bluuebunny/crossref_metadata_2025 huggingface dataset:
A Method For Recording Electrical Activity From the Body Wall Nerve Nets in Sea Anemones
Authors: Cho Kwangwook , Mcfarlane Ian D.
Published: April 2021

Glass microelectrodes were used to record electrical activity from thin rings cut from the column of the sea anemone Calliactis parasitica. This is the first time that pulses have been recorded from the nervous system in the column. Three pulse types were detected, types A, B and C. Type A pulses are probably associated with neurones of the through-conducting nerve net. Type B pulses may be from the endodermal slow conduction system (SS2). Type C pulses have not previously been recorded and are thought to represent activity in a local nerve net. At this stage we cannot positively state whether the recordings are intracellular from endodermal myoepithelial cells or are extracellular from the sub-epithelial region.
Creep Rupture of Wallaby Tail Tendons
Authors: Wang Xiao Tong , Ker Robert F.
Published: April 2021

The tail tendons from wallabies (Macropus rufogriseus) suffer creep rupture at stresses of 10 MPa or above, whereas their yield stress in a dynamic test is about 144 MPa. At stresses between 20 and 80 MPa, the time-to-rupture decreases exponentially with stress, but at 10 MPa, the lifetime is well above this exponential. For comparison, the stress on a wallaby tail tendon, when its muscle contracts isometrically, is about 13.5 MPa. Creep lifetime depends sharply on temperature and on specimen length, in contrast to strength and stiffness as observed in dynamic tests. The creep curve (strain versus time) can be considered as a combination of primary creep (decelerating strain) and tertiary creep (accelerating strain). Primary creep is non-damaging, but tertiary creep is accompanied by accumulating damage, with loss of stiffness and strength. ‘Damage’ is quantitatively defined as the fractional loss of stiffness. A creep theory is developed in which the whole of tertiary creep and, in particular, the creep lifetime are predicted from measurements made at the onset of creep, when the tendon is undamaged. This theory is based on a ‘damage hypothesis’, which can be stated as: damaged material no longer contributes to stiffness and strength, whereas intact material makes its full contribution to both.
Neuromuscular Control and Kinematics of Intermittent Flight in the European Starling (Sturnus Vulgaris)
Authors: Tobalske Bret W.
Published: April 2021

Electromyographic (EMG) and kinematic data were collected from European starlings (Sturnus vulgaris) flying at a range of speeds from 8 to 18 m s−1 in a variable-speed windtunnel. Their flight at all speeds consisted of alternating flapping and non-flapping phases. Wing postures during non-flapping phases included glides, partial-bounds and bounds. Glides were performed proportionally more often within each speed and were longer in duration than either of the other two non-flapping postures, but the percentage of bounds increased markedly with increasing flight speed. The shift from flap-gliding at slow speeds towards flap-bounding at fast speeds was consistent with reducing mean power output relative to continuous flapping.

The starlings often combined more than one non-flapping posture within a single non-flapping period. Transitions between non-flapping postures, as well as transitions between bounds and subsequent flapping, were classified as ‘pull-outs’. Pull-outs consisted of an increase in wingspan but no change in wingtip elevation. The pectoralis and supracoracoideus exhibited electrical activity during glides but not during bounds. The scapulohumeralis caudalis was not active during glides, but this muscle and the supracoracoideus were typically active during partial-bounds and pull-out phases. The scapulohumeralis caudalis occasionally showed activity during bounds, which may reflect its role as a humeral retractor. The frequency and duration of non-flapping intervals in starlings were less during EMG experiments than during non-implanted flights.

During flapping phases, relative intensity and duration of EMG signal and wingbeat frequency increased with flight speed, whereas flapping or non-flapping cycle duration, the percentage of a cycle spent flapping and the number of wingbeats in a cycle were all greatest at 8 m s−1. Wingbeat amplitude was smaller at intermediate speeds, but differences among speeds were not significant. These variables allowed indirect estimates of power output and suggested that minimum power speed for starlings was near 12 m s−1 and that power output increased at both slower and faster speeds. Within windtunnel speeds, muscle activity changed in relation to wingspan at mid-upstroke, wingtip excursion, wingbeat frequency, acceleration, velocity, altitude and horizontal position.
Static Forces and Moments Generated in the Insect Leg: Comparison of a Three-Dimensional Musculo-Skeletal Computer Model With Experimental Measurements
Authors: Full R. J. , Ahn A. N.
Published: April 2021

As a first step towards the integration of information on neural control, biomechanics and isolated muscle function, we constructed a three-dimensional musculo-skeletal model of the hind leg of the death-head cockroach Blaberus discoidalis. We tested the model by measuring the maximum force generated in vivo by the hind leg of the cockroach, the coxa–femur joint angle and the position of this leg during a behavior, wedging, that was likely to require maximum torque or moment production. The product of the maximum force of the leg and its moment arm yielded a measured coxa–femur joint moment for wedging behavior. The maximum musculo-apodeme moment predicted by summing all extensor muscle moments in the model was adequate to explain the magnitude of the coxa–femur joint moment produced in vivo by the cockroach and occurred at the same joint angle measured during wedging. Active isometric muscle forces predicted from our model varied by 3.5-fold among muscles and by as much as 70 % with joint angle. Sums of active and passive forces varied by less than 3.5 % over the entire range of possible joint angles (0–125 °). Maximum musculo-apodeme moment arms varied nearly twofold among muscles. Moment arm lengths decreased to zero and switched to the opposite side of the center of rotation at joint angles within the normal range of motion. At large joint angles (>100 °), extensors acted as flexors. The effective mechanical advantage (musculo-apodeme moment arm/leg moment arm = 0.10) resulted in the six femoral extensor muscles of the model developing a summed force (1.4 N) equal to over 50 times the body weight. The model’s three major force-producing extensor muscles attained 95 % of their maximum force, moment arm and moment at the joint angle used by the animal during wedging.
Reactivation of Ubiquitination in Artemia Franciscana Embryos During Recovery From Anoxia-Induced Quiescence
Authors: Anchordoguy Thomas J. , Hand Steven C.
Published: April 2021

