A meta‐analysis of plasma corticosterone and heterophil : lymphocyte ratios – is there conservation of physiological stress responses over time?

Corticosterone treatment results in fat deposition and body mass maintenance without effects on feeding behaviour or immunity in female lizards (Tropidurus catalanensis)

Throughout life, animals must maintain homeostasis while coping with challenging events. The period after reproduction can be challenging for oviparous females to maintain homeostasis since they direct most of their energy stores to vitellogenesis, possibly increasing the vulnerability to stressors. Changes in glucocorticoids' (GC) secretion promote various behavioural and physiological adjustments daily and to restore balance after facing stressors. However, when GC are elevated for extended periods, which usually occurs in response to chronic exposure to stressors, they can affect feeding behaviour and suppress the immune function. We aim to elucidate the effects of chronic corticosterone (CORT) exposure on feeding behaviour, body condition and immune function in female lizards, Tropidurus catalanensis, in the post-reproductive period. Thirty animals were divided into three groups: 1. Control (no experimental procedure performed); 2. Empty Implant (animals implanted with empty silastic tube); and 3. CORT Implant (animals implanted with silastic tube filled with CORT, with a chronic continuous release for at least a week). CORT plasma levels feeding behaviour, body condition (body index [BI] and fat index [FI]), leukocyte count, and several immune function variables (bacterial killing ability [BKA], hemagglutination titer, phytohemagglutinin [PHA] immune challenge and leukocyte count) were evaluated. After implantation, CORT treated animals maintained stable body mass through the experiment, while Control and Empty Implant groups displayed weight loss. In the CORT treated animals, there was also a positive relation between BI and FI, and higher FI when compared to groups 1 and 2. No effects of CORT were observed on feeding behaviour nor on the immune function.

Relationships between Spatial Biology and Physiological Ecology in the Gopher Tortoise, Gopherus polyphemus

AbstractThe overlap between spatial and physiological ecology is generally understudied, yet both fields are fundamentally related in assessing how individuals balance limited resources. Herein, we quantified the relationships between spatial ecology using two parameters of home range (annual home range area and number of burrows used in 1 yr) and four measures of physiology that integrate stress and immunity (baseline plasma corticosterone [CORT] concentration, plasma lactate concentration, heterophil-to-lymphocyte [H∶L] ratio, and bactericidal ability [BA]) in a wild free-ranging population of the gopher tortoise (Gopherus polyphemus) to test the hypothesis that space usage is correlated with physiological state. We also used structural equation models (SEMs) to test for causative relationships between the spatial and physiological parameters. We predicted that larger home ranges would be negatively correlated with traditional biomarkers of stress and positively correlated with immunity, consistent with our hypothesis that home ranges are determined based on individual condition. Males had larger home ranges, used more burrows, and had higher baseline CORT than females. We found significant negative correlations between lactate and home range (r = -0.456 , df = 21 , P = 0.029 ). CORT was negatively correlated with the number of burrows used in both sexes (F = 7.322 , df = 2, 20 , P = 0.003 , adjusted R 2 = 0.383 ). No correlations were observed between space use and BA or, notably, H∶L ratio. SEMs suggested that variation in the number of burrows used was a result of variation in baseline CORT. The lack of a relationship between H∶L ratio and home range suggests that home range differences are not associated with differences in chronic stress, despite the pattern between baseline CORT and number of burrows used. Instead, this study indicates that animals balance trade-offs in energetics, likely by way of baseline corticosteroid, in such a way as to maintain function across continuously variable home range strategies.

Testing androgen-induced immunosuppression: Environmental androgens as a model system for steroid-immune interaction

It is well known that hormones influence and direct most facets of physiology; however, there is still contention regarding the directions of certain relationships, for example, between gonadal hormones and immunity. Among the many proposed relationships relating to gonadal-immune interactions, support for immunosuppressive effects of androgens remains prominent within physiological literature. Although ample study has been directed toward the immunosuppressive effects of androgens, considerable disagreement remains regarding their influence on immune function. In this study, we test the hypothesis that androgens inhibit immunocompetence in the American alligator (Alligator mississippiensis). Developing alligators were incubated at female-producing temperatures with a subset of individuals being exposed to 17-α-methyltestosterone (MT) before sexual determination. 17-α-methyltestosterone is a potent androgen, not aromatizable by crocodilians, that has been found to exert masculinizing effects in exposed crocodilian populations in vivo and in vitro. Additionally, a subset of animals was exposed to a novel antigen to quantify innate and acquired immune function. We recovered no significant differences in leukocyte ratios or proportions between groups and found no significant differences in innate immune function as measured by hemolysis-hemagglutination. However, we did find significant differences in acquired immune function, where masculinized individuals expressed greater antibody titers. Our findings reject the hypothesis that androgens suppress immune function; rather, androgens may be immunoenhancing to acquired humoral responses and neutral to innate humoral immunity in crocodilians.

How do different concentrations of aluminum and zinc affect the survival, body size, morphology and immune system of Physalaemus cuvieri (Fitzinger, 1826) tadpole?

The assessment of amphibian responses as bioindicators of exposure to chemical pollutants is an important tool for conservation of native species. This study aimed to investigate the effects of chronic aluminum (Al) and zinc (Zn) exposure on survival, body size, morphology (malformations), and immune system (leukocyte profile) in P. cuvieri tadpoles. Ecotoxicological analyses were performed utilizing chronic toxicity tests in which 210 tadpoles at the 25th Gosner developmental stage were exposed to Al and Zn. Individuals of P. cuvieri were maintained in glass containers containing various concentrations of aluminum sulfate (0.1, 0.2, or 0.3 mg/L) and zinc sulfate (0.18, 0.27 or 0.35 mg/L), and tests were performed in triplicate. After 14 days, amphibians were weighed, measured and survival rate, malformations in the oral and intestine apparatus, leukocyte profile, and ratio between neutrophils and lymphocytes determined. The differing concentrations of Al and Zn did not produce lethality in P. cuvieri where 95% of the animals survived 326 hr following metal exposure. Individuals exposed to Zn achieved greater body growth and weight gain compared to controls. Aluminum increased weight gain compared controls. These metals also produced malformations of the oral and intestine apparatus and enhanced occurrence of hemorrhages, especially at the highest doses. Lymphocytes were the predominant cells among leukocytes, with lymphopenia and neutrophilia observed following Al and Zn treatment, as evidenced by elevated neutrophil/lymphocyte ratio, an important indicator of stress in animals. Data suggest that further studies need to be carried out, even with metal concentrations higher than those prescribed by CONAMA, to ensure the conservation of this species.

