Showing papers in "Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology in 2012"

Glucose metabolism in fish: a review

Abstract: Teleost fishes represent a highly diverse group consisting of more than 20,000 species living across all aquatic environments. This group has significant economical, societal and environmental impacts, yet research efforts have concentrated primarily on salmonid and cyprinid species. This review examines carbohydrate/glucose metabolism and its regulation in these model species including the role of hormones and diet. Over the past decade, molecular tools have been used to address some of the downstream components of these processes and these are incorporated to better understand the roles played by carbohydrates and their regulatory paths. Glucose metabolism remains a contentious area as many fish species are traditionally considered glucose intolerant and, therefore, one might expect that the use and storage of glucose would be considered of minor importance. However, the actual picture is not so clear since the apparent intolerance of fish to carbohydrates is not evident in herbivorous and omnivorous species and even in carnivorous species, glucose is important for specific tissues and/or for specific activities. Thus, our aim is to up-date carbohydrate metabolism in fish, placing it to the context of these new experimental tools and its relationship to dietary intake. Finally, we suggest that new research directions ultimately will lead to a better understanding of these processes.

Diversity and function of the avian gut microbiota

Abstract: The intestinal microbiota have now been shown to largely affect host health through various functional roles in terms of nutrition, immunity, and other physiological systems. However, the majority of these studies have been carried out in mammalian hosts, which differ in their physiological traits from other taxa. For example, birds possess several unique life history traits, such as hatching from eggs, which may alter the interactions with and transmission of intestinal microbes compared to most mammals. This review covers the diversity of microbial taxa hosted by birds. It also discusses how avian microbial communities strongly influence nutrition, immune function, and processing of toxins in avian hosts, in manners similar to and different from mammalian systems. Finally, areas demanding further research are identified, along with descriptions of existing techniques that could be employed to answer these questions.

Evolution of osmoregulatory patterns and gill ion transport mechanisms in the decapod Crustacea: a review

Abstract: Decapod crustaceans exhibit a wide range of osmoregulatory patterns and capabilities from marine osmoconformers to brackish and freshwater hyperregulators to terrestrial hyporegulators. The principal gill salt transport mechanisms proposed to underlie the ability of the better-known taxa to occupy these specific habitats are examined here. Traditional thinking suggests that a graduated series of successively stronger adaptive mechanisms may have driven the occupation of ever more dilute osmotic niches, culminating in the conquest of freshwater and dry land. However, when habitat and osmoregulatory parameters are analyzed quantitatively against the phylogenies of the taxa examined, as illustrated here using a palaemonid shrimp clade, their association becomes questionable and may hold true only in specific cases. We also propose a putative evolution for gill epithelial ion pump and transporter arrangement in a eubrachyuran crab clade whose lineages occupy distinct osmotic niches. By including the systematics of these selected groups, this review incorporates the notion of a protracted time scale, here termed ‘phylophysiology’, into decapod osmoregulation, allowing the examination of putative physiological transformations and their underlying evolutionary processes. This approach assumes that species are temporally linked, a factor that can impart phylogenetic structuring, which must be considered in comparative studies. Future experimental models in decapod osmoregulatory physiology should contemplate the phylogenetic relationships among the taxa chosen to better allow comprehension of the transformations arising during their evolution.

Interpreting indices of physiological stress in free-living vertebrates

Abstract: When vertebrate physiological ecologists use the terms ‘stress’ or ‘physiological stress’, they typically mean the level of hypothalamus–pituitary–adrenal (HPA-) axis activation. Measurements of stress hormone concentrations (e.g. glucocorticoids in blood, urine or faeces), leukocytes (e.g. the neutrophil–lymphocyte ratio or heterophil equivalent), immunofunction (e.g. innate, cell-mediated or humoral immunity measures) and regenerative anaemia (e.g. mean erythrocyte volume and red blood cell distribution width) have all been used to estimate HPA-axis activity in free-living vertebrates. Stress metrics have provided insights into aspects of autecology or population regulation that could not have been easily obtained using other indices of population wellbeing, such as body condition or relative abundance. However, short- and long-term stress (often problematically termed acute and chronic stress, respectively) can interact in unpredictable ways. When animals experience trapping and handling stress before blood, faeces and/or urine is sampled, the interaction of short- and long-term stress can confound interpretation of the data, a fact not always acknowledged in studies of stress in free-living vertebrates. This review examines how stress metrics can be confounded when estimates of HPA-axis activation are collected for free-living vertebrates and outlines some approaches that can be used to help circumvent the influence of potentially confounding factors.

Impacts of ocean acidification on respiratory gas exchange and acid-base balance in a marine teleost, Opsanus beta

