Journal of Comparative Physiology B-Biochemical Systems and Environmental Physiology最新文献

In this study, we investigated the influence of environmental temperature and immune challenge on organ and body mass in juvenile degus (Octodon degus). Using an experimental design with two temperature treatments (15 °C and 30 °C) and a lipopolysaccharide (LPS)-induced immune challenge, we measured the mass of key organs (kidney, heart, liver, spleen, lung) as well as body mass. Our results showed that temperature alone significantly affected kidney, heart, lung, and body mass, with individuals reared at 30 °C exhibiting larger organs and greater body mass, consistent with thermoneutral conditions. Immune challenge with LPS primarily affected lung mass, with challenged individuals showing larger lungs regardless of temperature. However, no significant changes were observed in spleen or liver mass, and no interactions between temperature and immune challenge were detected. These findings suggest that temperature-driven developmental plasticity plays a dominant role in shaping organ and body traits, while immune activation induces organ-specific responses. Our results highlight the importance of environmental temperature in shaping physiological traits and raise questions about the long-term effects of immune challenges and temperature interactions on wildlife health and fitness.

Cyclic changes in snowshoe hare (Lepus americanus) fecundity have been attributed to changes in winter forage availability and predation pressure. Disentangling how nutrition and predation pressure affect snowshoe hare physiology is complex. As an herbivore of the northern boreal forests, snowshoe hares cope with extreme seasonal changes in diet, ambient temperature, and energy demands. We examined seasonal variation in the body condition index, blood biomarkers indicative of nutritional status, and fecal cortisol metabolite concentrations, in snowshoe hares across five ecologically distinct times of year in relation to adult survival rates. Snowshoe hares sampled from a high-density population in northern Alaska during 2018 showed decreases in survival and in plasma concentrations of total protein (TP), blood urea nitrogen (BUN), hematocrit (Hct), Chloride (Cl) and glucose during March and October. Increased survival and concentrations of Cl, TP, BUN, Hct, sodium (Na) and glucose were observed during August. Decreases in mass and survival from August to October suggest limited forage. Increases in TP, BUN, Hct and glucose in December suggest higher metabolic turnover. Fecal cortisol concentrations were not significantly associated with seasonal nutritional condition. A two-fold increase in mean cortisol was observed during August, potentially associated with energetically costly processes such as increased movement and reproduction. This work provides seasonal observations of snowshoe hare plasma biochemical values (N = 164) indicative of nutritional status, and supports the idea of using a collective biomarker approach to advance our understanding of how seasonality may play a role in snowshoe hare physiology.

Calorie restriction has been shown to dramatically extend lifespan in a range of species. Beyond longevity, calorie restriction is also reported to improve cognitive function, ameliorate neurodegeneration and peripheral nerve damage, reduce cancer incidence, and is commonly used to increase motivation in studies of behaviour. The mouse has been the most common species for these experiments and whilst efforts are ongoing to demonstrate the benefits of calorie restriction in humans, the evidence in mice is most compelling. Many mechanisms have been proposed for the beneficial effects of calorie restriction, but we note that one potentially important factor has seldom been considered: namely that mice readily enter torpor in response to food restriction. Torpor is a remarkable protective physiological state characterized by profound reductions in body temperature, oxygen consumption, heart rate, and activity. In this review, we describe the dietary protocols used to study the effects of calorie restriction and present the case that mice in these studies are highly likely to have entered torpor. We discuss the extent to which torpor might influence or mediate the measured outcomes. We highlight that induction of torpor is an important confound that is rarely, if at all, considered in calorie restriction research and make recommendations for the design and conduct of future studies.