Hemoparasites Do Not Affect Life-History Traits and Cellular Immune Response in Treefrog Hosts Boana cordobae

We provide the first evidence for hemoparasites in the endemic Cordoba treefrog Boana cordobae. We collected 37 adult frogs at 1200 m a.s.l. in the Comechingones Mountains in the Córdoba province (Argentina). Each individual was sexed, then snout-vent length and body mass were recorded, a toe was collected for skeletochronological age determination, and a slide with a blood smear was prepared for hemoparasite screening, before releasing the frogs in situ. A total of 81% (n = 30) of the frogs were infected by hemogregarines and trypanosomes with a high intensity of infections. Dactylosoma was found for the first time in Argentina. Hemoparasites had no significant effect on the leukocyte profile, which we assessed from the May-Grünwald-Giemsa-stained blood smears. The neutrophils/lymphocytes ratio, indicative of stress, was insignificantly higher (0.06) in parasitized frogs than in parasite-free individuals (0.04). Infected frogs were larger than the controls, but this effect vanished when correcting size data for age. Young frogs (first-breeders) dominated the age distribution of parasite-free individuals, suggesting that infection of frogs takes usually place after sexual maturation. Vectors transmitting hemoparasites to B. cordobae remain to be identified. We demonstrate that moderate to high intensities of hemoparasites do not significantly affect the cellular immune response of B. cordobae, or any of the life-history traits studied, nor did they show any external sign of disease.

INFLUENCE OF SEASON, ENVIRONMENT, AND SEX ON SELECTED BLOOD PARAMETERS OF GEOFFROY'S SIDE-NECKED TURTLES, PHRYNOPS GEOFFROANUS (SCHWEIGGER, 1812)

Laboratory tests help to determine a diagnosis, to plan treatment, and to indicate prognosis of diseases. However, the interpretation of test results in reptiles is challenging, because they are influenced by environmental and individual factors. Therefore, the objective of this study was to establish hematologic parameters of Geoffroy's side-necked turtle (Phrynops geoffroanus), including variables such as season, environment, sex, and straight carapace length (SCL). Blood samples were analyzed from 38 P. geoffroanus (23 males and 15 females) collected during the rainy and dry seasons. Some of the animals were from captivity and others from an urban stream. To verify the influence of the variables on blood parameters, the general linear model was performed. The Pearson correlation coefficient was also used to verify the association between SCL and hematologic parameters. Among these parameters, hemoglobin (P = 0.008) and mean corpuscular hemoglobin concentration (P = 0.001) were statistically higher during the rainy season. On the other hand, WBC (P = 0.011), heterophils (P = 0.045), eosinophils (P < 0.001), lymphocytes (P = 0.014), and monocytes (P = 0.039) were higher in the dry season. The RBC count (P = 0.035), PCV (P = 0.029), basophils (P = 0.013), and monocytes (P = 0,013) were significantly higher in individuals from captivity, but lymphocytes (P = 0.033) were higher in the urban turtles. Only eosinophils (P = 0.025) were higher in females than in males. There was no influence of the variables season, environment, and sex on the mean corpuscular volume (P = 0.071; P = 0.458; P = 0.052), total solids (P = 0.773; P = 0.121; P = 0.131), and heterophil:lymphocyte ratio (P = 0.992; P = 0.58; P = 0.119). No influence of the size on hematologic parameters was observed. Season, environment, and sex may influence the blood parameters of P. geoffroanus, and these factors should be routinely considered in the interpretation of laboratory results.

Females with Increased Costs Maintain Reproductive Output: A Field Experiment in a Common Songbird

Reproduction and self-maintenance are energetically costly activities involved in classic life history trade-offs. However, few studies have measured the responses of wild organisms to simultaneous changes in reproductive and self-maintenance costs, which may have interactive effects. In free-living female Barn Swallows (Hirundo rustica), we simultaneously manipulated reproductive costs (by adding or removing two nestlings) and self-maintenance costs (by attaching a ∼1 g weight in the form of a GPS tag to half of our study birds) and measured mass, immune status, blood glucose, feather growth, and reproductive output (likelihood of a second clutch, number of eggs, and time between clutches). GPS tags allowed us to analyze how movement range size affected response to brood size manipulation. Tagging altered females' immune function as evidenced by an elevated heterophil to lymphocyte (H:L) ratio, but all females were equally likely to lay more eggs. There was no evidence of interactive effects of the tagging and brood size treatment. Range size was highly variable, and birds with large ranges grew feathers more slowly, but analyzing the effect of brood size manipulation while accounting for variation in range size did not result in any physiological response. Our results support the theoretical prediction that short-lived vertebrates do face a trade-off between reproduction and self-maintenance and, when faced with increased costs, tend to preserve investment in reproduction at the expense of parental condition. This experiment also helps us to understand how movement patterns may be relevant to life history trade-offs in wild birds.

Short-term impact of a wildfire on the homeostasis of Tropidurus oreadicus lizards

Wildfires cause significant changes in natural habitats and can impact lizard populations. Through changes in the thermal environment, reduced prey availability, and increased exposure to parasite vectors, wildfires affect lizard physiology, immunity, and health. We sampled 56 Tropidurus oreadicus lizards from Cerrado savannas of Brazil living in two adjacent sites: one burned 14 days before the study, and the other unburned for 6 years. We logged the air temperatures of those sites throughout fieldwork. We assessed the short-term possible homeostatic imbalances caused by the fires via measuring body mass, circulating levels of corticosterone (CORT), leukocytes profile changes in heterophile-lymphocyte ratios (HLRs), innate immunity using the bacterial killing assay (BKA), and the diagnosis of hemoparasites using molecular techniques. The air temperature was significantly higher in the burned site. There was no difference in lizard body mass between the two sites, suggesting that prey availability was not affected by the wildfire. While parasite presence was seemingly not affected by fire, the timing of initial parasite infection for animals in the study was unknown, so we also evaluated parasitism as an independent variable relative to the other metrics. Our results showed that parasitic infections lead to reduced bactericidal capacity and body mass in lizards, suggesting clinical disease and depletion of innate immune resources. Moreover, we observed increased HLR with fire and parasitic infections and a strong negative correlation with BKA. These findings suggest that the increased environmental temperature following wildfires may lead to increased CORT and decreased BKA.

Effects of Changing Veterinary Handling Techniques on Canine Behaviour and Physiology Part 1: Physiological Measurements

Signs of distress in dogs are often normalized during routine veterinary care, creating an animal welfare concern. We sought to test whether targeted interventions during veterinary visits affect physiological indicators of stress in dogs. Some 28 dogs were examined within four visits across 8 weeks. All dogs received the same care during the first visit and were then randomized into control and intervention groups for visits 2-4. In the intervention group, 14 dogs underwent procedures designed to reduce stress and to enlist their collaboration during examination. The 14 dogs in the control group received routine care. At each visit, heart rate (HR), serum cortisol (CORT), neutrophil lymphocyte ratio (NLR), and creatine kinase (CK) were measured. A composite stress index based on the summed standardized scores for these markers was constructed. No differences in HR, NLR, and CK parameters between groups were found, and both groups had a decrease in CORT by visit four. However, the intervention group showed a greater overall decrease in CORT between the first and fourth visit than the control group (p < 0.04). The composite stress index differed between the first and fourth visits for the intervention group, but not for the control group (Intervention p = 0.03; Control p= 0.288). There was a tendency for the composite stress index to worsen at visit four vs. visit one for the control group. The findings suggest that dogs that participated in adaptive, collaborative exams and procedures designed to minimize fear had a greater reduction in stress over time compared to those receiving standard care.

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.