Abstract: The oceanic carbonate system is changing rapidly due to rising atmospheric CO(2), with current levels expected to rise to between 750 and 1,000 μatm by 2100, and over 1,900 μatm by year 2300. The effects of elevated CO(2) on marine calcifying organisms have been extensively studied; however, effects of imminent CO(2) levels on teleost acid-base and respiratory physiology have yet to be examined. Examination of these physiological processes, using a paired experimental design, showed that 24 h exposure to 1,000 and 1,900 μatm CO(2) resulted in a characteristic compensated respiratory acidosis response in the gulf toadfish (Opsanus beta). Time course experiments showed the onset of acidosis occurred after 15 min of exposure to 1,900 and 1,000 μatm CO(2), with full compensation by 2 and 4 h, respectively. 1,900-μatm exposure also resulted in significantly increased intracellular white muscle pH after 24 h. No effect of 1,900 μatm was observed on branchial acid flux; however, exposure to hypercapnia and HCO(3)(-) free seawater compromised compensation. This suggests branchial HCO(3)(-) uptake rather than acid extrusion is part of the compensatory response to low-level hypercapnia. Exposure to 1,900 μatm resulted in downregulation in branchial carbonic anhydrase and slc4a2 expression, as well as decreased Na(+)/K(+) ATPase activity after 24 h of exposure. Infusion of bovine carbonic anhydrase had no effect on blood acid-base status during 1,900 μatm exposures, but eliminated the respiratory impacts of 1,000 μatm CO(2). The results of the current study clearly show that predicted near-future CO(2) levels impact respiratory gas transport and acid-base balance. While the full physiological impacts of increased blood HCO(3)(-) are not known, it seems likely that chronically elevated blood HCO(3)(-) levels could compromise several physiological systems and furthermore may explain recent reports of increased otolith growth during exposure to elevated CO(2).

Osmoregulation and epithelial water transport: lessons from the intestine of marine teleost fish

Abstract: For teleost fish living in seawater, drinking the surrounding medium is necessary to avoid dehydration. This is a key component of their osmoregulatory strategy presenting the challenge of excreting excess salts while achieving a net retention of water. The intestine has an established role in osmoregulation, and its ability to effectively absorb fluid is crucial to compensating for water losses to the hyperosmotic environment. Despite this, the potential for the teleost intestine to serve as a comparative model for detailed, integrative experimental studies on epithelial water transport has so far gone largely untapped. The following review aims to present an assessment of the teleost intestine as a fluid-transporting epithelium. Beginning with a brief overview of marine teleost osmoregulation, emphasis shifts to the processing of ingested seawater by the gastrointestinal tract and the characteristics of intestinal ion and fluid transport. Particular attention is given to acid–base transfers by the intestine, specifically bicarbonate secretion, which creates the distinctly alkaline gut fluids responsible for the formation of solid calcium carbonate precipitates. The respective contributions of these unique features to intestinal fluid absorption, alongside other recognised ion transport processes, are then subsequently considered within the wider context of the classic physiological problem of epithelial water transport.

The metabolic effects of prolonged starvation and refeeding in sturgeon and rainbow trout

Abstract: The present study examines the particular metabolic strategies of the sturgeon Acipenser naccarii in facing a period of prolonged starvation (72 days) and subsequent refeeding (60 days) compared to the trout Oncorhynchus mykiss response under similar conditions. Plasma metabolites, endogenous reserves, and the activity of intermediate enzymes in liver and white muscle were evaluated. This study shows the mobilization of tissue reserves during a starvation period in both species with an associated enzymatic response. The sturgeon displayed an early increase in hepatic glycolysis during starvation. The trout preferentially used lactate for gluconeogenesis in liver and white muscle. The sturgeon had higher lipid-degradation capacity and greater synthesis of hepatic ketone bodies than the trout, although this latter species also showed strong synthesis of ketone bodies during starvation. During refeeding, the metabolic activity present before starvation was recovered in both fish, with a reestablishment of tissue reserves, plasmatic parameters (glucemia and cholesterol), and enzymatic activities in the liver and muscle. A compensatory effect in enzymes regarding lipids, ketone bodies, and oxidative metabolism was displayed in the liver of both species. There are metabolic differences between sturgeon and trout that support the contention that the sturgeon has common characteristics with elasmobranchs and teleosts.

The regulation of food intake in mammalian hibernators: a review

Abstract: One of the most profound hallmarks of mammalian hibernation is the dramatic reduction in food intake during the winter months. Several species of hibernator completely cease food intake (aphagia) for nearly 7 months regardless of ambient temperature and in many cases, whether or not food is available to them. Food intake regulation has been studied in mammals that hibernate for over 50 years and still little is known about the physiological mechanisms that control this important behavior in hibernators. It is well known from lesion experiments in non-hibernators that the hypothalamus is the main brain region controlling food intake and therefore body mass. In hibernators, the regulation of food intake and body mass is presumably governed by a circannual rhythm since there is a clear seasonal rhythm to food intake: animals increase food intake in the summer and early autumn, food intake declines in autumn and actually ceases in winter in many species, and resumes again in spring as food becomes available in the environment. Changes in circulating hormones (e.g., leptin, insulin, and ghrelin), nutrients (glucose, and free fatty acids), and cellular enzymes such as AMP-activated protein kinase (AMPK) have been shown to determine the activity of neurons involved in the food intake pathway. Thus, it appears likely that the food intake pathway is controlled by a variety of inputs, but is also acted upon by upstream regulators that are presumably rhythmic in nature. Current research examining the molecular mechanisms and integration of environmental signals (e.g., temperature and light) with these molecular mechanisms will hopefully shed light on how animals can turn off food intake and survive without eating for months on end.

