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

The Australian brushtail possum (Trichosurus vulpecula) is adapted to a wide range of food plants across its range and is exposed to numerous physiological challenges. Populations that are resistant to the plant toxin sodium fluoroacetate are of particular interest as this compound has been used since the 1940s for vertebrate pest management around the world. Candidate gene identification is an important first step in understanding how spatial populations have responded to local selection resulting in local physiological divergence. We employ differential gene expression of liver samples from wild-caught brushtail possums from toxin-resistant and toxin-susceptible populations to identify candidate genes that might be involved in metabolic pathways associated with toxin-resistance. This allowed us to identify genetic pathways involved in resistance to the plant toxin sodium fluoroacetate in Western Australian possums but not those originally from south eastern Australia. We identified differentially expressed genes in the liver that are associated with cell signalling, encapsulating structure, cell mobility, and tricarboxylic acid cycle. The gene expression differences detected indicate which metabolic pathways are most likely to be associated with sodium fluoroacetate resistance in these marsupials and we provide a comprehensive list of candidate genes and pathways to focus on for future studies.

During the transition from fresh waters to terrestrial habitats, significant adaptive changes occurred in kidney function of vertebrates to cope with varying osmotic challenges. We investigated the mechanisms driving water conservation in the mammalian nephron, focusing on the relative contributions of active ion transport and Starling forces. We constructed a thermodynamic model to estimate the entropy generation associated with different processes within the nephron, and analyzed their relative importance in urine formation. We demonstrate that active ionic reabsorption exerts a pressure above 15,000 torr, a value more than 500 times greater than Starling forces. The entropy generation of the reabsorption process is found to be 20-fold higher than that of renal blood perfusion. These findings imply that the evolutionary history of vertebrates, particularly terrestrial mammals, has shaped the renal architecture to prioritize water conservation by means of an entropically costly process. This approach to the nephron function provides insights into the physiological adaptations of terrestrial vertebrates to conserve water and sheds light on the intricate interplay between environmental conditions and evolutionary responses in renal physiology.

Global warming is a major threat to reptiles because temperature strongly affects their development. High incubation temperatures reduce hatchling body size and physiological performance; however, its effects on brain development and learning abilities are less well understood. In particular, it remains unclear if the effects of elevated temperatures on learning are restricted to hatchlings or instead will persist later in life. To address this gap, we examined the effect of 'current' and 'future' (end-of-century, + 4 °C) incubation temperatures on hatchling and juvenile geckos Amalosia lesueurii, to test: (1) if elevated temperatures affect hatchling learning ability; (2) if the effects on learning persist in juvenile lizards, and (3) if and how elevated temperatures affect hatchling and juvenile brain anatomy and neuronal count. We found that fewer future-incubated hatchlings succeeded in the learning tasks. Nonetheless, the successful ones needed fewer trials to learn compared to current-incubated hatchlings, possibly due to a higher motivation. Reduced learning ability was still observed at the juvenile stage, but it did not differ between treatments due to a reduced cognitive performance of current-incubated juveniles. Future-incubated hatchlings had a smaller telencephalon, but this pattern was not found in juveniles. Neuron number and density in hatchlings or juveniles from both treatments were not different. Our results suggest that global warming will affect hatchling survival in the wild but it remains unclear if future-incubated lizards could compensate for the harmful effects of elevated temperatures. Further testing beyond the laboratory is required to understand whether phenotypic plasticity in lizards is sufficient to track global warming.

Elasmobranchs are commonly carnivores and are important in energy transfer across marine ecosystems. Despite this, relatively few studies have examined the physiological underpinnings of nutrient acquisition in these animals. Here, we investigated the mechanisms of uptake at the spiral valve intestine for two representative amino acids (_L-alanine, _L-leucine) and one representative fatty acid (oleic acid), each common to the diet of a carnivore, the Pacific spiny dogfish (Squalus suckleyi). Transport was saturable for all three nutrients, depending upon transport calculation metric (i.e., mucosal disappearance, serosal appearance, or tissue accumulation). Over 0-10 mM range of amino acids the concentration at which ½ maximal transport occurred (K_m; a measure of transporter affinity) was 11.9 and 11.2 mM for tissue accumulation of alanine and leucine, respectively. Oleic acid transport was measured at lower concentrations (0-200 µM) and tissue accumulation did not reach saturation. Putative amino acid transport systems were delineated upon confirmation of sodium dependence and competitive inhibition with threonine, glycine, and lysine. The interplay of nutrient combinations on the modulation of nutrient acquisition rates, which better mimics the complex composition of both a meal and the internal osmolytes, was next investigated. Here, the application of serosal oleic acid led to diminished mucosal disappearance of leucine. Feeding did not significantly alter transport rates, perhaps indicative of maximal transport of these energy sources whenever the substrate is available given their importance both as metabolic fuels and precursors to the osmolyte urea.