The Impacts of Transdermal Application of Corticosterone on Toad (Rhinella icterica) Immunity

Recent studies have shown that acute physiological increases in endogenous glucocorticoid levels have immunostimulatory effects. Although post-acute stress immunosuppressive effects have also been described, the difference between enhancing and suppressing the immune response seems mediated by the stressor's duration, intensity, and the immune component under analysis. To elicit physiologically relevant corticosterone levels that can be found in Rhinella icterica toads after stressful events (e.g., restraint or captivity) and understand how acute increased glucocorticoid levels of different intensities affect corticosterone and testosterone plasma levels and immune parameters (in vitro plasma bacterial killing ability, neutrophil-to-lymphocyte ratio, and in vivo phagocytosis of peritoneal leukocytes), we submitted toads to the transdermal application of two corticosterone doses (1 and 10 μg). Corticosterone transdermal application increased corticosterone plasma levels with different intensities: 3 times for 1 μg and fourteen times for 10 μg, compared to the vehicle, and the neutrophil-to-lymphocyte ratio increased regardless of the corticosterone dose. However, there was no effect on testosterone levels and bacterial killing ability. Interestingly, both corticosterone doses promoted immunosuppression, decreasing peritoneal leukocytes' phagocytosis activity by 60% for toads receiving the dose of 1µg and 40% for those receiving 10 μg. Our results show the complexity of the relationship between increased corticosterone levels and immunomodulation. The different corticosterone doses promoted increases of distinct magnitudes in corticosterone plasma levels, with the less intense increase in corticosterone levels generating greater cell-mediated immunosuppression. Future studies using different corticosterone doses to achieve and compare physiological vs. pharmacological hormone levels are imperative to understanding these interrelationships between corticosterone and immune response.

Effects of urbanisation and pollution on the heterophil/lymphocyte ratio in birds from Brazilian Cerrado

Stressing agents can cause morphophysiological and behavioural changes in several animals, including birds, which are good study models for environmental biomonitoring. The heterophil/lymphocyte ratio (H/L) is an efficient indicator of chronic stresses in birds. In this study, we aimed to compare the H/L ratio of birds between the areas with different levels of urbanisation, anthropogenic noise and carbon monoxide (CO) emission rates. A total of 1288 birds were captured in six Cerrado forest fragments between 2013 and 2019, from which we took blood samples to produce blood smears. In each of these fragments, the noise level was measured with a sound pressure level metre. The CO rates were obtained from the National Institute for Space Research database (INPE-Brazil). There was a higher H/L ratio in individuals captured in urban areas or close to urbanisation with high anthropogenic noise levels and high CO rates, and a lower H/L ratio in individuals from preserved areas, far from urban environments with low noise levels and low CO rates. Six species (Antilophia galeata, Leoptopogon amaurocephalus, Cnemotriccus fuscatus, Lathrotriccus euleri, Turdus leucomelas and Eucometis penicillata) showed a significant difference between the areas and followed the pattern shown by the individuals. The present study showed that birds living in the urban and peri-urban sites have higher values of H/L ratio than birds from rural sites. These results suggest that the H/L ratio can be used as an environmental biomonitoring tool and an efficient parameter to assess chronic stress in birds in degraded environments.

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.

Over a decade of field physiology reveals life-history specific strategies to drought in garter snakes (Thamnophis legans)

Changing climates and severe weather events can affect population viability. Individuals need to buffer such negative fitness consequences through physiological plasticity. Whether certain life-history strategies are more conducive to surviving changing climates is unknown, but theory predicts that strategies prioritizing maintenance and survival over current reproduction should be better able to withstand such change. We tested this hypothesis in a meta-population of garter snakes having naturally occurring variation in life-history strategies. We tested whether slow pace-of-life (POL) animals, that prioritize survival over reproduction, are more resilient than fast POL animals as measured by several physiological biomarkers. From 2006 to 2019, which included two multi-year droughts, baseline and stress-induced reactivity of plasma corticosterone and glucose varied annually with directionalities consistent with life-history theory. Slow POL animals exhibited higher baseline corticosterone and lower baseline glucose, relative to fast POL animals. These patterns were also observed in stress-induced measures; thus, reactivity was equivalent between ecotypes. However, in drought years, measures of corticosterone did not differ between different life histories. Immune cell distribution showed annual variation independent of drought or life history. These persistent physiological patterns form a backdrop to several extirpations of fast POL populations, suggesting a limited physiological toolkit to surviving periods of extreme drought.

Repeated stimulation of the HPA axis alters white blood cell count without increasing oxidative stress or inflammatory cytokines in fasting elephant seal pups

The hypothalamic-pituitary-adrenal (HPA) axis controls the release of glucocorticoids, which regulate immune and inflammatory function by modulating cytokines, white blood cells and oxidative stress via glucocorticoid receptor (GR) signaling. Although the response to HPA activation is well characterized in many species, little is known about the impacts of HPA activation during extreme physiological conditions. Hence, we challenged 18 simultaneously fasting and developing elephant seal pups with daily intramuscular injections of adrenocorticotropin (ACTH), a GR antagonist (RU486), or a combination of the two (ACTH+RU486) for 4 days. We collected blood at baseline, 2 h and 4 days after the beginning of treatment. ACTH and ACTH+RU486 elevated serum aldosterone and cortisol at 2 h, with effects diminishing at 4 days. RU486 alone induced a compensatory increase in aldosterone, but not cortisol, at 4 days. ACTH decreased neutrophils at 2 h, while decreasing lymphocytes and increasing the neutrophil:lymphocyte ratio at 4 days. These effects were abolished by RU486. Despite alterations in white blood cells, there was no effect of ACTH or RU486 on transforming growth factor-β or interleukin-6 levels; however, both cytokines decreased with the 4 day fasting progression. Similarly, ACTH did not impact protein oxidation, lipid peroxidation or antioxidant enzymes, but plasma isoprostanes and catalase activity decreased while glutathione peroxidase increased with fasting progression. These data demonstrate differential acute (2 h) and chronic (4 days) modulatory effects of HPA activation on white blood cells and that the chronic effect is mediated, at least in part, by GR. These results also underscore elephant seals' extraordinary resistance to oxidative stress derived from repeated HPA activation.

Chronic Exposure to Environmental DDT/DDE in 2 Species of Small Rodents: Measures of Contaminant Load, Immune Dysfunction, and Oxidative Stress

Persistent contaminants are ubiquitous in our water and soil, and thus chronic exposure to environmentally relevant levels of these contaminants may pose a risk to humans and wildlife. Two species of small mammals (deer mouse, Peromyscus maniculatus and cotton rat, Sigmodon hispidus) were collected from historically dichlorodiphenyltrichloroethane (DDT)-contaminated and reference areas at the Redstone Arsenal (Huntsville, AL, USA), a US Environmental Protection Agency (USEPA)-designated Superfund site. Soil samples taken concurrently with mammal collection from the DDT abatement site exhibited DDT and dichlorodiphenyldichloroethylene (DDE) levels >1 ppm (USEPA total threshold limit concentration for DDT and DDE <1 ppm), whereas soil samples from the reference area had undetectable levels. Liver samples from individuals of both species collected in the contaminated areas also had significantly elevated DDT/DDE levels, with P. maniculatus averaging an approximately 20× greater load than that documented for S. hispidus. Both rodent species collected from the contaminated site had significantly lower total leukocyte counts and total differential blood cell counts (p = 0.01 and p = 0.04, respectively) than those collected from the nearby (~7000-m) reference site. Cellular stress indices also trended higher in both species, suggesting a potential for chronic exposure to DDT to act as a mediator of oxidative damage. The present study provides support to the idea that environmental exposure to low levels of contaminants can cause physiological consequences that may influence immune responsiveness and initiate cellular stress in resident mammals. Environ Toxicol Chem 2021;40:1619-1629. © 2021 SETAC.

