Effects of temperature on plasma corticosterone in a native lizard

Ecophysiological responses of Liolaemus arambarensis juveniles to experimental temperature variations

Climate change increasingly influences the loss of biodiversity, especially in ectothermic organisms, which depend on environmental temperatures to obtain heat and regulate their life cycle. Studies that aim to understand the impact of temperature variation are important to better understand the possible impacts generated on the homeostasis of ectothermic organisms. Our objective was to characterize the responses of juvenile Liolaemus arambarensis lizards to abrupt changes in temperature, quantifying markers of body condition, intermediary and hormonal metabolism and oxidative balance. We collected 45 juvenile individuals of L. arambarensis (winter: 20 and summer: 25) in Barra do Ribeiro, Brazil. We transported the animals to the laboratory, where they were acclimatized for five days at a temperature of 20 °C, then divided and exposed to temperatures of 10 °C, 20 °C, 30 °C and 40 °C for 24 h. After exposure, the animals were euthanized and the brain, caudal muscle, thigh, and liver tissues were extracted for quantification of biomarkers of metabolism (glycogen and total proteins) and oxidative balance (acetylcholinesterase, superoxide dismutase, catalase, glutathione-S-transferase and lipoperoxidation) and plasma for corticosterone quantification. The results show that L. arambarensis is susceptible to sudden temperature variations, where higher temperatures caused greater activity of antioxidant enzymes, increased lipoperoxidation and higher plasma levels of corticosterone in animals eliminated in winter. The present study demonstrated that abrupt changes in temperature could significantly modify the homeostatic mechanisms of animals, which could lead to oxidative stress and a potential trade-off between survival and growth/reproduction. In this context, the organism mobilizes energy resources for survival, with possible damage to growth and reproduction. Demonstrate that a change in temperature can be a potential factor in extinction for a species given the profile of global climate change.

Cycling temperature treatments affect estimates of digestive performance in prairie lizards (Sceloporus consobrinus)

In nature, many organisms experience a daily range of body temperatures. Thermal performance at stable temperatures is often extrapolated to predict function in cyclical environments. However, temperature order and cyclicity may influence physiological processes. The current study compared energy intake, digestive passage time and energy budgets at a stable temperature (33°C) and two temperature cycles in lizards (Sceloporus consobrinus), to determine (1) whether stable treatments adequately project performance in a cycling environment and (2) whether temperature order influences performance. Cycles had a mean temperature of 33°C, and rotated through 30°C, 33°C and 36°C daily, with equal durations of time at each temperature but differing temperature order, with warm days and cool nights in cycle 1 and cool days and warm nights in cycle 2. For analyses, performance in the stable treatment was compared with that during cycles. If temperature is the primary factor regulating performance, then performance from the stable treatment and cycles should compare favorably. However, physiological performance varied based on temperature treatment. Energy intake and budgets were similar between the stable trial and cycle 1 but not cycle 2. However, passage time did not differ. Notably, the two cycling regimes consistently varied in performance, indicating that temperature order plays a primary role in regulating performance. Physiological data collection requires careful consideration of effects of cycling versus stable temperature treatments. Stable temperatures do not consistently represent performance in cycling regimes and consideration should be paid not only to which temperatures animals experience but also to how temperature is experienced in nature.

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.

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

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

Blood hematology and biochemical of four laying hen strains exposed to acute heat stress

This study is aimed at defining physiological responses to heat stress (HS) in four different lines to better understand the underlying mechanisms of various responses in these genotypes when exposed to heat for a short period. At the age of 30 weeks, 176 laying hens (44 each from the Fayoumi, Golden Sabahia, White Leghorn, and Lohman Brown) were allotted to 2 groups (thermoneutral temperature (26.0 ± 1 °C) and HS (35 ± 1 °C) with relative humidity 55 ± 5% for 6 h/day). Blood samples were collected after 6 h of heat. According to the findings of this study, acute HS increased the concentration of LH in hens by 20.2% while decreasing the concentration of FSH by 4.24. Genotype was found to have a significant effect on blood hematology and most blood biochemical. Significant differences were found between heat stress and genotype in most of the blood parameters. Golden sabahia laying hens had significantly higher WBC, IgY, and LH levels than other groups under HS. The findings of the current study suggested that Lohman Brown was less tolerant to acute HS than another genotype.

