bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinematics and Critical Swimming Speed of Juvenile Scalloped Hammerhead Sharks
Authors: Lowe Christopher G.
Published: April 2021

Kinematics and critical swimming speed (Ucrit) of juvenile scalloped hammerhead sharks Sphyrna lewini were measured in a Brett-type flume (635 l). Kinematic parameters were also measured in sharks swimming in a large pond for comparison with those of sharks swimming in the flume. Sharks in the flume exhibited a mean Ucrit of 65±11 cm s− (± S.D.) or 1.17±0.21 body lengths per second (L s−1), which are similar to values for other species of sharks. In both the flume and pond, tailbeat frequency (TBF) and stride length (LS) increased linearly with increases in relative swimming speed (Urel=body lengths traveled per second). In the flume, tailbeat amplitude (TBA) decreased with increasing speed whereas TBA did not change with speed in the pond. Differences in TBF and LS between sharks swimming in the flume and the pond decreased with increases in Urel. Sharks swimming at slow speeds (e.g. 0.55 L s−1) in the pond had LS 19 % longer and TBF 21 % lower than sharks in the flume at the same Urel. This implies that sharks in the flume expended more energy while swimming at comparable velocities. Comparative measurements of swimming kinematics from sharks in the pond can be used to correct for effects of the flume on shark swimming kinematics and energetics.
Size-Dependence of Water-Running Ability in Basilisk Lizards (Basiliscus Basiliscus)
Authors: Glasheen J. W. , Mcmahon T. A.
Published: April 2021

In the past, it has been proposed that basilisk lizards (Basiliscus basiliscus) are able to reach high population densities because the juveniles and adults have differing water-running abilities and therefore live in different habitats. However, there is no a priori reason to expect juveniles to be better able to run on water than adults. To determine the causal relationship between body size and water-running ability, we made three types of measurements: (1) direct morphological measurements on preserved specimens; (2) hydrodynamic measurements on physical models of the lizards’ feet; and (3) kinematic measurements on basilisk lizards running on water. The information gathered from these investigations was used to develop an allometric model which predicted the maximum upward force impulses that the lizards could generate. We find that small lizards have a capacity to generate large force surpluses. A 2 g lizard can generate a maximum upward impulse that is more than twice that needed to support its body weight (225 %). In contrast, a 200 g lizard, under optimal conditions, can just barely support its body weight (111 %).
Contralateral Sprouting and Compensatory Innervation Following the permanent Lesion of a Ganglionic Connective in the Snail
Authors: Baker Michael W. , Chiasson Bernard J. , Croll Roger P.
Published: April 2021

The fate of sprouted fibres was examined following long-term recovery from lesions to the central nervous system of the snail Achatina fulica. Axonal dye-labelling of one of the cerebrobuccal connectives (CBC), following either a cut or a crush to the opposite CBC, revealed supernumerary labelling of neuronal elements in both the cerebral and buccal ganglia in the weeks following treatment. A part of this sprouting response involved the rerouting of axonal projections from injured neurones that project contralaterally into the uninjured CBC. In addition, intracellular dye-fills, immunocytochemistry for detection of serotonin and electrophysiological measurements all revealed that a contralateral, uninjured neurone, the metacerebral giant (MCG) cell, sprouted new processes to invade the buccal ganglion denervated by the lesion. The contralateral MCG also increased synaptic drive over a neurone in the denervated buccal ganglion, a cell that normally receives strong input only from the lesioned ipsilateral MCG. After 5 weeks of recovery, morphological and electrophysiological measurements returned to normal levels in animals receiving a crush to the CBC, suggesting a retraction of sprouted projections following successful regeneration across the lesioned pathway. In contrast, the measurements indicative of sprouted fibres continued for up to 5 months when the regenerative response was prevented by cutting the CBC. Together, these results suggest that both the cessation of sprouting and the eventual retraction of sprouted fibres in Achatina fulica is contingent upon successful regeneration of the damaged axonal pathway.
Wave-Induced Forces on the Giant Kelp Macrocystis Pyrifera (Agardh): Field Test of a Computational Model
Authors: Utter Barbara D. , Denny Mark W.
Published: April 2021

We propose a hydro-mechanical numerical model that predicts the maximal tension to which stipes of the giant kelp Macrocystis pyrifera will be subjected when exposed to ocean waves. Predicted maximal tensions are close to those measured in the field. The strength of Macrocystis pyrifera stipes was measured, allowing our prediction of forces to be translated into a prediction of the fraction of stipes broken. Predicted breakage is low even for extreme storm waves, a testament to the mechanical design of individual kelp fronds. However, empirically measured rates of kelp mortality can be high, considerably higher than those predicted on the basis of hydrodynamic forces acting alone. This indicates that factors not taken into account in our model (such as holdfast dislodgment, entanglement of stipes, damage from herbivory and wave breaking) contribute substantially to mortality in Macrocystis pyrifera.
Differences in Thermal Balance, Body Temperature and Activity Between Non-Melanic and Melanic Two-Spot Ladybird Beetles (Adalia Bipunctata) Under Controlled Conditions
Authors: Jong Peter W. De , Gussekloo Sander W. S. , Brakefield Paul M.
Published: April 2021

