bluuebunny/crossref_metadata_2025_split huggingface dataset:
Passive Absorption of Hydrophilic Carbohydrate Probes by the House Sparrow Passer Domesticus
Authors: Chediack J. G. , Caviedes-Vidal E. , Karasov W. H. , Pestchanker M. 
Published: April 2021

ABSTRACT
To evaluate the permeability of the intestine of the house sparrow Passer domesticus to hydrophilic compounds, we applied a pharmacokinetic technique to measure in vivo absorption of two carbohydrate probes, L-arabinose and D-mannitol. Probes were fed or injected, and blood and excreta were subsequently collected and analyzed by gas chromatography/mass spectrometry. Following injection, plasma probe concentration decreased in a log-linear fashion, implying single-compartment, first-order kinetics. Following oral administration, plasma probe concentrations increased, reached a maximum at 10 min and then decreased in log-linear fashion. Mannitol and arabinose absorption were calculated from the areas under the post-absorption plasma curve and the respective distribution spaces and elimination constants. The amounts absorbed increased linearly with the concentration administered (range 1–1000 mmol l−1 ), implying a passive process. The mouth-to-cloaca retention time of digesta, measured using the non-absorbable compound potassium ferrocyanide, was independent of probe concentration. On average, 69 % of the oral dose of probe was absorbed and this was independent of the concentration of probe administered. This paper supports an earlier report of substantial passive glucose absorption in house sparrows and offers a method to study the extent of hydrophilic solute absorption, which has importance for future research in areas as diverse as biomedical, ecological and evolutionary physiology.
Anaerobic Sulfur Metabolism in Thiotrophic Symbioses
Authors: Arndt C. , Gaill F. , Felbeck H. 
Published: April 2021

ABSTRACT
Hydrogen sulfide is generally accepted to be the energy source for the establishment of sulfur-oxidizing symbiotic communities. Here, we show that sulfur-storing symbioses not only consume but also produce large amounts of hydrogen sulfide. The prerequisite for this process appears to be the absence of oxygen. Anaerobic sulfide production is widespread among different thiotrophic symbioses from vent and non-vent sites (Riftia pachyptila, Calyptogena magnifica, Bathymodiolus thermophilus, Lucinoma aequizonata and Calyptogena elongata). The extent of H2S generation correlates positively with the amount of elemental sulfur stored in the symbiont-bearing tissues of the hosts. Sulfide production starts a few hours after anoxia sets in, with H2S initially accumulating in the circulatory system before it is excreted into the surrounding environment. We propose that not sulfate but the elemental sulfur deposited in the symbionts serves as a terminal electron acceptor during anoxia and is reduced to sulfide. In anoxia-tolerant symbioses such as L. aequizonata, anaerobic sulfur respiration may be important for producing maintenance energy to help the species survive several months without oxygen. The increased levels of cysteine in the gills of L. aequizonata may be caused by a lack of reoxidation due to the absence of oxygen.
Magnetic Compass Orientation in the Blind Mole Rat Spalax Ehrenbergi
Authors: Kimchi Tali , Terkel Joseph 
Published: April 2021

