bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinematics of diving Atlantic puffins (Fratercula arcticaL.):evidence for an active upstroke
Authors: Johansson L. Christoffer , Aldrin Björn S. Wetterholm 
Published: April 2021

SUMMARYTo examine the propulsion mechanism of diving Atlantic puffins (Fratercula arctica), their three-dimensional kinematics was investigated by digital analysis of sequential video images of dorsal and lateral views. During the dives of this wing-propelled bird, the wings are partly folded, with the handwings directed backwards. The wings go through an oscillating motion in which the joint between the radius-ulna and the hand bones leads the motion, with the wing tip following. There is a large rotary motion of the wings during the stroke, with the wings being pronated at the beginning of the downstroke and supinated at the end of the downstroke/beginning of the upstroke. Calculated instantaneous velocities and accelerations of the bodies of the birds show that, during the downstroke, the birds accelerate upwards and forwards. During the upstroke, the birds accelerate downwards and, in some sequences analysed, also forwards, but in most cases the birds decelerate. In all the upstrokes analysed, the forward/backward acceleration shows the same pattern, with a reduced deceleration or even a forward acceleration during ‘mid’ upstroke indicating the production of a forward force, thrust. Our results show that the Atlantic puffin can use an active upstroke during diving, in contradiction to previous data. Furthermore, we suggest that the partly folded wings of diving puffins might act as efficient aft-swept wingtips, reducing the induced drag and increasing the lift-to-drag ratio.A movie is available on-line.
The pulmonary surfactant system matures upon pipping in the freshwater turtleChelydra serpentina
Authors: Johnston Sonya D. , Daniels Christopher B. , Cenzato David , Whitsett Jeffrey A. , Orgeig Sandra 
Published: April 2021

SUMMARYPulmonary surfactant (PS), a mixture of phospholipids (PL), neutral lipids and surfactant proteins (SP), lowers surface tension within the lung, which increases lung compliance and improves the removal of fluid at birth. Here, we have examined the expression of thyroid transcription factor-1 (TTF-1) and the surfactant protein SP-B, and also the composition of pulmonary surfactant lipids in the developing lung of the turtle Chelydra serpentina. Lavage and lung tissue were collected from late embryonic, pipped and hatchling turtles. TTF-1, a regulator of gene expression of surfactant proteins and cell differentiation in mammals, was detected using immunohistochemistry in epithelia of the gas-exchange area and conducting airways during late development. Expression declined in hatchlings. SP-B was detected in subsets of cells within the respiratory epithelium at all stages sampled. The same cell types also stained for TTF-1. Turtle surfactant lipids matured toward the end of incubation. Maximal secretion of both total phospholipids and disaturated phospholipid (DSP) occurred at the time of pipping, coincident with the onset of breathing. The DSP/PL ratio increased after pipping, whereas cholesterol levels (Chol) increased prior to pipping. This resulted in a decrease in the Chol/PL and Chol/DSP ratios after pipping. Thus, TTF-1 and SP-B appear to be highly conserved within the vertebrates. Maturation of surfactant phospholipid content occurred with the commencement of pulmonary ventilation.
Insect midgut K+ secretion: concerted run-down of apical/basolateral transporters with extra-/intracellular acidity
Authors: Zeiske Wolfgang , Meyer Heiko , Wieczorek Helmut 
Published: April 2021