Nestling white-footed mice (Peromyscus leucopus) are born in the earliest days of spring in cold climates. If the nestlings are by accident exposed to ambient temperatures near freezing (0-7 °C) at early ages (2-10 days old), they may experience body temperatures (T_bs) equally low. During such hypothermia, although their heart keeps beating, they become apneic (cease inhaling and exhaling). However, they have an exceptional ability (e.g., compared to Mus musculus) to tolerate these conditions for at least several hours, after which they revive if rewarmed by parents. This paper addresses the physiology of the apneic period. We show that apneic, hypothermic nestlings undergo physiologically important exchanges of gases with the atmosphere. These gas exchanges do not occur across the skin. Instead they occur via the trachea and lungs even though the animals are apneic. Most significantly, when hypothermic neonates are in apnea in ordinary air, they take up O₂ steadily from the atmosphere throughout the apneic period, and the evidence available indicates that this O₂ uptake is essential for the nestlings' survival. At T_bs of 2-7 °C, the nestlings' rate of O₂ consumption varies quasi-exponentially with T_b and averages 0.04 mL O₂ g^- 1 h^- 1, closely similar to the rate expressed by adult mammalian hibernators in hibernation at similar T_bs. Morphometric analysis indicates that, at all focal ages, O₂ transport along the full length of the trachea can take place by diffusion at rates adequate to meet the measured rates of metabolic O₂ consumption.

The combined stresses of fasting and hypoxia are common events during the life history of freshwater fish species. Hypoxia tolerance is vital for survival in aquatic environments, which requires organisms to down-regulate their maintenance energetic expenditure while simultaneously preserving physiological features such as oxygen supply capacity under conditions of food deprivation. Generally, infrequent-feeding species who commonly experience food shortages might evolve more adaptive strategies to cope with food deprivation than frequent-feeding species. Thus, the present study aimed to test whether the response of hypoxia tolerance in fish to short-term fasting (2 weeks) varied with different foraging modes. Fasting resulted in similar decreases in maintenance energetic expenditure and similar decreases in P_crit and P_loe between fishes with different foraging modes, whereas it resulted in decreased oxygen supply capacity only in frequent-feeding fishes. Furthermore, independent of foraging mode, fasting decreased P_crit and P_loe in all Cypriniformes and Siluriformes species but not in Perciformes species. The mechanism for decreased P_crit and P_loe in Cypriniformes and Siluriformes species is at least partially due to the downregulated metabolic demand and/or the maintenance of a high oxygen supply capacity while fasting. The present study found that the effect of fasting on hypoxia tolerance depends upon phylogeny in freshwater fish species. The information acquired in the present study is highly valuable in aquaculture industries and can be used for species conservation in the field.

The present study aimed to establish zebrafish as an experimental model for investigations into obesity and physical exercise, as well as to assess the effects of these factors on metabolism. The experiment spanned twelve weeks, comprising a feeding trial during which the last four weeks incorporated a physical exercise protocol. This protocol involved placing fifteen animals in a five-liter aquarium, where they were subjected to swimming at an approximate speed of 0.08 m/s for 30 min daily. Throughout the experiment, histological analyses of visceral, subcutaneous, and hepatic adipose tissues were conducted, along with biochemical analyses of total cholesterol and its fractions, triglycerides, glucose, lactate, and alanine aminotransferase (ALT) levels. Additionally, oxidative stress markers, such as reactive oxygen species (ROS) levels, superoxide dismutase (SOD) activity, and catalase activity and the formation of thiobarbituric acid-reactive substances, were investigated. The results revealed that the group fed a high-fat diet exhibited an increase in ROS production and SOD activity. In contrast, the group administered the high-fat diet and subjected to physical exercise demonstrated a notable reduction in visceral adipocyte area, hepatic steatosis levels, ALT levels, and SOD activity. These findings indicate that physical exercise has a positive effect on obesity and oxidative stress in zebrafish, providing promising evidence for future investigations in this field.