ABSTRACT
The blind mole rat Spalax ehrenbergi is a solitary, subterranean rodent that digs and inhabits a system of branching tunnels, with no above-ground exits, which it never leaves unless forced to. To survive, the mole rat must be able to orient efficiently in its tunnel system. The sensory channels available for spatial orientation in the subterranean environment are restricted in comparison with those existing above ground. This study examined the possibility that the mole rat is able to perceive and use the earth’s magnetic field to orient in space. Experiments were performed using a device constructed from a pair of electromagnetic ‘Helmholtz coils’, which create a magnetic field whose direction and strength can be altered. In the first experiment, we tested a group of mole rats (N=33) in an eight-armed maze under the earth’s natural magnetic field to determine whether they have directional preferences for the location of their sleeping nest, food chamber and toilet site. A second group of mole rats (N=30) was tested for their directional preference after the earth’s magnetic field had been experimentally shifted by 180 °. We found that the first group exhibited a significant preference (P&lt;0.001) to build both their sleeping nest and their food store in the southern sector of the maze, whereas the second group shifted the location of their nests (P&lt;0.01) and food store (P&lt;0.05), to the northern sector of the maze, corresponding to the shift in the magnetic field. In the second experiment, we tested whether the magnetic compass orientation found in the first experiment depends on a light stimulus by testing a group of mole rats in the eight-armed maze under total darkness. No significant difference in directional preference between light and dark test conditions was observed. It can be concluded, therefore, that, in contrast to some amphibians and birds, magnetic compass orientation in the mole rat is independent of light stimulation.
In the third experiment, we examined whether mole rats (N=24) use the earth’s magnetic field as a compass cue to orient in a labyrinth. In the first stage (trials 1–13), the animals were trained to reach a goal box at the end of a complex labyrinth until all individuals had learned the task. In the second stage (trial 14), half the trained mole rats underwent another labyrinth trial under the earth’s natural magnetic field, while the other half were tested under a magnetic field shifted by 180 °. We found a significant decrease (P&lt;0.001) in performance of the mole rats tested under the shifted magnetic field compared with the group tested under the natural magnetic field.
The findings from these experiments prove that the mole rat is able to perceive and use the earth’s magnetic field to orient in space.
Metabolic Rate and Thermal Stability During Honeybee Foraging at Different Reward Rates
Authors: Moffatt Luciano 
Published: April 2021

ABSTRACT
During honeybee foraging, the stabilization of thoracic temperature (Tth) at elevated values is necessary to meet the power requirements of flight at different air temperatures (Ta). To understand how the bee achieves thermal stability at different reward rates, the metabolic rates of undisturbed foraging bees were measured at different Ta values and different sucrose solution flow rates. Metabolic heat production, calculated from the rate of carbon dioxide production, decreased linearly from 49.7 to 23.4 mW as Ta increased from 19 to 29 °C (sucrose flow rate 1.75 μl min−1, 50 % w/w). In contrast, crop load and inspection rate remained constant. Metabolic rate displayed a linear relationship with both Ta and the logarithm of the flow rate of sucrose solution (range analyzed 0.44–13.1 μl min−1, 50 % w/w). Metabolic rate decreased by 3.13±0.52 mW (mean ± S.E.M., N=37) for every 1 °C increase in Ta and increased by 4.36±1.13 mW for a doubling in flow rate. These changes in metabolic power output might be used to achieve thermal stability during foraging. It is suggested that the foraging bee might increase its Tth in accordance with the reward rate.
A Comparative Analysis of the Evolutionary Patterning and Mechanistic Bases of Lactate Dehydrogenase Thermal Stability in Porcelain Crabs, Genus Petrolisthes
Authors: Stillman Jonathon H. , Somero George N. 
Published: April 2021

ABSTRACT
The kinetic properties of orthologous homologs (orthologs) of enzymes are typically correlated with environmental temperatures in species adapted to different thermal regimes, but correlations between adaptation temperature and enzyme thermal stability are less clear. Although the thermal stability of a protein is related chiefly to its primary structure (including post-translational modification), thermal stability can also be altered by extrinsic factors present in the intracellular milieu. Here, we present a comparative analysis of the thermal stability of lactate dehydrogenase (LDH) orthologs from 22 congeneric species of porcelain crab (genera Petrolisthes and Allopetrolisthes) from a broad range of thermal habitats. Interspecific diversity of LDH stability is high: temperatures required for a 50 % loss of activity in 10 min ranged from 65 to 75.5 °C, corresponding to half-lives of less than 1 min to more than 3 h at 70 °C. Although stability is positively correlated with maximal habitat temperature in some sister taxa, phylogenetic comparative analysis incorporating all 22 species does not indicate that the interspecific diversity of LDH stability represents an adaptive response to current thermal habitats. Examination of the mechanistic bases of LDH stabilization indicates that differences in stability are related both to properties of the LDH molecule itself (intrinsic stability) and to the effects of extrinsic protein(s). Intrinsic differences were shown by the unfolding of structure during heating, as measured by circular dichroism spectroscopy. Stabilizing effects of extrinsic proteins are implied by the results of cellular fractionation experiments that removed low-molecular-mass solutes and proteins from the muscle homogenates. We conclude that the overall structural stability and functional properties of proteins can evolve independently and that in vivo protein–protein interactions can provide another means to regulate protein stability selectively.
Detection of Cl− Flux in the Apical Microenvironment of Cultured Foetal Distal Lung Epithelial Cells
Authors: Land S. C. , Collett A. 
Published: April 2021