The consequences of the elytral colour difference between non-melanic (red) and melanic (black) two-spot ladybirds for their thermal properties were studied by applying and testing a biophysical model. The expected differential effects of variation in transmission through the elytra, body size, width of the subelytral cavity, ambient temperature, radiation intensity and wind speed are described, assuming that the two colour patterns represent differences in elytral reflectance and transmittance. The model predicts a higher body temperature for melanic beetles under most conditions. Invasive temperature measurements on living beetles under ranges of specified conditions with respect to ambient temperature, radiative regime and wind speed were in qualitative agreement with the model predictions and, considering the assumptions made, closely corresponded at the quantitative level. The consequences of the temperature differences for morph activity were studied by measuring walking speeds and the time needed to become active for each morph under the various conditions. The results are consistent with the differences in body temperature, assuming an optimum curve relating performance to body temperature. The colour difference between morphs appeared to be the principal factor influencing activity.
A Novel Type of Mechanoreception By the Flagella of Chlamydomonas
Authors: Yoshimura Kenjiro
Published: April 2021

A novel type of mechanosensory mechanism is found in Chlamydomonas reinhardtii. When a cell is captured with a suction pipette and a negative pressure is applied, the cell produces repetitive Ca2+ impulses at a frequency of 0.5–1.0 Hz. The impulse frequency increases with the applied pressure. The impulses are produced when the flagella are sucked into the pipette but not when the cell body is sucked in leaving the flagella outside the pipette. Cells with short flagella produce impulses of small amplitude. Thus, the site where the cell senses mechanical stimuli and generates the impulse current must be localized at the flagella. The amplitude, shape and ion selectivity of the pressure-induced impulses are distinct from the all-or-none flagellar current that is evoked by photostimulation. The impulses are possibly produced by a combination of currents passing through mechanosensitive channels and Ca2+ channels. This response probably functions to modulate flagellar beating and thereby to regulate the behaviour of the cell.
Control of Resting Ventilation Rate in Grasshoppers
Authors: Gulinson Scotti L. , Harrison Jon F.
Published: April 2021

We examined the effect of extracellular acid–base status and tracheal gas levels on the ventilation rate of resting Romalea guttata and Schistocerca americana grasshoppers. We manipulated haemolymph pH and [HCO3- ] within normal physiological ranges using injections of HCl, NaOH, NaHCO3 and NaCl into the haemocoel. In contrast to terrestrial vertebrates, there was no evidence that extracellular acidification increases ventilation rate in grasshoppers. Elevation of haemolymph bicarbonate levels (by NaHCO3 injection) increased ventilation rate, while depression of haemolymph bicarbonate levels (HCl injection) had no effect. Injection of NaHCO3 also increased tracheal , suggesting that the effect of the NaHCO3 injection might be mediated by a sensitivity of the ventilatory system to tracheal gases. We tested for effects of tracheal gases on ventilation rate by independently manipulating tracheal and using tracheal perfusions. Ventilation rate was positively correlated with tracheal and negatively correlated with tracheal . Increasing tracheal above normal resting levels or decreasing tracheal below normal levels decreased ventilation rate. We conclude that quiescent grasshoppers regulate tracheal and by varying ventilation rate and that both and in the trachea stimulate ventilation in normal, resting grasshoppers.
The Effects of Serotonin and Dopamine on Salivary Secretion by Isolated Cockroach Salivary Glands
Authors: Just Frank , Walz Bernd
Published: April 2021

We have studied the effects of 3-hydroxytyramine (dopamine) and 5-hydroxytryptamine (serotonin) on (1) the rates of salivation from isolated salivary glands of the cockroach Periplaneta americana, (2) the protein content of the saliva, and (3) the ultrastructure of the salivary gland epithelium. The rates of neurotransmitter-induced salivation varied in a dose-dependent manner within the concentration range 10−9 to 10−4 mol l−1. Half-maximal secretory rates were induced by 6×10−7 mol l−1 serotonin and 1.1×10−7 mol l−1 dopamine. Stimulation of the glands by serotonin resulted in the production of a protein-rich saliva, whereas saliva was protein-free after stimulation by dopamine. Electron microscopic studies revealed that the central cells, which are believed to produce the proteinaceous components of the saliva, secrete their vesicular content after stimulation by 10−6 mol l−1 serotonin for 20 min. In contrast, no morphological changes could be detected after stimulation by 10−6 mol l−1 dopamine. These data indicate that dopamine stimulates only the secretion of the fluid component of the saliva, whereas serotonin is necessary to stimulate secretion of the proteinaceous components.
Measuring Leg Thrust Forces in the Common Starling
Authors: Bonser Richard H. C. , Rayner Jeremy M. V.
Published: April 2021

