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

Metabolic rates in animals scale allometrically with body mass, a relationship well-established in terrestrial mammals. Whether these scaling laws apply to fully aquatic mammals remains uncertain, due to key physiological and ecological differences. We estimated field metabolic rates (FMRs) for five sympatric cetaceans of varying sizes, inhabiting sub-Arctic Icelandic waters: harbour porpoises (Phocoena phocoena; mean body length ± s.d = 1.35 ± 0.19 m), white-beaked dolphins (Lagenorhynchus albirostris; 2.42 ± 0.17 m), minke whales (Balaenoptera acutorostrata; 7.53 ±  0.82 m), humpback whales (Megaptera novaeangliae; 9.44 ± 1.13 m) and blue whales (Balaenoptera musculus; 21.97 ± 0.96 m). Unoccupied Aerial Vehicle (UAV) photogrammetry and published data were used to estimate body size, while respiration rates (breathes min^-1) were obtained from UAV focal follows, biologging tags, and literature sources. From these data we predicted daily FMRs (MJ day^-1) using existing bioenergetic models. As expected, mass-specific FMR declined with increasing body size among species, consistent with scaling laws. However, FMRs across all species were elevated relative to terrestrial predictions, likely reflecting the greater energetic demands of aquatic life. FMR also scaled positively with the surface-area-to-volume ratio (SVR) of each species, supporting the hypothesis that thermoregulatory costs are driven by body shape and size, and influence energy expenditure. This was further supported by the positive relationship between FMR and heat loss rates. Overall, our findings suggest that large mysticetes benefit from reduced mass-specific FMRs, enabling long migrations and extended fasting that broaden their habitat use. Smaller cetaceans face higher metabolic demands and may be more dependent on smaller, prey-rich habitats. These size-dependent energetic constraints may influence species plasticity and vulnerability to environmental changes.

Small mammals in the temperate zone often face environmental changes such as photoperiod and temperature, that may influence hematological parameters, innate immunity, and cytokines, all of which are indicative of host immunity and reflective of overall health. In order to test the winter immunoenhancement hypothesis which states that animals use short day length to up-regulate immune responses in winter, 34 adult female striped hamsters (Cricetulus barabensis) were randomly divided into long day (16 L:8D) and short day (8 L:16D) treatment groups, which were further assigned to either mild (23 ± 1℃) or low temperature (5 ± 1℃) treatment groups, respectively. We found that low temperature treatment, regardless of photoperiod, significantly increased red blood cell (RBC), and haematocrit (PCV), haemoglobin concentrations (HGB), and short photoperiod also increased RBC and PCV, implying their enhancing effect on the oxygen-transport in hamsters. However, low temperature treatment, but not photoperiod, decreased white blood cells (WBC), intermediate granulocytes (MID), percent of intermediate granulocytes (MID%), neutrophil granulocytes (GRAN), and percent of neutrophil granulocytes (GRAN%), suggesting its suppressive effect on immune function. In addition, bacteria killing capacity indicative of innate immunity increased in short day hamsters, which supported the winter immunoenhancement hypothesis. Interleukin-4 (IL-4) was reduced in low temperature-adapted hamsters, while IL-2, tumor necrosis factor alpha (TNF-α), interferon-γ (INF-γ) were not affected by low temperature treatment or short day length. Overall, low temperature and photoperiod exerted different influences on hematological parameters, innate immunity, and cytokines in striped hamsters.

Mammalian hibernation is a physiological and behavioural adaptation that permits survival during seasonal periods of energy shortage via a combination of pre-hibernal energy storage and hibernal metabolic depression (torpor). There is both seasonal preparation for the expression of torpor, and the spontaneous termination of hibernation at the end of the season. Small hibernating mammals repeatedly alternate between the torpid state, and the interbout euthermic state over a relatively short timescale (days-weeks) for the entire hibernation season. This is known as torpor arousal cycling (T-A cycling). Hibernation is therefore characterised by extreme shifts in energy homeostasis. Rheostasis is term referring to a change in a regulated homeostatic level or set point. Hibernation can be viewed as rheostasis both over the annual timescale of the seasonal hibernation cycle and over the much shorter T-A cycle. The brain sites through which these homeostatic shifts are controlled have not been identified. A specialised glial cell type lining the 3rd ventricle of the mediobasal hypothalamus (MBH tanycytes), are of particular interest. MBH tanycytes have a privileged anatomical position contacting the periphery and the hypothalamic control centres of the brain. They have documented sensing and signalling function within the hypothalamus, making them a strong candidate cell type for the control of energy homeostasis. Here, I propose that the MBH tanycytes could act as a "rheostat", shifting their sensitivity to metabolic feedback over the annual timescale and the T-A cycle, and therefore are a promising cell type to investigate in relation to the brain control of hibernation.