Hair cortisol: a parameter of chronic stress? Insights from a radiometabolism study in guinea pigs

Abstract: Measurement of hair cortisol has become popular in the evaluation of chronic stress in various species. However, a sound validation is still missing. Therefore, deposition of radioactivity in hair and excretion into feces and urine after repeated injection of 3H-cortisol was studied in guinea pigs (n = 8). Each animal was given intraperitoneally 243.6 kBq 3H-cortisol/day on 3 successive days. After the first injection, all voided excreta were collected for 3 days. After the second injection, hair was shaved off the animals’ back and newly grown hair was obtained on day 7. Following methanol extraction, radiolabeled and unlabeled glucocorticoid metabolites (GCM) in fecal and hair samples were characterized by high-performance liquid chromatography (HPLC) and enzyme immunoassays (EIA). In feces, maximum radioactivity was reached 8 h (median) post each injection, whereas maxima in urine were detected in the first samples (median 2.5 h). Metabolites excreted into feces (13.3 % ± 3.7) or urine (86.7 %) returned nearly to background levels. HPLC of fecal extracts showed minor variation between individuals and sexes. In hair, small amounts of radioactivity were present. However, two EIAs detected large amounts of unlabeled GCM, including high levels at the position of the cortisol standard; radioactivity was absent in this fraction, demonstrating that 3H-cortisol was metabolized. Furthermore, large amounts of immunoreactivity coinciding with a radioactive peak at the elution position of cortisone were found. These results show for the first time that only small amounts of systemically administered radioactive glucocorticoids are deposited in hair of guinea pigs, while measurement of large amounts of unlabeled GCM strongly suggests local production of glucocorticoids in hair follicles.

The physiology of hyper-salinity tolerance in teleost fish: a review

Abstract: Hyper-saline habitats (waters with salinity >35 ppt) are among the harshest aquatic environments. Relatively few species of teleost fish can tolerate salinities much above 50 ppt, because of the challenges to osmoregulation, but those that do, usually estuarine, euryhaline species, show a strong ability to osmoregulate in salinities well over 100 ppt. Typically, plasma Na+ and Cl− concentrations rise slowly or not at all up to about 65 ppt. At higher salinities ion levels do rise, but the increase is small relative to the magnitude of increase in concentrations of the surrounding water. A number of adjustments are responsible for such strong osmoregulation. Reduced branchial water permeability is indicated by the observation that with the exposure to hyper-salinities drinking rates rise more slowly than the branchial osmotic gradient. Lower water permeability limits osmotic water loss and greatly reduces the salt load incurred in replacing it. Still, increased gut Na+/K+-ATPase (NAK) activity is necessary to absorb the larger gut salt load and increased HCO3− secretion is required to precipitate Ca2+ and some Mg2+ in the imbibed water to facilitate water absorption. All Na+ and Cl− taken up must be excreted and increased branchial salt excreting capacity is indicated by elevated mitochondrion-rich cell density and size, gill NAK activity and expression of chloride channels. Excretion of Na+ and Cl− occurs against a larger gradient than in seawater and calculation of the equilibrium potential for Na+ across the gill epithelium indicates that the trans-epithelial potential required for excretion of Na+ climbs with salinity up to about 65 ppt before leveling off due to the increasing plasma Na+ levels. During acute transition to SW or mildly hyper-saline waters, some species have shown the ability to upregulate branchial NAK activity rapidly and this may play an important role in limiting disturbances at higher salinities. It does not appear that the opercular epithelium, which in SW acts in a way that is functionally similar to the gills, continues to do so in hyper-saline waters. Little is know about the hormones involved in acclimation to hyper-salinity, but the few studies available suggest a role for cortisol, but not growth hormone and insulin-like growth factor. Despite the increased transport capacity evident in both the gill and gut in hyper-saline waters there is no clear trend toward increased metabolic rate. These studies provide a general outline of the mechanisms of osmoregulation in these species, but significant questions still remain.

Factors affecting plasticity in whole-organism thermal tolerance in common killifish ( Fundulus heteroclitus )

Abstract: We characterized the degree of plasticity in thermal tolerance (assessed as critical thermal maxima; CTMax) and the relationship between thermal tolerance and underlying physiological and biochemical factors in two subspecies of a teleost fish, Fundulus heteroclitus. CTMax was not affected by repeated daily heat shock, but increased within a few days in response to warm acclimation. Loss of tolerance with acclimation to lowered temperatures occurred more slowly. Exposure to hypoxia decreased CTMax, and hyperoxia had no effect. CTMax showed a daily rhythm in both subspecies. Thermal acclimation changed the value of CTMax but did not affect the amplitude of the rhythm. Exposure to altered photoperiod had complex effects with a summer photoperiod producing a daily rhythm at higher CTMax than a spring photoperiod, and a winter photoperiod removing the rhythm. There was no daily rhythm in routine metabolic rate in either subspecies. There was no relationship between CTMax and the protein levels of the constitutive 70 and 90 kDa heat shock proteins (HSC70, HSP90β) in gill, or with mRNA levels of hsc70 in liver. There was a daily rhythm in the basal levels of the inducible hsp70-2 mRNA. Induction of hsp70-2 mRNA with mild heat shock occurred only in the evening and at night, and not during the day. These results demonstrate that there is substantial plasticity of thermal tolerance in killifish, and that this plasticity does not differ between subspecies. CTMax has a complex relationship with physiological and biochemical mechanisms that have been hypothesized to affect thermal tolerance.

A radical approach to beating hypoxia: depressed free radical release from heart fibres of the hypoxia-tolerant epaulette shark (Hemiscyllum ocellatum).

