bluuebunny/crossref_metadata_2025_split huggingface dataset:
The self-referencing oxygen-selective microelectrode: detection of transmembrane oxygen flux from single cells
Authors: Land S. C. , Porterfield D. M. , Sanger R. H. , Smith P. J. S. 
Published: April 2021

ABSTRACT
A self-referencing, polarographic, oxygen-selective microelectrode was developed for measuring oxygen fluxes from single cells. This technique is based on the translational movement of the microelectrode at a known frequency through an oxygen gradient, between known points. The differential current of the electrode was converted into a directional measurement of flux using the Fick equation. Operational characteristics of the technique were determined using artificial gradients. Calculated oxygen flux values matched theoretical values derived from static measurements. A test preparation, an isolated neuron, yielded an oxygen flux of 11.46±1.43 pmol cm−2 s−1 (mean ± S.E.M.), a value in agreement with those available in the literature for single cells. Microinjection of metabolic substrates or a metabolic uncoupler increased oxygen flux, whereas microinjection of KCN decreased oxygen flux. In the filamentous alga Spirogyra greveilina, the probe could easily differentiate a 16.6 % difference in oxygen flux with respect to the position of the spiral chloroplast (13.3±0.4 pmol cm−2 s−1 at the chloroplast and 11.4±0.4 pmol cm−2 s−1 between chloroplasts), despite the fact that these positions averaged only 10.6±1.8 μm apart (means ± S.E.M.). A light response experiment showed real-time changes in measured oxygen flux correlated with changes in lighting. Taken together, these results show that the self-referencing oxygen microelectrode technique can be used to detect local oxygen fluxes with a high level of sensitivity and spatial resolution in real time. The oxygen fluxes detected reliably correlated with the metabolic state of the cell.
Colour vision of the foraging swallowtail butterfly Papilio xuthus
Authors: Kinoshita Michiyo , Shimada Naoko , Arikawa Kentaro 
Published: April 2021

ABSTRACT
This paper demonstrates that foraging summer-form females of the Japanese yellow swallowtail butterfly Papilio xuthus have colour vision. The butterflies were trained to feed on sucrose solution placed on a disk of a particular colour in a cage set in the laboratory. After a few such training runs, a butterfly was presented with the training colour randomly positioned within an array of disks of other colours, but with no sucrose solution. The results indicate that the butterflies learn rapidly to select the training colour reliably among different colours. The training colour was also correctly selected when it was covered with neutral density filters to reduce its brightness, or even when the colour was presented together with disks of a variety of shades of grey. These results demonstrate convincingly, for the first time, that a butterfly has true colour vision.
The diving physiology of bottlenose dolphins (Tursiops truncatus): I. Balancing the demands of exercise for energy conservation at depth
Authors: Williams Terrie M. , Haun J. E. , Friedl W. A. 
Published: April 2021

ABSTRACT
During diving, marine mammals must rely on the efficient utilization of a limited oxygen reserve sequestered in the lungs, blood and muscles. To determine the effects of exercise and apnea on the use of these reserves, we examined the physiological responses of adult bottlenose dolphins (Tursiops truncatus) trained to breath-hold on the water surface or to dive to submerged targets at depths between 60 and 210 m. Changes in blood lactate levels, in partial pressures of oxygen and carbon dioxide and in heart rate were assessed while the dolphins performed sedentary breath-holds. The effects of exercise on breath-hold capacity were examined by measuring heart rate and postdive respiration rate and blood lactate concentration for dolphins diving in Kaneohe Bay, Oahu, Hawaii. Ascent and descent rates, stroke frequency and swimming patterns were monitored during the dives. The results showed that lactate concentration was 1.1±0.1 mmol l−1 at rest and increased non-linearly with the duration of the sedentary breath-hold or dive. Lactate concentration was consistently higher for the diving animals at all comparable periods of apnea. Breakpoints in plots of lactate concentration and blood gas levels against breath-hold duration for sedentary breath-holding dolphins occurred between 200 and 240 s. In comparison, the calculated aerobic dive limit for adult dolphins was 268 s. Descent and ascent rates ranged from 1.5 to 2.5 m s−1 during 210 m dives and were often outside the predicted range for swimming at low energetic cost. Rather than constant propulsion, diving dolphins used interrupted modes of swimming, with more than 75 % of the final ascent spent gliding. Physiological and behavioral measurements from this study indicate that superimposing swimming exercise on apnea was energetically costly for the diving dolphin but was circumvented in part by modifying the mode of swimming.
Vocal tract length and acoustics of vocalization in the domestic dog (Canis familiaris)
Authors: Riede Tobias , Fitch Tecumseh 
Published: April 2021