Encysted gastrulae of Artemia franciscana are known to enter a reversible state of quiescence promoted by anoxia, during which the half-life of cytochrome oxidase is prolonged up to 77-fold. This observation suggests that proteolytic pathways within mitochondria are inhibited, and indeed the suppression of the initial step in ubiquitin-mediated proteolysis under anoxia has been reported. Given that active embryos require efficient degradation of macromolecules, we investigated the reactivation of ubiquitination during recovery from anoxia and aerobic acidosis (elevated CO2 levels under aerobic conditions). During 6 h of recovery from anoxia, the levels of ubiquitin-conjugated proteins rose 6.5-fold, reaching 78 % of the pre-anoxia (control) values. Concomitant with the elevation in ubiquitin conjugates was a sharp decline in AMP level, a rise in ATP level and an alkalization of intracellular pH.

Our results suggest that the reinitiation of ubiquitin conjugation is partially dependent on decreasing AMP and/or increasing ATP levels. However, when anoxic embryos were transferred to aerobic acidosis, which promotes a return to control (aerobic) levels of adenylates yet maintains the acidic intracellular pH, 71 % of the total suppression of ubiquitination still remained. This observation reveals a predominant role of intracellular alkalization in the reactivation of ubiquitination during recovery. We suggest that the rapid reversibility of the factors regulating ubiquitin conjugation allows Artemia embryos readily to reinitiate the degradation of proteins via the ubiquitin-mediated pathway during recovery.
The Influence of Tracheal Pressure Changes on the Responses of the Tympanal Membrane and Auditory Receptors in the Locust Locusta Migratoria L.
Authors: Meyer Jens , Hedwig Berthold
Published: April 2021

In resting tethered locusts, the effect of slow changes in tracheal air pressure on peripheral auditory information processing was analysed. The tympanal membrane vibrations, the pressure inside the tracheal system and the summed activity of the auditory receptors were measured simultaneously.

With the membrane in the resting position, laser vibrometry and Fast Fourier Transformation analysis of sound-induced membrane vibrations demonstrated characteristic power spectra at the attachment sites of the high-frequency and low-frequency receptors. The spectra were different above 9 kHz, but very similar in the range 2–9 kHz.

During ventilation, tracheal pressure changed between -500 and 1500 Pa. This caused tympanal membrane peak-to-peak displacements in the range 70–90 μm outwards and 20–30 μm inwards, as measured by means of laser interferometry. For a quantitative analysis, sinusoidal tympanal membrane displacements with amplitudes such as those during natural ventilation could be induced by applying pressure to the tracheal system. There was a sigmoid relationship between the tracheal pressure and the corresponding membrane displacement.

Outward displacements of the tympanal membrane at the attachment site of the elevated process (a-cells) attenuated sound-induced membrane vibrations in the ranges 2–10 kHz and 14–22 kHz and increased them in the ranges 10–14 kHz and 22–25 kHz. At the pyriform vesicle (d-cells), the vibration sensitivity was reduced in the frequency range 2–14 kHz. Sensitivity was enhanced in the range 14–25 kHz.

As a consequence, the detection of acoustic signals was also influenced at the auditory receptor level. Tympanal membrane displacements during acoustic stimulation with 4 kHz sound pulses decreased the summed receptor response by approximately 15 dB. At 16 kHz, an increase of the response equivalent to 7 dB occurred. The effect on the response to white noise was intermediate.
Survival of Intracellular Freezing by the Antarctic Nematode Panagrolaimus Davidi
Authors: Wharton David A. , Ferns Donald J.
Published: April 2021

Animals are usually thought to survive ice formation in their bodies only if the ice is confined to the body cavity and to extracellular spaces. Intracellular ice formation is believed to be fatal. This conclusion is based on studies of the cryopreservation of mammalian cells. Intracellular freezing has been observed in some living insect cells but has not been observed in intact animals. Nematodes are transparent and so the location of ice in their bodies can be observed directly using a cryomicroscope stage. We have observed freezing and melting in all body compartments, including intracellular compartments, of the Antarctic nematode Panagrolaimus davidi. Inoculative freezing from the surrounding water occurs via the body openings, rather than across the cuticle; most frequently it occurs via the excretory pore. Individual nematodes that have frozen intracellularly will subsequently grow and reproduce in culture. Determining the mechanisms by which this nematode survives intracellular freezing could have important applications in the cryopreservation of a variety of biological materials.
An Endogenous Peptide Modulates The Activity Of A Sensory Neurone In The Leech Hirudo Medicinalis
Authors: Wenning Angela , Calabrese Ronald L.
Published: April 2021