Abstract: Hypoxia and warm ischemia are primary concerns in ischemic heart disease and transplant and trauma. Hypoxia impacts tissue ATP supply and can induce mitochondrial dysfunction that elevates reactive species release. The epaulette shark, Hemiscyllum ocellatum, is remarkably tolerant of severe hypoxia at temperatures up to 34°C, and therefore provides a valuable model to study warm hypoxia tolerance. Mitochondrial function was tested in saponin permeabilised ventricle fibres using high-resolution respirometry coupled with purpose-built fluorospectrometers. Ventricular mitochondrial function, stability and reactive species production of the epaulette shark was compared with that of the hypoxia-sensitive shovelnose ray, Aptychotrema rostrata. Fibres were prepared from each species acclimated to normoxic water conditions, or following a 2 h, acute hypoxic exposure at levels representing 40% of each species’ critical oxygen tension. Although mitochondrial respiratory fluxes for normoxia-acclimated animals were similar for both species, reactive species production in the epaulette shark was approximately half that of the shovelnose ray under normoxic conditions, even when normalised to tissue oxidative phosphorylation flux. The hypoxia-sensitive shovelnose ray halved oxidative phosphorylation flux and cytochrome c oxidase flux was depressed by 34% following hypoxic stress. In contrast, oxidative phosphorylation flux of the epaulette shark ventricular fibres isolated from acute hypoxia exposed the animals remained similar to those from normoxia-acclimated animals. However, uncoupling of respiration revealed depressed electron transport systems in both species following hypoxia exposure. Overall, the epaulette shark ventricular mitochondria showed greater oxidative phosphorylation stability and lower reactive species outputs with hypoxic exposure, and this may protect cardiac bioenergetic function in hypoxic tropical waters.

Coping with Physiological Oxidative Stress: A Review of Antioxidant Strategies in Seals

Abstract: While diving, seals are exposed to apnea-induced hypoxemia and repetitive cycles of ischemia/reperfusion. While on land, seals experience sleep apnea, as well as prolonged periods of food and water deprivation. Prolonged fasting, sleep apnea, hypoxemia and ischemia/reperfusion increase oxidant production and oxidative stress in terrestrial mammals. In seals, however, neither prolonged fasting nor apnea-induced hypoxemia or ischemia/reperfusion increase systemic or local oxidative damage. The strategies seals evolved to cope with increased oxidant production are reviewed in the present manuscript. Among these strategies, high antioxidant capacity and the oxidant-mediated activation of hormetic responses against hypoxia and oxidative stress are discussed. In addition to expanding our knowledge of the evolution of antioxidant defenses and adaptive responses to oxidative stress, understanding the mechanisms that naturally allow mammals to avoid oxidative damage has the potential to advance our knowledge of oxidative stress-induced pathologies and to enhance the translative value of biomedical therapies in the long term.

Does habitat fragmentation cause stress in the agile antechinus? A haematological approach

Abstract: Although the vertebrate stress response is essential for survival, frequent or prolonged stress responses can result in chronic physiological stress, which is associated with a suite of conditions that can impair survivorship and reproductive output. Anthropogenic habitat fragmentation and degradation are potential stressors of free-living vertebrates, and in theory could result in chronic stress. To address this issue, we compared haematological indicators of stress and condition in agile antechinus (Antechinus agilis) populations in 30 forest fragments and 30 undisturbed, continuous forest sites (pseudofragments) in south-eastern Australia over 2 years. In peripheral blood, the total leucocyte count was lower and the neutrophil/lymphocyte ratio and percentage of eosinophils in the total leucocyte population was higher in fragment than pseudofragment populations, indicating that fragment populations were probably experiencing higher levels of stress hormone-mediated and/or parasite infection-related chronic physiological stress. The total erythrocyte count and haematocrit were higher and mean erythrocyte haemoglobin content was lower in fragment than pseudofragment populations. This suggests that fragment populations showed possible signs of regenerative anaemia, a syndrome associated with elevated hypothalamus–pituitary–adrenal axis mediated stress. However, mean erythrocyte volume was also lower in fragments, and red blood cell distribution width did not differ between the study populations, findings which were not consistent with this diagnosis. Whole blood and mean cell haemoglobin concentrations were similar in fragment and pseudofragment populations. We suggest that where anthropogenic activity results in habitat fragmentation and degradation, chronic stress could contribute to a decline in agile antechinus populations. The broader implication is that chronic stress could be both symptomatic of, and contributing to, decline of some vertebrate populations in anthropogenically fragmented and degraded habitats.

Warming up for dinner: torpor and arousal in hibernating Natterer’s bats ( Myotis nattereri ) studied by radio telemetry

Abstract: The frequency and function of arousals during hibernation in free-living mammals are little known. We used temperature-sensitive radio transmitters to measure patterns of torpor, arousal and activity in wild Natterer’s bats Myotis nattereri during hibernation. Duration of torpor bouts ranged from 0.06 to 20.4 days with individual means ranging from 0.9 to 8.9 days. Arousals from torpor occurred most commonly coincident with the time (relative to sunset) typical for bats emerging from summer roosts to forage. Bats with lower body condition indices had a shorter average duration of their torpor bouts. We found a non-linear relationship between duration of torpor bout and ambient temperature: the longest average torpor bouts were at temperatures between 2 and 4°C with shorter bouts at lower and higher ambient temperatures. One individual was radio-tracked for ten nights, remained active for an average of 297 min each night and was active for longer on warmer nights. Our results suggest that vespertilionid bats use relatively short torpor bouts during hibernation in a location with a maritime climate. We hypothesise that Natterer’s bats time arousals to maximise opportunities for potential foraging during winter although winter feeding is not the sole determinant of arousal as bats still arouse at times when foraging is unlikely.