ABSTRACT
A self-referencing Cl−-selective microelectrode (Cl− SrE) was developed and used to detect changes in the direction and magnitude of the Cl− flux (JCl) from the apical region of cultured foetal distal lung epithelial cells (FDLEs) as a function of external Cl− concentration ([Cl−]e) and in response to pharmacological challenges. The technique, which is similar to that developed for other ion-selective microelectrodes, centres on the oscillation of a Cl−-selective microelectrode between known points, micrometres apart, orthogonal to the plasma membrane. Application of the Fick principle to the differential voltage obtained per excursion amplitude (the referenced signal) yields the Cl− flux (pmol cm−2 s−1). A Cl− effusion gradient was used to confirm that empirical measurements of JCl using the Cl− SrE were statistically similar to predicted flux values calculated from the fall in [Cl−] with distance from the tip of the effusion source. Apical JCl was then measured as a function of [Cl−]e from polarised FDLE cultures grown on permeable supports. At [Cl−]e&lt;50 mmol l−1, an apical-to-basolateral (inward) flux, maximal at 400 pmol cm−2 s−1, was observed; this reverted to a continuous basolateral-to-apical (outward) flux of 203 pmol cm−2 s−1 at [Cl]e&gt;100 mmol l−1. At [Cl−]e&gt;100 mmol l−1, isoproterenol (basolaterally applied, 10 μmol l−1) activated a Cl− influx of 561 pmol cm−2 s−1, whereas UTP (apically applied, 100 μmol l−1) stimulated a Cl− efflux of 300 pmol cm−2 s−1. In all cases, 50–70 % of JCl was abolished by Cl− channel blockade using 10 μmol l−1 diphenylamine-2-carboxylic acid (DPC) or 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB). We conclude that the Cl− SrE resolves a Cl− gradient in the microenvironment of the apical region of lung epithelia that varies in both direction and magnitude as a function of external [Cl−]e and in response to Cl− channel blockade and to β2 adrenoreceptor and P2Y receptor agonists.
Energetics of Terrestrial Locomotion of the Platypus Ornithorhynchus Anatinus
Authors: Fish F. E. , Frappell P. B. , Baudinette R. V. , Macfarlane P. M. 
Published: April 2021

ABSTRACT
The platypus Ornithorhynchus anatinus Shaw displays specializations in its limb structure for swimming that could negatively affect its terrestrial locomotion. Platypuses walked on a treadmill at speeds of 0.19–1.08 m s−1. Video recordings were used for gait analysis, and the metabolic rate of terrestrial locomotion was studied by measuring oxygen consumption. Platypuses used walking gaits (duty factor &gt;0.50) with a sprawled stance. To limit any potential interference from the extensive webbing on the forefeet, platypuses walk on their knuckles. Metabolic rate increased linearly over a 2.4-fold range with increasing walking speed in a manner similar to that of terrestrial mammals, but was low as a result of the relatively low standard metabolic rate of this monotreme. The dimensionless cost of transport decreased with increasing speed to a minimum of 0.79. Compared with the cost of transport for swimming, the metabolic cost for terrestrial locomotion was 2.1 times greater. This difference suggests that the platypus may pay a price in terrestrial locomotion by being more aquatically adapted than other semi-aquatic or terrestrial mammals.
Mite Not Make it Home: Tracheal Mites Reduce the Safety Margin for Oxygen Delivery of Flying Honeybees
Authors: Harrison Jon F. , Camazine Scott , Marden James H. , Kirkton Scott D. , Rozo Albert , Yang Xiaolong 
Published: April 2021

