bluuebunny/crossref_metadata_2025_split huggingface dataset:
Energetics of locomotion by the australian water rat (Hydromys chrysogaster): a comparison of swimming and running in a semi-aquatic mammal
Authors: Fish F. E. , Baudinette R. V. 
Published: April 2021

ABSTRACT
Semi-aquatic mammals occupy a precarious evolutionary position, having to function in both aquatic and terrestrial environments without specializing in locomotor performance in either environment. To examine possible energetic constraints on semi-aquatic mammals, we compared rates of oxygen consumption for the Australian water rat (Hydromys chrysogaster) using different locomotor behaviors: swimming and running. Aquatic locomotion was investigated as animals swam in a water flume at several speeds, whereas water rats were run on a treadmill to measure metabolic effort during terrestrial locomotion. Water rats swam at the surface using alternate pelvic paddling and locomoted on the treadmill using gaits that included walk, trot and half-bound. Water rats were able to run at twice their maximum swimming velocity. Swimming metabolic rate increased with velocity in a pattern similar to the ‘humps’ and ‘hollows’ for wave drag experienced by bodies moving at the water surface. Metabolic rate increased linearly during running. Over equivalent velocities, the metabolic rate for running was 13–40 % greater than for swimming. The minimum cost of transport for swimming (2.61 J N−1 m−1) was equivalent to values for other semi-aquatic mammals. The lowest cost for running (2.08 J N−1 m−1) was 20 % lower than for swimming. When compared with specialists at the extremes of the terrestrial–aquatic continuum, the energetic costs of locomoting either in water or on land were high for the semi-aquatic Hydromys chrysogaster. However, the relative costs for H. chrysogaster were lower than when an aquatic specialist attempts to move on land or a terrestrial specialist attempts to swim.
Expression of olfactory receptors during development in Xenopus laevis
Authors: Mezler Mario , Konzelmann Sidonie , Freitag Joachim , Rössler Patricia , Breer Heinz 
Published: April 2021

ABSTRACT
A coordinated expression of tissue- and cell-specific genes during development is required to establish the complex functional organization of the vertebrate olfactory system. Owing to the unique features of its olfactory system and the well-characterized phases of its development, Xenopus laevis was chosen as a model organism to study the onset and the temporal and spatial patterns of expression of olfactory-specific genes. Using RT-PCR and in situ hybridization, it was found that expression of Xenopus olfactory marker protein and of class I receptors, which are thought to be responsible for the perception of water-soluble odorants, was detectable as early as stage 32, less than 2 days after fertilization. In contrast, expression of class II receptors, which are thought to recognize airborne odours, was not detected before stage 49, approximately 12 days after fertilization. The results indicate that the expression of olfactory receptors and marker protein is governed by temporally regulated cues during development.
Micromechanics of the equine hoof wall: optimizing crack control and material stiffness through modulation of the properties of keratin
Authors: Kasapi Mario A. , Gosline John M. 
Published: April 2021

ABSTRACT
Small-scale components of the equine hoof wall were tested to determine their mechanical roles in the morphological hierarchy. Macroscale tensile tests conducted on samples of the inner wall tubules and intertubular material showed a sixfold difference in mean initial stiffnesses (0.47 and 0.08 GPa, respectively), indicating that the inner wall tubules stiffen the wall along its longitudinal axis. The similarity in material properties of tubule and intertubular samples from the mid-wall suggests that tubules in this region offer only minor reinforcement along the longitudinal axis.
Microscale tests conducted on rows of keratin strands from the inner wall tubules and intertubular material, and on intertubular keratin strands of the mid-wall, produced estimates of the stiffnesses of the hydrated matrix (0.03 GPa) and intermediate filament (IF; 3–4 GPa) components of the nanoscale (α-keratin) composite. The results from these tests also suggest that the properties of the keratin composite vary through the wall thickness. Birefringence measurements on inner wall and mid-wall regions agree with these observations and suggest that, although the keratin IF volume fraction is locally constant, the volume fraction changes through the thickness of the wall. These findings imply that modulation of the hoof wall properties has been achieved by varying the IF volume fraction, countering the effects of specific IF alignments which serve another function and would otherwise adversely affect the modulus of a particular region.
ATP reception and chemosensory adaptation in Tetrahymena thermophila
Authors: Kim M. Y. , Kuruvilla H. G. , Raghu S. , Hennessey T. M. 
Published: April 2021