Mitochondrial adaptations to utilize hydrogen sulfide for energy and signaling

Abstract: Sulfur is a versatile molecule with oxidation states ranging from −2 to +6. From the beginning, sulfur has been inexorably entwined with the evolution of organisms. Reduced sulfur, prevalent in the prebiotic Earth and supplied from interstellar sources, was an integral component of early life as it could provide energy through oxidization, even in a weakly oxidizing environment, and it spontaneously reacted with iron to form iron–sulfur clusters that became the earliest biological catalysts and structural components of cells. The ability to cycle sulfur between reduced and oxidized states may have been key in the great endosymbiotic event that incorporated a sulfide-oxidizing α-protobacteria into a host sulfide-reducing Archea, resulting in the eukaryotic cell. As eukaryotes slowly adapted from a sulfidic and anoxic (euxinic) world to one that was highly oxidizing, numerous mechanisms developed to deal with increasing oxidants; namely, oxygen, and decreasing sulfide. Because there is rarely any reduced sulfur in the present-day environment, sulfur was historically ignored by biologists, except for an occasional report of sulfide toxicity. Twenty-five years ago, it became evident that the organisms in sulfide-rich environments could synthesize ATP from sulfide, 10 years later came the realization that animals might use sulfide as a signaling molecule, and only within the last 4 years did it become apparent that even mammals could derive energy from sulfide generated in the gastrointestinal tract. It has also become evident that, even in the present-day oxic environment, cells can exploit the redox chemistry of sulfide, most notably as a physiological transducer of oxygen availability. This review will examine how the legacy of sulfide metabolism has shaped natural selection and how some of these ancient biochemical pathways are still employed by modern-day eukaryotes.

Peripheral circadian rhythms and their regulatory mechanism in insects and some other arthropods: a review

Abstract: Many physiological functions of insects show a rhythmic change to adapt to daily environmental cycles. These rhythms are controlled by a multi-clock system. A principal clock located in the brain usually organizes the overall behavioral rhythms, so that it is called the “central clock”. However, the rhythms observed in a variety of peripheral tissues are often driven by clocks that reside in those tissues. Such autonomous rhythms can be found in sensory organs, digestive and reproductive systems. Using Drosophila melanogaster as a model organism, researchers have revealed that the peripheral clocks are self-sustained oscillators with a molecular machinery slightly different from that of the central clock. However, individual clocks normally run in harmony with each other to keep a coordinated temporal structure within an animal. How can this be achieved? What is the molecular mechanism underlying the oscillation? Also how are the peripheral clocks entrained by light–dark cycles? There are still many questions remaining in this research field. In the last several years, molecular techniques have become available in non-model insects so that the molecular oscillatory mechanisms are comparatively investigated among different insects, which give us more hints to understand the essential regulatory mechanism of the multi-oscillatory system across insects and other arthropods. Here we review current knowledge on arthropod’s peripheral clocks and discuss their physiological roles and molecular mechanisms.

High manoeuvring costs force narrow-winged molossid bats to forage in open space

Abstract: Molossid bats are specialised aerial-hawkers that, like their diurnal ecological counterparts, swallows and swifts, hunt for insects in open spaces. The long and narrow wings of molossids are considered energetically adapted to fast flight between resource patches, but less suited for manoeuvring in more confined spaces, such as between tree-tops or in forest gaps. To understand whether a potential increase in metabolic costs of manoeuvring excludes molossids from foraging in more confined spaces, we measured energy costs and speed of manoeuvring flight in two tropical molossids, 18 g Molossus currentium and 23 g Molossus sinaloae, when flying in a ~500 m3 hexagonal enclosure (~120 m2 area), which is of similar dimensions as typical forest gaps. Flight metabolism averaged 10.21 ± 3.00 and 11.32 ± 3.54 ml CO2 min−1, and flight speeds 5.65 ± 0.47 and 6.27 ± 0.68 m s−1 for M. currentium and M. sinaloae respectively. Metabolic rate during flight was higher for the M. currentium than for the similar-sized, but broader-winged frugivore Carollia sowelli, corroborating that broad-winged bats are better adapted to flying in confined spaces. These higher metabolic costs of manoeuvring flight may be caused by having to fly slower than the optimal foraging speed, and by the additional metabolic costs for centripetal acceleration in curves. This may preclude molossids from foraging efficiently between canopy trees or in forest gaps. The surprisingly brief burst of foraging activity at dusk of many molossids might be related to the cooling of the air column after sunset, which drives airborne insects to lower strata. Accordingly, foraging activity of molossids may quickly turn unprofitable when the abundance of insects decreases above the canopy.

HIF-1α regulation in mammalian hibernators: role of non-coding RNA in HIF-1α control during torpor in ground squirrels and bats

Abstract: A potential role for non-coding RNAs, miR-106b and antisense hypoxia inducible transcription factor-1 (HIF-1α), in HIF-1α regulation during mammalian hibernation was investigated in two species, the thirteen-lined ground squirrel (Ictidomys tridecemlineatus) and the little brown bat (Myotis lucifugus). Both species showed differential regulation of HIF-1α during hibernation. HIF-1α protein levels increased significantly in skeletal muscle of both species when animals entered torpor, as well as in bat liver. HIF-1α mRNA levels correlated with the protein increase in bat skeletal muscle and liver but not in squirrel skeletal muscle. Antisense HIF-1α transcripts were identified in skeletal muscle of both hibernators. The expression of antisense HIF-1α was reduced in skeletal muscle of torpid bats compared with euthermic controls, suggesting that release of inhibition by the antisense RNA contributes to regulating HIF-1α translation in this tissue during torpor. The expression of miR-106b, a microRNA associated with HIF-1α regulation, also decreased during torpor in both skeletal muscle and liver of bats and in ground squirrel skeletal muscle. These data present the first evidence that non-coding RNA provides novel post-transcriptional mechanisms of HIF-1α regulation when hibernators descend into deep cold torpor, and also demonstrate that these mechanisms are conserved in two divergent mammalian orders (Rodentia and Chiroptera).

