The maintenance of body temperature (Tb) and hydration state within tolerable ranges is crucial for effective physiological functioning and thus survival. It is well established that deviations in Tb and hydration state can have immediate effects on organismal health, and recent work has demonstrated that, despite surviving the initial impacts of such challenges, individuals may experience profound long-term impacts on fitness, though the mechanisms driving these long-term impacts remain unclear. One potential mechanism underlying detrimental long-term effects is oxidative stress, yet the relationships among increased Tb, dehydration, and oxidative stress dynamics, as well as whether these relationships can be altered through adaptation, are mostly unexplored. Accordingly, we conducted complementary field and lab experiments to investigate seasonal, behavioral, thermal, and hydric effects on oxidative stress in two species of arid-adapted Crotalus rattlesnakes representing three populations from two xeric locations with differing aridity. Regardless of experiment or treatment, we found that C. pyrrhus, the most abundant species in the more arid location, had consistently lower reactive oxygen metabolite (ROM) concentrations than did C. atrox from the same and the less arid locations. Furthermore, the C. atrox population from the more arid site had ROM concentrations intermediate and often significantly different from the other two populations. Interestingly, when Tb and activity were similar between the C. atrox populations (e.g., in Spring), ROM concentrations were similar. Contrary to our hypotheses, we found no consistent patterns relating antioxidant capacity to any environmental or phylogenetic variable. Lastly, hydration state did not influence either ROM concentration or antioxidant capacity. Overall, our study demonstrates that while water deprivation and increased temperatures don't necessarily induce oxidative stress in species tolerant of these conditions, results are consistent with the hypothesis that species that are more specialized for extremely arid environments have reduced ROM concentrations. Such insight is critical as we attempt to understand how species have adapted to arid conditions and how species may respond to a warming and drying globe.

In invertebrates, hemocytes are the principal effector cells of innate immunity, and a growing body of evidence indicates that the circulation of immune cells is under circadian and nycthemeral control across both vertebrate and invertebrate taxa. Yet whether such temporal organisation extends to terrestrial gastropods, increasingly used as comparative models in physiology and ecotoxicology through hemocyte-based biomarkers, remains poorly documented. This study investigated nycthemeral variations in hemocyte-related parameters in juvenile, sub-adult and adult Cornu aspersum maintained under controlled laboratory conditions. Snails were sampled at four time points over a 24 h cycle (06:00, 12:00, 18:00 and 24:00; n = 20 per developmental stage and sampling time). Circulating hemocyte concentration, hemocyte viability, proportions of hemocyte types I and II, and micronucleus frequency were assessed following standardised procedures. Significant temporal variations were observed in circulating hemocyte concentration, with lower values generally recorded during evening and nocturnal sampling periods (18:00 and 24:00). Similar nycthemeral patterns were observed across developmental stages, although they were less pronounced in juveniles. In contrast, hemocyte viability, hemocyte profile distribution and micronucleus frequency remained comparatively stable throughout the 24 h cycle, suggesting the absence of marked cytogenomic fluctuations associated with sampling time under the tested conditions. These findings indicate that nycthemeral physiological rhythms may substantially influence hemocyte circulation dynamics and hemolymph accessibility in terrestrial gastropods, while exerting limited effects on basal cellular integrity. The study highlights the importance of temporal standardisation in hemocyte-based biomarker protocols and supports the integration of chronobiological considerations into ecotoxicological and comparative physiological investigations involving terrestrial molluscs.

The exact location of the dominant pacemaker site in adult bird heart continues to be ill-defined. The aim of this study was to identify the localization of the dominant pacemaker and to investigate its electrophysiological characteristics in isolated sinoatrial preparations of the adult chicken (Gallus gallus domesticus) heart. The dominant pacemaker was localized at the base of the right leaflet of the valve of the right cranial vena cava and at the base of both leaflets of the valve of the caudal vena cava. But latent pacemakers were also identified in regions around these valves. Additionally, the valve leaflets generated conducting-like APs that with high amplitude, fast maximal upstroke velocity (greater than in working myocardium) and with diastolic depolarization. The avian sinoatrial junction is electrophysiologically heterogeneous. The avian dominant pacemaker site is more extensive than that in mammals. These findings establish a foundation for understanding species-specific pacemaker mechanisms and their evolution.

