The role of phenotypic plasticity and corticosterone in coping with pond drying conditions in yellow-bellied toad (Bombina variegata, Linnaeus 1758) tadpoles

Amphibian larvae inhabiting temporary ponds often exhibit the capacity to accelerate development and undergo metamorphosis in challenging conditions like desiccation. However, not all species exhibit this ability, the yellow-bellied toad (Bombina variegata) is one such example. The underlying mechanisms behind the inability to accelerate development under desiccation remain largely unexplored. The hypothalamic-pituitary-interrenal (HPI) axis and corticosterone (CORT), which act synergistically with thyroid hormone, are thought to facilitate metamorphosis in response to desiccation stress. In this study, we aimed to investigate whether modification in the HPI axis, particularly CORT levels, contributes to the absence of adaptive plasticity in B. variegata under desiccation stress. The study design included four treatments: high water level, high water level with exogenous CORT, low water level, and low water level with metyrapone (a CORT synthesis inhibitor). The main objective was to evaluate the effects of these treatments on whole-body corticosterone levels, life history, morphological traits, and oxidative stress parameters during the prometamorphic and metamorphic climax developmental stages. While low water level had no effect on total corticosterone levels, larval period, body condition index, and metamorphic body shape, it negatively affected metamorph size, mass, and growth rate. Our findings suggest that constant exposure to desiccation stress over generations may have led to modifications in the HPI axis activity in B. variegata, resulting in adaptation to changes in water level, evident through the absence of stress response. Consequently, CORT may not be a relevant stress indicator in desiccation conditions for this species.

Context-dependent effects of thermal acclimation on physiological correlates of animal personality in Asiatic toads

Persistent individual variation in behaviour, or 'personality', is a widespread phenomenon in animals, and understanding the evolution of animal personality is a key task of current biology. Natural selection has been proposed to promote the integration of personality with animal 'intrinsic states', such as metabolic or endocrine traits, and this integration varies with ecological conditions. However, these external ecological modulatory effects have rarely been examined. Here, we investigate the effects of thermal acclimation on between-individual covariations between physiology and behaviour in Asiatic toads (Bufo gargarizans) along an altitudinal gradient. Our results reveal that the thermal modulatory effects on the covariations depend on the altitudinal population. Specifically, at low altitudes, between-individual covariations are highly plastic, with risk-taking behaviour covarying with baseline glucocorticoids (GCs) under warm acclimation, but risk-taking and exploration behaviour covarying with resting metabolic rate (RMR) under cold acclimation. In contrast, between-individual covariations are relatively fixed at high altitudes, with risk-taking behaviour consistently covarying with baseline GCs. Furthermore, at low altitudes, changes in covariations between RMR and personality are associated with adjustment of energy management models. Evidently, animal physiological states that determine or covary with personality can adapt according to the seasonal thermal environment and the thermal evolutionary background of populations. Our findings highlight the importance of a multi-system physiological approach to understand the evolution of animal personality.

Life-history stage influences immune investment and oxidative stress in response to environmental heterogeneity in Antarctic fur seals

Immune defenses are crucial for survival but costly to develop and maintain. Increased immune investment is therefore hypothesized to trade-off with other life-history traits. Here, we examined innate and adaptive immune responses to environmental heterogeneity in wild Antarctic fur seals. In a fully crossed, repeated measures design, we sampled 100 pups and their mothers from colonies of contrasting density during seasons of contrasting food availability. Biometric and cortisol data as well as blood for the analysis of 13 immune and oxidative status markers were collected at two key life-history stages. We show that immune responses of pups are more responsive than adults to variation in food availability, but not population density, and are modulated by cortisol and condition. Immune investment is associated with different oxidative status markers in pups and mothers. Our results suggest that early life stages show greater sensitivity to extrinsic and intrinsic effectors, and that immunity may be a strong target for natural selection even in low-pathogen environments such as Antarctica.

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.

A prenatal acoustic signal of heat reduces a biomarker of chronic stress at adulthood across seasons

During development, phenotype can be adaptively modulated by environmental conditions, sometimes in the long-term. However, with weather variability increasing under climate change, the potential for maladaptive long-term responses to environmental variations may increase. In the arid-adapted zebra finch, parents emit "heat-calls" when experiencing heat during incubation, which adaptively affects offspring growth in the heat, and adult heat tolerance. This suggests that heat-call exposure may adjust individual phenotype to hot conditions, potentially compromising individual sensitivity to cool weather conditions. To test this hypothesis, we manipulated individual prenatal acoustic and postnatal thermal experiences during development, and sought to assess subsequent chronic responses to thermal fluctuations at adulthood. We thus measured heterophil to lymphocyte (H/L) ratios in adults, when held in outdoor aviaries during two summers and two winters. We found that birds exposed to heat-calls as embryos, had consistently lower H/L ratios than controls at adulthood, indicative of lower chronic stress, irrespective of the season. Nonetheless, in all birds, the H/L ratio did vary with short-term weather fluctuations (2, 5 or 7 days), increasing at more extreme (low and high) air temperatures. In addition, the H/L ratio was higher in males than females. Overall, while H/L ratio may reflect how individuals were being impacted by temperature, heat-call exposed individuals did not show a stronger chronic response in winter, and instead appeared more resilient to thermal variability than control individuals. Our findings therefore suggest that heat-call exposure did not compromise individual sensitivity to low temperatures at adulthood. Our study also reveals that prenatal sound can lead to long-term differences in individual physiology or quality/condition, as reflected by H/L ratios, which are consistent with previously-demonstrated reproductive fitness differences.

Determinants of spring migration departure dates in a New World sparrow: Weather variables reign supreme

Numerous factors influence the timing of spring migration in birds, yet the relative importance of intrinsic and extrinsic variables on migration initiation remains unclear. To test for interactions among weather, migration distance, parasitism, and physiology in determining spring departure date, we used the Dark-eyed Junco (Junco hyemalis) as a model migratory species known to harbor diverse and common haemosporidian parasites. Prior to spring migration departure from their wintering grounds in Indiana, USA, we quantified the intrinsic variables of fat, body condition (i.e., mass ~ tarsus residuals), physiological stress (i.e., ratio of heterophils to lymphocytes), cellular immunity (i.e., leukocyte composition and total count), migration distance (i.e., distance to the breeding grounds) using stable isotopes of hydrogen from feathers, and haemosporidian parasite intensity. We then attached nanotags to determine the timing of spring migration departure date using the Motus Wildlife Tracking System. We used additive Cox proportional hazard mixed models to test how risk of spring migratory departure was predicted by the combined intrinsic measures, along with meteorological predictors on the evening of departure (i.e., average wind speed and direction, relative humidity, and temperature). Model comparisons found that the best predictor of spring departure date was average nightly wind direction and a principal component combining relative humidity and temperature. Juncos were more likely to depart for spring migration on nights with largely southwestern winds and on warmer and drier evenings (relative to cooler and more humid evenings). Our results indicate that weather conditions at take-off are more critical to departure decisions than the measured physiological and parasitism variables.