Surviving winter: Physiological regulation of energy balance in a temperate ectotherm entering and exiting brumation

Characterizing the physiological response to prolonged cold exposure is essential for understanding the maintenance of long-term energy balance. As part of their natural life cycle, temperate ectotherms are often exposed to seasonal variation in temperatures, including extended periods of cold well below their activity range. Relatively little is known about variation in physiological responses as vertebrate ectotherms enter and exit brumation in response to sustained cold temperatures. We tested the influence of temperature on physiology before, during, and after a simulated brumation in the checkered garter snake (Thamnophis marcianus), a widespread ectothermic vertebrate. We tested for the relative effect of immediate temperature and physiological context (entering or exiting brumation) on hormones regulating energy balance, indicators of energy availability, and resting metabolic rate (V̇_O2). Plasma corticosterone, glucose, and insulin, as well as immune cell heterophil: lymphocyte ratios responded to temperature, though they did so with different thermal response curves. Thermal sensitivity varied both among and within physiological measures depending on whether animals were going into or coming out of brumation. Additionally, V̇_O2 was regulated beyond simple temperature-dependence, whereby post-brumation measures were depressed relative to pre-brumation measures at the same temperature. This pattern was characterized by a change in the temperature coefficient (Q₁₀), with a larger pre-brumation Q_10, suggesting reduced thermal sensitivity of metabolic rate following a period of extended cold exposure. The integrated physiological response presented here demonstrates not only temperature dependence across physiological axes, but seasonal variation in thermal responsiveness. Our results suggest that energy allocation decisions and hormonal regulation of underlying processes promote differing levels of thermal sensitivity when entering or exiting brumation.

Who rules over immunology? Sseasonal variation in body temperature,, steroid hormones, and immune variables in a tegu lizard

Multiple factors can influence the immune response of ectothermic vertebrates, including body temperature, gonadal steroids, and seasonality, in ways that are thought to reflect trade-offs between energetic investment in immunity vs. reproduction. Hibernating tegu lizards (Salvator merianae) are a unique model to investigate how immunocompetence might be influenced by different factors during their annual cycle. We assessed immunological measures (plasma bacterial killing ability, total and differential leukocyte count), plasma hormone levels (testosterone in males, estradiol and progesterone in females, and corticosterone in both sexes), body temperature, and body condition from adult tegus during each stage of their annual cycle: reproduction, post-reproduction/preparation for hibernation, and hibernation. Our hypothesis that immune traits present higher values during the reproductive phase, and a sharp decrease during hibernation, was partially supported. Immune variables did not change between life history stages, except for total number of leukocytes, which was higher at the beginning of the reproductive season (September) in both males and females. Average body temperature of the week prior to sampling was positively correlated with number of eosinophils, basophils, monocytes and azurophils, corroborating other studies showing that when animals maintain a high Tb, there is an increase in immune activity. Surprisingly, no clear relationship between immune traits and gonadal steroids or corticosterone levels was observed, even when including life history stage in the model. When gonadal hormones peaked in males and females, heterophil:lymphocyte ratio (which often elevates during physiological stress) also increased. Additionally, we did not observe any trade-off between reproduction and immunity traits, sex differences in immune traits or a correlation between body condition and immune response. Our results suggest that variation in patterns of immune response and correlations with body condition and hormone secretion across the year can depend upon the specific hormone and immune trait, and that experienced Tb is an important variable determining immune response in ectotherms.

Blood Will Tell: What Hematological Analyses Can Reveal About Fish Welfare

Blood analyses provide substantial information about the physiological aspects of animal welfare assessment, including the activation status of the neuroendocrine and immune system, acute and long-term impacts due to adverse husbandry conditions, potential diseases, and genetic predispositions. However, fish blood is still not routinely analyzed in research or aquaculture for the assessment of health and/or welfare. Over the years, the investigative techniques have evolved from antibody-based or PCR-based single-parameter analyses to now include transcriptomic, metabolomic, and proteomic approaches and from hematological observations to fluorescence-activated blood cell sorting in high-throughput modes. The range of testing techniques established for blood is now broader than for any other biogenic test material. Evaluation of the particular characteristics of fish blood, such as its cell composition, the nucleation of distinct blood cells, or the multiple isoforms of certain immune factors, requires adapted protocols and careful attention to the experimental designs and interpretation of the data. Analyses of fish blood can provide an integrated picture of the endocrine, immunological, reproductive, and genetic functions under defined environmental conditions and treatments. Therefore, the scarcity of high-throughput approaches using fish blood as a test material for fish physiology studies is surprising. This review summarizes the wide range of techniques that allow monitoring of informative fish blood parameters that are modulated by different stressors, conditions, and/or treatments. We provide a compact overview of several simple plasma tests and of multiparametric analyses of fish blood, and we discuss their potential use in the assessment of fish welfare and pathologies.

Effect of handling and crowding on the susceptibility of Atlantic salmon (Salmo salar L.) to Lepeophtheirus salmonis (Krøyer) copepodids

Lepeophtheirus salmonis is an ectoparasite causing economic concerns in Atlantic salmon farming. Salmon lice infestation management methods can be stressful and impact fish welfare. This work investigated the stress effect on the attachment of L. salmonis copepodids to Atlantic salmon through two approaches: (a) handling by netting and air exposure (acute stress), and (b) crowding with restricted surface access in a tank (chronic stress). In the first experiment, we compared the number of attached L. salmonis and cortisol levels between a group of handled salmon and a control group. In the second experiment, a group of densely packed salmon was compared to a control group based on the number of attached copepodids, cortisol levels and neutrophil:lymphocyte ratios. Handled salmon showed significantly higher plasma cortisol levels (p < .001) and more attached copepodids (p = .01) than control salmon. Conversely, the cortisol level and number of attached copepodids were not significantly different between the densely packed and control salmon (p > .05). The neutrophil:lymphocyte ratio was significantly higher (p = .0014) in the densely packed salmon than in the control salmon. Handling salmon increased their risk of infestation by L. salmonis. This has implications for reinfestation rates following delousing treatments in commercial salmon aquaculture, which often involve crowding and handling salmon.