SUMMARYIn lepidopteran larvae, three transport mechanisms are involved in the active and electrogenic K+ secretion that occurs in the epithelial goblet cells of the midgut. These consist of (i) basolateral K+ channels, allowing K+ entry from the haemolymph into the cytosol, (ii) apical electrogenic K+/2H+ antiporters, which are responsible for secondary active extrusion of K+ from the cell into the gut lumen via the goblet cavity and (iii) apical V-ATPase-type proton pumps. The latter energize apical K+ exit by building up a large, cavity-positive electrical potential that drives the antiporters. Net K+ secretion (IK) can be measured as short-circuit current (Isc) across the in vitro midgut mounted in an Ussing chamber. We investigated the influence of protons on the transepithelial IK and the partial reactions of the basolateral K+ permeability (PK) and the apical, lumped ‘K+ pump’ current (IP) at various extra- and intracellular pH values. In particular, we wanted to know whether increased cellular acidity could counteract the reversible dissociation of the V-ATPase into its V1 and Vo parts, as occurs in yeast after glucose deprivation and in the midgut of Manduca sexta during starvation or moulting, thus possibly enhancing K+ transport.When intact epithelia were perfused with high-[K+] (32 mmol l–1) salines with different pH values, IK was reversibly reduced when pH values fell below 6 on either side of the epithelium. Attempts to modify the intracellular pH by pulsing with NH4+ or propionate showed that intracellular acidification caused a reduction in IK similar to that obtained in response to application of external protons. Treatment with azide, a well-known inhibitor of the mitochondrial ATP synthase, had the same effect as pulsing with ammonium or propionate with, however, much faster kinetics and higher reversibility. Breakdown of the basolateral or apical barrier using the antibiotic nystatin allowed the intracellular pH to be clamped to that of the saline facing the nystatin-treated epithelial border. Cell acidification achieved by this manipulation led to a reduction in both apical IP and basolateral PK. The transepithelial IK showed an approximately half-maximal reduction at external pH values close to 5 in intact tissues, and a similar reduction in IP and PK values was seen at an intracellular pH of 5 in nystatin-permeabilised epithelia. Thus, the hypothesized V1Vo stabilization by cell acidity is not reflected in the pH-sensitivity of IP. Moreover, all components that transport K+ are synchronously inhibited below pH 6. The significance of our findings for the midgut in vivo is discussed.
Evolution of voltage-gated Na+ channels
Authors: Goldin Alan L. 
Published: April 2021

SUMMARY
Voltage-gated Na+ channels play important functional roles in the generation of electrical excitability in most vertebrate and invertebrate species. These channels are members of a superfamily that includes voltage-gated K+, voltage-gated Ca2+ and cyclic-nucleotide-gated channels. There are nine genes encoding voltage-gated Na+ channels in mammals, with a tenth homologous gene that has not been shown to encode a functional channel. Other vertebrate and invertebrate species have a smaller number of Na+ channel genes. The mammalian genes can be classified into five branches in a phylogenetic tree, and they are localized on four chromosomes. Four of the branches representing the four chromosomal locations probably resulted from the chromosomal duplications that led to the four Hox gene clusters. These duplications occurred close to the emergence of the first vertebrates. The fifth branch probably evolved from a separate ancestral Na+ channel gene. There are two branches in the invertebrate tree, although members of only one of those branches have been demonstrated to encode functional voltage-gated Na+ channels. It is possible that the other branch may have diverged, so that its members do not represent true voltage-gated Na+ channels. Vertebrate and invertebrate Na+ channels appear to be derived from a single primordial channel that subsequently evolved independently in the two lineages.
Ticking of the clockwork cricket: the role of the escapement mechanism
Authors: Bennet-Clark H. C. , Bailey Winston J. 
Published: April 2021

SUMMARYThe ‘clockwork cricket’ model for cricket sound production suggests that the catch-and-release of the file of one forewing by the plectrum on the opposite wing act as an ‘escapement’ to provide the phasic impulses that initiate and sustain the vibration of the resonant regions of the wings from which the sounds are produced. The action of the escapement produces the familiar ticking sound of clocks.The higher-frequency components of the songs of twelve species of cricket were analysed after removing the dominant low-frequency components and amplifying the remaining higher-frequency components. In normal song pulses of all species, the higher-frequency components showed a close phase-locking to the waveform of the dominant frequency, but the amplitude of the higher-frequency components did not correlate with that at the dominant frequency.Anomalous pulses occurred spontaneously in the songs of several species: multimodal, interrupted or curtailed pulses are described. In all of these, the anomalous pulse envelope was associated with changes in the amplitude and/or instantaneous frequency of the higher-frequency components of the sound.A model of the escapement suggests that the frequency of the residual components of the song depends on the symmetry of action of the plectrum on the teeth of the file.
How the efficiency of rainbow trout (Oncorhynchus mykiss) ventricular muscle changes with cycle frequency
Authors: Harwood Claire L. , Young Iain S. , Altringham John D. 
Published: April 2021