Estuarine fishes experience marked environmental variability and rely on tightly regulated osmoregulatory mechanisms to maintain internal homeostasis. Settleable atmospheric particulate matter (SePM), a complex mixture of metals and metalloids, is an emerging stressor in aquatic systems and may interfere with regulatory processes. This study investigated the effects of SePM exposure on osmoregulatory homeostasis in the estuarine fish Centropomus parallelus. Fish were exposed for 96 h to either 0 g.L[-1] (control) or 1 g.L[-1] SePM, and key physiological endpoints associated with ion and water balance were assessed, including plasma osmolality and Na[+], Cl[-], and K[+] concentrations; Na[+]/K[+]-ATPase (NKA), V-type H[+]-ATPase (VAT), and total ATPase activities in the gills and kidneys; and ionocyte abundance and transporter protein levels in gill ionocytes and renal tubules. Aluminum, iron, vanadium, and chromium levels were accumulated in the gills and kidneys. SePM exposure disrupted osmoregulatory homeostasis, as evidenced by reduced plasma osmolality and decreased Cl[-] and K[+] concentrations. NKA activity was upregulated in the gills, accompanied by an increase in the density of NKA-positive ionocytes. Conversely, total ATPase and VAT activities were downregulated in the kidneys, whereas the abundance of NKA, the symporter Na[+],K[+],2Cl[-] (NKCC), and the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride (Cl[-]) channel, remained unchanged in renal tubules. These findings suggest that SePM exposure is associated with tissue-specific modulation of osmoregulatory parameters, including increased branchial Na[+]/K[+]-ATPase activity and NKA-positive ionocyte density, and reduced renal ATPase activities, accompanied by alterations in plasma osmolality and ion concentrations. The physiological disturbances associated with SePM exposure may impair organismal performance and reduce ecological fitness in estuarine fishes inhabiting metal-impacted coastal environments.

Transient receptor potential (TRP) channels mediate insect thermosensation, yet the downstream neurotransmitter pathways linking TRP activation to behavioral output remain unclear. We investigated the role of nicotinic acetylcholine receptors (nAChRs) in thermoregulatory and neural responses induced by TRP ligands in the American cockroach, Periplaneta americana. Extracellular recordings from the ventral nerve cord showed that capsaicin reduced spontaneous neuronal firing, whereas the selective α7-containing nAChR antagonist MG 624 increased baseline activity. Notably, nicotinic receptor blockade prevented the capsaicin-induced suppression of neuronal activity, suggesting an interaction between cholinergic signaling and capsaicin-induced neuronal modulation. Behaviorally, capsaicin shifted thermal preference toward cooler temperatures, consistent with TRP-mediated heat avoidance. This response, as well as the effect of the TRPV1 antagonist capsazepine, was markedly attenuated by MG 624 pretreatment. Grooming assays revealed differential modulation of antennal and leg grooming, suggesting distinct neural mechanisms and partial interaction between cholinergic and monoaminergic pathways. Despite pronounced neural and behavioral effects, neither TRP ligands nor nicotinic receptor blockade significantly altered whole-animal metabolic rate, as assessed by CO2 production. Together, these findings indicate that cholinergic signaling contributes to behavioral responses induced by TRP ligands and interacts with capsaicin-induced neuronal modulation in P. americana. The results provide new insight into the neurochemical integration of thermosensory signaling and highlight cholinergic pathways as important contributors to insect thermoregulatory responses.