Sensory and neurosecretory innervation of each leech excretory complex, a nephridium and its bladder, is accomplished by a single neurone, the nephridial nerve cell (NNC). The NNC monitors the extracellular Cl− concentration, which ranges between 20 and 100 mmol l−1 depending on the physiological state. The NNC contains FMRFamide in its soma and sensory terminals in the nephridium. Bath or focal application of FMRFamide leads to hyperpolarization and decreases the rate of firing of the NNC, suggesting autoregulation of peptide release. Experiments under single-electrode current-clamp and voltage-clamp show that FMRFamide turns off the receptor-specific Cl− current of the NNC, indicating that FMRFamide also modulates the receptor gain.
Electrical Activity, Growth Cone Motility And The Cytoskeleton
Authors: Neely M. Diana , Nicholls John G.
Published: April 2021

The development of the nervous system takes place in two main steps: first an extensive preliminary network is formed and then it is pruned and trimmed to establish the final form. This refinement is achieved by mechanisms that include cell death, selective growth and loss of neurites and the stabilization and elimination of synapses. The focus of this review is on selective neurite retraction during development, with particular emphasis on the role of electrical activity.

In many developing vertebrate and invertebrate neurones, the frequency and duration of ongoing impulse activity determine the final arborizations and the pattern of connections. When impulse traffic is silenced, axons fail to retract branches that had grown to inappropriate destinations in the mammalian visual system, cerebellum and neuromuscular junctions. Similarly, in crustaceans, Drosophila melanogaster and leeches, refinements in axonal morphology during development are influenced by impulse activity. From experiments made in culture, it has been possible to mimic these events and to show a clear link between the density of voltage-activated calcium channels in a neurite and its retraction following stimulation. The distribution of these calcium channels in turn is determined by the substratum with which the neurites are in contact or by the formation of synapses. Several lines of evidence suggest that calcium entry into the growth cone leads to collapse by disruption of actin filaments. One candidate for coupling membrane events to neurite retraction is the microfilament-associated protein gelsolin which, in its calcium-activated state, severs actin filaments. Open questions that remain concern the differential effects of activity on dendrites and axons as well as the mechanisms by which the growth cone integrates information derived from stimuli in the cell and in the extracellular environment.
The Distal Sperm Flagellum: Its Potential For Motility After Separation From The Basal Structures
Authors: Woolley D. M. , Bozkurt H. H.
Published: April 2021

The distal region of the sperm flagellum of Gallus domesticus has been separated and purified. It consists of a 9+2 axoneme, without basal or accessory structures. Such distal segments have been demembranated and then reactivated, either by adding ATP or by releasing ATP photolytically from caged ATP: we find that they are capable of a period of independent motility. Bends form repetitively and travel towards the tip, though it is an abnormal, irregular pattern of beating. It is argued that this motility is not dependent on damage to the flagellum at the fracture site. Evidence is presented that the potential for such motility depends upon the existence of bends on the axoneme before the reactivation. The reactivated motility is short-lived: 50 % of the distal flagellar segments, placed in the reactivating solution, become quiescent and straight within 60 s. However, vigorous beating can be induced in such quiescent segments of axoneme by compressing one end with a glass microneedle. We record, provisionally, that the site of compression does not determine the direction in which bends move along the flagellar segment. The effect of compression in re-initiating motility suggests that a mechanical resistance is necessary, somewhere along the axoneme, for normal, sustained motility; it is proposed that the specialized basal structures, collectively, provide such a resistance in the intact flagellum.
How Should Enzyme Activities be Used in Fish Growth Studies?
Authors: Pelletier Dany , Blier Pierre U. , Dutil Jean-Denis , Guderley Helga
Published: April 2021

The activity of glycolytic and oxidative enzymes was monitored in the white muscle of Atlantic cod Gadus morhua experiencing different growth rates. A strong positive relationship between the activity of two glycolytic enzymes and individual growth rate was observed regardless of whether the enzyme activity was expressed as units per gram wet mass, units per gram dry mass or with respect to muscle protein and DNA content. The most sensitive response to growth rate was observed when pyruvate kinase and lactate dehydrogenase activities were expressed as units per microgram DNA, and this may be useful as an indicator of growth rate in wild fish. In contrast, no relationship between the activities of oxidative enzymes and growth rate was observed when cytochrome c oxidase and citrate synthase activities were expressed as units per gram protein. Apparently, the aerobic capacity of white muscle in cod is not specifically increased to match growth rate.
Effects of Solar Radiation and Wind Speed on Metabolic Heat Production by Two Mammals With Contrasting Coat Colours
Authors: Walsberg Glenn E. , Wolf Blair O.
Published: April 2021