SUMMARYDifferent species of animals require different cardiac performance and, in turn, their cardiac muscle exhibits different properties. A comparative approach can reveal a great deal about the mechanisms underlying myocardial contraction. Differences in myocardial Ca2+ handling between fish and mammals suggest a greater energy cost of activation in fish. Further, while there is considerable evidence that heart rate (or cycle frequency) should have a profound effect on the efficiency of teleost cardiac muscle, this effect has been largely overlooked. We set out to determine how cycle frequency affects the power output and efficiency of rainbow trout (Oncorhynchus mykiss) ventricular muscle and to relate this to the heart’s function in life. We measured power output and the rate of oxygen consumption (V̇O2) and then calculated efficiency over a physiologically realistic range of cycle frequencies.In contrast to mammalian cardiac muscle, in which V̇O2 increases with increasing heart rate, we found no significant change in V̇O2 in the teleost. However, power output increased by 25 % as cycle frequency was increased from 0.6 to 1.0 Hz, so net and total efficiency increased. A maximum total efficiency of 20 % was achieved at 0.8 Hz, whereas maximum power output occurred at 1.0 Hz. We propose that, since the heart operates continuously, high mechanical efficiency is a major adaptive advantage, particularly at lower heart rates corresponding to the more commonly used slower, sustainable swimming speeds. Efficiency was lower at the higher heart rates required during very fast swimming, which are used during escape or prey capture.If a fixed amount of Ca2+ is released and then resequestered each time the muscle is activated, the activation cost should increase with frequency. We had anticipated that this would have a large effect on the total energy cost of contraction. However, since V̇O2 remains constant, less oxygen is consumed per cycle at high frequencies. We suggest that a constant V̇O2 would be observed if the amount of activator Ca2+ were to decrease with frequency. This decrease in activation energy is consistent with the decrease in the systolic intracellular Ca2+ ([Ca2+]i) transient with increasing stimulation frequency seen in earlier studies.
Oocyte apoptosis during the transition from ovary-like tissue to testes during sex differentiation of juvenile zebrafish
Authors: Uchida Daisuke , Yamashita Michiaki , Kitano Takeshi , Iguchi Taisen 
Published: April 2021

SUMMARY
Large numbers of apoptotic early diplotene oocytes were observed during the transition from ovary-like undifferentiated gonadal tissue to testes during sex differentiation in presumptive males of the zebrafish (Danio rerio). The percentage of terminal-deoxynucleotidyl-transferase-mediated dUTP nick-end labelling (TUNEL)-positive apoptotic oocytes in the gonads of presumptive males was approximately eight- to 12-fold higher than in genetic all-females. By 29 days post-hatching, all oocytes had disappeared from the gonads of presumptive males. In these males, we also observed apoptotic somatic cells in the ovarian cavity between 23 and 35 days post-hatching. Therefore, the disappearance of oocytes and the decomposition of the ovarian cavity caused by apoptosis during sex differentiation were male-specific events. In genetic all-females, apoptosis in a proportion of early diplotene oocytes was found in the undifferentiated gonads at 15–19 days post-hatching, probably as a result of programmed oocyte loss during ovarian development. These findings suggest that oocyte apoptosis is the mechanism of testicular and ovarian differentiation in zebrafish.
Peripheral oxygen transport in skeletal muscle of Antarctic and sub-Antarctic notothenioid fish
Authors: Egginton S. , Skilbeck C. , Hoofd L. , Calvo J. , Johnston I. A. 
Published: April 2021