ABSTRACT
Micromolar concentrations of adenosine triphosphate (ATP) and its non-hydrolyzable analog β-γ-methylene ATP are both effective depolarizing chemorepellents in Tetrahymena thermophila. Chemorepellent behavior consists of repeated bouts of backward swimming (avoidance reactions) that can easily be quantified to provide a convenient bioassay for purinergic reception studies. Chemosensory adaptation occurs following prolonged exposure (10 min) to the repellents, and cells regain normal swimming behavior. Adaptation is specific since cells that are behaviorally adapted to either ATP or β-γ-methylene ATP still retain full responsiveness to the chemorepellents GTP and lysozyme. However, cross adaptation occurs between ATP and β-γ-methylene ATP, suggesting that they involve the same receptor. Behavioral sensitivity to both ATP and β-γ-methylene ATP is increased by the addition of Na+, but addition of either Ca2+ or Mg2+ dramatically decreases the response to ATP. These ionic effects are correlated with in vivo ATP hydrolysis, suggesting that divalent ions decrease purinergic sensitivity by activating a Ca2+- or Mg2+-dependent ecto-ATPase to hydrolyze the ATP signal. In vivo [32P]ATP binding studies and Scatchard analysis suggest that the behavioral adaptation is due to a decrease in the number of surface binding sites, as represented by decreased Bmax values. All these changes are reversible (de-adaptation) after 12 min in a repellent-free buffer. Electrophysiological analysis showed that both β-γ-methylene ATP (10 μmol l−1) and ATP (500 μmol l−1) elicited sustained, reversible depolarizations while GTP (10 μmol l−1) produced a transient depolarization, suggesting that the chemosensory response pathways for ATP and GTP reception may differ. There may be separate ATP and GTP receptors since ATP and GTP responses do not cross-adapt and ‘cold’ (unlabeled) GTP is not a good inhibitor of [32P]ATP binding. These results suggests that T. thermophila possess high-affinity surface receptors for ATP that are down-regulated during chemosensory adaptation. These ATP receptors may act as chemorepellent receptors to enable T. thermophila to recognize recently lysed cells and avoid a possibly deleterious situation. This is the simplest eukaryotic organism to show an electrophysiological response to external ATP.
A comparison of the release of a vasoactive-intestinal-peptide-like peptide and acetylcholine in the giant axon–Schwann cell preparation of the tropical squid Sepioteuthis sepioidea
Authors: Evans Peter D. , Reale Vincenzina , Merzon Rosa Maria , Villegas Jorge 
Published: April 2021

ABSTRACT
A vasoactive intestinal peptide (VIP)-like peptide is released by axonal stimulation in the giant axon–Schwann cell preparation from the tropical squid Sepioteuthis sepioidea. It is also released by direct application of L-glutamate, the giant axon–Schwann cell signalling molecule in this preparation. The release of the peptide parallels the release of acetylcholine from the Schwann cells themselves in this preparation in a number of different ways. The release of both acetylcholine and the VIP-like peptide have the same threshold (between 2×10−10 and 5×10−10 mol l−1) for L-glutamate application and the same recovery time after inhibition of release by exposure of the preparation to a prolonged pulse of L-glutamate. A prolonged L-glutamate pulse of 10−8 mol l−1 releases both substances for as long as the pulse is applied to the preparation, whereas a prolonged pulse of 10−9 mol l−1 L-glutamate releases acetylcholine in the same way but releases the VIP-like peptide only transiently. The VIP-like peptide is likely to be co-released with acetylcholine from the Schwann cells.
Fuel use in flight and its dependence on nectar feeding in the hawkmoth Amphion floridensis
Authors: O’Brien Diane M. 
Published: April 2021