We report the first empirical data describing the interactive effects of simultaneous changes in irradiance and convection on energy expenditure by live mammals. Whole-animal rates of solar heat gain and convective heat loss were measured for representatives of two ground squirrel species, Spermophilus lateralis and Spermophilus saturatus, that contrast in coloration. Radiative heat gain was quantified as the decrease in metabolic heat production caused by the animal’s exposure to simulated solar radiation. Changes in convective heat loss were quantified as the variation in metabolic heat production caused by changes in wind speed. For both species, exposure to 780W m-2 of simulated solar radiation significantly reduced metabolic heat production at all wind speeds measured. Reductions were greatest at lower wind speeds, reaching 42 % in S. lateralis and 29 % in S. saturatus. Solar heat gain, expressed per unit body surface area, did not differ significantly between the two species. This heat gain equalled 14–21 % of the radiant energy intercepted by S. lateralis and 18–22 % of that intercepted by S. saturatus. Body resistance, an index of animal insulation, declined by only 10 % in S. saturatus and 13 % in S. lateralis as wind speed increased from 0.5 to 4.0 m s-1. These data demonstrate that solar heat gain can be essentially constant, despite marked differences in animal coloration, and that variable exposure to wind and sunlight can have important consequences for both thermoregulatory stress experienced by animals and their patterns of energy allocation.
Octopaminergic Dorsal Unpaired Median (Dum) Neurones Innervating the Colleterial Glands of the Female Cockroach Periplaneta Americana
Authors: Sinakevitch I. G. , Geffard M. , Pelhate M. , Lapied B.
Published: April 2021

The musculature of the colleterial glands receives innervation from branch 4B4a of the nerves designated 4B, which arise from the posterior part of the terminal abdominal ganglion in the female cockroach Periplaneta americana (L). Using Methylene Blue staining, the gross anatomy of the colleterial gland innervation has been described. Cobalt backfilling via branch 4B4 of nerve 4B revealed about 21 dorsal unpaired median (DUM) neurones located on both median and posterior parts of the terminal abdominal ganglion. Octopamine immunohistochemistry has shown that at least 15 octopamine-immunoreactive DUM neurones from median and posterior groups projected via branch 4B4a to the left and right colleterial glands. These data, together with results reporting the presence of octopamine-immunoreactive branches supplying these colleterial glands, make octopaminergic DUM neurones suitable candidates to modulate the muscle activity of the colleterial glands in female Periplaneta americana.
Ammonia and Urea Metabolism in Relation to Gill Function and Acid–Base Balance in A Marine Elasmobranch, the Spiny Dogfish (Squalus Acanthias)
Authors: Wood Chris. M. , Pärt Peter , Wright Patricia A.
Published: April 2021

Nitrogenous waste excretion in resting dogfish occurred largely (>90 %) as urea-nitrogen (urea-N) efflux across the gills, with a very small urea efflux via the kidney. Ammonia excretion, almost entirely at the gills, accounted for less than 3 % of total nitrogen excretion. Given the extremely high blood urea levels (approximately 640 mmol-N l−1) ‘retained’ for osmoregulation, and blood ammonia levels (approximately 80 μmol-N l−1) comparable to those of teleosts, the gills of resting dogfish were exceptionally impermeable to both urea and ammonia. Experiments investigated the origins of these low permeabilities and the responses of urea-N and ammonia-N excretion and acid–base status to 6 h infusions with iso-osmotic solutions of NaCl (control), NH4Cl, NaHCO3, urea and its analogues thiourea and acetamide. NaCl had no effects, whereas NH4Cl loading caused intense acidosis and marked elevation of acidic equivalent, ammonia-N and urea-N excretion rates, the latter despite unchanged blood levels of urea-N. Apparent branchial ammonia permeability increased greatly. Acidosis resulted from both stimulated urea production and branchial NH3 loss, the former making the larger contribution. NaHCO3 loading caused intense alkalosis, a marked elevation of basic equivalent excretion and a moderate stimulation of urea-N excretion. Blood urea-N levels were again unchanged. Infusion of urea itself raised blood urea-N levels, but initially reduced branchial urea-N excretion. Acetamide and thiourea infusions both moderately elevated branchial urea-N excretion. We suggest that the low ammonia permeability may arise metabolically from an ammonia scavenging system in the gills, that a ‘back-transport’ mechanism in the gills may contribute to the low urea permeability, and that the dissociation between blood urea-N levels and excretion rates may reflect urea production at extrahepatic sites. These studies demonstrate that urea synthesis in the dogfish is linked more to nitrogen availability than to acid–base status.
Effects of Feeding and Confinement on Nitrogen Metabolism and Excretion in the Gulf Toadfish Opsanus Beta
Authors: Walsh Patrick J. , Milligan C. Louise
Published: April 2021

In order to elucidate further the cues for, and the biochemical mechanisms of, the transition to ureogenesis in the gulf toadfish Opsanus beta, experiments on the effects of feeding (i.e. nitrogen loading) were carried out. Baseline nitrogen excretion rates were first measured on solitary toadfish in large water volumes (i.e. unconfined conditions). These nitrogen excretion rates were higher, and had a higher proportion as ammonia (61 %), than previously published ‘control’ measurements. Feeding of unconfined toadfish elevated total nitrogen excretion approximately threefold, with little change in the proportion of urea versus ammonia. During the first 24 h of confinement of unfed toadfish, absolute levels of urea excretion remained constant while ammonia excretion rates fell to near zero, so that toadfish became 90 % ureotelic. When fed prior to confinement, urea excretion rates remained constant for the first 24 h, and the bulk of the nitrogen was excreted as ammonia (80 %); excretion of the excess dietary nitrogen took up to 48 h to complete. If pre-adapted to confinement and then fed, toadfish excreted only about 55 % of their nitrogenous waste as ammonia, and excretion of excess dietary nitrogen was completed by 24 h. Elevations of hepatic glutamine synthetase (GNS) activities accompanied confinement and were shown to be almost exclusively in the cytosolic compartment and to be correlated with a decrease in the ratio of hepatic levels of glutamate:glutamine. These GNS activity increases also appear to account in part for the decrease in the percentage of ammoniotely in toadfish under conditions of nitrogen loading after confinement. However, additional means of regulating total nitrogen excretion (e.g. changes in protein turnover rates) and the degree of ureogenesis versus ammoniogenesis (e.g. N-acetylglutamate stimulation of carbamoylphosphate synthetase) must be postulated to account fully for changes in nitrogen excretion rates and activation of ureogenesis under some circumstances.
Hydroplaning by Ducklings: Overcoming Limitations to Swimming at the Water Surface
Authors: Aigeldinger Terrye L. , Fish Frank E.
Published: April 2021