Water and electrolyte regulation is essential for organismal survival. In mammals, the nephron operates a futile cycle of ultrafiltration and reabsorption that accounts for most of the entropy generation of the kidney. In contrast, insect Malpighian tubules form urine primarily through electrolyte secretion. Here, we develop a thermodynamic model of Malpighian tubule function in which entropy generation is estimated from electrical dissipation, with cationic urinary flow treated as current and transepithelial voltage as the potential difference. The model is applied to fluid secretion in the Malpighian tubules of the yellow fever mosquito, the stick insect, and the fruit fly, and to fluid reabsorption in the rectum of the desert locust and the fruit fly. The criterion of efficacy is the ratio between entropy generation and water flow, representing the energy dissipated per unit urinary volume. The results are compared with estimates for humans, mice, and dairy cattle, spanning eight orders of magnitude in body mass. The excretory systems of insects are shown to be more economical than those of mammals. Nevertheless, the differences are remarkably small across all species examined, despite the enormous variation in body size. These results confirm the hypothesis, proposed in the 1980s, that Malpighian tubules operate with greater efficacy than mammalian nephrons and further suggest that fundamental thermodynamic constraints shape the efficiency of epithelial transport systems across widely divergent organisms.

Testosterone (T) and dehydroepiandrosterone sulfate (DHEAS) are two steroids integral to male primate development. For humans, both are high in early infancy (for T, this is known as minipuberty) then rapidly decline. DHEAS then increases beginning in early childhood, resulting in a process known as adrenarche, which signals the maturation of the zona reticularis of the adrenal gland. T increases a few years thereafter, marking the beginning of puberty. These processes are relatively well-studied in humans, but data is lacking for the other great apes. Particularly for adrenarche, strikingly little is known about its distribution across the primate order. Here, we draw on a large sample of wild male mountain gorilla fecal samples collected over the full course of the gorilla lifespan to examine how the hormones T and DHEAS change with age. We use enzyme-linked immunosorbent assays to quantify metabolites of both hormones, and validate these assays using high-performance liquid chromatography-tandem mass spectrometry analyses. We find that both hormones are high in male gorilla infancy, and then decline before T rises again at 9.3 years of age. Surprisingly, DHEAS rises afterwards at 10.7 years old, showing a departure from the human developmental pattern. T then peaks at 18 years of age, while DHEAS plateaus at ~ 23 years of age. More research is needed to assess intra-order variation in primate hormonal development.

Understanding the physiological regulation of cardiac activity in insects remains a central topic in insect biochemistry and physiology. In Lepidoptera, direct electrophysiological characterization of cardiac function is still limited, particularly under anesthetic conditions commonly used during experimental manipulation. In this study, we evaluated the effects of isoflurane anesthesia on cardiac electrophysiology in adult Anteos menippe butterflies during anesthetic induction and recovery. A total of eighteen newly emerged adults were subjected to two experiments. Experiment 1 - behavior during anesthetic induction and recovery with isoflurane (n = 6). Experiment 2 - the animals were divided into a control group (n = 6) and a group treated with isoflurane (n = 6). The animals were monitored during anesthetic induction and recovery with isoflurane; in this case, electrocardiographic signals (ECG) were obtained using 0.06 mm diameter tungsten steel alloy electrodes, implanted to acquire cardiac recordings lasting 30 min under controlled conditions. Isoflurane induced mild and reversible anesthesia, with induction and recovery times of 48.5 ± 8.9 s and 117.7 ± 16.2 s, respectively, without observable excitatory responses. During anesthesia, the frequency of cardiac action potentials decreased significantly, followed by a gradual recovery accompanied by increases in amplitude and linear signal power. Spectral analysis revealed a dynamic redistribution of energy during anesthetic elimination, consistent with chronotropic modulation of cardiac activity. These findings provide new electrophysiological insights into the cardiac physiology of butterflies and support the use of isoflurane as a reliable anesthetic for experimental studies involving cardiac monitoring in lepidoptera and other insects.

Regulatory mechanisms underlying seasonal fluctuations in the activity of the hypothalamic-pituitary-gonadal (HPG)-axis are poorly understood. Since 2016, following the publication of a medical hypothesis highlighting irisin's involvement in reproductive function, extensive research on this aspect has been conducted; however, studies on seasonal variation remain limited. The purpose of this study was to examine seasonal variations in hypothalamic irisin/FNDC5 expression relative to the seasonally fluctuating HPG-axis activity in male rhesus monkeys. Hypothalamic tissues for immunocytochemistry (ICC), RT-qPCR, and testicular tissues for H&E staining were used. The experimental model was validated by assessing mean testicular volume, seminiferous epithelial height, seminiferous tubular diameter, and plasma testosterone, which were significantly higher in reproductively active than in reproductively inactive male monkeys. The present study revealed that reproductively active monkeys exhibited significantly higher mean numbers of hypothalamic irisin-like immunoreactive cell bodies and elevated FNDC5 mRNA expression levels compared with reproductively inactive monkeys. This showed a positive correlation with testicular volume, seminiferous tubular diameter/epithelial height, and plasma testosterone levels. The current study suggests the possibility that irisin may be a novel positive regulator of HPG-axis activity during the breeding season in male rhesus monkeys.