ABSTRACT
Fuel use varies widely among insects; however, the potential determinants of variation in fuel use have not been explored experimentally. This study examines whether fuel use during tethered flight depends upon feeding status in the nectarivorous hawkmoth Amphion floridensis. Fuel use in this study is characterized by the respiratory quotient, measured at intervals during a flight using modified closed-chamber respirometry. Moths were either fed twice daily to satiation with 30 % sucrose or unfed, and their fuel use was measured during flights on the first, third and fifth day after eclosion. Flights lasted up to 30 min, with measurements taken at their onset and at 10 min intervals thereafter. Nectar feeding greatly affected fuel use in A. floridensis: fed moths relied primarily on carbohydrate, whereas unfed moths relied almost exclusively on fat reserves. Fuel use did not change during a flight, even when flights lasted 30 min or more. Males were initially more extreme than females in their response to feeding treatment: they burned more carbohydrate when fed and more fat when unfed. By the third day after eclosion, however, fuel use in males and females became identical. Rates of oxygen consumption were uncorrelated with respiratory quotient, were higher in fed moths and declined during a flight. These data indicate that fuel use in this nectarivorous hawkmoth is flexible, that carbohydrate is important as a primary flight fuel and that an understanding of ecological factors, particularly foraging habit, is critical to understanding fuel use in insects.
Plasmodium gallinaceum ookinetes adhere specifically to the midgut epithelium of Aedes aegypti by interaction with a carbohydrate ligand
Authors: Zieler Helge , Nawrocki Joseph P. , Shahabuddin Mohammed 
Published: April 2021

ABSTRACT
During the course of its development in the mosquito and transmission to a new vertebrate host, the malaria parasite must interact with the mosquito midgut and invade the gut epithelium. To investigate how the parasite recognizes the midgut before invasion, we have developed an in vitro adhesion assay based on combining fluorescently labelled ookinetes with isolated midgut epithelia from blood-fed mosquitoes. Using this assay, we found that Plasmodium gallinaceum ookinetes readily adhered to midguts of Aedes aegypti, mimicking the natural recognition of the epithelium by the parasite. This interaction is specific: the ookinetes preferentially adhered to the lumen (microvillar) side of the gut epithelium and did not bind to other mosquito tissues. Conversely, the binding was not due to a non-specific adhesive property of the midguts, because a variety of other cell types, including untransformed P. gallinaceum zygotes or macrogametes, did not show similar binding to the midguts. High concentrations of glycosylated (fetuin, orosomucoid, ovalbumin) or non-glycosylated (bovine serum albumin) proteins, added as non-specific competitors, failed to compete with the ookinetes in binding assays. We also found that the adhesion of ookinetes to the midgut surface is necessary for sporogonic development of the parasite in the mosquito. Antibodies and other reagents that blocked adhesion in vitro also reduced oocyst formation when these reagents were combined with mature ookinetes and fed to mosquitoes. Chemical modification of the midguts with sodium periodate at pH 5.5 destroyed adhesion, indicating that the ookinete binds to a carbohydrate ligand on the surface of the midgut. The ligand is sensitive to periodate concentrations of less than 1 mmol l−1, suggesting that it may contain sialic-acid-like sugars. Furthermore, free N-acetylneuraminic acid competed with the ookinetes in binding aasays, while other monosaccharides had no effect. However, in agreement with the current belief that adult insects do not contain sialic acids, we were unable to detect any sialic acids in mosquito midguts using the most sensitive HPLC-based fluorometric assay currently available. We postulate that a specific carbohydrate group is used by the ookinete to recognize the midgut epithelium and to attach to its surface. This is the first receptor–ligand interaction demonstrated for the ookinete stage of a malaria parasite. Further characterization of the midgut ligand and its parasite counterpart may lead to novel strategies of blocking oocyst development in the mosquito.
Ionic exchanges of turtle shell in vitro and their relevance to shell function in the anoxic turtle
Authors: Jackson Donald C. , Goldberger Zachary , Visuri Susanna , Armstrong Ryan N. 
Published: April 2021