Body temperature and activity patterns modulate glucocorticoid levels across lizard species: A macrophysiological approach

Environmental and intrinsic factors interact to determine energy requirements in vertebrates. Glucocorticoid hormones (GCs) are key mediators of this interaction, as they fluctuate with energetic demands and regulate physiological and behavioral responses to environmental challenges. While a great body of research has focused on GC variation among individuals, the mechanisms driving GC variation across species and at broad spatial scales remain largely unexplored. Here, we adopted a macrophysiological approach to investigate the environmental factors and life-history traits driving variation in baseline GCs across lizard species. We tested three hypotheses: (1) If GCs increase with body temperature to meet higher metabolic demand, we expect an association between average baseline GCs and the mean species’ body temperature in the field (GC-temperature dependence hypothesis); (2) If GCs mediate behavioral responses to avoid thermal extremes, we expect that individuals frequently exposed to extreme conditions exhibit higher baseline GC levels (Behavioral thermoregulation hypothesis); (3) If GCs increase to support higher energy demands in active foragers during their period of activity, we expect that active foraging species have higher baseline GCs than sit-and-wait foragers, and that GC levels increase in relation to the duration of daily activity windows (Activity hypothesis). We used biophysical models to calculate operative temperatures and the activity patterns of lizards in sun-exposed and shaded microenvironments. Then, we tested the association between baseline GCs, body temperature, operative temperatures, foraging mode, and activity windows across 37 lizard species, using data from HormoneBase. Our comparative analyses showed that variation in baseline GCs was primarily related to the mean field body temperature and foraging mode, with higher baseline GCs in active foragers with higher body temperatures. Our results suggest that body temperature and foraging mode drive GC variation through their effects on energy requirements across lizard species.

Hematology and biochemistry of critically endangered radiated tortoises (Astrochelys radiata): Reference intervals in previously confiscated subadults and variability based on common techniques

Madagascar's radiated tortoises (Astrochelys radiata) are critically endangered, threatened by illegal collection, and confiscated in alarming numbers in recent years. Robust population- and technique-specific hematology and biochemistry reference intervals are valuable yet heretofore missing tools for triage, rehabilitation, and reintroduction of confiscated radiated tortoises. We determined reference intervals in 120 previously confiscated, clinically healthy subadult radiated tortoises living under human care within their native habitat at the Tortoise Conservation Center (TCC). Specific analytes measured were manual packed cell volume, total solids, white blood cell (WBC) count and differentials, and biochemistry analytes using a point of care system. To evaluate the effects of different commonly used techniques on these analytes, we compared results between two venipuncture sites (subcarapacial sinus and brachial vein) and three different WBC quantification methods (Natt and Herrick, Leukopet, and slide estimate). Reference intervals were narrower for most analytes, and sodium and potassium were qualitatively higher in the TCC population compared to previously published values from radiated tortoises housed in North American institutions. Creatine kinase, aspartate aminotransferase, glucose and inorganic phosphorus were all significantly greater in brachial samples than in subcarapacial samples. There was poor agreement and evidence of constant and/or proportional bias between all WBC quantification methods. Differences based on time of sample collection were incidentally found in some analytes. These results highlight the need for considering technique, demographic, and environmental factors in creating and applying reference intervals, and contribute foundational knowledge for improving care of radiated tortoises throughout the confiscation-to-release pathway.