SUMMARYTranscellular oxygen flux was modelled mathematically in the aerobic skeletal muscles of perciform fish species living at widely different temperatures (Antarctica, sub-Antarctica and the Mediterranean Sea). Using structural data derived from stereological analysis of electron micrographs, mean fibre PO2 was calculated on the basis of temperature-corrected rates of mitochondrial respiration and oxygen diffusion. The mean muscle fibre diameter (MFD) among Antarctic notothenioids was in the range 17–61 μm and mitochondrial volume density, Vv(mit,f), was 0.27–0.53, but capillary-to-fibre ratio varied only between 1.2 and 1.5. For a mean capillary PO2 of 6 kPa, the model predicted a mean tissue PO2 in the range 0.7–5.8 kPa at the estimated maximum aerobic capacity (ṀO2max). The lowest levels of tissue oxygenation were found in the pectoral muscle fibres of the icefish Chaenocephalus aceratus, which lacks the respiratory pigments haemoglobin and myoglobin. Red-blooded notothenioids found in the sub-Antarctic had a similar muscle fine structure to those caught south of the Antarctic Convergence, with an MFD of 20–41 μm and Vv(mit,f) of 0.27–0.33, resulting in an estimated mean PO2 of 4–5 kPa at ṀO2max. Mean tissue PO2 in the sub-Antarctic icefish Champsocephalus esox, with greater MFD and Vv(mit,f), 56 μm and 0.51, respectively, was calculated to exceed 1 kPa at winter temperatures (4°C), although oxidative metabolism was predicted to be impaired at the summer maximum of 10°C. At the high end of the thermal range, related perciform species from the Mediterranean had a negligible drop in intracellular PO2 across their small-diameter fibres, to a minimum of 5.4 kPa, comparable with that predicted for Trematomus newnesi from the Antarctic (5.6 kPa) with a similar MFD. These data suggest that, within a single phylogenetic group, integrative structural adaptations potentially enable a similar degree of tissue oxygenation over a 20°C range of environmental temperature in the red-blooded notothenioids, and that this is compromised by the lack of respiratory pigments in the icefishes. The mean capillary radius was 1.5 times greater in the two icefish than in the other notothenioids, and the model simulations indicate that the evolution of wide-bore capillaries is essential to maintain tissue oxygenation in the absence of respiratory pigments.
Cn11, the first example of a scorpion toxin that is a true blocker of Na+ currents in crayfish neurons
Authors: Ramirez-Dominguez Martha E. , Olamendi-Portugal Timoteo , Garcia Ubaldo , Garcia Consuelo , Arechiga Hugo , Possani Lourival D. 
Published: April 2021

SUMMARYA novel crustacean toxin (Cn11) was isolated and characterized from the venom of the Mexican scorpion Centruroides noxius Hoffmann. It contains 63 amino acid residues and is stabilized by four disulphide bridges. It is lethal to crustaceans (Cambarellus montezumae), less toxic to insects (crickets) and non-toxic to mammals (mice) at the doses assayed. In neurons isolated from the X organ–sinus gland system of the crayfish Procambarus clarkii, it blocks the Na+ currents with an estimated Km of 320 nmol l–1, without affecting the Ca2+ and K+ currents. The voltage-gated tetrodotoxin-sensitive Na+ current was recorded from X organ neurons in culture 24 h after plating using the whole-cell clamp configuration. The Na+ current was isolated by blocking Ca2+ currents with Cd2+ and Cs+ and K+ currents with tetraethylammonium and 4-aminopyridine. Under control conditions, the Na+ currents were activated at –40 mV with a maximum amplitude at 0 mV. In the presence of 1 μmol l–1 Cn11, the Na+ current amplitude was reduced by 75 % without apparent modifications to the gating mechanism. These findings suggest that Cn11 selectively blocks a Na+ channel. It is the first representative of a new group of scorpion toxins specific for this molecular target.
Visual pigments and oil droplets in diurnal lizards
Authors: Loew Ellis R. , Fleishman Leo J. , Foster Russell G. , Provencio Ignacio 
Published: April 2021

SUMMARYWe report microspectrophotometric (MSP) data for the visual pigments and oil droplets of 17 species of Caribbean anoline lizard known to live in differing photic habitats and having distinctly different dewlap colors. The outgroup Polychrus marmoratus was also examined to gain insight into the ancestral condition. Except for Anolis carolinensis, which is known to use vitamin A2 as its visual pigment chromophore, all anoline species examined possessed at least four vitamin-A1-based visual pigments with maximum absorbance (λmax) at 564, 495,455 and 365 nm. To the previously reported visual pigments for A. carolinensis we add an ultraviolet-sensitive one withλ max at 365 nm. Five common classes of oil droplet were measured, named according to apparent color and associated with specific cone classes — yellow and green in long-wavelength-sensitive (LWS) cones,green only in medium-wavelength-sensitive (MWS) cones and colorless in short-wavelength-sensitive (SWS) and ultraviolet-sensitive (UVS) cones. MSP data showed that the colorless droplet in the SWS cone had significant absorption between 350 and 400 nm, while the colorless droplet in the UVS cone did not. The pattern for Polychrus marmoratus was identical to that for the anoles except for the presence of a previously undescribed visual cell with a rod-like outer segment, a visual pigment with a λmaxof 497 nm and a colorless oil droplet like that in the UVS cones. These findings suggest that anoline visual pigments, as far as they determine visual system spectral sensitivity, are not necessarily adapted to the photic environment or to the color of significant visual targets (e.g. dewlaps).
Effects of temperature on sustained swimming performance and swimming kinematics of the chub mackerelScomber japonicus
Authors: Dickson Kathryn A. , Donley Jeanine M. , Sepulveda Chugey , Bhoopat Lisa 
Published: April 2021