Hypoxic conditions naturally occur in nests of egg laying reptiles including the American alligator, Alligator mississippiensis. The effects of developmental hypoxia have been delineated in several studies of this species, with changes in cardiovascular function persisting into juvenile life. However, several questions regarding the effects of developmental hypoxia remain. In this study we designed a series of experiments to quantify the effects of developmental hypoxia on permeabilized cardiac muscle fiber mitochondrial respiration, reactive oxygen species production, and response to acute anoxia in American alligators. Alligator eggs were incubated in 21% O₂ (normoxia) or 10% O₂ (hypoxia) at 30 °C beginning on day 14 of a 72-day incubation period through hatching. Animals were studied at two ages, at 90% of incubation and 1-year post hatching. Mitochondrial respiration and ROS production under leak and oxidative phosphorylation states were measured in permeabilized cardiac muscle fibers with high-resolution respirometry coupled with fluorometry. To examine the response of mitochondria to acute anoxia and subsequent reoxygenation, permeabilized cardiac muscle fibers were exposed to 20 min of anoxia, followed by reoxygenation during measurement of mitochondria respiration and ROS production. Hypoxic incubation resulted in a decrease in embryos mass which was maintained through the first year of juvenile life. Hypoxic incubation had no effect on cardiac mitochondria respiration or ROS production at either 90% of incubation or 1-year post hatching. After exposure to anoxia for 20 min, the rate of mitochondria respiration did not differ between the pre-anoxia respiration levels for all animals tested. There was no change in ROS production observed upon reoxygenation of the permeabilized cardiac muscle. Our results suggest that hypoxic incubation has little influence on cardiac myocyte mitochondrial physiology in the developing alligator and the cardiac mitochondria are resistant to acute bouts of anoxic exposure.

Population density is one of the most important factors influencing immune function. Social stress induced by higher density may account for the immunosuppression according to the endocrine hypothesis. To test this hypothesis, male striped hamsters (Cricetulus barabensis) were classified into the One/Cage (n = 9), Two/Cage (n = 6), and Three/Cage (n = 9) groups, and the treatment lasted for 45 days. The titers of immunoglobin (Ig)G15 and IgM 10 were lower in the Two/Cage group compared to the One/Cage group, indicating that higher housing density suppressed humoral immunity. However, the masses of thymus and spleen, phytohaemagglutinin (PHA) responses at 6 h, 12 h, 24 h, 48 h, and 72 h after PHA injection, the titers of IgG 5, IgG10, IgM5, and IgM15 were all not affected by housing density. Blood glucose level was higher in the One/Cage group than the other two groups, leptin titers did not differ among the three groups, whereas corticosterone concentration was higher in the Two/Cage and Three/Cage groups than in the One/Cage group. Moreover, negative correlation was observed between corticosterone concentration and the titers of IgG5, IgG10, IgG15, and IgM10. These results suggested that humoral immunity was reduced by higher stress levels induced by higher housing density, which supported the endocrine hypothesis. White blood cell (WBC) count was higher in the Two/Cage group than in the One/Cage group, and intermediate granulocytes (MID) were higher in the Two/Cage group than in the One/Cage and Three/Cage groups, indicating the fight and injury might have arisen in the higher housing density.

The peptide hormone ghrelin, also known as "hunger hormone", is primarily secreted by the stomach and plays a key role in the regulation of vertebrate appetite and energy balance. While the hunger hormone and its functions have been extensively researched in mammalian species, its physiological roles have received less attention in birds and knowledge on the ghrelin system is especially poor in wild avian species. In contrast to mammals, ghrelin acts as an anorexigenic signal in birds and suppresses food intake. In this study, we focussed on the altricial chicks of thin-billed prions (Pachyptila belcheri) which are subjected to irregular, up to 8 day-long fasts, while waiting for their parents to return from feeding trips. We show that thin-billed prion chicks, which received a meal in the night prior to sampling, had higher circulating ghrelin levels than fasting conspecifics. Ghrelin levels did not correlate with chick body condition, meal size, or the length of a fast. Our study adds to past literature supporting an anorexigenic effect of avian ghrelin and is among the first to describe ghrelin profiles in seabirds, thereby significantly contributing to the scarce literature on ghrelin in wild avian species.

The impacts of heat exposure on mitochondrial physiology are poorly understood in most mammals. We examined the thermal effects on muscle mitochondrial function in deer mice (Peromyscus maniculatus), a species in which running endurance is impaired when heat exposure increases body temperature beyond 40 °C. Mitochondrial physiology was examined at 37, 40, and 42 °C using both permeabilized fibres and isolated mitochondria from the gastrocnemius muscle. Hot temperatures increased leak respiration, reduced the coupling efficiency of oxidative phosphorylation, and increased reactive oxygen species (ROS) emission. These results suggest that heat exposure reduces mitochondrial efficiency, which could contribute to impairments in running performance, and may also induce oxidative stress. Thermal effects on mitochondrial function may thus represent a potential vulnerability during heat exposure in mammals.

