in the dorsal medial parvicellular (mpd) part of the paraventricular nucleus of the hypothalamus (PVH). They form the final common pathway for adrenocortical stress responses. Their activity is controlled by sets of GABA-, glutamate-, and catecholamine-containing inputs arranged in an interactive pre-motor network. Defining the nature and arrangement of these inputs can help clarify how stressor type and intensity information is conveyed to neuroendocrine neurons. Here we use immunohistochemistry with high-resolution 3-dimensional image analyses to examine the arrangement of single- and co-occurring GABA, glutamate, and catecholamine markers in synaptophysin-defined pre-synaptic terminals in the PVHmpd of unstressed rats and Crh-IRES-Cre;Ai14 transgenic mice: respectively, vesicular glutamate transporter 2 (VGluT2), vesicular GABA transporter (VGAT), dopamine β-hydroxylase (DBH), and phenylethanolamine n-methyltransferase (PNMT). Just over half of all PVHmpd pre-synaptic terminals contain VGAT, with slightly less containing VGluT2. The vast majority of terminal appositions with mouse CRH neurons occur non-somatically. However, there are significantly more somatic VGAT than VGluT2 appositions. In the rat PVHmpd, about five times as many pre-synaptic terminals contain PNMT than DBH only. However, because epinephrine release has never been detected in the PVH, PNMT terminals may functionally be noradrenergic not adrenergic. PNMT and VGluT2 co-occur in some pre-synaptic terminals indicating the potential for co-transmission of glutamate and norepinephrine. Collectively, these results provide a structural basis for how GABA/glutamate/catecholamine interactions enable adrenocortical responses to fast-onset interosensory stimuli, and more broadly, how combinations of PVH neurotransmitters and neuromodulators interact dynamically to control adrenocortical activity.

Adrenocortical Stress Response during the Course of Critical Illness.

Critically ill patients have elevated plasma cortisol concentrations, in proportion to illness severity. This was traditionally attributed exclusively to a central activation of the hypothalamus-pituitary axis. However, low rather than high plasma ACTH concentrations have been reported in critically ill patients, with loss of diurnal ACTH and cortisol rhythm. Low ACTH together with high cortisol is referred to as "ACTH-cortisol dissociation." Although cortisol production is somewhat increased with inflammation, a reduced cortisol breakdown explains to a larger extent the hypercortisolism during critical illness. Inflammation-driven decrease in cortisol binding proteins further increase the active free cortisol fraction. Several drugs administered to ICU patients suppress plasma cortisol in a dose-dependent manner. Sustained low circulating ACTH might contribute to adrenal atrophy and dysfunction in the prolonged phase of critical illness. In the acute phase of sepsis or septic shock, a condition referred to as "relative adrenal insufficiency" has been suggested to ensue from glucocorticoid resistance and insufficiently elevated circulating cortisol to overcome such resistance, with pathological changes possibly occurring at every level of the HPA axis. However, it remains highly controversial whether tissue-specific glucocorticoid resistance is adaptive or maladaptive, how to diagnose "relative" adrenal insufficiency, and how it should be treated. Large RCTs, investigating the effect of 200 mg/d hydrocortisone treatment for sepsis or septic shock have shown conflicting, mainly negative, results. Not taking into account the reduced cortisol breakdown, which increases the risk of overdosing hydrocortisone, might have played a role. Further research on diagnostic, therapeutic and dosing aspects is urgently warranted. Compr Physiol 8:283-298, 2018.

0230 Using hair cortisol concentrations to assess the adrenocortical stress response in beef cattle administered corticotrophin-release hormone

0230 Using hair cortisol concentrations to assess the adrenocortical stress response in beef cattle administered corticotrophin-release hormone

Neonatal proinflammatory challenge in male Wistar rats: Effects on behavior, synaptic plasticity, and adrenocortical stress response