ABSTRACT
Many physiological systems appear to have safety margins, with excess capacity relative to normal functional needs, but the significance of such excess capacity remains controversial. In this study, we investigate the effects of parasitic tracheal mites (Acarapis woodi) on the safety margin for oxygen delivery and flight performance of honeybees. Tracheal mites did not affect the flight metabolic rate of honeybees in normoxic (21 % oxygen) or hyperoxic (40 % oxygen) air, but did reduce their metabolic rate relative to uninfected bees when flying in hypoxic air (5 or 10 % oxygen), demonstrating that mites reduced the safety margin for tracheal oxygen delivery. The negative effects of mites on flight metabolic rate in hypoxic atmospheres were graded with the number of mites per trachea. For example, in 10 % oxygen atmospheres, flight metabolic rate was reduced by 20 % by moderate mite infection and by 40 % by severe mite infection. Thus, the safety margin for oxygen delivery in honeybees allows them to retain normal flight metabolic rate and behavior despite tracheal mite infection under most conditions. However, the reduction in tracheal gas-exchange capacity may constrain activities requiring the highest metabolic rates, such as flying in cool weather. In support of this hypothesis, bees that were unable to return to the hive during late-winter flights showed significantly higher levels of mite infection than bees that returned safely.
Effects of Water Salinity on Acid–Base Balance in Decapod Crustaceans
Authors: Whiteley N. M. , Scott J. L. , Breeze S. J. , Mccann L. 
Published: April 2021

ABSTRACT
Extracellular acid–base balance in decapod crustaceans is influenced by water salinity, although the nature of this relationship is unclear. In euryhaline crabs, a decrease in salinity results in a metabolic alkalosis in the haemolymph and an increase in salinity results in a metabolic acidosis. Alterations in acid–base status by external changes in salinity are thought to be secondary to the adjustments required for ionic and osmotic regulation. In the present study, acid–base adjustments in the haemolymph of Eriocheir sinensis after transfer to 30 % sea water accompanied alterations in muscle pH and [HCO3−], as an initial acidosis coincided with an alkalosis in the leg muscle. By 48 h transfer, haemolymph pH increased as muscle pH and HCO3− declined. Haemolymph [Cl−] decreased significantly 3 h after transfer to a new steady state but haemolymph [Na+] and muscle [Na+] and [Cl−] remained unchanged. Muscle free amino acid concentration increased twofold 6 h after transfer, followed by a 2.5-fold increase in the haemolymph after 24 h. In contrast, 30 % sea water had no effect on haemolymph acid–base adjustments in the osmoconforming crab, Necora puber, which lacks ion and osmo-regulatory mechansims. Collectively these observations support the view that salinity-induced alterations in acid–base status are caused by adjustments consistent with cell volume regulation.
Ontogeny of Decapod Crustacean Hemocyanin: Effects of Temperature and Nutrition
Authors: Terwilliger Nora B. , Dumler Karen 
Published: April 2021

ABSTRACT
Hemocyanin is present throughout the decapod crustacean’s life, usually as one-hexamer and two-hexamer oligomers. Hemocyanins of some decapod crustaceans undergo changes in subunit composition and oxygen affinity during development. Maternal hemocyanin is taken up from the hemolymph via endocytosis by the oocyte. Embryo hemocyanin differs in subunit composition from hemocyanin of oocyte and adult crab and may represent the onset of hemocyanin synthesis. Complex changes in expression of hemocyanin subunits occur through megalopa and early juvenile stages of the crab Cancer magister, culminating in the pattern of adult hemocyanin. The influences of food availability and temperature on development, growth and hemocyanin ontogeny in early juvenile C. magister have been studied. Crabs were raised in warm or cold sea water and fed high or low levels of food for 6 months. While intermolt period was shorter in crabs fed high food levels, especially those raised in warm water, crabs reared in cold water with high food levels attained the largest sizes. Thus increased food availability affects growth more than increased temperature. Adult hemocyanin appeared at about the same number of weeks after the start of the experiment for crabs in the warm water/high food, warm water/low food and cold water/high food groups, even though warm water/low food crabs had molted fewer times. Crabs in the cold water/low food group expressed adult hemocyanin much later than the other groups. Molt stage and maturation from juvenile to adult are not absolutely coupled, and food availability has a greater influence than temperature on hemocyanin ontogeny.
Binding of Urate and Caffeine to Haemocyanin Analysed by Isothermal Titration Calorimetry
Authors: Menze Michael A. , Hellmann Nadja , Decker Heinz , Grieshaber Manfred K. 
Published: April 2021