Effects of Salinity on Hatchling Diamond-Backed Terrapin (Malaclemys terrapin) Growth, Behavior, and Stress Physiology

Diamond-backed Terrapins inhabit coastal salt marshes along the eastern and Gulf coasts of North America. Terrapins are adapted to intermediate salinities yet frequently face saltwater-inundated marsh habitat exceeding 25 ppt (or grams/kilogram). We investigated the effect of salinity on the growth of hatchling terrapins and on their compensatory responses to salinity stress. We randomly assigned 30 terrapin hatchlings each to one of five salinity treatments (1, 5, 10, 20, or 35 ppt). Over 75 d, we regularly monitored behavior, appetite, and changes in growth; and calculated ratios of heterophils to lymphocytes (H:L ratio) to assess responses to prolonged salinity stress. Consistent with prior studies, chronic exposure to high salinity significantly reduced hatchling growth. Hatchlings in 20-ppt and 35-ppt salinities exhibited appetite suppression and saltwater avoidance and were more likely to show freshwater-seeking behaviors. H:L ratios were higher among hatchlings in 20-and 35-ppt salinities, consistent with a corticosterone-driven stress response to sustained high-salinity exposure, which may play a role in limiting growth. Our findings suggest hatchling growth and distribution among local habitats will vary spatially depending on habitat salinity and freshwater accessibility. The growth-limiting effects of chronically high salinity or limited access to freshwater could therefore increase hatchling mortality and be an important driver of spatial variation in terrapin demography and abundance. However, when freshwater sources are available, compensatory behaviors might reduce growth-limiting effects. Terrapin recruitment is likely to be impacted as rising sea levels, increased human water use, land development, and other anthropogenic changes alter freshwater inputs to coastal marshes.

Physiological responses of gopher tortoises (Gopherus polyphemus) to trapping

With a growing number of species of conservation concern, understanding the physiological effects of routine sampling of vertebrate species remains a priority to maintain the welfare status of wildlife and ensure such activities are not counter to conservation goals. The gopher tortoise (Gopherus polyphemus) is a species of conservation concern throughout its range and is among the most frequently trapped turtles globally (for both research and conservation activities). Several studies have found equivocal results on the effects of trapping and handling on the glucocorticoid stress response. In this study, we tested how multiple physiological biomarkers (i.e. plasma lactate, corticosterone (cort), heterophil:lymphocyte ratio (HLR) and bactericidal ability (BA)) respond to four different combinations of trapping conditions in comparison to baseline reference sampling. We found that trapping and handling of gopher tortoises yielded a rapid rise in plasma lactate concentration followed by elevations of cort and stress-associated immune changes. In visibly distressed animals that were in traps for fewer than 2 hours, lactate, cort, HLR and BA were all elevated, and generally more so than animals that remained calm in traps for a similar amount of time. Animals that had been trapped and then held for a 3-hour restraint showed similar degrees of physiological alteration as those that showed outward signs of distress. This study demonstrates that trapping may yield physiological disturbances in gopher tortoises, although the intensity of this response is highly variable between individuals and the duration of such alterations remains unknown. This research emphasizes the need for continued work to refine trapping and handling processes in an effort to minimize impacts on individuals and populations.

Physiological costs and age constraints of a sexual ornament: an experimental study in a wild bird

Sexual ornaments are often considered honest signals of quality because potential costs or constraints prevent their display by low-quality individuals. Testing for potential physiological costs of ornaments is difficult, as this requires experimentally forcing individuals to produce and display elaborate ornaments. We use this approach to test whether a sexually selected trait is physiologically costly to male superb fairy-wrens (Malurus cyaneus). Male fairy-wrens molt from brown to blue breeding plumage at different times of the year, and females strongly prefer the few males that are blue early, during winter. We used short-acting testosterone implants to stimulate males to produce “early-blue” plumage and assessed costs during and after molt using a panel of physiological indices. Testosterone-implanted, T-males molted in winter and produced blue plumage 6 weeks before control-implanted, C-males. T-males molted while in lower body condition, tended to have lower fat reserves, and were more likely to be parasitized by lice. However, we detected no negative effects on immune function, blood parasites, exposure to stressors, or survival. Juvenile males never naturally display early-blue plumage, but we found no evidence for increased costs paid by juvenile T-males. Instead, juvenile T-males molted later than adult T-males, suggesting that age presents an absolute constraint on ornament exaggeration that cannot be fully overcome by testosterone treatment. Together, these small costs and large, age-related constraints may enforce signal honesty, and explain female preference for early-blue males.

Sex-specific signalling of individual personality by a mutual plumage ornament in a passerine

Abstract

The significance of colour signals in species with strong sexual dimorphism and/or elaborated visual ornaments is rather well-understood. Less attention has, however, been devoted to study colour signals in species with weak or no apparent sexual dimorphism. In such species, an interesting possibility arises as both sexes can bear the same colour ornament(s) (i.e. sexes are mutually ornamented), but their signalling value might differ in males and females. We aimed to explore this possibility by investigating the phenotypic correlates of the black bib, a melanin-based plumage ornament, in the Eurasian tree sparrow (Passer montanus). More specifically, we studied the sex-dependent relationships between bib size and three aspects of individuals’ phenotype: body condition (i.e. size-corrected body mass), physiology (i.e. cellular innate immunity/inflammation status, expressed through total leucocyte counts, and chronic physiological stress, expressed through the ratio of heterophils to lymphocytes) and individual personality (i.e. activity in a novel environment). We found that bib size was not associated with body condition and cellular innate immunity/inflammation status, but was positively related to physiological stress levels independent of sex. Furthermore, bib size was negatively associated with activity in males but positively in females. Our findings bring important correlative evidence that mutual ornamental traits may have sex-specific signalling value.

Significance statement

The signalling role of elaborated colourful ornaments, that are usually possessed only by males in sexually dimorphic species, is well-established. The function of various colour traits which are borne by both sexes (i.e. mutual ornaments), however, is less obvious. Do they have a signalling value in both sexes? If yes, do they signal the same information in males and females? Or, most intriguingly, can they convey different information in the two sexes? To test these alternatives, we studied the signalling value of the black bib, a melanin-based mutual plumage ornament, in Eurasian tree sparrows (Passer montanus). Apart from being correlated with chronic stress in both sexes, bib size was positively related to activity in females but negatively in males. Our results suggest that the information content of the same colour trait in males and females can be different in mutually ornamented species.

Social groups with diverse personalities mitigate physiological stress in a songbird

Social groups often consist of diverse phenotypes, including personality types, and this diversity is known to affect the functioning of the group as a whole. Social selection theory proposes that group composition (i.e. social environment) also influences the performance of individual group members. However, the effect of group behavioural composition on group members remains largely unexplored, and it is still contentious whether individuals benefit more in a social environment with homogeneous or diverse behavioural composition. We experimentally formed groups of house sparrows Passer domesticus with high and low diversity of personality (exploratory behaviour), and found that their physiological state (body condition, physiological stress and oxidative damage) improved with increasing group-level diversity of personality. These findings demonstrate that group personality composition affects the condition of group members and individuals benefit from social heterosis (i.e. associating with a diverse set of behavioural types). This aspect of the social life can play a key role in affiliation rules of social animals and might explain the evolutionary coexistence of different personalities in nature.