Effects of neonatal proinflammatory stress (NPS) on the development of anxiety and depressive-like behavior, stress responsiveness, hippocampal plasticity and conditioned fear response were studied in adolescent and adult male Wistar rats. On PND 3 and PND 5, the pups were subcutaneously injected with bacterial lipopolysaccharide (LPS, 50μg/kg). In the open field test, signs of increased anxiety were demonstrated in adolescent (PND 32), but not in adult (PND 101) rats. In the elevated plus maze, no changes could be detected in adolescent rats, however, in the adults the number of entries into the open arms decreased suggesting increased anxiety after NPS. Signs of “behavioral despair” in the forced swim test, expressed in adolescent rats as a trend, became significant in the adults indicating depression-like behavior. In the majority of brain slices from PND 19-PND 33 rats subjected to NPS, deficit of LTP in the hippocampal CA1 field was detected, this deficit being associated with the impaired mechanisms of LTP induction. In the adult rats, NPS enhanced fear conditioning promoting improved formation of the novel context-foot shock association in the contextual fear conditioning paradigm without effect on cued fear conditioning. NPS significantly impaired functioning of the hypothalamic–pituitary–adrenal axis (HPAA), resulting in an elevated corticosterone level maintained in the adolescents but not in the adults and in modified corticosterone response to behavioral sub-chronic stress in both adolescent and adult rats. Thus, NPS induces “perinatal malprogramming” resulting in development of depression-like behaviors, associated with abnormalities in functioning of the HPAA, impaired hippocampal neuroplasticity (LTP) and changes in hippocampus-dependent memory formation.

Two seconds is all it takes: European starlings (Sturnus vulgaris) increase levels of circulating glucocorticoids after witnessing a brief raptor attack

Researchers typically study “acute” activation of the hypothalamic–pituitary–adrenal (HPA) axis by measuring levels of circulating glucocorticoids in animals that have been exposed to a predator or a cue from a predator (e.g., odor), or have experienced a standardized capture-and-restraint protocol, all of which are many minutes in duration. However, exposure to predators in the “wild”, either as the subject of an attack or as a witness to an attack, is generally much shorter as most depredation attempts upon free-living animals last <5s. Yet, whether a stimulus lasting only seconds can activate the HPA axis is unknown. To determine if a stimulus of a few seconds triggers a glucocorticoid response, we measured levels of corticosterone (CORT; the primary avian glucocorticoid) in wild-caught European starlings (Sturnus vulgaris) after they witnessed a brief (<2–8s) raptor attack upon a conspecific, a human “attack” (i.e., a researcher handling a conspecific), and an undisturbed control. Witnesses of a raptor attack responded with CORT levels comparable to that induced by a standardized capture-and-restraint protocol. Glucocorticoid levels of individuals following the control treatment were similar to baseline levels, and those that witnessed a human “attack” had intermediate levels. Our results demonstrate that witnessing a predator attack of very brief duration triggers a profound adrenocortical stress response. Given the considerable evidence of a role for glucocorticoids in learning and memory, such a response may affect how individuals learn to recognize and appropriately react to predators.

Cis-3-Hexenol and trans-2-hexenal mixture prevents development of PTSD-like phenotype in rats

Several green leaf volatiles have anxiolytic/antidepressant properties and attenuate adrenocortical stress response in rodents. However, it remains unknown whether a mixture of cis-3-hexenol and trans-2-hexenal so-called ‘green odor (GO)’ affects fear-associated post-traumatic stress disorder (PTSD)-like behavior. In the present study, fear memory of the initial conditioning stimulus was stably maintained by weekly presentation of conditioned tone. Examination of open field behavior, acoustic startle response, prepulse inhibition, and immobility in the forced swim test for 2 weeks after initial conditioning revealed that conditioned rats sustained anxiety, enhanced startle response, hypervigilance, depression-like behavior, and hypocortisolism, which is consistent with PTSD symptoms. Daily, not acute, GO presentation facilitated fear extinction and reduced PTSD-like behavioral and endocrinal responses. To further investigate the mechanism of effect of GO, we examined the effect of paroxetine (a selective serotonin reuptake inhibitor), p-chlorophenylalanine (PCPA, an irreversible serotonin synthesis inhibitor), alone or in combination of GO on PTSD-like phenotype. The alleviative effects of GO were masked by simultaneous paroxetine administration. PCPA-induced serotonin depletion abolished the effects of GO. Our results suggest that daily GO presentation facilitates fear extinction and prevents development of PTSD-like symptoms.

