nils-herrmann/clean_scirepeval huggingface dataset:
Di- and tripeptide transport in vertebrates: the contribution of teleost fish models
Venue: Journal of Comparative Physiology B

Solute Carrier 15 (SLC15) family, alias H+-coupled oligopeptide cotransporter family, is a group of membrane transporters known for their role in the cellular uptake of di- and tripeptides (di/tripeptides) and peptide-like molecules. Of its members, SLC15A1 (PEPT1) chiefly mediates intestinal absorption of luminal di/tripeptides from dietary protein digestion, while SLC15A2 (PEPT2) mainly allows renal tubular reabsorption of di/tripeptides from ultrafiltration, SLC15A3 (PHT2) and SLC15A4 (PHT1) possibly interact with di/tripeptides and histidine in certain immune cells, and SLC15A5 has unknown function. Our understanding of this family in vertebrates has steadily increased, also due to the surge of genomic-to-functional information from ‘non-conventional’ animal models, livestock, poultry, and aquaculture fish species. Here, we review the literature on the SLC15 transporters in teleost fish with emphasis on SLC15A1 (PEPT1), one of the solute carriers better studied amongst teleost fish because of its relevance in animal nutrition. We report on the operativity of the transporter, the molecular diversity, and multiplicity of structural–functional solutions of the teleost fish orthologs with respect to higher vertebrates, its relevance at the intersection of the alimentary and osmoregulative functions of the gut, its response under various physiological states and dietary solicitations, and its possible involvement in examples of total body plasticity, such as growth and compensatory growth. By a comparative approach, we also review the few studies in teleost fish on SLC15A2 (PEPT2), SLC15A4 (PHT1), and SLC15A3 (PHT2). By representing the contribution of teleost fish to the knowledge of the physiology of di/tripeptide transport and transporters, we aim to fill the gap between higher and lower vertebrates.
Swimming metabolic rates vary by sex and development stage, but not by species, in three species of Australian otariid seals
Venue: Journal of Comparative Physiology B

Physiology may limit the ability for marine mammals to adapt to changing environments. Depth and duration of foraging dives are a function of total available oxygen stores, which theoretically increase as animals grow, and metabolic costs. To evaluate how physiology may influence the travelling costs for seals to foraging patches in the wild, we measured metabolic rates of a cross-section of New Zealand fur seals, Australian fur seals and Australian sea lions representing different foraging strategies, development stages, sexes and sizes. We report values for standard metabolic rate, active metabolic rate (obtained from submerged swimming), along with estimates of cost of transport (COT), measured via respirometry. We found a decline in mass-specific metabolic rate with increased duration of submerged swimming. For most seals mass-specific metabolic rate increased with speed and for all seals mass-specific COT decreased with speed. Mass-specific metabolic rate was higher for subadult than adult fur seals and sea lions, corresponding to an overall higher minimum COT. Some sex differences were also apparent, such that female Australian fur seals and Australian sea lions had higher mass-specific metabolic rates than males. There were no species differences in standard or active metabolic rates for adult males or females. The seals in our study appear to operate at their physiological optimum during submerged swimming. However, the higher metabolic rates of young and female fur seals and sea lions may limit their scope for increasing foraging effort during times of resource limitation.
Thermal implications of interactions between insulation, solar reflectance, and fur structure in the summer coats of diverse species of kangaroo
Venue: Journal of Comparative Physiology B