Multiple morphophysiological responses of a tropical frog to urbanization conform to the pace-of-life syndrome

The Pace-of-Life syndrome proposes that behavioural, physiological and immune characteristics vary along a slow-fast gradient. Urbanization poses several physiological challenges to organisms. However, little is known about how the health status of frogs is affected by urbanization in the Tropics, which have a faster and more recent urbanization than the northern hemisphere. Here, we analysed a suite of physiological variables that reflect whole organism health, reproduction, metabolic and circulatory physiology and leukocyte responses in Leptodactylus podicipinus. Specifically, we tested how leukocyte profile, erythrocyte morphometrics and germ cell density, as well as somatic indices and erythrocyte nuclear abnormalities differ throughout the adult life span between urban and rural populations. We used Phenotypic Trajectory Analysis to test the effect of age and site on each of the multivariate data sets; and a Generalised Linear Model to test the effect of site and age on nuclear abnormalities. Somatic indices, erythrocyte nuclear abnormalities, erythrocyte morphometrics and leukocyte profile differed between populations, but less so for germ cell density. We found a large effect of site on nuclear abnormalities, with urban frogs having twice as many abnormalities as rural frogs. Our results suggest that urban frogs have a faster pace of life, but the response of phenotypic compartments is not fully concerted.

The effects of annual cycle, source population, and body condition on leukocyte profile and immune challenge in a basal reptile, the tuatara (Sphenodon punctatus)

Leukocyte profiles are broadly used to assess the health status of many species. Reference intervals, and an understanding of the factors that may influence these intervals, are necessary for adequate interpretation of leukograms. Using a data set that spans over three decades, we investigated variation in leukocyte profile in several populations of the evolutionarily unique reptile, the tuatara (Sphenodon punctatus). To do this, we first established reference intervals for each leukocyte type according to best practices. Next, we determined that source population and sampling date were the two most important predictors of leukocyte makeup. We found significant differences in the ratio of heterophils: lymphocytes (H:L) between populations, with tuatara on the more resource-stressed sampling island having a significantly higher ratio of H:L. Finally, we found that sampling location, sex, and life stage did not explain variation in the responses of tuatara to stimulation with Concanavalin A and lipopolysaccharide in both 3-(4,5-dimethylthiazol-2-yl)-2,5-di-phenyltetrazolium bromide and Griess assay experiments. Our results offer important insight into the function of leukocytes in reptiles.

Does the provision of live black soldier fly and yellow mealworm larvae improve Muscovy duck welfare?

BACKGROUND

The provision of environmental enrichments to Muscovy ducks could reduce the expression of the aggressive behaviors. The aim of the present study was to evaluate the effects of black soldier fly (BSF) and yellow mealworm (YM) live larva provision on Muscovy duck performance, excreta corticosterone metabolites (ECM), behavior, and blood parameters.

METHODS

A total of 126 3-day-old female Muscovy ducklings were allotted to 18 pens (6 replicates/treatment, 7 birds/pen) and assigned to 3 experimental treatments: a control group fed commercial feed, and two experimental treatments fed commercial feed plus the 5% (based on the expected daily feed intake, as fed basis) of BSF and YM live larvae (BSF and YM groups, respectively). A two-phase feeding program was applied: starter (from 3 to 31 days of age) and grower-finisher (from 32 to 55 days of age). The live weight, average daily gain, average daily feed intake, and feed conversion ratio were calculated. Larva consumption times were collected, and video recordings were performed during 3 periods (P) each day: the hour before (P1), during (P2), and after (P3) the larva administration. ECM were evaluated at 3, 31, and 55-day-old. Finally, the total red and white blood cell counts, serum proteins, lipids, and liver and renal function serum enzymes were evaluated on 12 birds/treatment.

RESULTS

The experimental treatment did not affect the growth performance of the birds (P > 0.05). Larva consumption times were always similar between the two insect species, except at 14-18 days of age, were BSF larvae were consumed faster than YM larvae (P < 0.001). The birds showed less walking activity during P2, and preening behavior increased in YM birds during P3. The C birds increased the attack behavior over the weeks (P < 0.05). During weeks 1-3 the YM group reduced the attack frequency (P1 > P3; P < 0.05). Finally, the provision of live BSF and YM larvae significantly reduced the ECM at 55 days of age and the heterophil to lymphocyte ratio (P < 0.05).

CONCLUSIONS

Live BSF and YM larva supplementation in Muscovy duck improves duck welfare, without impairing birds' growth performance.

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.

Effects of acute maternal stress induced by predator cues on spatial learning and memory of offspring in the subterranean rodent Ctenomys talarum

One of the main selection pressures to which animals are exposed in nature is predation, which affects a wide variety of biological traits. When the mother experiences this stressor during pregnancy and/or lactation, behavioral and physiological responses may be triggered in the offspring as well. Thus, in order to broaden and deepen knowledge on the transgenerational effects of predation stress, we evaluated how maternal stress experienced during pregnancy and/or lactation affects the spatial abilities of progeny at the onset of adulthood in the subterranean rodent Ctenomys talarum. The results showed that, contrary to what was observed in other rodent species, maternal exposure to predator cues during pregnancy and lactation did not negatively affect the spatial abilities of the offspring, even registering some minor positive effects. Concomitantly, no effects of predatory cues on physiological parameters associated with stress were observed in the progeny. This difference in results between the present study and previous works on maternal stress highlights the importance of considering the species to be evaluated (strain, age and origin-wild or captive-) and the type of stressor used (artificial or natural, intensity of exposure) in the evaluation of the possible transgenerational effects of maternal stress.

Physiological, haematological and electroencephalographic responses to heat stress in Katjang and Boer goats

The present study aimed to determine the effect of repeated heat stress on serum levels of cortisol (CORT), acute phase proteins (APP) and heat shock protein (HSP) 70, haematological indicators, and electroencephalographic (EEG) response in the native Katjang and exotic Boer goats. Six female Katjang (15.7 kg ± 0.68) and six female Boer (16.8 kg ± 1.16) goats aged 5 to 6 months old were exposed to 38 ± 1℃ for 8 h, and the procedure was repeated at three different weeks (weeks 1, 2 and 3). Measurements of rectal temperatures and EEG activity and collection of blood samples were conducted before heat exposure (0 h), immediately after the heat exposure (8 h), and 8 h after completion of heat exposure (16 h) (recovery period). The current results revealed that the Boer animals had significantly higher rectal temperatures (RT), haemoglobin (Hb) and packed cell volume (PCV) counts than their Kajang counterparts. There were significant breed × stage of heat treatment (SHT) × week of heat treatment (WHT) interactions for neutrophil to lymphocyte ratios (NLR). In general, the Katjang animals had elevated NLR compared to those of Boer. The Boer goats had reduced capacity to express serum HSP70 compared to their Katjang counterparts following the heat challenge at week 3. Boer goats demonstrated higher delta waves than the Katjang group, which suggested the former were more stressed following the heat exposure. Breed had a negligible effect on CORT, APP, WBC counts and backfat thickness. Our findings suggested that the Katjang breed, as measured by RT, HB and PCV count, and EEG activity, could be more tolerant to heat stress than Boer. The Katjang goats showed higher HSP70 expression than their Boer counterparts, suggesting improved thermoregulation in the former.