Pigment-specific relationships between feather corticosterone concentrations and sexual coloration

The adrenocortical stress response may divert energy away from sexual ornamentation, such that ornaments signal exposure or resistance to physiological stress. Alternatively, steroid glucocorticoids released via the stress response may support ornament development by stimulating foraging and metabolism. The relationship between glucocorticoids and ornamentation may vary with ornament type and across age and sex classes that experience different resource allocation tradeoffs. In yellow warblers (Setophaga petechia), we conducted the first study to simultaneously assess whether relationships between corticosterone (the primary avian glucocorticoid) and ornamentation depend on sexual pigment type, age, and sex. We quantified carotenoid- and phaeomelanin-based pigmentation using spectrometry, and assayed corticosterone in feathers (CORTf) to derive an integrative metric of corticosterone levels during molt. Yellow warblers with lower carotenoid hue (lambda R50) had higher CORTf, suggesting that carotenoid hue may signal stress during molt across age and sex classes. Carotenoid chroma also negatively correlated with CORTf. However, this correlation was absent in older males, seemingly because these males display more saturated carotenoid pigmentation, and thus less variance in carotenoid chroma. Young males with higher CORTf also tended to have poorer quality tertial feathers, indicating poor condition at molt. Phaeomelanin-based pigmentation was largely unrelated to CORTf, suggesting that pleiotropic effects do not link phaeomelanogenesis and CORT release. Finally, CORTf was repeatable across years within individuals. Thus, carotenoid- and phaeomelanin-based pigmentation communicate nonequivalent information about physiological stress, with carotenoid pigmentation having the potential to signal stable differences in stress levels that could affect fitness.

Variation in adrenocortical stress physiology and condition metrics within a heterogeneous urban environment in the song sparrow Melospiza melodia

In urban habitats, organisms face unique fitness challenges including disturbance from human activity and noise. One physiological mechanism that may be plastically or evolutionarily modified to ameliorate deleterious effects of anthropogenic disturbance is the adrenocortical stress response. Individuals in urban environments may display smaller stress responses, which may prevent pathologies associated with consistent elevation of stress hormones, and may also show differences in baseline corticosterone (CORT, the primary avian stress hormone), due to altered energetic demands or chronic stress. We examined whether stress physiology and condition metrics in male song sparrows Melospiza melodia vary as a function of discrete differences in anthropogenic disturbance level (activity centers and refuges) or with continuous variation in an urbanization score and noise environment. Males breeding in activity centers displayed lower maximal (acute) CORT levels than activity refuge males, and acute CORT also tended to negatively correlate with urbanization score. Baseline CORT did not differ between habitat types, and activity center males also showed no evidence of changes in body mass, hematocrit, or antioxidant capacity. Further, activity center males had higher quality feathers (indicative of higher condition at molt) than activity refuge males. We found no indication that the noise environment altered stress physiology or condition in song sparrows. Overall, results suggest that song sparrows are an urban adapter species, which are not detrimentally affected by unique selective pressures encountered in the urban environment.

Wet- and dry-season steroid hormone profiles and stress reactivity of an insular dwarf snake, the Hog Island boa (Boa constrictor imperator).

Field endocrine studies providing new comparisons for inference into the evolutionary and ecological factors shaping organismal physiology are important, often yielding novel physiological insights. Here, we explored factors associated with the sex steroid hormone concentrations and adrenocortical response to capture stress in Hog Island boas (Boa constrictor imperator) in the Cayos Cochinos archipelago of Honduras to generate comparative field hormone data from a tropical reptile and test the island tameness hypothesis. Baseline concentrations of testosterone, corticosterone, estradiol, and progesterone were measured during the wet and dry seasons, and an acute stressor of 1 h in a cloth bag was used to assess the stress response. Plasma steroid concentrations in these snakes were generally low in comparison to other taxa. Higher testosterone concentrations in males and higher estradiol and corticosterone concentrations in females were observed during the wet season compared to the dry season, which may be indicative of mating activities and vitellogenesis during this period. Snakes displayed a 15-fold increase in corticosterone concentrations in response to capture stress, a rise that was not impacted by whether a snake had been captured during previous years. The adrenocortical stress response was greater in males and positively related to body temperature. We suggest that this system merits future inquiries into the physiology and behavior of B. c. imperator, particularly as a model for studying insular impacts on diverse life history characters.