ABSTRACT
Haemocyanin serves as an oxygen carrier in the haemolymph of decapod crustaceans. The oxygen-binding behaviour of the pigment is modulated by the two major anaerobic metabolites, L-lactate and urate. The binding of these two metabolites to haemocyanin has been investigated mainly indirectly by following the effector-induced changes in the oxygen-binding properties of the respiratory pigment. Only a few direct investigations of effector binding, employing ultracentrifugation techniques and equilibrium dialysis, have been carried out. No evidence for cooperative binding for either effector was detected using these methods. However, isothermal titration calorimetry (ITC) offers a useful tool to gain additional insight into the binding of effectors to these highly allosterically regulated macromolecules. By applying the ITC method to the fully oxygenated dodecameric haemocyanin of the lobster Homarus vulgaris, cooperativity in binding has been found for the urate analogue caffeine but not for urate itself: using urate and the urate analogue caffeine as ligands, two conformations of the oxygenated pigment were detected.
Mechanical Forces Imposed on Echinoid Eggs During Spawning: Mitigation of Forces by Fibrous Networks within Egg Extracellular Layers
Authors: Thomas Florence I. M. , Bolton Toby F. , Sastry Ann Marie 
Published: April 2021

ABSTRACT
Many echinoderms spawn large numbers of eggs in rapid spawning bouts directly into the water column. During spawning, the eggs pass from the gonad along a narrow oviduct and through a rigid gonopore before reaching the water. As the eggs traverse this pathway, they are exposed to shear stress induced by the development of a velocity gradient within the fluid formed by the eggs. In some species, the diameter of the eggs is larger than the diameter of the gonopore. In these cases, the eggs also experience strain resulting from compression of the egg as it passes through the relatively small gonopore. The magnitude of shear stress experienced by eggs differs among species depending upon the viscosity of the eggs. The degree of strain experienced by eggs differs among species depending upon the relative sizes of the egg and gonopore and also changes within species as they grow. Recent evidence suggests that these forces have the propensity to damage eggs, thereby reducing their fertilizability, or to destroy them. Experimental evidence shows that the jelly coat around the eggs can protect them from shear stresses and reduce the strain imposed on them under a compressive force. Echinoderm eggs are surrounded by a jelly coat that has a composite structure of irregularly arranged fibrous networks embedded in a jelly matrix. These fibrous networks have characteristics that are similar to those of engineered and biological materials that are known to reduce the transmission of mechanical forces to other structures. Given this similarity to other materials, three possible mechanisms for the action of the jelly coat may be identified. First, the apparent viscosity of the eggs of echinoids declines as the rate at which they are sheared during spawning increases. This reduction in viscosity with increasing shear rate (shear-thinning) may, in part, be due to the structure of the jelly coat and its resultant non-Newtonian nature. Second, experimental evidence indicates that the jelly coat preferentially deforms under a compressive load, reducing the transmission of that load to the egg. Third, the jelly (but not the fibers in the coating) may deform in a nearly viscous manner. In this case, the fibers may serve to provide an elastic ‘backbone’ to the layer and remain in place to stiffen the outer layer of the egg. The composite structure of the jelly coat and the morphology of the fibrous network are likely to be critical to all these mechanisms.
Ca2+ in Specification of Vegetal Cell Fate in Early sea Urchin Embryos
Authors: Yazaki I. 
Published: April 2021

ABSTRACT
In sea urchin embryos, the first specification of cell fate occurs at the fourth cleavage, when small cells (the micromeres) are formed at the vegetal pole. The fate of other blastomeres is dependent on the receipt of cell signals originating from the micromeres. The micromeres are fated to become skeletogenic cells and show the ability to induce the endoderm (the archenteron) in the neighbouring cells during the 16-to 60-cell stage. Several molecules involved in signaling pathways, i.e. Notch for mesoderm specification, bone morphogenic protein (BMP) for ectoderm specification and β-catenin for endoderm specification, are spatially and temporally expressed during development. In the micromeres, β-catenin increases and subsequently localizes to the nuclei under the regulation of TCF, a nuclear binding partner of β-catenin, until the 60-cell stage. However, the mechanisms activating these signaling substances are still unclear. In this article, I demonstrate some specific properties of the membrane and cytoplasm of micromeres including new findings on intracellular Ca2+ concentration, and propose a mechanism by which the functional micromeres are autonoumously formed. The possible roles of these in the specification of vegetal cell fate in early development are discussed.