Range expansion into cooler climates frequently drives phenotypic changes within a species to increase thermal tolerance. The oxygen and capacity-limited thermal tolerance (OCLTT) hypothesis maintains that thermal tolerance changes when animals move from one climate to a cooler or warmer one based on rates of oxygen demand and supply in the new environments. We tested central tenets of the OCLTT hypothesis across the north-south distribution of the green anole lizard (Anolis carolinensis) in North America, predicting that northern populations in cooler climates would have higher cold tolerance due to decreased standard metabolic rates (SMR; decreased oxygen demand), greater heart ventricle mass or hemoglobin concentrations (increased oxygen supply), or both. We further predicted that the adaptations leading to greater cold tolerance would also increase endurance capacity, with a corresponding decrease in sprint speed and exertion. Our results provided mixed support for the OCLTT hypothesis. Heart ventricle mass of the northern populations was greater, but only for females. There was no difference in SMR across populations, and hemoglobin concentrations did not follow a latitudinal pattern. However, performance traits generally matched our predictions, as endurance increased with latitude and sprint speed decreased, likely due to physiological tradeoffs associated with increased aerobic capacity. There are clearly selection pressures other than temperature acting on these populations to cause patterns differing from those expected under the OCLTT hypothesis.

Energy expenditure (EE) is the dynamic physiological process that balances energy intake to maintain body weight and body temperature. Environmental changes induce EE adaptations that limit fluctuations in body weight or body temperature by balancing between body temperature defense and energy conservation. The central nervous system (CNS) orchestrates these adaptations by integrating multiple external and internal cues to coordinate thermogenesis together with other behavioral and metabolic processes. Key hypothalamic and brainstem nuclei form a distributed network that modulates autonomic output to peripheral organs, including sympathetic tone to brown and white adipose tissues. Here, we review known neural circuits and neurotransmitter systems, their integration with sensory pathways and functionally opposing output discrepancies that reveal knowledge gaps how the CNS switches between body temperature defense and energy preservation.

Ultraviolet-B (UVB) radiation is a critical environmental stressor that affects aquatic organisms, particularly during vulnerable early life stages. This study investigated the effects of low ambient UVB exposure (1.0 W/m[2], corresponding to 6-12% of ambient summer UVB in the low-to-mid altitudes of the Indian Himalayas) on the sac-fry larvae of golden mahseer (Tor putitora) over a 7-day period. Four experimental groups were established: two UVB-exposed groups maintained under dark (UVD) and visible light (UVL) conditions, and two unexposed control groups maintained under dark (CTD) and visible light (CTL) conditions. The light treatments (UVL and CTL) were utilized to determine the potential of visible light to modulate UVB-induced effects and to rule out the light induced changes. UVB exposure significantly increased mortality and induced developmental malformations, however, heart rate remained unaffected across all treatments. Thermal tolerance was significantly impaired; specifically, the lower critical thermal minimum (CTmin) increased in both UVD and UVL treatments, while the upper critical thermal maximum (CTmax) and overall thermal scope decreased significantly in the UVD treatment alone. Gene expression analysis revealed a marked upregulation of key molecular markers involved in DNA repair (p53), apoptosis (bcl2, caspase3a), oxidative stress (nrf2a2), inflammatory response (il-1β), and proteostatic protection (hsp70) in both UV-exposed groups. Our findings demonstrate that direct exposure to even low levels of ambient UVB can induce acute physiological and molecular stress in T. putitora larvae. Given the projected increase in UVB penetration due to climate change and anthropogenic activity, these stressors may overwhelm the adaptive repair mechanisms of early life stages, potentially leading to long-term population-level declines. The study provides a preliminary information on the impact of ambient UVB on the early larval stages of mid-to-hight altitude dwelling fishes of Indian Himalayas.