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.

Damage on DNA and hematological parameters of two bat species due to heavy metal exposure in a nickel-mining area in central Brazil

Exposure to heavy metals in mining zones is a significant threat, which can affect ecosystem services and contribute to the decline of wild bat populations. The present study investigated the impacts caused by mining on two bat species in central Brazil, the nectarivorous Glossophaga soricina and the frugivorous Carollia perspicillata. The bats were collected from a nickel-mining zone (treatment) and a protected area (control). The leukocyte profile of each species was compiled and genotoxicity (comet assay) and mutagenicity (micronucleus test) were determined using the appropriate procedures. Glossophaga soricina presented significantly higher frequencies of eosinophils and monocytes in the mining zone in comparison with the protected area, whereas C. perspicillata presented higher frequencies of lymphocytes in the mining zone, but significantly lower frequencies of monocytes. Concomitantly, G. soricina also presented a higher frequency of DNA damage, although no variation was found in this parameter in C. perspicillata when comparing environments. We also found no significant differences between populations in terms of the frequency of micronuclei and other nuclear abnormalities. Overall, the results of the study indicate that bats are susceptible to immunological disorders and DNA damage in mining zones, with the nectarivorous G. soricina appearing to be relatively more susceptible and thus a potentially effective bioindicator of the impact of contamination in these environments.

Zoo Animal Welfare Assessment: Where Do We Stand?

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

Assessing stress physiology within a conservation breeding program for an endangered species

Conservation breeding programs typically involve the management of individuals both in and ex situ, so it is vital to understand how the physiology of managed species changes in these environments to maximize program outcomes. The Vancouver Island marmot (VIM; Marmota vancouverensis) is one species that has been managed in a conservation breeding program to recover the critically low wild population. Previous research has shown there are differences in hair glucocorticoid concentrations for VIMs in different managed groups in the program. Therefore, we used >1000 blood samples collected since the program's inception to assess the neutrophil to lymphocyte (N:L) ratio among captive, pre-release, post-release and wild populations as another metric of stress. In situ VIM populations were found to have a significantly higher N:L ratio than ex situ populations, suggesting that the wild is a more physiologically challenging environment than managed care. Moreover, the effect of age, sex and the month of sampling on the N:L ratio were found to be different for each population. Age had the greatest magnitude of effect in the wild population, and sex was only significant in ex situ populations. This study provided previously unknown insights into the physiology of VIMs and increased post-release monitoring will be useful in the future to fully understand how physiology may be contributing to differences in survival of VIMs in the program.

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.

Resident wild koalas show resilience to large-scale translocation of bushfire-rescued koalas

Wildlife translocation is increasingly utilized as a conservation management action, to mitigate the immediate negative effects of habitat loss and fragmentation (e.g. from land clearing or bushfires). Previous research has shown that stress responses can help or hinder survival in translocated wildlife and determine the efficacy of translocation as a conservation action. Yet these translocated animals are only one side of the equation, with translocation also potentially impacting the animals in the recipient population. We measured physiological markers of stress (faecal cortisol metabolite concentrations and neutrophil-lymphocyte ratios) and assessed health condition in a wild koala population one year after a major translocation of bushfire-rescued koalas on Kangaroo Island. We expected to find a high population density at the site (>0.75 koalas per hectare) and that resident koalas would show signs of chronic stress and ill health as a result of territorial conflict over food trees and reproductive opportunities. In contrast, we found that only one-fifth of the population remaining at the site were translocated koalas. The overall population density was also much lower (0.21 koalas per hectare) than anticipated. With no evidence of mass mortality at the site, we suggest that the majority of translocated koalas dispersed away from the site. Our stress marker measurements did not differ between the wild koalas and a sample of captive (non-display) koalas at the nearby Kangaroo Island Wildlife Park and were generally low compared to other studies. Veterinary examinations found that most koalas were in good body condition with very few diagnostic indicators of systemic ill health. Overall, our results suggest that, if there is adequate landscape-scale habitat connectivity and opportunity for dispersal, translocated koalas are likely to disperse from the site of release, with limited impacts on recipient koala populations at translocation release sites.

Assessing Leukocyte Profiles of Salamanders and Other Amphibians: A Herpetologists' Guide

Assessing numbers of leukocytes in salamanders and other amphibians can be useful metrics for understanding health or stress levels of individuals in a population. In this chapter we describe the procedures for obtaining blood samples from amphibians, preparing blood films for microscopy, counting, and identifying cells. We also provide reference values for amphibian leukocytes for use in interpreting leukocyte data. From our assessment of the published and unpublished literature, "non-stressed" salamanders would have a leukocyte profile where 60-70% of cells are lymphocytes, 17-30% are neutrophils, 1-4% are eosinophils, 4-12% are basophils, and 2-6% are monocytes. In Ambystoma spp., the eosinophil abundance can be notably higher (30% of all white blood cells), for reasons unknown. Finally, the neutrophil-lymphocyte ratio of most non-stressed salamanders tends to be between 0.3 and 0.4 (sometimes less), while the ratios of stressed salamanders tend to be over 1.0.

Age and spatio-temporal variations in food resources modulate stress-immunity relationships in three populations of wild roe deer

Living in variable and unpredictable environments, organisms face recurrent stressful situations. The endocrine stress response, which includes the secretion of glucocorticoids, helps organisms to cope with these perturbations. Although short-term elevations of glucocorticoid levels are often associated with immediate beneficial consequences for individuals, long-term glucocorticoid elevation can compromise key physiological functions such as immunity. While laboratory works highlighted the immunosuppressive effect of long-term elevated glucocorticoids, it remains largely unknown, especially in wild animals, whether this relationship is modulated by individual and environmental characteristics. In this study, we explored the co-variation between integrated cortisol levels, assessed non-invasively using faecal cortisol metabolites (FCMs), and 12 constitutive indices of innate, inflammatory, and adaptive immune functions, in wild roe deer living in three populations with previously known contrasting environmental conditions. Using longitudinal data on 564 individuals, we further investigated whether age and spatio-temporal variations in the quantity and quality of food resources modulate the relationship between FCMs and immunity. Negative covariation with glucocorticoids was evident only for innate and inflammatory markers of immunity, while adaptive immunity appeared to be positively or not linked to glucocorticoids. In addition, the negative covariations were generally stronger in individuals facing harsh environmental constraints and in old individuals. Therefore, our results highlight the importance of measuring multiple immune markers of immunity in individuals from contrasted environments to unravel the complex relationships between glucocorticoids and immunity in wild animals. Our results also help explain conflicting results found in the literature and could improve our understanding of the link between elevated glucocorticoid levels and disease spread, and its consequences on population dynamics.