Single fluff-spray application of mother hen uropygial secretion analogue positively influences bursa of Fabricius development and the heterophil-to-lymphocyte ratio in ROSS 308 chicks

Stress is an important cause of illness and mortality in chick production. Stressors such as manipulation, absence of maternal care, transport, and housing can lead to welfare issues, immunodepression, and decreased productivity. The mother hen uropygial secretion analogue (MHUSA), a synthetic analog of a maternal semiochemical secretion, has been proven to protect chicks and broilers against stress, significantly reducing the heterophil-to-lymphocyte ratio. The aim of the present study was to test the effects of the MHUSA on chicks' stress when single-sprayed on their fluff at the age of 1 d. Two-hundred eighty ROSS 308 chicks were included in the study. At day 1, each chick received a spray of 200 μL of a 2% MHUSA aqueous solution (140 chicks) or the same amount of the excipient (control group, 140 chicks), and then chicks were housed in 2 separate rooms. To assess the persistence of the MHUSA after this single application, fluff was sampled from 10 chicks every day for 7 d and at day 13 and 19, weighed, placed in dichloromethane, and analyzed by gas chromatography. Blood smears and the bursa of Fabricius were collected every 3 d from 10 chicks of each group for 36 d to assess the heterophil-to-lymphocyte ratio and the bursa weight-to-BW ratio, respectively. Gas chromatography analysis showed that the MHUSA was present on chick fluff until day 5. The statistical analysis revealed that the heterophil-to-lymphocyte ratio was lower in the MHUSA group at day 4, 7, and 9 (P < 0.0001 for day 4 and 7; P = 0.0377 for day 9). The bursa weight-to-BW ratio was significantly higher in the MHUSA group than in the control group from day 4 until day 29. These results confirm the beneficial effects of the MHUSA on chicks' adaptation to the new environment and on bursa of Fabricius development, suggesting its potential role in improving chicks' immune response.

Temperature affects the host hematological and cytokine response following experimental ranavirus infection in red-eared sliders (Trachemys scripta elegans)

Pathogen-host interactions are important components of epidemiological research, but are scarcely investigated in chelonians. Red-eared sliders (Trachemys scripta elegans), are recognized as a model for frog virus-3 infection (FV3), a ranavirus in the family Iridoviridae that infects multiple classes of ectothermic vertebrates. Previous challenge studies observed differences in disease outcome based on environmental temperature in this species, but the host response was minimally evaluated. We challenged red-eared sliders with an FV3-like ranavirus at both 28°C and 22°C. We monitored several host response variables for 30 days, including: survival (binary outcome and duration), clinical signs, total and differential leukocytes, and select cytokine transcription in the buffy coat (IL-1β, TNFα, IFYg, IL-10). After 30 days, 17% of challenged turtles survived at 28°C (Median survival time [MST]: 15 days, range: 10–30 days) and 50% survived (MST: 28.5 days, range: 23–30 days) at 22°C (range 23–30 days). The most common clinical signs were injection site swelling, palpebral swelling, and lethargy. The heterophil/lymphocyte ratio at 22°C and interleukin-1 beta (IL1β) transcription at both 22°C and 28°C were significantly greater on days 9, 16, and 23 in FV3 challenged groups. Tumor necrosis factor alpha and interleukin-10 were transcribed at detectable levels, but did not display significant differences in mean relative transcription quantity over time. Overall, evidence indicates an over-robust immune response leading to death in the challenged turtles. FV3 remains a risk for captive and free-ranging chelonian populations, and insight to host/pathogen interaction through this model helps to elucidate the timing and intensity of the host response that contribute to mortality.

Sex-based trade-offs in the innate and acquired immune systems of Sternotherus minor

Longevity patterns in most vertebrates suggest that females benefit most from maintenance investment. A reversed longevity pattern in loggerhead musk turtles (Sternotherus minor) allowed us to test trade-offs between maintenance and survivorship. We tested the hypothesis that the sex with greater longevity has greater maintenance than the sex with shorter longevity. We also compared the following parameters between sexes: Bactericidal ability (BA) and heterophil:lymphocyte ratios (HLR). Baseline blood samples were collected from turtles in the field; a subset of turtles was returned to a laboratory for experiments of acquired immune responses to sheep red blood cells (SRBC). We found no support for the original hypothesis of reversal in sex-dependent immune trade-offs (difference between sex SRBC titers: p = .102; interaction between treatment and sex: p = .177; difference between treatments: p < .001; effect of sex on BA: p = .830; effect of sex on HLR: p = .717). However, we did find support for sex-dependent differences in immunity in the relationship between HLR and body condition (BCI) (effect of BCI on HLR: p = .015). In field conditions, we found that males with higher body condition indices express stressed phenotypes more than males with lower body condition indices (p = .002). However, females expressed similar stress loads across all body conditions (p = .900). Testosterone concentrations were assayed in free-living turtles and were not related to any of the immune parameters. Our results suggest that the immune systems play an important role in balancing sex-specific responses to different selective pressures in S. minor.

Analyzing Stress as a Multivariate Phenotype

The stress phenotype is multivariate. Recent advances have broadened our understanding beyond characterizing the stress response in a single dimension. Simultaneously, the toolbox available to ecophysiologists has expanded greatly in recent years, allowing the measurement of multiple biomarkers from an individual at a single point in time. Yet these advances-in our conceptual understanding and available methodologies-have not yet been combined in a unifying multivariate statistical framework. Here, we offer a brief review of the multivariate stress phenotype and describe a general statistical approach for analysis using nonparametric multivariate analysis of variance with residual randomization in permutation procedures (RRPP) implemented using the "RRPP" package in R. We also provide an example illustrating the novel insights that can be gained from a holistic multivariate approach to stress and provide a tutorial for how we analyzed these data, including annotated R code and a guide to interpretation of outputs (Online Appendix 1). We hope that this statistical methodology will provide a quantitative framework facilitating the unification of our theoretical understanding and empirical observations into a quantitative, multivariate theory of stress.

Stress and immunity: Field comparisons among populations of invasive cane toads in Florida

Cane toads (Rhinella marina) were introduced worldwide and have become invasive in multiple locations, representing a major driver of biodiversity loss through competition (food, shelter, territory), predation, and the poisoning of native species. These toads have been used in Australia as a model for studies concerning invasion biology and ecoimmunology, as longer-established (core) and invasion front (edge) populations show altered stress and immune response profiles. Although cane toads were also introduced into the United States in the 1950s, these patterns have yet to be evaluated for the populations spanning Florida. Toads introduced into Florida have dispersed primarily northward along a latitudinal gradient, where they encounter cooler temperatures that may further impact stress and immune differences between core and edge populations. In this study, we sampled cane toads from nine different locations spanning their invasion in Florida. Cane toads from southern populations showed higher plasma bacterial killing ability and natural antibody titers than the toads from the northern populations, indicating they have a better immune surveillance system. Also, southern toads were more responsive to a novel stressor (1 hr restraint), showing a higher increase in corticosterone levels. These results indicate that possible trade-offs have occurred between immune and stress responses as these toads have become established in northern cooler areas in Florida.