ABSTRACT
The physical nature of the vocal tract results in the production of formants during vocalisation. In some animals (including humans), receivers can derive information (such as body size) about sender characteristics on the basis of formant characteristics. Domestication and selective breeding have resulted in a high variability in head size and shape in the dog (Canis familiaris), suggesting that there might be large differences in the vocal tract length, which could cause formant behaviour to affect interbreed communication.
Lateral radiographs were made of dogs from several breeds ranging in size from a Yorkshire terrier (2.5 kg) to a German shepherd (50 kg) and were used to measure vocal tract length. In addition, we recorded an acoustic signal (growling) from some dogs. Significant correlations were found between vocal tract length, body mass and formant dispersion, suggesting that formant dispersion can deliver information about the body size of the vocalizer. Because of the low correlation between vocal tract length and the first formant, we predict a non-uniform vocal tract shape.
Avoidance reaction of yolk-sac larvae of the inland silverside Menidia beryllina (Atherinidae) to hypoxia
Authors: Weltzien Finn-Arne , Døving Kjell B. , Carr William E. S. 
Published: April 2021

ABSTRACT
Larvae of the inland silverside Menidia beryllina (Atherinidae) were observed in a chamber with two horizontal water layers to study their aversive response to hypoxia. When larvae descended from an upper normoxic layer into a lower hypoxic layer, they displayed a characteristic avoidance reaction consisting of a burst of fast swimming that always ended in an upward direction leading the larva away from the hypoxic region. Each swimming burst lasted for approximately 2–3 s, with a maximum speed of approximately 25 mm s−1, which is approximately four times the maximum swimming speed observed in the normoxic layer. The avoidance reaction was present in larvae from 6 h until 64 h post hatching. At 72 h we observed 50 % mortality as a result of starvation. The avoidance reaction was correlated with the O2concentration but not with the N2 concentration nor with salinity or with salinity gradients. The avoidance response was observed at O2 levels ranging from 4.7 to 0.8 mg O2 l−1. For all concentrations below 3.8 mg O2 l−1, the distribution was significantly different from that observed in normoxic control layers of the same salinity. No avoidance responses were observed at 6.6 mg O2 l−1. We propose that the avoidance reaction of larvae of M. beryllina to hypoxic water is an innate behavioural adaptation to the hypoxic conditions present in the estuaries that are the spawning, hatching and nursery grounds of this species.
Maps of the somata of efferent neurones with axons in the lateral nerves of locust abdominal ganglia
Authors: Bevan S. , Burrows M. 
Published: April 2021

ABSTRACT
We used the cobalt-backfilling method to map the somata of neurones with axons that project in the two paired lateral nerves of the abdominal neuromeres of the locust Schistocerca gregaria with the objective of expanding and bringing together the incomplete and scattered information on these efferent neurones. We compared somata sizes and positions, and the pathways of primary neurites, with information from previous studies on individual, or groups of, abdominal neurones and we identify many of the somata we mapped.
The stained somata belong to paired motor neurones and paired neurosecretory neurones, to unpaired neuromodulatory neurones (dorsal unpaired median, DUM, neurones) and unpaired bilaterally projecting neurones. In different neuromeres, the total number of somata with axons in these lateral nerves ranges from 73 to 106. Within an individual segmental neuromere, approximately 25 % of the somata belong to neurones with axons in nerve 1 (N1) and 35 % to those with axons in nerve 2 (N2) of that segment, while the remaining 40 % belong to neurones with axons in N1 of the next posterior segment. This basic pattern is repeated in all abdominal neuromeres, with differences in the percentages depending on whether the neuromeres are pregenital fused, pregenital unfused or genital.
Nerve 1 contains the axons of 26–37 neurones with central somata in different neuromeres, of which 40 % are in the segmental neuromere and 60 % in the next anterior neuromere. In the segmental neuromere, 15 % of somata are ipsilateral to the nerve, 30 % are at the midline and 55 % are contralateral, whereas in the next anterior neuromere, 70 % are ipsilateral, 10 % are at the midline and 20 % are contralateral.
Nerve 2 contains the axons of 11–28 neurones in different neuromeres, all of which have somata in the same segmental neuromere from which the nerve projects. Of these, approximately 70 % are ipsilateral, 30 % at the midline and none contralateral, except for the first abdominal and eighth male abdominal neuromeres, where one and two somata, respectively, are contralateral.
Egg-laying hormone peptides in the aplysiidae family
Authors: Li Lingjun , Garden Rebecca W. , Floyd Philip D. , Moroz Tatiana P. , Gleeson Juliann M. , Sweedler Jonathan V. , Pasa-Tolic Ljiljana , Smith Richard D. 
Published: April 2021