Temperature Extreme Events Decrease Endocrine and Immune Reactive Scope in Bullfrogs (Lithobates catesbeianus)

Currently, effects of increased atmospheric temperature, in the context of ongoing climate change, have been investigated in multiple organisms and levels of biological organization. While there has been a focus on the impacts of increased mean temperature, an emergent and equally important point is the consequences of recurrent exposure to extreme temperature events, simulating heat waves. This study investigated the effects of serial exposure to high temperatures on immune and endocrine variables before and after exposure to an acute secondary stressor in bullfrogs (Lithobates catesbeianus). Adult males were divided into three groups and subjected to three thermal regimes: control (c; constant 22°C); experimental 1 (E1; kept at 22°C and exposed to 4 days of 30°C every 16 days); and experimental 2 (E2; kept at 22°C and exposed to 4 days of 30°C every 6 days). Blood samples were collected on the last day of key extreme heat events. Two weeks after the last extreme heat event, animals were subjected to restraint stress (1 h) and sampled again. Blood samples were used to determine neutrophil: lymphocyte ratio, plasma bacterial killing ability, as well as, corticosterone and plasma testosterone levels. Overall, we found exposure to extreme heat events did not affect immune and endocrine variables over time. Meanwhile, the previous exposure to extreme heat events modulated the responsiveness to restraint. The amplitude of increased corticosterone plasma levels and neutrophil: lymphocyte ratio in response to restraint decreased with the number of previous exposures to extreme heat events. These results suggest that exposure to extreme climatic events has hidden effects on bullfrog's stress response, expressed as diminished reactive scope to a novel stressor. This represents a highly deleterious facet of climate change since diminished responsiveness prevents proper coping with wildlife challenges.

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.

Immunoendocrinology and Ecoimmunology in Brazilian Anurans

This paper reviews several aspects of immunoendocrinology and ecoimmunology in Brazilian species of anurans under investigation for more than a decade, including (1) patterns of annual covariation of circulating steroids, calling behavior and innate immunity, (2) endocrine and immune correlates of calling performance, (3) behavioral and physiological correlates of parasite load, (4) thermal sensitivity of immune function, and (5) endocrine and immunomodulation by experimental exposure to acute and chronic stressors, as well as to endocrine manipulations and simulated infections. Integrated results have shown an immunoprotective role of increased steroid plasma levels during reproductive activity in calling males. Moreover, a higher helminth parasite load is associated with changes in several behavioral and physiological traits under field conditions. We also found anuran innate immunity is generally characterized by eurythermy, with maximal performance observed in temperatures close to normal and fever thermal preferendum. Moreover, the aerobic scope of innate immune response is decreased at fever thermal preferendum. Experimental exposure to stressors results in increased corticosterone plasma levels and immune redistribution, with an impact on immune function depending on the duration of the stress exposure. Interestingly, the fate of immunomodulation by chronic stressors also depends in part on individual body condition. Acute treatment with corticosterone generally enhances immune function, while prolonged exposure results in immunosuppression. Still, the results of hormonal treatment are complex and depend on the dose, duration of treatment, and the immune variable considered. Finally, simulated infection results in complex modulation of the expression of cytokines, increased immune function, activation of the Hypothalamus-Pituitary-Interrenal axis, and decreased activity of the Hypothalamus-Pituitary-Gonadal axis, as well as reduced melatonin plasma levels, suggesting that anurans have a functional Immune-Pineal axis, homologous to that previously described for mammals. These integrated and complementary approaches have contributed to a better understanding of physiological mechanisms and processes, as well as ecological and evolutionary implications of anuran immunoendocrinology.

Light color and the commercial broiler: effect on behavior, fear, and stress

Light is an important component in poultry production, and it may impact bird behavior, an important component of animal welfare. Light-emitting diode (LED) lamps are of interest for broiler production since they are inexpensive to run and provide monochromatic colors. This study aimed to understand the impact of three light colors (blue, green, or white), provided by LED lighting, on behavioral expression, stress and fear levels of broilers. A total of 14,256 male and female broilers of 2 genotypes (Ross EPMx708 and Ross YPMx708) were housed in 9 rooms in 2 blocked trials (3 room replicates per light per trial), with sexes and genotypes housed in 12 separate pens per room. Behavioral expression was recorded using an infrared camera and analyzed using a scan sampling technique. To assess fear, 3 tests were conducted: tonic immobility, novel object, and response to observer. Blood was collected to evaluate chronic stress using the heterophil:lymphocyte (H:L) ratio. Data were statistically analyzed using SAS (MIXED procedure) in a 3 × 2 × 2 factorial design, with lighting treatment nested within room. Fear tests indicated reduced fear levels in birds raised under blue light (lower latency to rise during the tonic immobility test and a lower percentage of birds moving due to the passage by of an observer). No differences were observed for the novel object test. Light color resulted in changes in stress levels, indicated by a lower H:L ratio for broilers raised under blue light compared to those raised under white light. Behavior was influenced by light color, especially at 33 to 34 d of age, where birds raised under white light were more active, and birds raised under blue light spent more time resting. Overall, results indicated that light color has minor influences on behavioral expression. Utilizing blue light during the brooding and rearing phase leads to lower stress and a reduction in fear, suggesting that blue light may improve the emotional states of fear and stress, thereby improving the welfare of poultry.

Physiological stress responses to nonmimetic model brood parasite eggs: Leukocyte profiles and heat-shock protein Hsp70 levels

Obligate avian brood parasites lay their eggs in the nest of other bird species, known as hosts. Brood parasitism often imposes severe fitness costs on hosts, selecting for the evolution of effective antiparasitic defences, such as recognition and rejection of brood parasite eggs. Glucocorticoids have been recently found to mediate host physiological and behavioral adjustments in response to brood parasite eggs; however, it remains unclear whether brood parasitism triggers a general response involving multiple physiological elements. In this study, we experimentally investigated whether a salient brood parasitic stimulus (the presence of a nonmimetic model egg in the nest) causes physiological adjustments in adult Eurasian blackbirds (Turdus merula) at immune (leukocyte profiles) and cellular (heat-shock protein Hsp70 synthesis) level. Also, we explored whether these physiological changes are mediated by variations in corticosterone (CORT) levels. We found that experimental brood parasitism caused an increase in heterophils and a decrease in lymphocytes, leading to higher heterophils and lymphocytes ratios in parasitized birds. Nevertheless, we did not find tradeoffs between immune function and CORT levels. Hsp70 synthesis was not affected by our experimental manipulation. Our findings provide evidence that brood parasite eggs trigger a general stress response in egg-rejecter hosts, including changes in cellular immune profiles.