An individual's energetic demands and hence metabolic rate can strongly change during adolescence, a phase characterized by profound morphological, physiological, and endocrine changes. Glucocorticoid hormones (e.g. cortisol) are released in response to hypothalamic-pituitary-adrenal-axis activity, modulate several metabolic processes, and can also be linked to increased metabolic rate. In domestic guinea pigs (Cavia aperea f. porcellus) housed in same-sex groups, cortisol concentrations increase during adolescence in males but remain stable in females, which was suggested to be related to different energetic demands by age. We therefore measured metabolic rate through oxygen (O₂) consumption over 2.5 h in male and female guinea pigs housed in same-sex groups during adolescence at ages of 60, 120, and 180 days, which was paralleled by analyses of saliva cortisol concentrations before and after the measurement. The statistical analyses involved whole body metabolic rate (ml O₂/h), body mass-corrected metabolic rate (ml O₂/h/kg), and body mass-independent metabolic rate (ml O₂/h statistically corrected for body mass). We found increasing cortisol concentrations with age in males only, but none of the three metabolic rate analyses revealed a sex difference by age. On the individual level, repeatability across ages was found in metabolic rate as well as in body mass and cortisol concentrations after the measurement, but not in "basal" cortisol concentrations. Our results suggest no sex-specific changes in metabolic rate and hence equal energetic demands in male and female guinea pigs during adolescence. Moreover, metabolic rate clearly represents a highly stable physiological trait already early in a guinea pig's life irrespective of rather fluctuating cortisol concentrations.

With climate change increasing not just mean temperatures but the frequency of cold snaps and heat waves, animals occupying thermally variable areas may be faced with thermal conditions for which they are not prepared. Studies of physiological adaptations of temperate resident birds to such thermal variability are largely lacking in the literature. To address this gap, we acclimated winter-phenotype house sparrows (Passer domesticus) to stable warm, stable cold, and fluctuating cold temperatures. We then measured several metrics of the oxidative stress (OS) system, including enzymatic and non-enzymatic antioxidants and lipid oxidative damage, in brain (post-mitotic), kidney (mitotic), liver (mitotic) and pectoralis muscle (post-mitotic). We predicted that high metabolic flexibility could be linked to increases in reactive oxygen damage. Alternatively, if variation in ROS production is not associated with metabolic flexibility, then we predict no antioxidant compensation with thermal variation. Our data suggest that ROS production is not associated with metabolic flexibility, as we found no differences across thermal treatment groups. However, we did find differences across tissues. Brain catalase activity demonstrated the lowest values compared with kidney, liver and muscle. In contrast, brain glutathione peroxidase (GPx) activities were higher than those in kidney and liver. Muscle GPx activities were intermediate to brain and kidney/liver. Lipid peroxidation damage was lowest in the kidney and highest in muscle tissue.

Many flatfish species are partially euryhaline, such as the Pacific sanddab which spawn and feed in highly dynamic estuaries ranging from seawater to near freshwater. With the rapid increase in saltwater invasion of freshwater habitats, it is very likely that in these estuaries, flatfish will be exposed to increasing levels of dissolved organic carbon (DOC) of freshwater origin at a range of salinities. As salinity fluctuations often coincide with changes in DOC concentration, two natural freshwater DOCs [Luther Marsh (LM, allochthonous) and Lake Ontario (LO, autochthonous) were investigated at salinities of 30 and 7.5 ppt. Optical characterization of the two natural DOC sources indicate salinity-dependent differences in their physicochemistry. LO and LM DOCs, as well as three model compounds [tannic acid (TA), sodium dodecyl sulfate (SDS) and bovine serum albumin (BSA)] representing key chemical moieties of DOC, were used to evaluate physiological effects on sanddabs. In the absence of added DOC, an acute decrease in salinity resulted in an increase in diffusive water flux (a proxy for transcellular water permeability), ammonia excretion and a change in TEP from positive (inside) to negative (inside). The effects of DOC (10 mg C L^-1) were salinity and source-dependent, with generally more pronounced effects at 30 than 7.5 ppt, and greater potency of LM relative to LO. Both LM DOC and SDS increased diffusive water flux at 30 ppt but only SDS had an effect at 7.5 ppt. TA decreased ammonia excretion at 7.5 ppt. LO DOC decreased urea-N excretion at both salinities whereas the stimulatory effect of BSA occurred only at 30 ppt. Likewise, the effects of LM DOC and BSA to reduce TEP were present at 30 ppt but not 7.5 ppt. None of the treatments affected oxygen consumption rates. Our results demonstrate that DOCs and salinity interact to alter key physiological processes in marine flatfish, reflecting changes in both gill function and the physicochemistry of DOCs between 30 and 7.5 ppt.