Rapid escape behavior by mallard (Anas platyrhynchos) ducklings is restricted to burst swimming at the water surface. Maximum speed may be limited because of the pattern of waves created as the duckling’s body moves through the water (hull speed). Burst speeds for 9-day-old ducklings were compared with predicted hull speeds, based on the waterline length of ducklings either resting in water or actively swimming. Kinematic analysis of video tapes showed a mean maximum burst speed of 1.73 m s-1, which was four times greater than the predicted hull speed. At burst velocities, stroke frequency was 1.9 times higher than the stroke frequency measured during steady low-speed paddling. Transition to burst speeds from steady paddling occurred near predicted hull speed. The paddling motions of the webbed feet were used to generate both thrust and lift. By using lift to raise the body above the water surface, the influence of waves in restricting maximum swimming speed is negated. The duckling’s body becomes a planing type of hull and skims on the water surface.
Small-Diameter White Myotomal Muscle Fibres Associated With Growth Hyperplasia in the Carp (Cyprinus Carpio) ExPress a Distinct Myosin Heavy Chain Gene
Authors: Ennion Steven , Gauvry Laurent , Butterworth Peter , Goldspink Geoffrey
Published: April 2021

A carp myosin heavy chain gene isoform was isolated from a genomic clone, restriction mapped and partially sequenced to reveal the location of various exons. The clone contains a complete gene of approximately 12.0 kb which is half the size of the corresponding mammalian and avian myosin heavy chain genes. The mRNA transcript of this gene, however, is the same size as mammalian and avian striated muscle myosin heavy chain genes (about 6000 nucleotides), illustrating that the difference in size at the genomic level is due to shorter introns. A 169 bp NsiI restriction fragment containing only the 3′ untranslated region of this gene was subcloned and used as an isoform-specific probe to study the expression of this particular isoform. Hybridisation analysis could only detect expression of this myosin heavy chain gene in the white muscle of adult carp that had been subjected to an increased environmental temperature. No expression of this gene was detected in carp under 1 year of age. In situ hybridisation demonstrated that expression of this gene is limited to small-diameter white muscle fibres of adult carp, which are thought to be responsible for muscle growth by fibre hyperplasia.
Fluid Reabsorption And Ion Transport By The Lower Malpighian Tubules Of Adult Female Drosophila
Authors: O’Donnell Michael J. , Maddrell Simon H. P.
Published: April 2021

The properties of the Malpighian tubules of Drosophila melanogaster change along their length. The upstream main segments secrete K+-rich fluid at a high rate. From this, the lower tubules reabsorb significant amounts of water and K+. Under stimulation, K+ reabsorption is accelerated. In addition, the lower tubules acidify the fluid passed to them by the main segments and secrete Ca2+ into it, adding to that transported there by the upstream epithelium. In contrast to the lumen-positive transepithelial potential difference (TEP) of the main segments, the TEP in the lower tubules is much lower and becomes lumen-negative close to their downstream junction with the common ureter. We suggest that the role of the lower tubule is to reduce the flow of K+-rich fluid that passes to the hindgut; this allows the hindgut to process the flow of excretory fluid more thoroughly.
The Moment of Inertia of Bird Wings and the Inertial Power Requirement for Flapping Flight
Authors: Berg Coen Van Den , Rayner Jeremy M. V.
Published: April 2021

The agility and manoeuvrability of a flying animal and the inertial power required to flap the wings are related to the moment of inertia of the wings. The moments of inertia of the wings of 29 bird species and three bat species were determined using wing strip analysis. We also measured wing length, wing span, wing area, wing mass and body mass. A strong correlation (r2=0.997) was found between the moment of inertia and the product of wing mass and the square of wing length. Using this relationship, it was found that all birds that use their wings for underwater flight had a higher than average moment of inertia. Assuming sinusoidal wing movement, the inertial power requirement was found to be proportional to (body mass)0.799, an exponent close to literature values for both metabolic power output and minimum power required for flight. Ignoring wing retraction, a fairly approximate estimate showed that the inertial power required is 11–15 % of the minimum flight power. If the kinetic energy of the wings is partly converted into aerodynamic (useful) work at stroke reversal, the power loss due to inertial effects may be smaller.
An Elaborate Tension Receptor System Highlights Sensory Complexity in the Hind Leg of the Locust
Authors: Matheson Thomas , Field Laurence H.
Published: April 2021