Physiological links with behavior and fitness: The acute adrenocortical response predicts trappability but not survival in male and female deermice

The "Cort-Fitness" hypothesis predicts a negative relationship between baseline glucocorticoids (GCs) and fitness, although evidence for this hypothesis remains mixed. Such ambiguity could partially exist because blood GCs, typically used in field studies, can fluctuate too rapidly to measure accurately, while the relationship between GCs and trappability is often neglected. Here, by addressing these factors, we examined relationships between GC measures and survival of North American deermice (Peromyscus maniculatus; hereafter deermice) as a model system. To do this, we used more stable GC measures, including the integrated measures of baseline and stress response fecal corticosterone metabolites (FCMs), and downstream measures of neutrophil/lymphocyte ratio (N/L ratio), and body condition score (BCS), to characterize their relationships with survival and trappability. Over two years, deermice were live-trapped monthly, evaluated for BCS, and sampled for feces and blood. Stress response FCMs were evaluated only at first capture. Mark-recapture models, with GC measures as predictors of either survival or trappability, were compared to identify top models. We found that stress response FCMs negatively predicted trappability, and weaker evidence that BCS positively predicted survival. Although the latter provides some support for the "Cort-Fitness" hypothesis, there was no support when using integrated measures. Instead, our findings suggest that deermice with a lower adrenocortical response (i.e. stress response FCMs) were more likely to be captured. Therefore, GC-trappability relationships must be investigated in field studies to avoid linking the wrong GC profile to fitness, and physiological measures other than blood GCs may be useful for detecting GC-fitness patterns.

From the Field to the Lab: Physiological and Behavioural Consequences of Environmental Salinity in a Coastal Frog

Environmental salinization is recognized as a global threat affecting biodiversity, particularly in coastal ecosystems (affected by sea level rise and increased frequency and severity of storms), and the consequent osmoregulatory challenges can negatively affect wildlife. In order to assess whether coastal species can respond to changes in environmental salinity, it remains essential to investigate the consequences of exposure to salinity in an environmentally-relevant context. In this study, we assessed the consequences of exposure to environmental salinity in coastal frogs (Pelophylax sp., N = 156) both in the field and experimentally, using a comprehensive combination of markers of physiology, behaviour and ecology. Exposure to salinity in the field negatively affected physiological parameters (osmolality, monocytes and eosinophils counts), as well as body condition and locomotor performance, and influenced size- and sex-specific habitat selection. Further, we demonstrated in a controlled experiment that short-term exposure to salinity strongly affected physiological parameters (salt influxes, water effluxes, immunity-related stress markers) and locomotor performance. Most of these effects were transient (water and salt fluxes, locomotor performance) once optimal conditions resumed (i.e., freshwater). Taken together, our results highlight the need to investigate whether exposure to environmental salinity can ultimately affect individual fitness and population persistence across taxa.

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.

Comparative Study of Physiological Changes in Turbot Scophthalmus maximus in Different Living Conditions

The aim of this study was to compare the organismal responses of farmed and wild-caught turbot, Scophthalmus maximus, based on analyses of biochemical plasma parameters, leukocyte profile, and histological tissue profile of gills, kidney, liver, intestine, and spleen, as well as gene expression of stress proteins in kidney and liver tissue. The results revealed significant differences in plasma triglycerides (TRIG), total protein (TP), albumin (ALB), globulin (GLOB), bilirubin (TBIL), creatinine (CRE) levels, creatine kinase (CK), and superoxide dismutase (SOD) activities that were higher, and A/G ratio, calcium (Ca) and phosphorus (P) concentrations, alkaline phosphatase (ALP), and glutathione peroxidase (GPx) activity, which were lower in farmed population. The neutrophil-leukocyte (N:L) ratio and gene expression of HSP70, HSP90, and WAP65-2 were increased in the wild-caught turbot. The wild-caught turbot were infested with the gill digenean parasite Dactylogyrus sp. and tapeworm Bothriocephalus scorpii. The obtained results provide valuable data for the assessment of the physiological responses of turbot for future comparative studies of the effects of various endogenous and exogenous factors on homeostasis of this species.

Telomere length declines with age, but relates to immune function independent of age in a wild passerine

Telomere length (TL) shortens with age but telomere dynamics can relate to fitness components independent of age. Immune function often relates to such fitness components and can also interact with telomeres. Studying the link between TL and immune function may therefore help us understand telomere-fitness associations. We assessed the relationships between erythrocyte TL and four immune indices (haptoglobin, natural antibodies (NAbs), complement activity (CA) and heterophil-lymphocyte (HL) ratio; n = 477-589), from known-aged individuals of a wild passerine (Malurus coronatus). As expected, we find that TL significantly declined with age. To verify whether associations between TL and immune function were independent of parallel age-related changes (e.g. immunosenescence), we statistically controlled for sampling age and used within-subject centring of TL to separate relationships within or between individuals. We found that TL positively predicted CA at the between-individual level (individuals with longer average TL had higher CA), but no other immune indices. By contrast, age predicted the levels of NAbs and HL ratio, allowing inference that respective associations between TL and age with immune indices are independent. Any links existing between TL and fitness are therefore unlikely to be strongly mediated by innate immune function, while TL and immune indices appear independent expressions of individual heterogeneity.

Serum Cortisol and Its Correlation with Leucocyte Profile and Circulating Lipids in Donkeys (Equus asinus)

The values for basal serum cortisol concentrations of horses are available in many studies. However, there are limited data about serum cortisol in donkeys. The present study aimed to determine the baseline values for serum cortisol, to evaluate the influence of age and pregnancy on its levels, and to correlate its values with leucocyte profile, serum cholesterol, and triglycerides. Serum samples were collected from 97 healthy donkeys. Cortisol was analyzed by chemo-luminescent assay. The median and the 2.5th and 97.5th percentiles of serum cortisol measured and calculated in all donkeys were 5.64, 3.40, and 10.54 µg/dL, respectively. Females (n.91) were divided into three groups: Group A (young), Group B (adult), and Group C (pregnant at the 9th−11th months). The effect of age and physiological status was investigated by the Mann−Whitney test. Group C showed significantly higher levels than Group B (p < 0.05). Significant correlations were found in Group B with monocytes (r = 0.37, p < 0.01) and triglycerides (r = 0.30, p < 0.05), and in Group C with monocytes (r = 0.79, p < 0.01), basophils (r = 0.6, p < 0.05), and neutrophil/lymphocyte ratio (r = −0.63, p < 0.05). Higher cortisol values related to late pregnancy are also found in this species. These preliminary results provide evidence for a relationship between cortisol and the immune system as well as cortisol and lipid metabolism modulated by age and pregnancy when parameters are within normal values.