Not all of the solar radiation that impinges on a mammalian coat is absorbed and converted into thermal energy at the coat surface. Some is reflected back to the environment, while another portion is reflected further into the coat where it is absorbed and manifested as heat at differing levels. Substantial insulation in a coat limits the thermal impact at the skin of solar radiation, irrespective where in the coat it is absorbed. In coats with low insulation, the zone where solar radiation is absorbed may govern the consequent heat load on the skin (HL-SR). Thin summer furs of four species of kangaroo from differing climatic zones were used to determine how variation in insulation and in coat spectral and structural characteristics influence the HL-SR. Coat depth, structure, and solar reflectance varied between body regions, as well as between species. The modulation of solar radiation and resultant heat flows in these coats were measured at low (1 m s−1) and high (6 m s−1) wind speeds by mounting them on a heat flux transducer/temperature-controlled plate apparatus in a wind tunnel. A lamp with a spectrum similar to solar radiation was used as a proxy for the sun. We established that coat insulation was largely determined by coat depth at natural fur lie, despite large variations in fibre density, fibre diameter, and fur mass. Higher wind speed decreased coat insulation, but depth still determined the overall level. A multiple regression analysis that included coat depth (insulation), fibre diameter, fibre density, and solar reflectance was used to determine the best predictors of HL-SR. Only depth and reflectance had significant impacts and both factors had negative weights, so, as either insulation or reflectance increased, HL-SR declined, the larger impact coming from coat reflectance. This reverses the pattern observed in deep coats where insulation dominates over effects of reflectance. Across all coats, as insulation declined, reflectance increased. An increase in reflectance in the thinnest coats was not the sole reason for the limited rise in HL-SR. Higher reflectance should increase the depth of penetrance of solar radiation, thus increasing HL-SR. But in M. antilopinus and Macropus rufus, which had the highest of coat reflectances, penetrance was relatively shallow. This effect appears due to high fibre density (M. rufus) and major modifications in the fibre structure (M. antilopinus). The differing adaptations likely relate to the habitats of these species, desert in the case of M. rufus and monsoon tropical woodland with M. antilopinus.
Enzymatic regulation of seasonal glycogen cycling in the freeze-tolerant wood frog, Rana sylvatica
Venue: Journal of Comparative Physiology B

Liver glycogen is an important energy store in vertebrates, and in the freeze-tolerant wood frog, Rana sylvatica, this carbohydrate also serves as a major source of the cryoprotectant glucose. We investigated how variation in the levels of the catalytic subunit of protein kinase A (PKAc), glycogen phosphorylase (GP), and glycogen synthase (GS) relates to seasonal glycogen cycling in a temperate (Ohioan) and subarctic (Alaskan) populations of this species. In spring, Ohioan frogs had reduced potential for glycogen synthesis, as evidenced by low GS activity and high PKAc protein levels. In addition, glycogen levels in spring were the lowest of four seasonal samples, as energy input was likely directed towards metabolism and somatic growth during this period. Near-maximal glycogen levels were reached by mid-summer, and remained unchanged in fall and winter, suggesting that glycogenesis was curtailed during this period. Ohioan frogs had a high potential for glycogenolysis and glycogenesis in winter, as evidenced by large glycogen reserves, high levels of GP and GS proteins, and high GS activity, which likely allows for rapid mobilization of cryoprotectant during freezing and replenishing of glycogen reserves during thawing. Alaskan frogs also achieved a near-maximal liver glycogen concentration by summer and displayed high glycogenic and glycogenolytic potential in winter, but, unlike Ohioan frogs, started replenishing their energy reserves early in spring. We conclude that variation in levels of both glycogenolytic and glycogenic enzymes likely happens in response to seasonal changes in energetic strategies and demands, with winter survival being a key component to understanding the regulation of glycogen cycling in this species.
Changes of hemoglobin expression in response to hypoxia in a Tibetan schizothoracine fish, Schizopygopsis pylzovi
Venue: Journal of Comparative Physiology B

Fishes endemic to the Qinghai–Tibetan Plateau are comparatively well adapted to aquatic environments with low oxygen partial pressures (hypoxia). Here, we cloned the complete cDNA of hemoglobin (Hb) α and β from the Tibetan schizothoracine fish Schizopygopsis pylzovi, and then investigated changes in Hb mRNA and protein levels in spleen, liver and kidney in response to hypoxia. We applied severe hypoxia (4 h at PO2 = 0.6 kPa) and moderate hypoxia (72 h at PO2 = 6.0 kPa) to adult S. pylzovi. Changes of Hb expression under hypoxia, together with the investigations of spleen somatic index, kidney somatic index and Hb concentration in circulation, suggest that the kidney may not only serve as the erythropoietic organ, but also act as the major blood reservoir in S. pylzovi. From this perspective, the transcriptional activity of Hb in S. pylzovi, as reflected in the kidney, was turned down quickly after the onset of severe hypoxia, while under moderate hypoxia the transcriptional activity of Hb showed upregulation for a short time, but then the transcriptional machinery was turned down slowly on prolonged exposure. Notably, the changes in Hb protein levels in spleen, liver and kidney in response to severe and moderate hypoxia were not in line with the changes in mRNA levels, which are related with the blood reservoir in the kidney. Tibetan schizothoracine fish, at least S. pylzovi, show a particular response of the transcription regulation of Hb to moderate hypoxia, which is different from that of other fish species.
Physiological and molecular mechanisms underlying photoperiodism in the spider mite: comparisons with insects
Venue: Journal of Comparative Physiology B