The tibia of each leg of the locust is moved by two antagonistic muscles, the extensor and flexor tibiae. A variety of sense organs on and in each leg provide feedback about this joint’s position and movement and about forces acting on the exoskeleton and muscles. One such organ is a muscle tension receptor found within the flexor tibiae muscle of the mesothoracic leg. We now show that an apparently homologous multipolar receptor is present in the hind leg, but that here it is associated with a specialised flexor muscle, the accessory flexor. This muscle comprises 13 fibres, innervated by five of the thirteen motor neurones that innervate the main flexor muscle and, since these are slow motor units, the response properties of the receptor are constrained. The multipolar receptor attaches to the muscle fibres near their proximal insertion onto the femoral cuticle. It generally has four primary dendrites, which do not branch extensively within the muscle.

We show that the receptor responds strongly to active, isometric contractions but only poorly to imposed changes of accessory flexor muscle length (i.e. passive changes in tibial position). It does not respond to tension generated by the main flexor muscle or by the extensor muscle. The tension receptor causes short-latency (0.9–1.8 ms) excitatory inputs onto the three common inhibitory motor neurones and longer-latency (3.7–8.1 ms) inhibitory inputs onto the slow extensor tibiae motor neurone. In quiescent animals, it causes excitatory inputs onto flexor tibiae motor neurones (2.2–3.8 ms) but, in more active animals, its inputs onto these neurones are often inhibitory, with delays of 6–10 ms.

The slow nature of the accessory flexor muscle and the pattern of central connections of the receptor suggest that together they are involved in the control of slow movements or posture, potentially acting through a servomechanism.
Ventilation and pulmonary Gas Exchange During Exercise in the Savannah Monitor Lizard (Varanus Exanthematicus)
Authors: Hopkins S. R. , Hicks J. W. , Cooper T. K. , Powell F. L.
Published: April 2021

During exercise, pulmonary gas exchange in reptiles was predicted to differ from that in mammals because of their less complex lung structure, which might reduce ventilation–perfusion heterogeneity at the expense of pulmonary diffusion limitation. To investigate this, the multiple inert gas elimination technique was used in six Varanus exanthematicus at rest and during maximal exercise. Trace amounts of six inert gases were infused into the external jugular vein and blood samples were collected from the pulmonary artery and the left atrium. Mixed expired gas samples and ventilatory and metabolic data were acquired. Indices of heterogeneity, calculated using a 50-compartment model, were low at rest (log standard deviation of perfusion distribution, logSDQ⨗=0.39) and increased significantly with exercise (logSDQ⨗=0.78). Oxygen diffusion limitation was apparent during exercise and was comparable to reported mammalian values. A molecular-mass-dependent limitation, suggesting limited intrapulmonary gas mixing, was evident only at rest. An increase in left atrial from 82 mmHg at rest to 96 mmHg during exercise was associated with a corresponding decrease in . These data indicate adequacy of pulmonary ventilation and gas exchange for metabolic demands in exercising varanid lizards and suggest that less complex lung structures are not necessarily linked to increased pulmonary diffusion limitation.
Taurine Metabolism In Larvae Of Marine Molluscs (Bivalvia, Gastropoda)
Authors: Welborn J. R. , Manahan D. T.
Published: April 2021

Nonfeeding larvae of the gastropod Haliotis rufescens maintained a constant amount of taurine during embryonic and larval development and, since no de novo synthesis of taurine was observed in these larvae, the maternal endowment of taurine to the egg was sufficient for larval development to metamorphosis. In contrast, feeding larvae of the bivalve Crassostrea gigas increased their taurine content by a factor of 43 during growth to metamorphosis (from 86 to 311 μm, valve length). Taurine was not present in algae used to feed the larvae, suggesting that de novo synthesis of taurine by the larvae met their requirements. In unfed larvae, cysteic acid, cysteine sulfinic acid and hypotaurine were labeled from a [35S]cysteine precursor, but taurine was not. Hyperosmotic treatment (from 33 ‰ to 44 ‰ salinity for up to 3 h) did not induce taurine synthesis in unfed larvae. However, larvae fed the alga Isochrysis galbana up-regulated their taurine synthesis from [35S]cysteine by a factor of 11 (fed, 11.7±2.2 fmol taurine larva-1 h-1; unfed controls, 1.08±0.33 fmol taurine larva-1 h-1; means ± S.E.M.). Fed larvae also synthesized taurine from [35S]methionine (18.4 fmol larva-1 h-1). I. galbana contained 5 fmol cell-1 of cysteine and methionine (combined) and, based on known feeding rates, we calculated that there were sufficient taurine precursors in the algae to supply the taurine requirements of growing larvae. The lack of significant de novo taurine synthesis reported for adult bivalve molluscs has led to the conclusion that taurine is a dietary requirement. Our findings for larval forms differ in that there is significant de novo synthesis of taurine during development.
The Mechanical Power Output and Hydromechanical Efficiency of Northern Pike (Esox Lucius) Fast-Starts
Authors: Frith H. Russ , Blake Robert W.
Published: April 2021

The mechanical power output and hydrodynamic efficiency of northern pike, Esox lucius, during acceleration from rest (fast-start) are calculated from hydrodynamic theory for two kinematic patterns, C-starts (used in escape) and S-starts (used in prey capture). The Weihs model is employed and modified to calculate the mechanical power produced by a fish during a fast-start. A term is included for the power required to accelerate body sections laterally. Lateral deceleration of fish body sections and their associated added mass are expressed as an active process requiring energy expenditure or as a passive process requiring no energy expenditure. In addition, two methods of calculating useful power (the power used to accelerate the virtual mass of the fish, i.e. fish body mass + longitudinal added mass, in the direction of motion), one derived from the Weihs model and the second by summing the changes in kinetic energy of the virtual mass of the fish during a fast-start, are compared and found to give similar estimates of useful power (not significantly different; differences average 22 %).