Stress Response, Immunity, and Organ Mass in Toads (Rhinella diptycha) Living in Metal-Contaminated Areas

Mining is one of the main activities that drive the economy of Brazil. Mining activity is associated with risk of contamination of environment and local fauna by metals. Amphibians have a life cycle that requires a transition between aquatic and terrestrial environments, increasing their vulnerability to metal contamination in the water and substrate. Metals are ubiquitous, with high bioaccumulative and biomagnifying potential, and may lead to immune and endocrine disruption. In this study, we analyzed two different components of the innate immune response, bacterial killing ability (BKA) and phytohemagglutinin edema (PHA), and two stress biomarkers, corticosterone plasma levels (CORT) and the neutrophil to lymphocyte ratio (N:L), of toads (Rhinella diptycha) living in places contaminated by metals. Blood samples were collected pre- and post-restraint (1h), followed by an immune challenge with PHA and tissue collection (liver, spleen, and kidneys). Toads liver metal bioaccumulation did not correlate with the immune response or stress biomarkers. Post-restraint, animals had increased CORT and reduced BKA, independently of the collection site, and these variables were not correlated with liver metal bioaccumulation. Interestingly, toads with the larger spleen (immune organ) showed increased N:L post-restraint and greater edema after the PHA challenge. Our results indicate that toads living in metal-contaminated environments responded to acute stressor, activating the hypothalamic-pituitary-interrenal axis and the immune response. Keep tracking the physiological variables of these animals and the presence of metals in the environment and tissues should provide valuable health status indicators for the population, which is vital for proposing amphibian conservation strategies in these areas.

The contribution of sleep to the neuroendocrine regulation of rhythms in human leukocyte traffic

Twenty-four-hour rhythms in immune parameters and functions are robustly observed phenomena in biomedicine. Here, we summarize the important role of sleep and associated parameters on the neuroendocrine regulation of rhythmic immune cell traffic to different compartments, with a focus on human leukocyte subsets. Blood counts of "stress leukocytes" such as neutrophils, natural killer cells, and highly differentiated cytotoxic T cells present a rhythm with a daytime peak. It is mediated by morning increases in epinephrine, leading to a mobilization of these cells out of the marginal pool into the circulation following a fast, beta2-adrenoceptor-dependent inhibition of adhesive integrin signaling. In contrast, other subsets such as eosinophils and less differentiated T cells are redirected out of the circulation during daytime. This is mediated by stimulation of the glucocorticoid receptor following morning increases in cortisol, which promotes CXCR4-driven leukocyte traffic, presumably to the bone marrow. Hence, these cells show highest numbers in blood at night when cortisol levels are lowest. Sleep adds to these rhythms by actively suppressing epinephrine and cortisol levels. In addition, sleep increases levels of immunosupportive mediators, such as aldosterone and growth hormone, which are assumed to promote T-cell homing to lymph nodes, thus facilitating the initiation of adaptive immune responses during sleep. Taken together, sleep-wake behavior with its unique neuroendocrine changes regulates human leukocyte traffic with overall immunosupportive effects during nocturnal sleep. In contrast, integrin de-activation and redistribution of certain leukocytes to the bone marrow during daytime activity presumably serves immune regulation and homeostasis.

Do Microbiota in the Soil Affect Embryonic Development and Immunocompetence in Hatchling Reptiles?

Reptile eggs develop in intimate association with microbiota in the soil, raising the possibility that embryogenesis may be affected by shifts in soil microbiota caused by anthropogenic disturbance, translocation of eggs for conservation purposes, or laboratory incubation in sterile media. To test this idea we incubated eggs of keelback snakes (Tropidonophis mairii, Colubridae) in untreated versus autoclaved soil, and injected lipopolysaccharide (LPS) into the egg to induce an immune response in the embryo. Neither treatment modified hatching success, water uptake, incubation period, or white-blood-cell profiles, but both treatments affected hatchling size. Eggs incubated on autoclaved soil produced smaller hatchlings than did eggs on untreated soil, suggesting that heat and/or pressure treatment decrease the soil’s suitability for incubation. Injection of LPS reduced hatchling size, suggesting that the presence of pathogen cues disrupts embryogenesis, possibly by initiating immune reactions unassociated with white-blood-cell profiles. Smaller neonates had higher ratios of heterophils to leucocytes, consistent with higher stress in smaller snakes, or body-size effects on investment into different types of immune cells. Microbiota in the incubation medium thus can affect viability-relevant phenotypic traits of hatchling reptiles. We need further studies to explore the complex mechanisms and impacts of environmental conditions on reptilian embryogenesis.

Physiological parameters of a plover during nonbreeding and breeding seasons in Patagonia, Argentina

Migratory shorebirds are the most threatened avian species due to the effects of human activities and climate change. Physiological parameters are useful to evaluate the health status of free-living animals. Here we investigated lymphocytes, heterophils, heterophils/lymphocytes, and glucose for female and male Two-banded Plovers (Charadrius falklandicus Latham, 1790) during nonbreeding (body moult) and breeding (incubation) seasons in coastal areas of northern Patagonia, Argentina. We also measured corticosterone for the first time for this species during the breeding season. Nonbreeding Two-banded Plovers were more likely to have higher physiological measurements that were not dependent on body moult nor body condition, being similar between sexes. Differences found in glucose are likely related to recent feeding in nonbreeding birds compared with fasting during incubation. The gregarious nonbreeding behaviour in comparison with the isolated breeding pairs would increase the risk of acquiring parasites and (or) pathogens inducing a response of the immune system reflected in higher values of lymphocytes. Baseline corticosterone during breeding was similar between sexes and were lower compared with other values reported for breeding plovers. Two-banded Plovers undergo energetically demanding physiological changes during the nonbreeding stage, strengthening the idea that conservation of the environmental resources at these locations may be more important than previously thought.

No Evidence for Constitutive Innate Immune Senescence in a Longitudinal Study of a Wild Bird

AbstractAging is associated with declines in physiological performance; declining immune defenses particularly could have consequences for age-related fitness and survival. In aging vertebrates, adaptive (memory-based) immune responses typically become impaired, innate (nonspecific) responses undergo lesser declines, and inflammation increases. Longitudinal studies of immune functions in wild animals are rare, yet they are needed to understand immunosenescence under evolutionarily relevant conditions. Using longitudinal data from a tropical passerine (Malurus coronatus) population, we investigate how population trends emerge from within-individual changes and between-individual heterogeneity (e.g., selective disappearance) in immune status. We quantified constitutive immune indexes (haptoglobin [inflammation associated], natural antibodies, complement [lytic] activity, and heterophil-lymphocyte ratio; n=505-631) in individuals sampled one to seven times over 5 yr. Unexpectedly, longitudinal analyses showed no age-related change within individuals in any immune index, despite sufficient power to detect within-individual change. Between individuals, we found age-related declines in natural antibodies and increases in heterophil-lymphocyte ratios. However, selective disappearance could not adequately explain between-individual age effects, and longitudinal models could not explain our data better than cross-sectional analyses. The lack of clear within-individual immunosenescence is itself notable. Persistent levels of haptoglobin, complement activity, and natural antibodies into old age suggests that these immune components are maintained, potentially with adaptive significance.