Acute temperature adaptation mechanisms in the native reptile species Eremias argus

Reptiles are sensitive to temperature changes as ectotherm animals. The climate warming may pose more serious threat to reptiles. Although the behavior effect and reproduction biology have been well studied, little information is available about the adaptation mechanisms of reptiles to temperature stress. In this study, the native Chinese species, Eremias argus were incubated at 15 (cold stress), 25 (control group) and 35 °C (thermal stress) for 24 h. The transcriptome and metabolome technology were applied to investigate the molecular regulation mechanisms of lizards to acute temperature changes. The CIRBP and HSPA8 were hub genes in response to temperature adaptation. The increased expression of PER gene in lizard circadian rhythm is associated with tyrosine metabolism after cold or thermal stress. The poly-unsaturated fatty acids in female lizard liver were significantly increased with up-regulation of FASN and ACACA genes after thermal stress, which proved the disruption of fatty acid biosynthesis pathway in corporation with the altered body weight. The cortisol and testosterone were important steroid hormones in response to temperature changes especially in male lizard liver. The increased CIRBP gene expression in lizard gonads suppressed the KDM6B gene, which regulates the testis development and may induce sex reversal in male lizard after thermal stress. The adaptation responses of lizards to temperature stress may threaten the health status of wild population.

Two stressors are worse than one: combined heatwave and drought affect hydration state and glucocorticoid levels in a temperate ectotherm

Heatwaves and droughts are becoming more intense and frequent with climate change. These extreme weather events often occur simultaneously and may alter organismal physiology, yet their combined impacts remain largely unknown. Here, we experimentally investigated physiological responses of a temperate ectotherm, the asp viper (Vipera aspis), to a simulated heatwave and drought. We applied a two-by-two factorial design by manipulating the daily temperature cycle (control vs. heatwave) and the water availability (water available vs. water-deprived) over a month followed by exposure to standard thermal conditions with ad libium access to water. Simulated heatwave and water deprivation additively increased mass loss, while water deprivation led to greater plasma osmolality (dehydration). Mass gain from drinking after the treatment period was higher in vipers from the heatwave and water-deprived group suggesting that thirst was synergistically influenced by thermal and water constraints. Heatwave conditions and water deprivation also additively increased baseline corticosterone levels but did not influence basal metabolic rates and plasma markers of oxidative stress. Our results demonstrate that a short-term exposure to combined heatwave and drought can exacerbate physiological stress through additive effects, and interactively impact behavioral responses to dehydration. Considering combined effects of temperature and water availability is thus crucial to assess organismal responses to climate change.

Fecal glucocorticoid metabolites and ectoparasites as biomarkers of heat stress close to roads in a Mediterranean lizard

Differences between air and ground temperatures are expected to narrow with the advance of the season in temperate regions (aka seasonal restriction in the availability of thermal microhabitats), which may activate behavioral and physiological responses of ectotherm species adapted to temperate climates. However, according to cost-benefit models of ectotherm thermoregulation, we hypothesize that these responses may also carry some costs. We quantified seasonal shifts in thermoregulatory precision, concentration of fecal glucocorticoid metabolites, and load of ectoparasites in a Mediterranean lizard, Psammodromus algirus. We also tested whether the proximity to a road, a putative source of chronic stress, can facilitate the glucocorticoid-mediated response of lizards to heat stress. As expected, differences between body and environmental temperatures narrowed during the reproductive season and lizards responded by increasing their thermoregulatory precision and the secretion of glucocorticoids, as indicated by metabolites in feces. Interestingly, lizards tended to have higher glucocorticoid concentration when captured far from the road. This might reflect either a putative impairment of the glucocorticoid-mediated response of the lizards to heat stress close to the road or the plastic capability of P. algirus to acclimate to sources of moderate chronic stress. In the latter direction, the increase of both glucocorticoid metabolites and thermoregulatory precision supported that this Mediterranean species responds to environmental thermal restrictions with adaptive behavioral and physiological mechanisms. However, this was also associated with an increase in its susceptibility to ectoparasites, which represents an added cost to the current cost-benefit models of ectotherm thermoregulation.