ABSTRACT
The neuropeptidergic bag cells of the marine mollusc Aplysia californica are involved in the egg-laying behavior of the animal. These neurosecretory cells synthesize an egg-laying hormone (ELH) precursor protein, yielding multiple bioactive peptides, including ELH, several bag cell peptides (BCP) and acidic peptide (AP). While immunohistochemical studies have involved a number of species, homologous peptides have been biochemically characterized in relatively few Aplysiidae species. In this study, a combination of matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry (MS) and electrospray ionization Fourier transform ion cyclotron resonance MS is used to characterize and compare the ELH peptides from related opisthobranch molluscs including Aplysia vaccaria and Phyllaplysia taylori. The peptide profiles of bag cells from these two Aplysiidae species are similar to that of A. californica bag cells. In an effort to characterize further several of these peptides, peptides from multiple groups of cells of each species were extracted, and microbore liquid chromatography was used to separate and isolate them. Several MS-based sequencing approaches are applied to obtain the primary structures of bag cell peptides and ELH. Our studies reveal that α-BCPs are 100 % conserved across all species studied. In addition, the complete sequences of ε-BCP and ELH of A. vaccaria were determined. They show a high degree of homology to their counterparts in A. californica, with only a few amino acid residue substitutions.
The effects of hypercapnia on force and rate of contraction and intracellular pH of perfused ventricles from the land snail Helix lucorum (L.)
Authors: Michaelidis Basile , Rofalikou Evangelia , Grieshaber Manfred K. 
Published: April 2021

ABSTRACT
The effects of hypercapnia, together with low and high levels of extracellular Ca2+, on heart activity and intracellular pH were examined in isolated perfused hearts from the land snail Helix lucorum. In addition, the intracellular level of Ca2+ was determined in slices of ventricles superfused with both normal and hypercapnic salines, containing low and high concentrations of Ca2+, to investigate whether low extracellular pH affects the entry of Ca2+ into the heart cells. We also examined the effect of a saline that simulated the composition of the haemolymph of snails after estivating for 3 months on the heart activity and intracellular pH. The results showed that hypercapnia causes decreases in the rate and force of heart contraction, and these are more pronounced in the presence of low levels of extracellular Ca2+. Moreover, the present results indicate that Ca2+ maintains the contractility of the heart muscle under acidic conditions and seems to act by competing with protons for the Ca2+ binding sites on sarcolemma. The negative effect of hypercapnia on heart activity appears to be due to a reduction in extracellular pH rather than to changes in intracellular pH.
The relationship between leg stepping pattern and yaw torque oscillations in curve walking of two crayfish species
Authors: Domenici Paolo , Schmitz Josef , Jamon Marc 
Published: April 2021