Total white blood cell counts but not HL ratio changes in the transition from post-juvenile molt to autumn migration in the first-year Eurasian blackcap (Sylvia atricapilla)

Theoretically, seasonal changes in immune functioning in animals are shaped by the trade-off between a probability of encountering pathogens and availability of resources. We used leukocyte profile (absolute and relative leukocyte counts) as a simple measure of immune system condition to study how it changes during the transition from postjuvenile molt to autumn migration in a free-living migratory songbird, the Eurasian blackcap (Sylvia atricapilla). We observed the higher white blood cells (WBC) and lymphocyte counts in molting birds compared to migrating individuals, but we did not find differences in heterophils and ratio of heterophils to lymphocytes (HL ratio). We suppose that the high number of WBC in molting blackcaps could reflect the heightened ability of their immune system to resists infections. The lower WBC counts in migrants compared to molting birds were mostly due to reduced lymphocyte numbers, thus representing in a downregulation of specific immunity. An absence of heterophil differences between molt and migration might indicate that various components of immunity can change relatively independently (or at different pace). Fat scores had no effect on WBC counts and HL ratio. Therefore, we found no strong evidence for a resource-immune functionality trade-off during transition from postjuvenile molt to autumn migration in immature Eurasian blackcap. This study is an important step in understanding how immune system in general and leukocyte profile in particular changes in transition between life-history stages in migratory songbirds.

Short-term stressors and corticosterone effects on immunity in male toads (Rhinella icterica): A neuroimmune-endocrine approach

In the last decades, it is growing the idea that stress-induced immunomodulation is bimodal: with acute stress associated with enhancing effects while chronic stress with suppressive effects. However, the immune-endocrine interactions and its implications are often overlooked in ectotherms. We investigated the impact of corticosterone (CORT) treatment and short-term stressors on CORT plasma levels and the immunity of male toads (Rhinella icterica), using three distinct protocols: restraint, immune challenge (with lipopolysaccharide, LPS), and CORT transdermal application (TA). Our results showed increased CORT and neutrophil: lymphocyte ratio (NLR) regardless of the stress input (restraint, LPS challenge) or CORT TA. In the meantime, the bacterial killing ability (BKA) was not affected by any treatment, suggesting this immune parameter might be a more constitutive and robust response. Interestingly, the cellular immune response showed distinct patterns. Increased phagocytosis of blood leukocytes and phytohemagglutinin edema followed LPS and CORT TA (15 ​μg), respectively. In contrast, the phagocytosis of peritoneal leukocytes decreased after CORT TA (1 and 10 ​μg), indicating that short-term increases in CORT levels might impair local immune function. Such differences in cellular immunity might also be associated with CORT doses or the interaction between CORT and other immune mediators, such as melatonin, testosterone, and cytokines. Overall, our results highlight the immune-enhancing effects of the acute stress response and CORT TA, and the complexity of the immune-endocrine interaction in anurans. It also highlights the relevance of investigating distinct contexts for CORT increase arising from different situations, as well as diverse immune components for a better understanding of the stress-induced immunomodulation.

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Restraint, LPS and exogenous CORT increased CORT plasma levels in Rhinella icterica.

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Distinct acute stressors and exogenous CORT increased neutrophil: lymphocyte ratio.

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LPS induced increased phagocytosis of blood cells.

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Exogenous CORT increased PHA edema, and decreased phagocytosis of peritoneal cells.

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BKA were sustained in all acute stress protocols and exogenous CORT treatment.

Physiological Health and Survival of Captive-Reared and Released Juvenile Blanding's Turtles

AbstractConservation translocations are important in maintaining viable wildlife populations of vulnerable species within their indigenous ranges. To be effective, population restoration efforts (e.g., head start programs) must consider the species' life history, regional ecology, and physiology and the health status of wild and translocated populations. The decline of Blanding's turtles (Emydoidea blandingii) has prompted the initiation of head start programs, but the health and short-term survival of head-started juveniles released to the wild is largely unknown. From May to October 2016 and 2017, we radio tracked captive-reared, recently released juvenile Blanding's turtles and monitored their survivorship and monthly physiological health. We aimed to (1) compare physiological metrics of juveniles before and after release from captivity and between head-started cohorts, (2) identify seasonal trends in physiological metrics of recently released juveniles, (3) compare physiological metrics of recently released and formerly released juveniles, and (4) identify predictors of juvenile survivorship after release from captivity. Juvenile short-term survival was low compared with other studies. Most physiological metrics did not change after release from captivity, negating significant juvenile stress before or after release. Physiological metrics for recently released cohorts varied seasonally, suggesting that these juveniles were likely in good health. Some physiological metrics differed between recently released and formerly released juveniles, demonstrating a potential postrelease acclimatization period. Finally, no physiological metrics significantly predicted survival, but surviving juveniles had a higher percentage of fat. In all, juvenile deaths were not due to poor turtle health but rather to predation from human-subsidized mesocarnivores. Therefore, head-started juvenile Blanding's turtles released in suburban areas may benefit from antipredator training and mesocarnivore control at release sites.

Physiological impacts of temperature variability and climate warming in hellbenders (Cryptobranchus alleganiensis)

Cold-adapted hellbender salamanders that inhabit cool mountain streams are expected to fare poorly under warmer projected climate scenarios. This study investigated the physiological consequences of long-term, naturalistic temperature variation on juvenile hellbenders under simulated current and warmer (+1.6 C) climates vs. controlled steady temperatures. Mean temperature and temperature variability were both important predictors of growth as indicated by monthly body mass change (%), stress as indicated by neutrophil:lymphocyte (N:L) ratio and bacteria-killing ability of blood. Cold exposure in hellbenders was associated with weight loss, increased N:L ratios and reduced Escherichia coli killing ability of blood, and these effects were less pronounced under a warmer climate scenario. These observations suggest that cold periods may be more stressful for hellbenders than previously understood. Growth rates peaked in late spring and late fall around 14-17°C. Hellbenders experiencing warmer simulated climates retained body condition better in winter, but this was counter-balanced by a prolonged lack of growth in the 3-month summer period leading up to the fall breeding season where warmer simulated conditions resulted in an average loss of -0.6% body mass/month, compared to a gain +1.5% body mass/month under current climate scenario. Hellbenders can physiologically tolerate projected warmer temperatures and temperature fluctuations, but warmer summers may cause animals to enter the fall breeding season with a caloric deficit that may have population-level consequences.

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.