Modulation of corticosterone secretion in tuatara (Sphenodon punctatus): Evidence of a dampened stress response in gravid females

Baseline and stress response glucocorticoid (GC) secretion can be modulated by individuals to support activities and physiological functions connected with reproduction (migration, mating, oviposition and/or parturition, care of young). Corticosterone (CORT) is the primary GC in reptiles and, in accordance with other vertebrates, an adrenocortical stress response is observed. Modulation of CORT secretion occurs in several reptile species, such that elevated baseline CORT concentration and/or a dampened CORT response are common during reproductive life-history events. We investigated CORT secretion after 24h capture-restraint in the oviparous tuatara (Sphenodon punctatus), the last living rhynchocephalian, and tested whether gravid females have a dampened CORT response compared with non-gravid females. We also included males as a comparison. We confirmed that gravid females have significantly higher baseline plasma CORT concentrations than non-gravid females, suggesting increased CORT secretion during nesting. Furthermore, we found that gravid females exhibit a dampened CORT response compared to non-gravid females and males. Our results demonstrate that female reproductive condition influences CORT secretion in tuatara, and suggest that gravid females modulate CORT secretion during nesting to maintain homeostasis, effectively increasing chances of reproductive success and promoting overall fitness.

Song complexity, song rate, and variation in the adrenocortical stress response in song sparrows (Melospiza melodia)

Physiological mechanisms that pleiotropically affect condition, life-history decisions, and fitness may covary with the expression of sexually selected ornaments. The adrenocortical stress response regulates energy balance, controls vertebrate responses to survival threats, and may divert energy expenditure away from investment in costly sexual displays. Further, developmental stress may induce correlations between the stress response during adulthood and sexual signals that develop early in life, such as song in oscine birds. We examined the relationship between the adrenocortical stress response (measured by plasma corticosterone concentrations) and the sexually selected traits of song complexity and song rate in song sparrows (Melospiza melodia). Additionally, we explored whether the stress response, song complexity, or song rate predict other male quality and fitness metrics. In contrast to prior research, which reports negative relationships between song complexity and the stress response in this species, males with larger song repertoires had larger stress responses. Song rate was unrelated to the stress response, but positively correlated with male body mass and nestling mass. In addition, males with higher syllable diversity had longer wingchords and lower hematocrit, males with larger song repertoires had heavier nestlings and higher hematocrit, and males with larger stress responses and baseline corticosterone had higher hematocrit. Results suggest that the relationship between the stress response and song complexity is context-dependent, and that song repertoire size, syllable diversity, and song rate serve distinct signaling functions.

Adrenocortical stress responses influence an invasive vertebrate's fitness in an extreme environment

Continued range expansion into physiologically challenging environments requires invasive species to maintain adaptive phenotypic performance. The adrenocortical stress response, governed in part by glucocorticoid hormones, influences physiological and behavioural responses of vertebrates to environmental stressors. However, any adaptive role of this response in invasive populations that are expanding into extreme environments is currently unclear. We experimentally manipulated the adrenocortical stress response of invasive cane toads (Rhinella marina) to investigate its effect on phenotypic performance and fitness at the species' range front in the Tanami Desert, Australia. Here, toads are vulnerable to overheating and dehydration during the annual hot-dry season and display elevated plasma corticosterone levels indicative of severe environmental stress. By comparing unmanipulated control toads with toads whose adrenocortical stress response was manipulated to increase acute physiological stress responsiveness, we found that control toads had significantly reduced daily evaporative water loss and higher survival relative to the experimental animals. The adrenocortical stress response hence appears essential in facilitating complex phenotypic performance and setting fitness trajectories of individuals from invasive species during range expansion.