Comparisons of the kinematics and performance of C-and S-starts reveal that C-starts are consistently terminated after two tail flips (stages 1 and 2) whereas S-starts continue for 3–6 tail flips (stages 3–6). In addition, acceleration during C-starts is more rapid and velocities are higher (2.3–2.8 m s−1) than during S-starts (0.8–1.8 m s−1) over the first 100 ms. However, the peak velocities achieved during S-starts and C-starts are similar over the duration of a fast-start. The superior acceleration rates achieved during the initial stages of a C-start can be explained, in part, by the use of greater maximum angles of attack, higher lateral and perpendicular velocities and larger maximum forces by the caudal fin.

Hydrodynamic efficiencies for fast-starts range from 0.16 to 0.39, values that are lower than those observed during either burst-and-coast or steady swimming. Efficiencies are lower for S-starts than for C-starts during the first two tail beats. S-start efficiencies increase with each subsequent tail flip and the maximum efficiencies realised are similar to those achieved during C-starts.

Power output during C-and S-starts (449.0 and 394.9 W kg−1 muscle fibre, respectively) approaches the theoretical maximum for vertebrate striated muscle (500 W kg−1). Also, the inferred muscle stress is close to the predicted optimum for maximum power output, at 30 % of the maximum isometric stress recorded for isolated fast muscle fibres. These measurements suggest that fast-start performance is near a physiological limit and is probably constrained by muscle function. The superior acceleration rates achieved by C-starts over S-starts are explained in part by differences in hydrodynamic efficiency, whereas power outputs are similar.
Osmotic and Thermal Effects on In Situ Atpase Activity in Permeabilized Gill Epithelial Cells of the Fish Gillichthys Mirabilis
Authors: Kültz Dietmar , Somero George N.
Published: April 2021

Long-jawed mudsuckers (Gillichthys mirabilis) were acclimated to sea water (SW) at 7 °C, SW at 26 °C or dilute sea water (DSW) at 26 °C for 5 months. Gill cells were isolated and the proportion of mitochondria-rich (MR) cells was determined. The number of cells harvested amounted to 4.7X107±0.6X107 to 10.6X107±1.1X107 and the yield was between 7.1X108±0.6X108 and 10.7X108±1.4X108 cells g-1 gill epithelial mass. Cell viability was 96.8±0.4 to 97.8±0.6 %. The number, size and volume of MR cells decreased significantly during DSW acclimation, but did not change during thermal acclimation. The protein content was not influenced by osmotic or thermal acclimation and ranged between 20.0±1.6 and 22.1±1.5 pg cell−1. Using a new method, which is based on the formation of plasma membrane channels by alamethicin, we were able to permeabilize gill cells. For the first time, the Na+/K+-ATPase and H+-ATPase activities of fish gills were determined in intact cells in situ. The activity of both ATPases was dependent on alamethicin concentration (optimum 100 μg mg−1 protein) and on preincubation time (optimum 10 min). The in situ activity of both ATPases was influenced by osmotic, but not thermal, acclimation. A positive linear correlation was found between in situ Na+/K+-ATPase activity and total MR cell volume. However, we show, for the first time, that a negative linear correlation exists between H+-ATPase activity and total MR cell volume, suggesting a localization of H+-ATPase in pavement cells. In permeabilized cells, the activity of both ATPases was 2.6–3.9 times higher than that of crude homogenates and 1.6–2.1 times higher than that of permeabilized homogenate vesicles. We hypothesize that in crude homogenates three-quarters of Na+/K+-ATPase and two-thirds of H+-ATPase activity are not detectable both because of a mixture of inside-out and right-side-out vesicles and because of the disruption of membrane and enzyme integrity.
Pore Properties of Lymnaea Stagnalis Neuron Stretch-Activated K+ Channels
Authors: Small Daniel L. , Morris Catherine E.
Published: April 2021

In many neurons, variations in membrane excitability are determined by a resting K+ conductance whose magnitude is modulated via neurotransmitters. The S-channel in Aplysia californica mechanosensory neurons is such a conductance, but it has also been shown to be a stretch-activated K+ channel. In this, it resembles stretch-activated K+ channels common to all molluscan neurons. Comparable channels are widespread, having been reported in molluscan and insect muscle and various vertebrate cells. The pore properties of the S-channel and similar stretch-activated K+ channels have received only sporadic attention. Here we examine, at the single-channel level, the permeation characteristics of a stretch-activated K+ channel from neurons of the mollusc Lymnaea stagnalis.