Water absorption and bicarbonate secretion in the intestine of the sea bream are regulated by transmembrane and soluble adenylyl cyclase stimulation

Abstract: In the marine fish intestine luminal, HCO₃⁻ can remove divalent ions (calcium and magnesium) by precipitation in the form of carbonate aggregates. The process of epithelial HCO₃⁻ secretion is under endocrine control, therefore, in this study we aimed to characterize the involvement of transmembrane (tmACs) and soluble (sACs) adenylyl cyclases on the regulation of bicarbonate secretion (BCS) and water absorption in the intestine of the sea bream (Sparus aurata). We observed that all sections of sea bream intestine are able to secrete bicarbonate as measured by pH-Stat in Ussing chambers. In addition, gut sac preparations reveal net water absorption in all segments of the intestine, with significantly higher absorption rates in the anterior intestine that in the rectum. BCS and water absorption are positively correlated in all regions of the sea bream intestinal tract. Furthermore, stimulation of tmACs (10 μM FK + 500 μM IBMX) causes a significant decrease in BCS, bulk water absorption and short circuit current (Isc) in a region dependent manner. In turn, stimulation of sACs with elevated HCO₃⁻ results in a significant increase in BCS, and bulk water absorption in the anterior intestine, an action completely reversed by the sAC inhibitor KH7 (200 μM). Overall, the results reveal a functional relationship between BCS and water absorption in marine fish intestine and modulation by tmACs and sAC. In light of the present observations, it is hypothesized that the endocrine effects on intestinal BCS and water absorption mediated by tmACs are locally and reciprocally modulated by the action of sACs in the fish enterocyte, thus fine-tuning the process of carbonate aggregate production in the intestinal lumen.

Comparative patterns of adrenal activity in captive and wild Canada lynx (Lynx canadensis)

Abstract: Stress and animal well-being are often assessed using concentrations of glucocorticoids (GCs), a product of the hypothalamic–pituitary–adrenal axis. However, GC concentrations can also be modulated by predictable events, such as changes in season or life history stage. Understanding normative patterns of adrenal activity is critical for making valid conclusions about changes in GC concentrations. In this study, we validated an assay for monitoring fecal glucocorticoid metabolites (FGM) in Canada lynx. We then used this technique to assess patterns of adrenal activity in Canada lynx across several contexts. Our results show that captive lynx have higher FGM concentrations than wild lynx, which may be related to differences in stress levels, metabolic rate, diet, or body condition. We also found that FGM concentrations are correlated with reproductive status in females, but not in males. For males, seasonal increases in FGM expression coincide with the onset of the breeding season, whereas in females, FGM increase toward the end of the breeding season. This information provides a valuable foundation for making inferences about normative versus stress-induced changes in adrenal activity in Canada lynx.

Thermoregulatory changes anticipate hibernation onset by 45 days: data from free-living arctic ground squirrels

Abstract: Hibernation is a strategy of reducing energy expenditure, body temperature (Tb) and activity used by endotherms to escape unpredictable or seasonally reduced food availability. Despite extensive research on thermo- regulatory adjustments during hibernation, less is known about transitions in thermoregulatory state, particularly under natural conditions. Laboratory studies on hibernating ground squirrels have demonstrated that thermoregulatory adjustments may occur over short intervals when animals undergo several brief, preliminary torpor bouts prior to entering multiday torpor. These short torpor bouts have been suggested to reflect a resetting of hypothalamic regions that control Tb or to precondition animals before they undergo deep, multiday torpor. Here, we examined continuous records of Tb in 240 arctic ground squirrels (Urocitellus parryii) prior to hibernation in the wild and in captivity. In free-living squirrels, Tb began to decline 45 days prior to hibernation, and average Tb had decreased 4.28 C at the onset of torpor. Further, we found that 75 % of free-living squirrels and 35 % of captive squirrels entered bouts of multiday torpor with a single Tb decline and without previously showing short preliminary bouts. This study provides evidence that adjustments in the ther- moregulatory component of hibernation begin far earlier than previously demonstrated. The gradual reduction in Tb is likely a component of the suite of metabolic and behavioral adjust- ments, controlled by an endogenous, circannual rhythm, that vary seasonally in hibernating ground squirrels.