Photoperiodism is an adaptive, seasonal timing system that enables organisms to coordinate their development and physiology to annual changes in the environment using day length (photoperiod) as a cue. This review summarizes our knowledge of the physiological mechanisms underlying photoperiodism in spider mites. In particular, the two-spotted spider mite Tetranychus urticae is focussed, which has long been used as a model species for studying photoperiodism. Photoperiodism is established by several physiological modules, such as the photoreceptor, photoperiodic time measurement system, counter system, and endocrine effector. It is now clear that retinal photoreception through the ocelli is indispensable for the function of photoperiodism, at least in T. urticae. Visual pigment, which comprised opsin protein and a vitamin A-based pigment, is involved in photoreception. The physiological basis of the photoperiodic time measurement system is still under debate, and we have controversial evidence for the hourglass-based time measurement and the oscillator-based time measurement. Less attention has been centred on the counter system in insects and mites. Mite reproduction is possibly regulated by the ecdysteroid, ponasterone A. Prior physiological knowledge has laid the foundation for the next steps essential for the elucidation of the molecular mechanisms driving photoperiodism.
Natural variations of cold tolerance and temperature acclimation in Caenorhabditis elegans
Venue: Journal of Comparative Physiology B

Temperature is critical for the survival and proliferation of animals, which must be adapted to cope with environmental temperature changes. In this study, we demonstrated natural variations in the phenotypes of temperature tolerance and temperature acclimation of the nematode Caenorhabditis elegans, and we decoded whole genome sequence of six natural variations, which enabled us to map responsible gene polymorphisms onto specific chromosomal regions. The C. elegans laboratory strain, N2, survives at 2 °C after cultivation at 15 °C but is unable to survive at 2 °C after cultivation at 20 or 25 °C. This cultivation-temperature-dependent cold tolerance occurs within a few hours after the temperature shift and is termed cold acclimation. We measured the cold tolerance and cold acclimation phenotypes of many natural variants isolated from various areas. CB4854 showed weaker cold tolerance associated with gene polymorphisms on the sex chromosome decoded by whole genome sequencing. Variable cold acclimation phenotypes were exhibited in twelve natural isolates and the large difference was seen between CB4856 and AB1 strains. CB4856, isolated from Hawaii, acclimated slowly to a new temperature, whereas AB1, isolated from Australia, acclimated rapidly. By the whole genome sequencing analysis, two different polymorphisms responsible for the accelerated cold acclimation in AB1 were mapped to specific chromosomal regions.
Chronic environmental warming alters cardiovascular and haematological stress responses in European perch (Perca fluviatilis)
Venue: Journal of Comparative Physiology B

Environmental warming and acute stress increase cardiorespiratory activity in ectothermic animals like fish. While thermal acclimation can buffer the direct thermal effects on basal cardiorespiratory function during chronic warming, little is known about how acclimation affects stress-induced cardiorespiratory responses. We compared cardiovascular and haematological responses to chasing stress in cannulated wild European perch (Perca fluviatilis) from a reference area at natural temperature (16 °C) with perch from the ‘Biotest enclosure’; an experimental system chronically warmed (22 °C) by effluents from a nuclear power plant. Routine blood pressure was similar, but Biotest perch had slightly higher resting heart rate (59.9 ± 2.8 vs 51.3 ± 2.9 beats min−1), although the Q10 for heart rate was 1.3, indicating pronounced thermal compensation. Chasing stress caused hypertension and a delayed tachycardia in both groups, but the maximum heart rate increase was 2.5-fold greater in Biotest fish (43.3 ± 4.3 vs 16.9 ± 2.7 beats min−1). Moreover, the pulse pressure response after stress was greater in reference fish, possibly due to the less pronounced tachycardia or a greater ventricular pressure generating capacity and thermally mediated differences in aortic compliance. Baseline haematological status was also similar, but after chasing stress, the haematocrit was higher in Biotest fish due to exacerbated red blood cell swelling. This study highlights that while eurythermal fishes can greatly compensate routine cardiorespiratory functions through acclimation processes, stress-induced responses may still differ markedly. This knowledge is essential when utilising cardiorespiratory variables to quantify and compare stress responses across environmental temperatures, and to forecast energetic costs and physiological constraints in ectothermic animals under global warming.
Vagal tone regulates cardiac shunts during activity and at low temperatures in the South American rattlesnake, Crotalus durissus
Venue: Journal of Comparative Physiology B