ABSTRACT
Curve walking in two species of crayfish, Procambarus clarkii and Astacus leptodactylus, was investigated to test whether the mechanism underlying curve walking is the synchronous action of a centrally pre-programmed leg tripod or whether it is the action of one principal leg that produces the main body yaw torque. Curve walking was induced by an optomotor visual stimulus, and the yaw torque produced by the tethered animals was measured in open-loop conditions. Our main results suggest that the yaw torque oscillations in both P. clarkii and A. leptodactylus are related to the movement of outer leg 4 (i.e. leg 4 on the outside of the turn). That is, the peaks in the yaw torque occur, on average, in synchrony with the power stroke of outer leg 4. When comparing the results of this open-loop experiment on P. clarkii with results previously obtained for curve walking in untethered individuals of the same species, we found a much higher variability in leg coordination in the open-loop situation. Similarly, here we did not find the same level of synchrony in the tripod (formed by outer leg 4 and inner legs 2 and 5) observed during untethered free walking. Therefore, we suggest that tethered conditions may diminish the need for stability and thus allow outer leg 4 to produce a body rotation regardless of the leg stepping configuration. The characteristics of leg 4 are in line with its major role in turning. According to previous studies, legs 4 provide the largest force and the largest step amplitude during walking, and their force includes both a pulling and a pushing component which can facilitate the control of turning. Although it is apparent that outer leg 4 is not the only leg that can produce an inward yaw torque, its major role in modulating the yaw torque suggests that there may be a specific, centrally generated control of outer leg 4 during curve walking in crayfish.
Effects of lipid phase transitions on cuticular permeability: model membrane and in situ studies
Authors: Rourke Bryan C. , Gibbs Allen G. 
Published: April 2021

ABSTRACT
The role of lipid physical properties in cuticular water loss was examined in model membranes and intact insects. In model experiments, pure hydrocarbons of known melting point (Tm) were applied to a membrane, and the effects of temperature on permeability were quantified. Arrhenius plots of permeability were biphasic, and transition temperatures for water loss (Tc) were similar to Tm. In grasshoppers Melanoplus sanguinipes, changes in cuticular water loss were measured using flow-through respirometry. Transition temperatures were determined and compared with Tm values of cuticular lipids, determined using Fourier transform infrared spectroscopy, for the same individuals. Individual variation in Tm was highly correlated with Tc, although Tm values were slightly higher than Tc values. Our results show that, in both intact insects and model membranes, lipid melting results in greatly increased cuticular permeability.
Dissecting muscle power output
Authors: Josephson Robert K. 
Published: April 2021

ABSTRACT
The primary determinants of muscle force throughout a shortening–lengthening cycle, and therefore of the net work done during the cycle, are (1) the shortening or lengthening velocity of the muscle and the force–velocity relationship for the muscle, (2) muscle length and the length–tension relationship for the muscle, and (3) the pattern of stimulation and the time course of muscle activation following stimulation. In addition to these primary factors, there are what are termed secondary determinants of force and work output, which arise from interactions between the primary determinants. The secondary determinants are length-dependent changes in the kinetics of muscle activation, and shortening deactivation, the extent of which depends on the work that has been done during the preceding shortening. The primary and secondary determinants of muscle force and work are illustrated with examples drawn from studies of crustacean muscles.
Large-amplitude undulatory fish swimming: fluid mechanics coupled to internal mechanics
Authors: Pedley T. J. , Hill S. J. 
Published: April 2021

ABSTRACT
The load against which the swimming muscles contract, during the undulatory swimming of a fish, is composed principally of hydrodynamic pressure forces and body inertia. In the past this has been analysed, through an equation for bending moments, for small-amplitude swimming, using Lighthill’s elongated-body theory and a ‘vortex-ring panel method’, respectively, to compute the hydrodynamic forces. Those models are outlined in this review, and a summary is given of recent work on large-amplitude swimming that has (a) extended the bending moment equation to large amplitude, which involves the introduction of a new (though probably usually small) term, and (b) developed a large-amplitude vortex-ring panel method. The latter requires computation of the wake, which rolls up into concentrated vortex rings and filaments, and has a significant effect on the pressure on the body. Application is principally made to the saithe (Pollachius virens). The calculations confirm that the wave of muscle activation travels down the fish much more rapidly than the wave of bending.
Functional morphology of undulatory pectoral fin locomotion in the stingray taeniura lymma (Chondrichthyes: dasyatidae)
Authors: Rosenberger Lisa J. , Westneat Mark W. 
Published: April 2021