Widespread species often display traits of generalists, yet local adaptations may limit their ability to cope with diverse environmental conditions. With climate change being a pressing issue, distinguishing between the general ecological and physiological capacities of a species and those of individual populations is vital for assessing the capability to adapt rapidly to changing habitats. Despite its importance, physiological variation across broad range distributions, particularly among free-ranging bats in natural environments, has rarely been assessed. Studies focusing on physiological variation among different populations across seasons are even more limited. We investigated physiological variation in the Malagasy Trident Bat Triaenops menamena across three different roost types in Madagascar during the wet and dry season, examining aspects such as energy regimes, body temperature, and roost microclimates. We focused on patterns of torpor in relation to roosting conditions. We hypothesized that torpor occurrence would be higher during the colder, more demanding dry season. We predicted that populations roosting in more variable microclimates would expend less energy than those in mores stable ones due to more frequent use of torpor and greater metabolic rate reductions. Our findings highlight complex thermoregulatory strategies, with varying torpor expression across seasons and roosts. We observed an overall higher energy expenditure during the wet season but also greater energy savings during torpor in that season, regardless of roost type. We found that reductions in metabolic rate were positively correlated with greater fluctuations in ambient conditions, demonstrating these bats' adaptability to dynamic environments. Notably, we observed diverse torpor patterns, indicating the species' ability to use prolonged torpor under extreme conditions. This individual-level variation is crucial for adaptation to changing environmental conditions. Moreover, the flexibility in body temperature during torpor suggests caution in relying solely on it as an indicator for torpor use. Our study emphasizes the necessity to investigate thermoregulatory responses across different populations in their respective habitats to fully understand a species' adaptive potential.

Air-breathing vertebrates face many physiological challenges while breath-hold diving. In particular, they must endure intermittent periods of declining oxygen (O₂) stores, as well as the need to rapidly replenish depleted O₂ at the surface prior to their next dive. While many species show adaptive increases in the O₂ storage capacity of the blood or muscles, others increase the oxidative capacity of the muscles through changes in mitochondrial arrangement, abundance, or remodeling of key metabolic pathways. Here, we assess the diving phenotypes of two sympatric diving birds: the anhinga (Anhinga anhinga) and the double-crested cormorant (Nannopterum auritum). In each, we measured blood- and muscle-O₂ storage capacity, as well as phenotypic characteristics such as muscle fiber composition, capillarity, and mitochondrial arrangement and abundance in the primary flight (pectoralis) and swimming (gastrocnemius) muscles. Finally, we compared the maximal activities of 10 key enzymes in the pectoralis, gastrocnemius, and left ventricle of the heart to assess tissue level oxidative capacity and fuel use. Our results indicate that both species utilize enhanced muscle-O₂ stores over blood-O₂. This is most apparent in the large difference in available myoglobin in the gastrocnemius between the two species. Oxidative capacity varied significantly between the flight and swimming muscles and between the two species. However, both species showed lower oxidative capacity than expected compared to other diving birds. In particular, the anhinga exhibits a unique diving phenotype with a slightly higher reliance on glycolysis and lower aerobic ATP generation than double-crested cormorants.

Pacemaker atrioventricular (AV) rings, continuous with the AV node, have been shown to be present in the mammalian and avian hearts. There is conspicuous lack of electrophysiological data on the cardiac pacemakers in reptiles. We aimed to characterize the AV ring in the common lizard heart for the first time using conventional microelectrode technique. Detaching the sinoatrial (SA) area unmasked pacemaking in the AV junction. In all seven studied isolated AV ring preparations, we could record action potentials (APs) with characteristic diastolic depolarization, with a slow upstroke (dV/dt _max) of 3.5 ± 0.3 V s^-1 and a low amplitude of 57.8 ± 1.3 mV. The cells with pacemaking potentiality were found to surround the atrial orifice of the right AV valve. We identified some commonalities between phenotype of right AV ring pacemaker APs and SA dominant pacemaker ones. Thus, the AV ring in the reptile heart demonstrates pacemaking activity and contains cells that resemble the electrophysiological characteristics of mammalian and avian pacemaker myocytes in AV rings surrounded the atrial orifices of AV valves.