The undivided ventricle of non-crocodilian reptiles allows for intracardiac admixture of oxygen-poor and oxygen-rich blood returning via the atria from the systemic circuit and the lungs. The distribution of blood flow between the systemic and pulmonary circuits may vary, based on differences between systemic and pulmonary vascular conductances. The South American rattlesnake, Crotalus durissus, has a single pulmonary artery, innervated by the left vagus. Activity in this nerve controls pulmonary conductance so that left vagotomy abolishes this control. Experimental left vagotomy to abolish cardiac shunting had no effect on long-term survival and failed to identify a functional role in determining metabolic rate, growth or resistance to food deprivation. Accordingly, the present investigation sought to evaluate the extent to which cardiac shunt patterns are actively controlled during changes in body temperature and activity levels. We compared hemodynamic parameters between intact and left-vagotomized rattlesnakes held at different temperatures and subjected to enforced physical activity. Increased temperature and enforced activity raised heart rate, cardiac output, pulmonary and systemic blood flow in both groups, but net cardiac shunt was reversed in the vagotomized group at lower temperatures. We conclude that vagal control of pulmonary conductance is an active mechanism regulating cardiac shunts in C. durissus.
Comparative analysis of hepatic miRNA levels in male marathon mice reveals a link between obesity and endurance exercise capacities
Venue: Journal of Comparative Physiology B

Dummerstorf marathon mice (DUhTP) are characterized by increased accretion of peripheral body fat with fast mobilization in response to mild physical activity if running wheels were included in their home cages. The obese phenotype coincides with elevated hepatic lipogenesis if compared to unselected controls. We now asked, if microRNA (miRNA) species present in the liver may contribute to the obese phenotype of DUhTP mice and if miRNAs respond to mild physical activity in our mouse model. Total RNA was extracted from livers of sedentary or physically active marathon mice and controls and analyzed by array hybridization or real-time PCR using locked nucleic acid probes. Pathway analysis of altered miRNA concentrations identified fatty acid biosynthesis as the most important target for the effects of miRNAs in the liver. A miRNA signature consisting of miR-21, 27, 33, 122, and 143 was present at higher abundance (p < 0.01) in the liver of sedentary or active DUhTP mice indicating involvement of miRNAs with hepatic lipogenesis. Furthermore, in protein lysates from the liver of DUhTP mice, significantly reduced concentrations of total and phosphorylated AKT and lower levels of phosphorylated AMPK were found (p < 0.05). Our results indicate active involvement of miRNAs in the control of hepatic energy metabolism and discuss effects on signal transduction as a potentially direct effect of miR-143 in the liver of DUhTP mice.
The satiety factor oleoylethanolamide impacts hepatic lipid and glucose metabolism in goldfish
Venue: Journal of Comparative Physiology B