Molecular diversity, metabolic transformation, and evolution of carotenoid feather pigments in cotingas (Aves: Cotingidae)

Abstract: Carotenoid pigments were extracted from 29 feather patches from 25 species of cotingas (Cotingidae) representing all lineages of the family with carotenoid plumage coloration. Using high-performance liquid chromatography (HPLC), mass spectrometry, chemical analysis, and 1H-NMR, 16 different carotenoid molecules were documented in the plumages of the cotinga family. These included common dietary xanthophylls (lutein and zeaxanthin), canary xanthophylls A and B, four well known and broadly distributed avian ketocarotenoids (canthaxanthin, astaxanthin, α-doradexanthin, and adonixanthin), rhodoxanthin, and seven 4-methoxy-ketocarotenoids. Methoxy-ketocarotenoids were found in 12 species within seven cotinga genera, including a new, previously undescribed molecule isolated from the Andean Cock-of-the-Rock Rupicola peruviana, 3′-hydroxy-3-methoxy-β,β-carotene-4-one, which we name rupicolin. The diversity of cotinga plumage carotenoid pigments is hypothesized to be derived via four metabolic pathways from lutein, zeaxanthin, β-cryptoxanthin, and β-carotene. All metabolic transformations within the four pathways can be described by six or seven different enzymatic reactions. Three of these reactions are shared among three precursor pathways and are responsible for eight different metabolically derived carotenoid molecules. The function of cotinga plumage carotenoid diversity was analyzed with reflectance spectrophotometry of plumage patches and a tetrahedral model of avian color visual perception. The evolutionary history of the origin of this diversity is analyzed phylogenetically. The color space analyses document that the evolutionarily derived metabolic modifications of dietary xanthophylls have resulted in the creation of distinctive orange-red and purple visual colors.

Does size matter? Comparison of body temperature and activity of free-living Arabian oryx (Oryx leucoryx) and the smaller Arabian sand gazelle (Gazella subgutturosa marica) in the Saudi desert.

Abstract: Heterothermy, a variability in body temperature beyond the normal limits of homeothermy, is widely viewed as a key adaptation of arid-adapted ungulates. However, desert ungulates with a small body mass, i.e. a relatively large surface area-to-volume ratio and a small thermal inertia, are theoretically less likely to employ adaptive heterothermy than are larger ungulates. We measured body temperature and activity patterns, using implanted data loggers, in free-ranging Arabian oryx (Oryx leucoryx, ±70 kg) and the smaller Arabian sand gazelle (Gazella subgutturosa marica, ±15 kg) inhabiting the same Arabian desert environment, at the same time. Compared to oryx, sand gazelle had higher mean daily body temperatures (F 1,6 = 47.3, P = 0.0005), higher minimum daily body temperatures (F 1,6 = 42.6, P = 0.0006) and higher maximum daily body temperatures (F 1,6 = 11.0, P = 0.02). Despite these differences, both species responded similarly to changes in environmental conditions. As predicted for adaptive heterothermy, maximum daily body temperature increased (F 1,6 = 84.0, P < 0.0001), minimum daily body temperature decreased (F 1,6 = 92.2, P < 0.0001), and daily body temperature amplitude increased (F 1,6 = 97.6, P < 0.0001) as conditions got progressively hotter and drier. There were no species differences in activity levels, however, both gazelle and oryx showed a biphasic or crepuscular rhythm during the warm wet season but shifted to a more nocturnal rhythm during the hot dry season. Activity was attenuated during the heat of the day at times when both species selected cool microclimates. These two species of Arabian ungulates employ heterothermy, cathemerality and shade seeking very similarly to survive the extreme, arid conditions of Arabian deserts, despite their size difference.

Adaptation to thermally variable environments: capacity for acclimation of thermal limit and heat shock response in the shrimp Palaemonetes varians.

Abstract: In the context of climate change, there is a sustained interest in understanding better the functional mechanisms by which marine ectotherms maintain their physiological scope and define their ability to cope with thermal changes in their environment. Here, we present evidence that the variable shrimp Palaemonetes varians shows genuine acclimation capacities of both the thermal limit (CTmax) and the heat shock response (hsp70 induction temperature). During cold acclimation to 10 °C, the time lag to adjust the stress gene expression to the current environmental temperature proved to exceed 1 week, thereby highlighting the importance of long-term experiments in evaluating the species’ acclimation capacities. Cold and warm-acclimated specimens of P. varians can mobilise the heat shock response (HSR) at temperatures above those experienced in nature, which suggests that the species is potentially capable of expanding its upper thermal range. The shrimp also survived acute heat shock well above its thermal limit without subsequent induction of the HSR, which is discussed with regard to thermal adaptations required for life in highly variable environments.

Interspecific variation in thermoregulation among three sympatric bats inhabiting a hot, semi-arid environment.

Abstract: Bats in hot roosts experience some of the most thermally challenging environments of any endotherms, but little is known about how heat tolerance and evaporative cooling capacity vary among species. We investigated thermoregulation in three sympatric species (Nycteris thebaica, Taphozous mauritianus and Sauromys petrophilus) in a hot, semi-arid environment by measuring body temperature (T b), metabolic rate and evaporative water loss (EWL) at air temperatures (T a) of 10–42 °C. S. petrophilus was highly heterothermic with no clear thermoneutral zone, and exhibited rapid increases in EWL at high T a to a maximum of 23.7 ± 7.4 mg g−1 h−1 at T a ≈ 42 °C, with a concomitant maximum T b of 43.7 ± 1.0 °C. T. mauritianus remained largely normothermic at T as below thermoneutrality and increased EWL to 14.7 ± 1.3 mg g−1 h−1 at T a ≈ 42 °C, with a maximum T b of 42.9 ± 1.6 °C. In N. thebaica, EWL began increasing at lower T a than in either of the other species and reached a maximum of 18.6 ± 2.1 mg g−1 h−1 at T a = 39.4 °C, with comparatively high maximum T b values of 45.0 ± 0.9 °C. Under the conditions of our study, N. thebaica was considerably less heat tolerant than the other two species. Among seven species of bats for which data on T b as well as roost temperatures in comparison to outside T a are available, we found limited evidence for a correlation between overall heat tolerance and the extent to which roosts are buffered from high T a.