Male mating success is related to body condition and stress-induced leukocyte response in an anuran with scramble competition

Competition among males can be a decisive factor for successful mating in anuran explosive breeders with a male-biased population sex ratio. The Yungas Red-belly Toad (Melanophryniscus rubriventris (Vellard, 1947)) is an explosive breeder where males exhibit a classic scramble competition. We studied the body size, body condition, and stress-induced leukocyte response of M. rubriventris males under natural scenarios of scramble competition. We hand-captured adult males (categorised as single, in pairs, or in mating balls) and determined their body mass and length, body condition, and their leukocyte profile. We found that males in pairs had significantly higher body mass than single males and those in mating balls. We found the highest percentage of individuals with better body condition within the paired males who showed significantly higher body condition index value than singles or those in mating balls. Amplectant males (those collected in pairs or in mating balls) had a significantly lower proportion of lymphocytes and higher neutrophil–lymphocyte ratios than singles. Amplectant males showed significantly higher proportions of neutrophils or eosinophils than singles. Our results suggest that M. rubriventris males with better body condition can be more successful in acquiring mates, although scramble competition among males can trigger a stress response.

Effect of transportation and shackling on plasma concentrations of corticosterone and heterophil to lymphocyte ratios in market weight male turkeys in a commercial operation

There is limited information on the effects of stress and/or physiological manipulation on either plasma concentrations of corticosterone (CORT) and/or heterophil: lymphocyte (H : L) ratios in turkeys. The present studies examine the effects of catching/transportation/lairage in a holding shed and shackling on plasma concentrations of CORT and H : L ratios in male market weight turkeys. Plasma concentrations of CORT were increased after transportation and lairage but not further elevated by shackling, irrespective of its duration up to 240 s. In one study, there were increased H : L ratios following catching/placing birds into transportation cages/transportation/lairage. In one study, H : L ratios declined following shackling. It is concluded that while moving turkeys from the farm to immediately before the shackling line is stressful, shackling for up to 4 min was not perceived as more stressful in turkeys. There were also differences between farms/houses for both plasma concentrations of CORT and H : L ratios.

Assessment of hematologic and corticosterone response in free-living eastern box turtles (Terrapene carolina carolina) at capture and after handling

Hematology is a common tool for wildlife health assessments. Manual leukocyte counts are required in reptiles, however, disagreement between quantification methods has been observed in some chelonians. This study determined agreement between two methods of leukocyte quantification, eosinophilic leukopet, and blood film white blood cell (WBC) estimates, in free-living eastern box turtles (Terrapene carolina carolina). Simultaneously, we assessed the impact of handling duration on both leukocyte quantity and corticosterone levels. We collected blood at capture (<2 min from disturbance) and again before release 30-150 min later from 92 box turtles at six sites in Illinois and Tennessee. Constant and proportional error was present in the leukopet results for WBC, lymphocytes, and basophils compared to the estimate method. Both methods were in agreement for heterophils, monocytes, and eosinophils. Agreement between the methods was significantly more likely at WBC counts below 23,241/µl. All hematologic parameters were significantly higher at the final blood draw compared to the initial blood draw using both WBC determination methods, except relative eosinophil and basophil counts. Corticosterone levels varied with time, with maximum concentrations reached at 54 min postcapture, followed by a rapid return to baseline levels. Corticosterone level was not significantly associated with any hematologic parameter or sex. This study provides a framework for understanding the effects of animal handling methodology and diagnostic modality when evaluating hematologic health in box turtles.

Examining the Effects of Chronic Selenium Exposure on Traditionally Used Stress Parameters in Juvenile American Alligators (Alligator mississippiensis)

Environmental contaminants, such as the trace element selenium (Se), are a continuing concern to species worldwide due to their potential pathophysiological effects, including their influence on the stress response mediated through glucocorticoids (GCs; stress hormones). Environmental concentrations of Se are increasing due to anthropogenic activities, including the incomplete combustion of coal and subsequent disposal of coal combustion wastes. However, most studies examining how Se affects GCs have been focused on lower trophic organisms. The objectives of this study were to investigate the effects of long-term Se exposure on traditionally used stress parameters and to identify which of these parameters best indicate Se accumulation in liver and kidney of the American alligator (Alligator mississippiensis), a top trophic carnivore found in the southeastern United States and known to inhabit Se-containing areas. Alligators were divided into three dietary treatments and fed prey spiked with 1000 or 2000 ppm of selenomethionine (SeMet) or deionized water (control treatment) for 7 weeks. Following the 7-week treatment protocol, blood and tissue samples were obtained to measure plasma corticosterone (CORT; the main crocodilian GC), tail scute CORT, the ratio of peripheral blood heterophils (H) to lymphocytes (L) as H/L ratio, and body condition. To evaluate which parameter best indicated Se accumulation in the liver and kidney, principal component and discriminant analyses were performed. The only parameter significantly correlated with liver and kidney Se concentrations was scute CORT. Our results suggest that measurement of CORT in tail scutes compared with plasma CORT, H/L ratios, and body condition is the best indicator of Se-exposure and accumulation in crocodilians.

Rapid thermal immune acclimation in common musk turtles (Sternotherus odoratus)

As infectious diseases in ectothermic vertebrates increasingly threaten wild populations, understanding how host immune systems are affected by the environment is key to understanding the process of infection. In this study, we investigated how temperature change and simulated bacterial infection (via lipopolysaccharide [LPS] injection) interacted to regulate innate immunity, as measured by bactericidal ability (BA), phagocytosis rate, and heterophil:lymphocyte ratio (HLR) in common musk turtles (Sternotherus odoratus). We found that LPS stimulated an acute immune response, as measured by an increase in BA, phagocytosis rate, and HLR. When exposed to a 5 or 10°C temperature change for 48 hr, turtles rapidly acclimated to the new temperature by adjusting their immune output. This acclimation was compensatory as seen by elevated rates of immune output in colder animals and decreased rates of immune output in warmer animals. These results indicate that while temperature change may be a constraint on some animals, S. odoratus have the ability to rapidly adjust immunity to match environmental thermal demand. This rapid ability to adjust immunity may be related to the broad geographic distribution of musk turtles. Future research should focus on how immune acclimation in ectotherms varies both intraspecifically and interspecifically across regional scales and geographic distributions.

Effects of early nutritional stress on physiology, life-histories and their trade-offs in a model ectothermic vertebrate

Early-life experiences can have far-reaching consequences for phenotypes into adulthood. The effect of early-life experiences on fitness, particularly under adverse conditions, is mediated by resource allocation to particular life-history traits. Reptiles exhibit great variation in life-histories (e.g., indeterminate growth) thus selective pressures often mitigate the effects of early-life stress, particularly on growth and maturation. We examined the effects of early-life food restriction on growth, adult body size, physiology and reproduction in the checkered garter snake. Animals were placed on one of two early-life diet treatments: normal-diet (approximating ad libitum feeding) or low-diet (restricted to 20% of body mass in food weekly). At 15 weeks of age low-diet animals were switched to the normal-diet treatment. Individuals fed a restricted diet showed reduced growth rates, depressed immunocompetence and a heightened glucocorticoid response. Once food restriction was lifted, animals experiencing nutritional stress early in life (low-diet) caught up to the normal-diet group by increasing their growth, and were able to recover from the negative effects of nutritional stress on immune function and physiology. Growth restriction and the subsequent allocation of resources into increasing growth rates, however, had a negative effect on fitness. Mating success was reduced in low-diet males, while low-diet females gave birth to smaller offspring. In addition, although not a direct goal of our study, we found a sex-specific effect of early-life nutritional stress on median age of survival. Our study demonstrates both immediate and long-term effects of nutritional stress on physiology and growth, reproduction, and trade-offs among them.