Oleoylethanolamide (OEA) is an acylethanolamide synthesized mainly in the gastrointestinal tract with known effects in mammals on food intake and body mass through activation of peroxisome proliferator-activated receptor type α (PPARα). Since we previously demonstrated that acute treatment with OEA in goldfish resulted in decreased food intake and locomotor activity, as in mammals, we hypothesize that OEA would be involved in the control of energy metabolism in fish. Therefore, we assessed the effects of acute (for 6 h) and chronic (for 11 days) treatments with OEA (5 µg g−1 body mass) on metabolite concentrations and enzyme activities related to glucose and lipid metabolism in liver of goldfish (Carassius auratus). In the chronic treatment, OEA impairs the increase in body mass and reduces locomotor activity, without any signs of stress. The lipolytic capacity in liver decreased after both acute and chronic OEA treatments, whereas lipogenic capacity increased after acute and decreased after chronic treatment with OEA. These results are different from those observed to date in mammalian adipose tissue, but not so different from those known in liver, and might be attributed to the absence of changes in the expression of pparα, and/or to the increase in the expression of the clock gene bmal1a after chronic OEA treatment. As for glucose metabolism, a clear decrease in the capacity of hepatic tissue to use glucose was observed in OEA-treated fish. These results support an important role for OEA in the regulation of liver lipid and glucose metabolism, and could relate to the metabolic changes associated with circadian activity and the regulation of food intake in fish.
Glycogen dynamics of crucian carp (Carassius carassius) in prolonged anoxia
Venue: Journal of Comparative Physiology B

Mobilization of glycogen stores was examined in the anoxic crucian carp (Carassius carassius Linnaeus). Winter-acclimatized fish were exposed to anoxia for 1, 3, or 6 weeks at 2 °C, and changes in the size of glycogen deposits were followed. After 1 week of anoxia, a major part of the glycogen stores was mobilized in liver (79.5 %) and heart (75.6 %), and large decreases occurred in gill (46.7 %) and muscle (45.1 %). Brain was an exception in that its glycogen content remained unchanged. The amount of glycogen degraded during the first anoxic week was sufficient for the anaerobic ethanol production for more than 6 weeks of anoxia. After 3 and 6 weeks of anoxia, there was little further degradation of glycogen in other tissues except the brain where the stores were reduced by 30.1 and 49.9 % after 3 and 6 weeks of anoxia, respectively. One week of normoxic recovery following the 6-week anoxia was associated with a complete replenishment of the brain glycogen and partial recovery of liver, heart, and gill glycogen stores. Notably, the resynthesis of glycogen occurred at the expense of the existing energy reserves of the body in fasting fish. These findings indicate that in crucian carp, glycogen stores are quickly mobilized after the onset of anoxia, with the exception of the brain whose glycogen stores may be saved for putative emergency situations.
Life in a dark biosphere: a review of circadian physiology in “arrhythmic” environments
Venue: Journal of Comparative Physiology B

Most of the life with which humans interact is exposed to highly rhythmic and extremely predictable changes in illumination that occur with the daily events of sunrise and sunset. However, while the influence of the sun feels omnipotent to surface dwellers such as ourselves, life on earth is dominated, in terms of biomass, by organisms isolated from the direct effects of the sun. A limited understanding of what life is like away from the sun can be inferred from our knowledge of physiology and ecology in the light biosphere, but a full understanding can only be gained by studying animals from the dark biosphere, both in the laboratory and in their natural habitats. One of the least understood aspects of life in the dark biosphere is the rhythmicity of physiology and what it means to live in an environment of low or no rhythmicity. Here we describe methods that may be used to understand rhythmic physiology in the dark and summarise some of the studies of rhythmic physiology in “arrhythmic” environments, such as the poles, deep sea and caves. We review what can be understood about the adaptive value of rhythmic physiology on the Earth’s surface from studies of animals from arrhythmic environments and what role a circadian clock may play in the dark.
Aerial low-frequency hearing in captive and free-ranging harbour seals (Phoca vitulina) measured using auditory brainstem responses
Venue: Journal of Comparative Physiology A

The hearing sensitivity of 18 free-ranging and 10 captive harbour seals (Phoca vitulina) to aerial sounds was measured in the presence of typical environmental noise through auditory brainstem response measurements. A focus was put on the comparative hearing sensitivity at low frequencies. Low- and mid-frequency thresholds appeared to be elevated in both captive and free-ranging seals, but this is likely due to masking effects and limitations of the methodology used. The data also showed individual variability in hearing sensitivity with probable age-related hearing loss found in two old harbour seals. These results suggest that the acoustic sensitivity of free-ranging animals was not negatively affected by the soundscape they experienced in the wild.