Compensating for a stressful pregnancy? Glucocorticoid treatment during gravidity reduces metabolic rate in female fence lizards post-parturition

Reproduction is a critical part of an animal's life history, but one which incurs significant costs to survival and future reproductive potential. These physiological consequences are likely to be influenced by context - for example, if an individual is subject to environmental stressors, physiological and behavioral changes associated with reproduction may be altered. Glucocorticoids, hormones produced as part of the physiological response to stressors, may alter how reproduction affects female physiology and behavior, and therefore the outcomes of reproductive trade-offs. Glucocorticoids prioritize immediate survival over reproduction, for example through changes in immune function, metabolic rate, and foraging, which may reduce energy expenditure or increase energy gain. However, we previously found that female eastern fence lizards (Sceloporus undulatus) experiencing elevated glucocorticoid levels during gestation were nevertheless able to maintain reproductive output and body condition. Here we investigate compensatory mechanisms by which eastern fence lizard females may maintain reproduction under experimental increases in a glucocorticoid, corticosterone (CORT). We found that, although CORT-treated females had similar immune function and behavior, they had reduced metabolic rates 3-5 days post-parturition compared to control females. Given that CORT-treated females spent a similar time basking and had equal food intake compared to control females, we suggest that the reduced metabolic rate is a mechanism by which CORT-treated females maintain their energy balance and reduce the energetic costs of gestation during periods of stress. This study suggests that physiological responses to reproduction may be context-dependent and could act to minimize costs of reproduction in situations where CORT is elevated (such as during periods of environmental stress).

Interdependence of Thyroid and Corticosteroid Signaling in Vertebrate Developmental Transitions

Post-embryonic acute developmental processes mainly allow the transition from one life stage in a specific ecological niche to the next life stage in a different ecological niche. Metamorphosis, an emblematic type of these post-embryonic developmental processes, has occurred repeatedly and independently in various phylogenetic groups throughout metazoan evolution, such as in cnidarian, insects, molluscs, tunicates, or vertebrates. This review will focus on metamorphoses and developmental transitions in vertebrates, including typical larval metamorphosis in anuran amphibians, larval and secondary metamorphoses in teleost fishes, egg hatching in sauropsids and birth in mammals. Two neuroendocrine axes, the hypothalamic-pituitary-thyroid and the hypothalamic-pituitary-adrenal/interrenal axes, are central players in the regulation of these life transitions. The review will address the molecular and functional evolution of these axes and their interactions. Mechanisms of integration of internal and environmental cues, and activation of these neuroendocrine axes represent key questions in an “eco-evo-devo” perspective of metamorphosis. The roles played by developmental transitions in the innovation, adaptation, and plasticity of life cycles throughout vertebrates will be discussed. In the current context of global climate change and habitat destruction, the review will also address the impact of environmental factors, such as global warming and endocrine disruptors on hypothalamic-pituitary-thyroid and hypothalamic-pituitary-adrenal/interrenal axes, and regulation of developmental transitions.

Assay temperature affects corticosteroid-binding globulin and free corticosterone estimates across species

Glucocorticoid hormones are often measured to assess how organisms physiologically respond to challenges in their environment. In plasma, glucocorticoids circulate in two forms: bound to corticosteroid-binding globulins (CBG) or unbound (free). Measuring CBG allows us to estimate the amount of free glucocorticoids present in a plasma sample. However, free glucocorticoid estimates are affected by the assay temperature used when measuring CBG, with colder temperatures maximizing specific binding but likely underestimating glucocorticoid's affinity for CBG. Here, we test how a biologically relevant incubation temperature (41 °C) changes the disassociation constant (K_d; used to estimate free glucocorticoid levels) when compared to the traditional 4 °C incubation temperature, across four commonly studied avian species. We then apply the new K_d's calculated at 41 °C to existing data sets to examine how the change in K_d affects free corticosterone estimates and data interpretation. K_d's were generally higher (lower affinity for CORT) at warmer incubation temperatures which resulted in higher levels of estimated free CORT in all four species but differed among subspecies. This increase in free CORT levels did not qualitatively change previously reported statistical relationships, but did affect variance and alpha (P) values. We suggest that future assays be run at biologically relevant temperatures for more accurate estimates of free CORT levels in vivo and to increase the chances of detecting biological patterns of free-CORT that may not be revealed with the classic methodology that tends to underestimate free CORT levels.