Corticosterone in American alligator (Alligator mississippiensis) tail scutes: Evaluating the feasibility of using unconventional samples for investigating environmental stressors

Baseline plasma corticosterone (CORT) concentrations have been widely used to investigate the effects of stressors in wild and captive crocodilians. However, collecting baseline plasma CORT samples from wild crocodilians may be particularly difficult due to the capture and handling protocols used for large individuals. Thus, it may prove beneficial to use recently modified techniques for extracting CORT deposited in keratinized and non-keratinized tissues to better quantify the effects of long-term stress in crocodilians. In this study, we investigated the feasibility of using American alligator (Alligator mississippiensis) tail scute tissues to quantify CORT by collecting blood and tail scutes from 40 alligators before and after a short-term handling stressor. The objective of the current study was to better understand CORT deposition in crocodilian scutes and whether short-term increases in CORT could be detected. We found that CORT can be reliably extracted from alligator scute tissue and quantified using a commercially available enzyme immunoassay. However, there was a significant increase in scute CORT concentrations following an alligator being exposed to a short-term stressor (p = 0.017), although the magnitude of change was less than observed in plasma samples from the same individuals (p = 0.002). Furthermore, our results indicate that there was a significant effect of body condition on an alligator's post-stressor CORT concentration (p = 0.02). While our study is among the first to experimentally examine the usefulness of tissue CORT in crocodilians, a combination of field and laboratory experiments are needed to better understand deposition rates of CORT in scute tissues and to further validate the usefulness of tissue glucocorticoids for evaluating the effects of stress.

Assessment of Commercially Available Immunoassays to Measure Glucocorticoid Metabolites in African Grey Parrot (Psittacus Erithacus) Droppings: A Ready Tool for Non-Invasive Monitoring of Stress

Simple Summary

The African Grey Parrot is a very popular bird commonly found in zoological collections. However, captivity can prevent it from meeting its natural needs and so become an ongoing stressor, leading sometimes to clinical and/or behavioral disorders. Non-invasive forms of stress assessment are of definite interest for monitoring welfare in captive bird populations. One notable stress outcome is the excretion of glucocorticoid metabolites (from the stress hormone corticosterone) in droppings. The aim of this study was to carefully assess methods of glucocorticoid metabolites extraction and measurement in droppings from African Grey Parrots. Several extraction and enzyme immunoassays procedures were tested, based on the evaluation of analytical quality parameters and biological relevance. The best procedure was found to be a combination of a 60% methanol extraction with the use of a commercial corticosterone enzyme immunoassay. To determine whether this method was suitable for assessing different stress levels, a significant correlation with another reliable stress marker in birds, the Heterophil: Lymphocyte Ratio, was evidenced. This method can thus be used to evaluate stress in African Gray Parrots in a non-invasive way and help to monitor their welfare in zoo populations for instance.

Abstract

Despite being undomesticated, African Grey Parrots (Psittacus erithacus) are commonly found in captivity, in zoos or as pets. Captivity can be an ongoing stressor. Non-invasive glucocorticoid metabolites (GCM) measurements from bird droppings are of interest for assessing stress but require careful evaluation in each newly studied species. This study describes the assessment of such methods for Psittacus erithacus to provide tools for evaluating stress and monitoring welfare. We evaluated 12 method combinations of GCM extraction and enzyme immunoassay (EIA) from a pool of African Grey Parrot droppings, through the validation of several analytical parameters. Then, Heterophil: Lymphocyte Ratios (HLR), another reliable stress marker, were determined and correlated to individual dropping GCM concentrations for 29 birds to determine whether the method is biologically relevant. We found that the best procedure to measure GCM in African Grey Parrot droppings is a combination of 60% methanol extraction measured using a Corticosterone EIA kit (Cayman Chemical Company) from fresh or dry droppings. The establishment of a significant correlation (Pearson coefficient correlation = 0.48; p = 0.0082) between HLR and GCM in the studied population confirmed the method biological relevance. This method can thus be applied to assess stress in Psittacus erithacus and support welfare monitoring in zoo populations.

Effects of selenium exposure on the hematology, innate immunity, and metabolic rate of yellow-bellied sliders (Trachemys scripta scripta)

Selenium (Se) is a naturally occurring essential element that can be toxic to vertebrates at high concentrations. Despite studies that have documented that wild reptile species can accumulate copious amounts of Se, little is known regarding specific toxicologic effects of Se. In this study, 70 juvenile yellow-bellied sliders (Trachemys scripta scripta) were exposed to one of three seleno-L-methionine (SetMet) treatments (control, n = 24; 15 mg/kg, n = 23; and 30 mg/kg, n = 23) via weekly oral gavage for 5 weeks. At the conclusion of the experiment, kidney, liver, muscle, and blood samples were collected for quantitative Se analysis. Turtles in the SeMet treatment groups accumulated significantly higher amounts of Se in all tissue types relative to controls (all p < 0.001). Turtles in the 30 mg/kg SeMet group also accumulated significantly higher amounts of Se compared to the 15 mg/kg group (all p < 0.001). Although toxicity thresholds for reptiles have not been established, Se concentrations in liver tissue from both SeMet treatment groups exceeded reported avian toxicity thresholds for liver tissue. Neither oxygen consumption nor innate bactericidal capacity were impacted by SeMet exposure. However, turtles in the 30 mg/kg SeMet group exhibited anemia, which has been reported in other vertebrates exposed to Se. Furthermore, juvenile T. s. scripta in the 30 mg/kg SeMet group experienced 17% mortality compared to 0% in the 15 mg/kg treatment and control groups. To our knowledge, this study is the first to report dose-dependent Se-associated anemia and mortality in a chelonian species.

Seasonal Patterns of Variation in Steroid Plasma Levels and Immune Parameters in Anurans from Brazilian Semiarid Area

Elevated androgens and glucocorticoids displayed by males during the reproductive season have been proposed to mediate a possible trade-off between reproduction and immunocompetence. Anurans living in arid and semiarid environments display a strong seasonal reproduction, which could accentuate the variation in physiological, immunological, and behavioral parameters. We studied covariation between steroid plasma levels, morphometric variables associated with body condition and immunity, leukocyte profile, parasite load, and response to an immunological challenge across different phases of the annual life-history cycle of three anuran species from a Brazilian semiarid area. Our results showed a seasonal pattern of covariation among leukocyte parameters, kidney mass, and steroid plasma levels, with higher values measured during the reproductive season, particularly when males were sampled during calling activity. Moreover, these anurans showed a stronger response to an immunological challenge during the reproductive period. The immunosuppression during the dry period was particularly evident for the species that aestivate, indicating that the availability of energetic resources might be an important factor determining seasonal variation in inflammatory response. Intensity of the helminth infection was associated with eosinophil count but showed a more complex pattern with regard to androgens levels. These data emphasize that variations in the intensity of helminth infection might be more closely related to specific aspects of the immune response than to the general seasonal patterns of variation in steroid plasma levels, total circulating leukocytes, and inflammatory response.