Cloning, tissue expression pattern and daily rhythms of Period1, Period2, and Clock transcripts in the flatfish Senegalese sole, Solea senegalensis

Abstract: An extensive network of endogenous oscilla- tors governs vertebrate circadian rhythmicity. At the molec- ular level, they are composed of a set of clock genes that participate in transcriptional-translational feedback loops to control their own expression and that of downstream out- put genes. These clocks are synchronized with the environ- ment, although entrainment by external periodic cues remains little explored in Wsh. In this work, partial cDNA sequences of clock genes representing both positive (Clock) and negative (Period1, Period2) elements of the molecular feedback loops were obtained from the nocturnal XatWsh Senegalese sole, a relevant species for aquaculture and chronobiology. All of the above genes exhibited high iden- tities with their respective teleost clock genes, and Per- Arnt-Sim or basic helix-loop-helix binding domains were recognized in their primary structure. They showed a wide- spread distribution through the animal body and some of them displayed daily mRNA rhythms in central (retina, optic tectum, diencephalon, and cerebellum) and peripheral (liver) tissues. These rhythms were most robust in retina and liver, exhibiting marked Period1 and Clock daily oscillations in transcript levels as revealed by ANOVA and cosinor analysis. Interestingly, expression proWles were inverted in retina and optic tectum compared to liver. Such diVerences suggest the existence of tissue-dependent zeit- gebers for clock gene expression in this species (i.e., light for retina and optic tectum and feeding time for liver). This study provides novel insight into the location of the molecular clocks (central vs. peripheral) and their diVerent phasing and synchronization pathways, which contributes to better understand the teleost circadian systems and its plasticity.

Should I stay or should I go?: Physiological, metabolic and biochemical consequences of voluntary emersion upon aquatic hypoxia in the scaleless fish Galaxias maculatus

Abstract: Hypoxia represents a significant challenge to most fish, forcing the development of behavioural, physiological and biochemical adaptations to survive. It has been previously shown that inanga (Galaxias maculatus) display a complex behavioural repertoire to escape aquatic hypoxia, finishing with the fish voluntarily emerging from the water and aerially respiring. In the present study we evaluated the physiological, metabolic and biochemical consequences of both aquatic hypoxia and emersion in inanga. Inanga successfully tolerated up to 6 h of aquatic hypoxia or emersion. Initially, this involved enhancing blood oxygen-carrying capacity, followed by the induction of anaerobic metabolism. Only minor changes were noted between emersed fish and those maintained in aquatic hypoxia, with the latter group displaying a higher mean cell haemoglobin content and a reduced haematocrit after 6 h. Calculations suggest that inanga exposed to both aquatic hypoxia and air reduced oxygen uptake and also increased anaerobic contribution to meet energy demands, but the extent of these changes was small compared with hypoxia-tolerant fish species. Overall, these findings add to previous studies suggesting that inanga are relatively poorly adapted to survive aquatic hypoxia.

Taking the heat: thermoregulation in Asian elephants under different climatic conditions.

Abstract: Some mammals indigenous to desert environments, such as camels, cope with high heat load by tolerating an increase in body temperature (T b) during the hot day, and by dissipating excess heat during the cooler night hours, i.e., heterothermy. Because diurnal heat storage mechanisms should be favoured by large body size, we investigated whether this response also exists in Asian elephants when exposed to warm environmental conditions of their natural habitat. We compared daily cycles of intestinal T b of 11 adult Asian elephants living under natural ambient temperatures (T a) in Thailand (mean T a ~ 30°C) and in 6 Asian elephants exposed to cooler conditions (mean T a ~ 21°C) in Germany. Elephants in Thailand had mean daily ranges of T b oscillations (1.15°C) that were significantly larger than in animals kept in Germany (0.51°C). This was due to both increased maximum T b during the day and decreased minimum T b at late night. Elephant’s minimum T b lowered daily as T a increased and hence entered the day with a thermal reserve for additional heat storage, very similar to arid-zone ungulates. We conclude that these responses show all characteristics of heterothermy, and that this thermoregulatory strategy is not restricted to desert mammals, but is also employed by Asian elephants.

Cell cycle arrest associated with anoxia-induced quiescence, anoxic preconditioning, and embryonic diapause in embryos of the annual killifish Austrofundulus limnaeus

Abstract: Embryos of the annual killifish Austrofundulus limnaeus can enter into dormancy associated with diapause and anoxia-induced quiescence. Dormant embryos are composed primarily of cells arrested in the G1/G0 phase of the cell cycle based on flow cytometry analysis of DNA content. In fact, most cells in developing embryos contain only a diploid complement of DNA, with very few cells found in the S, G2, or M phases of the cell cycle. Diapause II embryos appear to be in a G0-like state with low levels of cyclin D1 and p53. However, the active form of pAKT is high during diapause II. Exposure to anoxia causes an increase in cyclin D1 and p53 expression in diapause II embryos, suggesting a possible re-entry into the cell cycle. Post-diapause II embryos exposed to anoxia or anoxic preconditioning have stable levels of cyclin D1 and stable or reduced levels of p53. The amount of pAKT is severely reduced in 12 dpd embryos exposed to anoxia or anoxic preconditioning. This study is the first to evaluate cell cycle control in embryos of A. limnaeus during embryonic diapause and in response to anoxia and builds a foundation for future research on the role of cell cycle arrest in supporting vertebrate dormancy.