Michaelis–Menten constants (Km) for the conductance, obtained separately for inward (28 mmol l−1) and outward (91 mmol l−1) K+ currents, suggest that the channel presents to the external medium, where [K+] is lower, a higher-affinity site than it presents to the cytoplasmic medium. This may help to ensure that influx is not diffusion-limited at potentials near the resting potential, i.e. near the K+ equilibrium constant. Anomalous mole fraction behavior, observed when the ratio of permeant ion (K+ and Rb+) was varied, indicated that the stretch-activated K+ channel is a multi-ion pore. The ion selectivity sequence determined using reversal potentials under bi-ionic conditions was Cs+>K+>Rb+>NH4+>Na+>Li+, and using relative conductance in symmetrical solutions, the sequence was Tl+=K+>Rb+>NH4+⪢Na+=Li+=Cs+. Extreme variations in extracellular pH from 4.7 to 11.4 had no effect on stretch-activated K+ channel conductance, whereas normal concentrations of extracellular Mg2+ reduced inward K+ current. Intracellular, but not extracellular, Ba2+ produced a slow, open channel block with an IC50 of 140±80 μmol l−1.

These pore properties are compared with those of other stretch-activated K+ channels and of K+ channels in general. In spite of a greater than half order of magnitude difference in the cytoplasmic [K+] in marine (Aplysia californica) and freshwater (Lymnaea stagnalis) molluscs, the conductances of stretch-activated K+ channels from the two groups are very similar.
Ballistics and Visual Targeting in Flea-Beetles (Alticinae)
Authors: Brackenbury John , Wang Richard
Published: April 2021

The kinematics of jumping was measured in seven species of flea-beetle (Alticinae). The accuracy of two species during targeted jumping was also investigated. Take-off accelerations ranged from 15 to 270 times gravity. Rotational energy accounted for 4–21 % of the total translational energy. Two species were able to control jump direction and landing. When presented with a high-contrast optical grid, Chalcoides aurata exhibited two alternative jump modes. In mode 1 or wingless jumping, the body rotated continuously, the insect rarely landed on its feet and no discrimination was shown between landing on the black or white stripes of the grid. In mode 2 jumping, recruitment of the wings eliminated rotation and virtually ensured a feet-first landing; there was also a significant preference for jumping towards the black stripes. Aphthona atrocaerulea could alter take-off angle in order to strike targets at inclinations of 0–90° to the horizontal. Targets consisting of a white illuminated cross on a black background were struck with equal accuracy, regardless of distance (within the normal jumping range). The beetle aimed specifically for the centre of the target and not for the high-contrast boundary. The distribution of hits about the target centre was radially symmetrical. Although take-off was wingless, rotation could be abolished in mid jump, within 10 ms, by extending the wings. This virtually guaranteed a feet-first landing. Targeting accuracy is discussed in the context of biomechanical steering mechanisms and visual control.
Distribution of 2-[125I]Iodomelatonin Binding Sites in the Brain of the Pied Flycatcher (Ficedula Hypoleuca) and the Zebra Finch (Taeniopygia Guttata)
Authors: Schneider Thomas
Published: April 2021

Using in vitro autoradiography, the distribution of 2-[125I]iodomelatonin (IMEL) binding sites in the brain of the pied flycatcher and the zebra finch was examined. The results show IMEL binding in retinofugal, tectofugal and thalamofugal brain areas of the visual system. Additionally, IMEL binding sites were detected in the ectostriatum, the thalamus, the mesencephalon and the limbic system. No IMEL binding could be demonstrated in the pineal gland, the hippocampus, the nucleus suprachiasmaticus, the visual wulst or the pituitary.
Motor Patterns for Horizontal and Upside-Down Walking and Vertical Climbing in the Locust
Authors: Duch C. , Pflüger H. J.
Published: April 2021

The motor patterns of the locust’s flexor tibiae and metathoracic subcoxal joint muscles were compared during unrestrained horizontal walking, vertical climbing and walking upside-down hanging from a branch. Combining anatomical and structural data with the results from myographic recordings revealed the role of these muscles during walking and their functional adjustments to different loads and gravity effects caused by changes in walking conditions. Motor patterns are remarkably constant during a given walking situation even at quite different walking speeds. In all walking situations, changes in step duration correlate strongly with changes in the duration of retraction but only weakly with the duration of protraction. Different motor units of one muscle can be distinguished by their spike amplitude. They may be active simultaneously or they may alternate and then fire in different phases of the step cycle. For example, during horizontal walking, the small unit of the first abductor (M125) is active during protraction and the large one during retraction. During retraction, the coxal muscles serve two functions: (1) the joint has to be brought back to the posterior extreme position by retractor muscles; (2) the joint has to be stabilized, that is held ‘stiffly’, by co-activity of functional antagonists. During protraction, it is moved to the anterior extreme position by powerful contractions of protractor muscles. The muscular activity patterns show marked differences depending on the walking situation. Some large motor units spike only sporadically during horizontal walking but burst during vertical climbing and upside-down walking (muscle M121p, the large units of muscles M126 and M120). During upside-down walking, muscles M120 and M121 and the large unit of muscle M125 are active during opposite phases of the step cycle when compared with horizontal walking and vertical climbing (for example, during walking and climbing, muscle M120 is active at the transition between retraction and protraction, whereas during upside-down walking, activity occurs during late protraction and early retraction). The results describe how motor patterns are adjusted to the different requirements of various walking situations.