ABSTRACT
To understand more fully the role of the in vivo turtle shell in buffering lactic acid produced during prolonged anoxia, powdered turtle shell was incubated in vitro at constant pH (6.0, 6.5, 7.0, 7.5 or 8.0) in electrolyte solutions simulating extracellular fluid. Exchanges of ions and CO2 between the shell and solution were evaluated by measuring pre- and post-incubation solution concentrations of calcium, magnesium, sodium, potassium, chloride, phosphate and lactate. The production of CO2 from the shell and lactate within the shell were also measured. We observed that calcium and magnesium, but not phosphate, were released from the shell in association with CO2 and that the magnitude of release of each increased with solution acidity. The amount of acid titration required to maintain constant pH also increased as solution pH fell. The CO2 loss, in mmol, was approximately half the acid titration (in mmol), indicating that the evolved CO2 derives from carbonate. When the incubating solution contained lactate (50 mmol l−1), lactate entered the shell and again the amount entering the shell increased with solution acidity. Shell samples containing high initial lactate levels lost lactate to the solution and at high pH (7.5) acidified the solution and required NaOH titration for pH-stat control. These results are consistent with observations on anoxic turtles in vivo and confirm the important role of the shell as a source of buffer and as a storage site for lactate.
Muscle strain histories in swimming milkfish in steady and sprinting gaits
Authors: Katz Stephen L. , Shadwick Robert E. , Rapoport H. Scott 
Published: April 2021

ABSTRACT
Adult milkfish (Chanos chanos) swam in a water-tunnel flume over a wide range of speeds. Fish were instrumented with sonomicrometers to measure shortening of red and white myotomal muscle. Muscle strain was also calculated from simultaneous overhead views of the swimming fish. This allowed us to test the hypothesis that the muscle shortens in phase with local body bending. The fish swam at slow speeds [U&lt;2.6 fork lengths s−1 (=FL s−1)] where only peripheral red muscle was powering body movements, and also at higher speeds (2.6&gt;U&gt;4.6 FL s−1) where they adopted a sprinting gait in which the white muscle is believed to power the body movements. For all combinations of speeds and body locations where we had simultaneous measurements of muscle strain and body bending (0.5 and 0.7FL), both techniques were equivalent predictors of muscle strain histories. Cross-correlation coefficients for comparisons between these techniques exceeded 0.95 in all cases and had temporal separations of less than 7 ms on average. Muscle strain measured using sonomicrometry within the speed range 0.9–2.6 FL s−1 showed that muscle strain did not increase substantially over that speed range, while tail-beat frequency increased by 140 %. While using a sprinting gait, muscle strains became bimodal, with strains within bursts being approximately double those between bursts. Muscle strain calculated from local body bending for a range of locations on the body indicated that muscle strain increases rostrally to caudally, but only by less than 4 %. These results suggest that swimming muscle, which forms a large fraction of the body volume in a fish, undergoes a history of strain that is similar to that expected for a homogeneous, continuous beam. This has been an implicit assumption for many studies of muscle function in many fish, but has not been tested explicitly until now. This result is achieved in spite of the presence of complex and inhomogeneous geometry in the folding of myotomes, collagenous myosepta and tendon, and the anatomical distinction between red and white muscle fibers.
The importance of the feeding current for oxygen uptake in the water flea Daphnia magna
Authors: Pirow R. , Wollinger F. , Paul R. J. 
Published: April 2021

ABSTRACT
In the planktonic crustacean Daphnia magna (Branchiopoda, Cladocera), different views exist on the mechanism of respiratory gas exchange, ranging from gill breathing to general integumentary respiration. The presumed structures for specialized gas exchange are located ventrally within the filter chamber, which is continuously perfused with the ambient medium for food gathering. To localize respiratory gas exchange in D. magna, we determined the contribution of the feeding current to total oxygen transport. Combining microscopy with special optical techniques, we used a phosphorescent oxygen-sensitive dye for oxygen partial pressure measurements and applied fluorescent microspheres for flow-rate analysis. Appendage beat rate was determined by digital image-processing. All experiments were carried out on hypoxia-adapted animals with a body length ranging from 2.3 to 2.7 mm at 20 °C. External measurement revealed oxygen depletion in the ventral body region but essentially no change at posterior, lateral and dorsal positions. The difference between the inflow and outflow of the feeding current was 13.0 mmHg (1.73 kPa). The flow rate of the feeding current ranged from 1.2 to 5.2 ml h−1 and showed a close correlation with appendage beat rate, which varied from 310.4 to 460.7 beats min−1. Model calculations based on the Fick principle suggest that oxygen extraction from the feeding current satisfies most of the total of oxygen requirement of D. magna.
The force–velocity properties of a crustacean muscle during lengthening
Authors: Josephson Robert K. , Stokes Darrell R. 
Published: April 2021