ABSTRACT
Rajiform locomotion is a unique swimming style found in the batoid fishes (skates and rays) in which thrust is generated by undulatory waves passing down the enlarged pectoral fins. We examined the kinematic patterns of fin motion and the motor patterns of pectoral fin muscles driving the locomotor system in the blue-spot stingray Taeniura lymma. Our goals in this study were to determine overall patterns of fin motion and motor control during undulatory locomotion, to discover how these patterns change with swimming velocity and to correlate muscle function with kinematics and pectoral morphology. Kinematic data were recorded from five individuals over a range of swimming speeds from 22 to 55 cm s−1 (0.9–3.0 DL s−1, where DL is body disc length). Electromyographic (EMG) data were recorded from three individuals over a range of velocities (1.2–3.0 DL s−1) at seven locations (four dorsal, three ventral) along the pectoral fin. As swimming velocity increases, fin-beat frequency, wavespeed and stride length increase, number of waves and reduced frequency decrease and fin amplitude remains constant. There is variability among individuals in frequency and amplitude at a given speed. An inverse relationship was found in which a high fin-beat frequency is associated with a low fin amplitude and a low fin-beat frequency is associated with a high fin amplitude. The motor pattern of undulatory locomotion is alternate firing activity in the dorsal and ventral muscles as the wave moves along the fin from anterior to posterior. Fin muscles are active along the entire length of the fin except at the lowest speeds. As swimming velocity and fin-beat frequency increase, the time of activation of posterior muscles becomes earlier relative to the onset of activity in the anterior dorsal muscles. The duration of muscle activity is longer in the ventral muscles than in the dorsal muscles, indicating that they play a central role in the power stroke of the fin-beat cycle. The anterior muscles (dorsal and ventral) are active for a relatively longer part of the stride cycle than the posterior muscles. Both the anterior position and the large duty factor of the anterior muscles reflect the role of these muscles in initial wave generation. Synchronous recordings of kinematic data with EMG data reveal that the anterior dorsal and middle ventral muscles do mostly positive work, whereas the dorsal and ventral posterior muscles do negative work at most swimming speeds.
Acceleration and balance in trotting dogs
Authors: Lee David V. , Bertram John E. A. , Todhunter Rory J. 
Published: April 2021

ABSTRACT
During quadrupedal trotting, diagonal pairs of limbs are set down in unison and exert forces on the ground simultaneously. Ground-reaction forces on individual limbs of trotting dogs were measured separately using a series of four force platforms. Vertical and fore–aft impulses were determined for each limb from the force/time recordings. When mean fore–aft acceleration of the body was zero in a given trotting step (steady state), the fraction of vertical impulse on the forelimb was equal to the fraction of body weight supported by the forelimbs during standing (approximately 60 %). When dogs accelerated or decelerated during a trotting step, the vertical impulse was redistributed to the hindlimb or forelimb, respectively. This redistribution of the vertical impulse is due to a moment exerted about the pitch axis of the body by fore–aft accelerating and decelerating forces. Vertical forces exerted by the forelimb and hindlimb resist this pitching moment, providing stability during fore–aft acceleration and deceleration.
Characterization of an endothelin ET(B) receptor in the gill of the dogfish shark Squalus acanthias
Authors: Evans David H. , Gunderson Mark P. 
Published: April 2021

ABSTRACT
Endothelins (ETs) are potent vasoconstrictive peptides that are secreted by the vascular endothelium and other tissues in vertebrates. Previous studies have demonstrated that ETs are expressed in a variety of fish tissues and contract various blood vessels. In order to determine if receptors for ET are expressed in fish gill tissue, we examined the binding kinetics of 125 I-labeled, human ET-1 to membrane fragments isolated from the gill of the dogfish shark, Squalus acanthias. 125 I-ET-1 bound at a single site, with a dissociation constant (Kd) and binding site number (Bmax) very similar to those described in a variety of mammalian blood vessels. ET-1 and ET-3 competed equally with 125 I-ET-1, suggesting that the receptor was ETB, which has been shown in mammalian systems to bind to both ligands equally. The ETB-specific agonists sarafotoxin S6c, IRL-1620, and BQ-3020 also competed against 125 I-ET-1 at a single site, supporting this hypothesis. We conclude that the shark gill expresses an ETB receptor with substantial homology to the mammalian receptor and that ET may play an important role in modulating such vital gill functions as gas exchange, ion regulation, acid–base balance, and excretion of nitrogen.