Pacific lamprey, an anadromous fish native to the North Pacific Ocean, are imperiled in parts of their range. Many aspects of their biology are not fully understood, including the physiology of their spawning migration. Pacific lamprey exhibit two divergent reproductive life histories: early-maturing and late-maturing. Interior Columbia River early-maturing lamprey complete the final stages of gonadal maturation ~ 10 months after entering freshwater. From the same migrating cohort, the late-maturing lamprey wait ~ 22 months to complete maturation. This study sought to characterize the reproductive phenotypes of these two Pacific lamprey life histories. Migrating adult Pacific lamprey that had entered fresh water were collected and held for close to two years to monitor changes in morphology and physiology. The lamprey in this study, of approximately equal sex ratio, clearly separated into early- or late-maturing life histories based on differences in timing of reproductive development, morphology of length, weight, interdorsal fin gap, and plasma concentrations of estradiol-17β (E2), but not plasma androstenedione. Average plasma E2 levels in females and males were significantly higher in the early-maturing fish compared to the late-maturing fish by November, nearly half a year before any morphological divergence. This novel physiological indicator could benefit restoration activities (translocation and artificial propagation) by providing advanced identification of the two maturation life histories present in the same migration cohort. In conclusion, this study provides several morphological and physiological features that can be used to identify early- and late-maturing Pacific lamprey within the 10 month period prior to when the early-maturing fish mature.

This experiment was conducted to evaluate the effects of dietary nanocurcumin on growth performance, feed utilization, innate immunity, antioxidant capacity, biochemical indices, and air exposure stress resistance in European seabass (Dicentrarchus labrax) fingerlings. Five isonitrogenous (47% crude protein) and isocaloric (21 MJ/kg dry matter) diets were formulated, supplemented with nanocurcumin at the following levels: 0, 100, 300, 600, and 900 mg/kg. The diets were administered to D. labrax (6.45 ± 0.08 g) for 65 days. Following the feeding trial, the fish were subjected to air exposure stress for 3 min followed by 2 h of recovery before sampling. The results indicated that dietary nanocurcumin significantly enhanced growth performance and feed utilization. Antioxidant status was improved, as evidenced by increased levels of reduced glutathione and catalase, along with decreased concentrations of malondialdehyde and hydrogen peroxide. In addition, nanocurcumin supplementation reduced the activities of hepatic enzymes, including aspartate aminotransferase and alanine aminotransferase, as well as stress indicators such as glucose, cortisol, and lactate dehydrogenase, both before and after air exposure stress. Immune responses were also enhanced, with higher levels of immunoglobulin M, immunoglobulin G, and complement components 3 and 4 observed in fish fed nanocurcumin-supplemented diets. Overall, dietary nanocurcumin improved growth performance, antioxidant capacity, and innate immunity, while mitigating stress responses in D. labrax, with optimum results obtained at a dietary inclusion level of 900 mg/kg.

Electrophysiology is an emerging approach in the context of environmental toxicology, where it represents a non-invasive biomarker that has been little studied in tropical fish. In this study, we evaluated electrocardiographic (ECG) and electromyographic (EMG) responses in Hyphessobrycon heterorhabdus, a native Amazonian species considered a promising biological model for ecotoxicological studies, and Menthol was selected as the pharmacological model for methodological validation in this species. Fish were exposed to 30 mg L[- 1] for three minutes and subsequently transferred to clean water to assess recovery. The ECG showed a reduction in heart rate and an increase in the wave intervals in fish exposed to menthol. The EMG recorded the occurrence of transient muscle spasms before a progressive decrease in contraction strength as anesthesia deepened. After recovery, both ECG and EMG tracings returned to baseline conditions, indicating the reversibility of menthol-induced anesthesia. Thus, electrophysiological markers in H. heterorhabdus proved to be effective tools for detecting short-term physiological changes and supports their application in studies involving environmental stressors or chemical exposures.