ABSTRACT
Muscle force during active lengthening was characterized for scaphognathite levator muscle L2B from the crab Carcinus maenas. The muscle was tetanically stimulated and, during the peak of the contraction, stretched at constant velocity. The total strain was approximately 4 %, the strain rates ranged from 0.03 to 1.6 muscle lengths s−1 (L s−1), and the temperature was 15 °C.
Force increased throughout stretch. During low-velocity stretch, up to approximately 0.3 L s−1, force rose during isovelocity stretch along an approximately exponential trajectory. The asymptotic force approached during the stretch increased and the time constant of the response decreased with increasing strain rate. With stretch at 0.6 L s−1 and greater, the force increased to a distinct yield point, reached after a strain of approximately 1 %, after which force continued to increase but with a slope approximately one-quarter as great as that before yield. Because force changes continuously during constant-velocity lengthening, the adequate descriptor for the force–velocity relationship in a lengthening crab muscle is not a two-dimensional force–velocity curve, but rather a three-dimensional force–velocity–time or force–velocity–strain surface.
Stimulating muscle L2B at 20 Hz or 50 Hz gives a smoothly fused tetanic contraction in which muscle activation is only partial and the plateau force reached is less than that at the optimum stimulus frequency of approximately 100 Hz. The force–velocity relationships of a partially activated muscle are not simply those of a fully activated one scaled down in proportion to the reduction in the maximum isometric force. At low stretch velocities, the asymptotic force approached is larger in proportion to the pre-stretch isometric tension, and the time constant of the force increase is greater, in partially activated than in fully activated muscles. At high stretch velocities, the force at yield relative to the pre-stretch force, and the relative values of the slopes of the force increase before and after yield, are all greater in partially activated than in fully activated muscles, while the strain at yield is smaller.
Does behavioural hypothermia promote post-exercise recovery in cold-submerged frogs?
Authors: Tattersall Glenn J. , Boutilier Robert G. 
Published: April 2021

ABSTRACT
At the low temperatures of the overwintering environment of the frog Rana temporaria, small changes in ambient temperature have large effects on metabolism and behaviour, especially since Q10 values are often greatly elevated in the cold. How the overwintering aquatic frog copes with variable thermal environments in terms of its overall activity metabolism and recovery from pursuit by predators is poorly understood, as is the role of behavioural thermoregulation in furthering recovery from intense activity. Exhaustive exercise was chosen as the method of evaluating activity capacity (defined by time to exhaustion, total distance swum and number of leg contractions before exhaustion) and was determined at 1.5 and 7 °C. Other cohorts of frogs were examined at both temperatures to determine the metabolic (acid–base, lactate, glucose, ATP and creatine phosphate) and respiratory responses to exercise in cold-submerged frogs. Finally, temperature preference before and after exercise was determined in a thermal gradient to define the importance of behavioural thermoregulation on the recovery rates of relevant metabolic and respiratory processes. Activity capacity was significantly reduced in frogs exercised at 1.5 versus 7 °C, although similar levels of tissue acid–base metabolites and lactate were reached. Blood pH, plasma and lactate levels recovered more rapidly at 1.5 °C than at 7 °C; however, intracellular pH and the recovery of tissue metabolite levels were independent of temperature. Resting aerobic metabolic rates were strongly affected by temperature (Q10=3.82); however, rates determined immediately after exercise showed a reduced temperature sensitivity (Q10=1.67) and, therefore, a reduced factorial aerobic scope. Excess oxygen consumption recovered to resting values after 5–6.25 h, and 67 % recovery times tended to be slightly faster at the lower temperatures. Exercise in the cold, therefore, provided an immediately higher factorial scope, which could be involved in the faster rate of recovery of blood lactate levels in the colder frogs. In addition, exercise significantly lowered the preferred temperature of the frogs from 6.7 to 3.6 °C for nearly 7 h, after which they returned to their normal, unstressed preferred temperatures. Thus, a transient behavioural hypothermia in the skin-breathing, overwintering frog may be an important strategy for minimising post-exercise stress and maintaining aerobic metabolism during recovery from intense activity.