SUMMARYThe effects of a 6°C difference in water temperature on maximum sustained swimming speed, swimming energetics and swimming kinematics were measured in the chub mackerel Scomber japonicus (Teleostei:Scombridae), a primarily coastal, pelagic predator that inhabits subtropical and temperate transition waters of the Atlantic, Pacific and Indian Oceans. New data for chub mackerel acclimated to 18°C are compared with published data from our laboratory at 24°C. Twelve individuals acclimated to each of two temperatures (15.6-26.3 cm fork length, FL, and 34-179g at 18°C; 14.0-24.7 cm FL and 26-156g at 24°C) swam at a range of speeds in a temperature-controlled Brett-type respirometer, at the respective acclimation temperature. At a given fish size, the maximum speed that S. japonicus was able to maintain for a 30-min period, while swimming steadily using slow, oxidative locomotor muscle (Umax,c),was significantly greater at 24 than at 18°C (52.5-97.5 cm s-1at 18°C and 70-120 cm s-1 at 24°C). At a given speed and fish size, the rate of oxygen consumption(V̇O2) was significantly higher at 24 than at 18°C because of a higher net cost of transport (1073-4617 J km-1 kg-1 at 18°C and 2708-14895 J km-1 kg-1 at 24°C). Standard metabolic rate, calculated by extrapolating the logV̇O2versus swimming speed relationship to zero speed, did not vary significantly with temperature or fish mass (126.4±67.2 mg O2 h-1 kg-1 at 18°C and 143.2±80.3 mg O2 h-1 kg-1 at 24°C; means ±S.D., N=12). Swimming kinematics was quantified from high-speed (120 Hz) video recordings analyzed with a computerized, two-dimensional motion-analysis system. At a given speed and fish size, there were no significant effects of temperature on tail-beat frequency, tail-beat amplitude or stride length, but propulsive wavelength increased significantly with temperature as a result of an increase in propulsive wave velocity. Thus, the main effects of temperature on chub mackerel swimming were increases in both Umax,c and the net cost of swimming at 24°C. Like other fishes, S. japonicus apparently must recruit more slow,oxidative muscle fibers to swim at a given sustainable speed at the lower temperature because of the reduced power output. Thus, the 24°C mackerel reach a higher speed before they must recruit the fast, glycolytic fibers,thereby increasing Umax,c at 24°C. By quantifying in vivo the effects of temperature on the swimming performance of an ectothermic species that is closely related to the endothermic tunas, this study also provides evidence that maintaining the temperature of the slow,oxidative locomotor muscle at 6°C or more above ambient water temperature in tunas should significantly increase sustainable swimming speeds, but also increase the energetic cost of swimming, unless cardiac output limits muscle performance.
Osmotic and volaemic effects on drinking rate in elasmobranch fish
Authors: Anderson W. Gary , Takei Y. , Hazon N. 
Published: April 2021

SUMMARYAn increase in drinking rate of two species of marine elasmobranch fish, Scyliorhinus canicula and Triakis scyllia, acclimated to 80% sea water was observed following the introduction of 100 % sea water to experimental tanks. The drinking response in both species was found to be maximal within 6 h, and a significant increase was sustained for up to 24 h in T. scyllia. Plasma osmolality was significantly increased within 6 h following introduction of 100 % sea water, and this increase was principally due to elevated plasma Na+ and Cl- concentrations. Administration of 2 mol l-1 mannitol, 75 % sucrose and vehicle(elasmobranch Ringer) did not induce a significant increase or decrease in the drinking rate of S. canicula. However, injection of 20 % NaCl was found to decrease drinking rate significantly in S. canicula 60 min after administration. Controlled haemorrhage of approximately 5.7 % of total blood volume in S. canicula induced a rapid 36-fold increase in drinking over basal levels. The present study demonstrates a physiological dipsogenesis in response to hypovolaemia in marine elasmobranch fish as part of their overall iso/hyperosmoregulatory strategy.