Most small mammalian hibernators spend the hibernation season cycling between bouts of torpor (with low body temperature (T_b) approximating ambient temperature (T_a), depressed heart and oxygen consumption rates as low as 1% active rates) and interbout arousals (IBA) where animals will spontaneously and rapidly arouse from torpor and resume most physiological functions. Kidneys are involved in numerous physiological functions including filtering the blood of metabolic waste. Due to the dramatic metabolic depression experienced during torpor and previous limitations in methods, studies inadequately addressed filtration during torpor. Here, we directly monitored clearance of sinistrin from ground squirrel circulation for up to 45 h during torpor bouts using transdermal fluorometry. In active squirrels (both summer active and interbout aroused), clearance by the kidneys was rapid with a clearance half-life (t_1/2) of 47.8 ± 5.4 and 73.4 ± 7.9 min, respectively. In contrast, clearance by the kidneys in torpid squirrels held at T_a= 4 °C was greatly reduced, but measurable, with t_1/2 of 7,103 ± 1,073 min (~ 97 to 149-fold increase in clearance time vs. active squirrels). Consistent with predictions based on metabolism, clearance by the kidneys during torpor at T_a=12 °C resulted in much faster clearance times than at T_a = 4 °C (T_1/2= 2,761 ± 375 min; 2.57-fold increase vs. 4 °C; Q₁₀ = 3.26). We demonstrate that hibernators do not completely cease excretion functions during torpor but that clearance quickly commences even at low temperatures as soon as the squirrel begins to arouse.

Deep metabolic transitions promoted by anoxia and diapause are tolerated for years by embryos of the brine shrimp, Artemia franciscana, whereas even short metabolic disruptions in mammals are accompanied by bursts of reactive oxygen species (ROS) that cause tissue damage during ischemia-reperfusion. We hypothesized mitochondria from these embryos are mechanistically poised to avoid ROS bursts and the associated oxidative stress during metabolic recovery. Isolated mitochondria that exhibited robust functional coupling were exposed to anoxia-reoxygenation (A/R) or continuous normoxia. H₂O₂ efflux was statistically identical between A/R versus normoxia groups (p = 0.221). Addition of auranofin and dinitrochlorobenzene, inhibitors of ROS scavenging pathways, promoted a five-fold increase in H₂O₂ release for the normoxic mitochondria, which confirmed that scavenging mechanisms substantially suppress routine ROS efflux. Yet when these same inhibitors were added to the A/R group, maximum H₂O₂ efflux was no greater than for normoxia. Treatment with rotenone, an inhibitor of Complex I and reverse electron transport (RET), produced only a modest decrease in H₂O₂ efflux. This result indicates that RET, a major contributor to ROS bursts in mammalian mitochondria, is not stimulated by A/R in A. franciscana. Lack of aconitase inactivation, protein carbonyl accumulation, and lipid hydroperoxide production demonstrate that bouts of A/R do not cause significant oxidative damage in A. franciscana mitochondria. Finally, the capacity to downregulate Complex I activity through active-deactive conformations was tested and is not operative. These data collectively suggest that Complex I from A. franciscana may not possess the capacity for RET and the associated ROS surge.

Climate change is predicted to continue elevating regional sea surface temperatures (SST) and increase the frequency and severity of localized heating events, phenomena which may threaten the biodiversity, integrity, and function of tropical coral reef ecosystems. The primary objective of this study was to determine physiological and behavioral responses to elevated SST in a Hawaiian surgeonfish, the yellow tang, Zebrasoma flavescens. We assessed standard metabolic rate (SMR), maximum metabolic rate (MMR), aerobic scope (AS), and swimming performance, as well as temperature preference (T_pref) in this ecologically and economically important coral reef fish. The Z. flavescens were acclimated to either the current maximum monthly summer SST around O'ahu, 27 °C, or an elevated SST, 31 °C. Acclimation temperature had no significant effect on SMR, MMR, AS, or swimming performance. Temperature preference was tested over a 24-hour period in an annular preference chamber with a gradient ranging from 24 to 34 °C. Our study found that Z. flavescens in both acclimation temperatures had a similar T_pref (median) of 27 °C with first and third quartiles of 25.7 to 29 °C. Analysis of relative use of available temperatures (compositional analysis) indicated a preference for the lowest available temperatures of 24 to 26 °C in both acclimation groups. These findings indicate that Z. flavescens can completely compensate AS and swimming ability to the elevated SST conditions, although T_pref remains near or below the current summer SST, suggesting other factors explain behavioral temperature preference.