Effects of psychogenic stress on some peripheral and central inflammatory markers in rats with the different level of excitability of the nervous system

Patients with post-stress pathologies display the signs of inflammation in the peripheral blood as well as in the brain. The mechanisms of such post-stress neuroimmune changes, their contribution to the behavior, the relationship of the intensity of inflammation with genetically determined features have not been clarified. The goal of this work was to evaluate the dynamics of post-stress inflammation in the blood and hippocampus of rats which differ in level of excitability of the nervous system. Rats of two strains (high/low excitability threshold) were subjected to stress according to the K. Hecht protocol and their behavior, neutrophil:lymphocyte ratio and the number of Iba+ cells in the hippocampus were analysed 24 hours, 7 and 24 days after stress exposure. Highly excitable animals show an increase in anxiety-like behavior, in the number of neutrophils compared to lymphocytes as well as in the number of Iba1+ cells in CA1, CA3 and DG areas of the hippocampus in response to stress. Thus, hereditary high excitability of the nervous system is a possible risk factor for the development of post-stress pathologies.

Leukocytes count and profile during early postnatal ontogenesis in domestic cat: Effect of litter size and multiple paternity

Since blood cells count is the most important indicator of animals' physiological status, we investigated the effects of age, litter size, and multiple paternity on the total number of white blood cells, the number of their individual types (lymphocytes, neutrophils, eosinophils, monocytes), and the ratio of neutrophils to lymphocytes in domestic cat during early postnatal ontogenesis. The study was conducted on kittens living in outdoor conditions, aged from birth to 6 months. The number of white blood cells was evaluated using a hemoanalyzer, the leukocyte formula and the proportion of cell types were determined manually from blood smears. Age significantly affected the number of leukocytes in the first 3 months of kittens' age. The number and proportion of neutrophils were the highest after birth and gradually decreased during the first month. Lymphocytes number, on the contrary, increased during this period. Monocytes and eosinophils increased in number in the first 2 months. The litter size affected the number of leukocytes and neutrophils in the first 2 months of life, their number being significantly higher in kittens from the small litters than from the large ones. In kittens from the litters with multiple paternity, the number of leukocytes and the proportion of neutrophils was higher than in litters from a single male. Thus, age, litter size and type of paternity may affect the hematological indices in domestic cats, which must be taken into account during the estimation of the health status of kittens in domestic and wild cats.

The stressed bird in the hand: Influence of sampling design on the physiological stress response in a free-living songbird

Despite the widely used application of standardized capture-handling protocols to collect blood and assess the physiological stress response, the actual sampling design (e.g., timing and the number of blood samples) often differs between studies, and the potential implications for the measured physiological endpoints remain understudied. We, therefore experimentally tested the effects of repeated handling and multiple blood sampling on the stress response in wintering free-living great tits (Parus major). We modified a well-established sampling protocol of avian studies by adding either an additional blood sample or a "sham-manipulation" (i.e., handling associated with the blood sampling procedure without venepuncture), to disentangle the effects of handling stress and blood loss. We combined three different stress metrics along the endocrine-immune interface to investigate the acute short-term stress response: total corticosterone concentrations (Cort), the heterophil/lymphocyte ratio (H:L), and the Leucocyte Coping Capacity (LCC). Our study provided three key results: i) no relationship between Cort levels, LCC and H:L, confirming that these three parameters represent different physiological endpoints within the stress response; ii) contrasting dynamics in response to stress by the measured parameters and iii) no difference in physiological stress levels 30 min after capture due to one additional blood sampling or handling event. By optimising the sampling design, our results provide implications for animal welfare and planning experimental procedures on stress physiology in passerine species.

Effects of two pesticides on northern leopard frog (Lithobates pipiens) stress metrics: Blood cell profiles and corticosterone concentrations

Amphibians are declining globally. Exposure to pesticides has been implicated in decreasing amphibian immune function, thus increasing their susceptibility to parasites and disease and thereby negatively affecting individuals and populations. Amphibians are likely exposed to neonicotinoids because these widely used insecticides are highly soluble in water and because amphibian freshwater habitats are often embedded in agroecosystems. Herein, we investigate the effects of long-term exposure to two individual neonicotinoids (clothianidin or thiamethoxam) at either low or high concentrations (2.5 or 250 µg/L) on northern leopard frog (Lithobates pipiens) blood cell profiles and concentrations of corticosterone, an energy-mediating hormone associated with stress. Larval frogs from Gosner stage 25 to 46 were exposed to pesticide and control treatments in outdoor mesocosms. Corticosterone concentrations were measured after 6 d of exposure, and blood cell profiles were assessed once frogs reached Gosner stage 46 (following 8 w of exposure). No significant changes were found in erythrocyte counts, leukocyte counts, monocyte to leukocyte ratios or corticosterone concentrations between treatments. However, exposure to either 2.5 or 250 µg/L of clothianidin, or 250 µg/L of thiamethoxam decreased neutrophil to lymphocyte ratios and neutrophil to leukocyte ratios, and exposure to 2.5 µg/L of clothianidin or 250 µg/L of thiamethoxam decreased eosinophil to leukocyte ratios. Our results indicate that long-term exposure to neonicotinoids can alter leukocyte profiles, indicative of a stress response. Future studies should investigate whether chronic exposure to neonicotinoids affect multiple measures of stress differently or influences the susceptibility of amphibians to parasites and pathogens. Our work underscores the importance of continued use of multiple measures of stress for different amphibian species when undertaking ecotoxicological assessments.

Trematodes coupled with neonicotinoids: effects on blood cell profiles of a model amphibian

Habitat loss, climate change, environmental contaminants, and parasites and pathogens are among the main factors thought to act singly or together in causing amphibian declines. We tested for combined effects of neonicotinoid pesticides and parasites (versus parasites-only) on mortality, growth, and white blood cell profiles of a model amphibian: the northern leopard frog (Rana pipiens). We first exposed infectious stages of frog trematodes (cercariae of Echinostoma spp.) to low and high concentrations of thiamethoxam or clothianidin versus water-only controls. There were no differences in survival of trematode cercariae between treatments. For the main experiment, we exposed tadpoles to clean water versus high concentrations of clothianidin or thiamethoxam for 2 weeks and added trematode cercariae to all tanks after 1 week. Exposure of tadpoles and parasites to high concentrations of thiamethoxam or clothianidin did not affect parasite infection success. Tadpole survival was not different between treatments before or after parasite addition and there were no significant differences in tadpole snout-to-vent lengths or developmental stages between treatments. Tadpoles exposed to thiamethoxam + parasites had smaller widths than parasite-only tadpoles, whereas tadpoles exposed to clothianidin + parasites had higher eosinophil to leukocyte ratios compared to parasite-only tadpoles. Tadpoles of both neonicotinoid + parasite treatments had significantly lower monocyte to leukocyte ratios relative to parasite-only tadpoles. High concentrations of neonicotinoid combined with parasites appear to influence tadpole immune function important for further defense against parasites and pathogens. This work highlights the need for more holistic approaches to ecotoxicity studies, using multiple stressors.

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.