We describe the design of a force-transducing perch which measures the reaction forces of small birds taking off and landing. In common starlings, landing forces are lower than take-off forces, because the bird may decelerate prior to landing by using its wings. Both landing and take-off forces are significantly correlated with body mass; however, the angles of these reaction forces show no significant mass-dependence and are not repeatable within individuals. Diversity in take-off or landing strategy could be advantageous in confusing predators.
Fat Body Cells and Calcium Phosphate Spherules Induce Ice Nucleation in the Freeze-Tolerant Larvae of the Gall Fly Eurosta Solidaginis (Diptera, Tephritidae)
Authors: Mugnano John A. , Lee Richard E. , Taylor Richard T.
Published: April 2021

During the autumn, the third-instar larvae of the gall fly Eurosta solidaginis acquire freeze tolerance and their crystallization temperatures increase into the −8 to −10 °C range. Despite conflicting reports, efficient endogenous ice nucleators have not been identified in this freeze-tolerant insect. We found large crystalloid spheres within the Malpighian tubules of overwintering larvae. Energy-dispersive X-ray microanalysis and infrared spectroscopy indicated that the spherules were a hydrate of tribasic calcium phosphate. To test for ice-nucleating activity, we placed the calcium phosphate spherules in 10 μl of Schneider’s insect medium and cooled them in a refrigerated bath. The addition of spherules increased the crystallization temperature of Schneider’s medium by approximately 8 °C, from -18.4±0.8 °C to −10.1±0.9 °C (mean ± S.E.M., N=20). Ice-nucleating activity (−10.9±0.9 °C) was also demonstrated in fat body cells suspended in 10 μl of Schneider’s medium. Both calcium phosphate spherules and fat body cells have ice-nucleating activity sufficiently high to explain whole-body crystallization temperatures. Furthermore, other crystalloid deposits, commonly found in diapausing or overwintering insects, also exhibited significant ice-nucleating activity. These endogenous crystalloid deposits represent a new class of heterogeneous ice nucleators that potentially regulate supercooling and promote freeze tolerance in E. solidaginis and possibly in other overwintering insects.
Adenosine Receptor Blockade and Hypoxia-Tolerance in Rainbow Trout and Pacific Hagfish II. Effects on Plasma Catecholamines and Erythrocytes
Authors: Bernier Nicholas J. , Fuentes Juan , Randall David J.
Published: April 2021

The purpose of this study was to examine the role of adenosine receptors (ARs) in (1) the regulation of catecholamine secretion and (2) the modulation of blood oxygen capacitance by catecholamines. To this end, we assessed the response of rainbow trout and Pacific hagfish treated with either an AR blocker, theophylline, or saline under hypoxic and normoxic conditions. Compared with the control hypoxic rainbow trout, AR blockade resulted in a smaller increase in haematocrit and haemoglobin (Hb) concentration of the blood, smaller red blood cell transmembrane pH differences and mean cellular [Hb] (MCHC), as well as a 16-fold higher plasma adrenaline concentration after only 10 min of acute hypoxic exposure.

In hypoxic hagfish, AR blockade had no effect on the [Hb] of the blood, and there was no regulation of red blood cell pH or changes in MCHC. However, whereas plasma [adrenaline] did not change following exposure to a of 1.33 kPa in the hypoxic sham group, the concentration increased 3.8-fold within 10 min in the theophylline-injected group. These results suggest that adenosine modulates the circulating level of catecholamines in both hypoxic rainbow trout and hypoxic Pacific hagfish.
Sensory Control Mechanisms of the Uropod Equilibrium Reflex During Walking in the Crayfish Procambarus Clarkii
Authors: Murayama Maki , Takahata Masakazu
Published: April 2021

The temporal characteristics of statocyst and leg proprioceptive inputs to the uropod motor system were investigated in crayfish using behavioural and electromyographic analyses to elucidate their functional roles in the control of the uropod steering response under natural conditions. When the animal, which was suspended in the air without a footboard, was actively extending its abdomen, prolonged stimulation of the statocysts by body rolling elicited a maintained asymmetrical configuration of the bilateral uropods. Prolonged stimulation of the walking legs by footboard tilting with the animal body held in the upright position elicited a transient uropod response. When the treadmill was tilted while the animal was walking on it in the upright position, the uropods showed the same transient response. However, when the animal body was rolled, together with the treadmill, while the animal was walking on it, the uropods showed a transient response which was reversed in direction compared with that observed during body rolling without a footboard. This transient response was abolished by the removal of the statoliths. The results show that the statocysts and leg proprioceptors exert sustained and transient control effects, respectively, on the uropod motor system during walking. It is also suggested that the uropod response to body rolling during walking is controlled primarily by leg proprioceptor signals which result from statocyst-induced changes in the leg position.
Efficiency of Uphill Locomotion in Nocturnal and Diurnal Lizards
Authors: Farley C. T. , Emshwiller M.
Published: April 2021

Nocturnal geckos can walk on level ground more economically than diurnal lizards. One hypothesis for why nocturnal geckos have a low cost of locomotion is that they can perform mechanical work during locomotion more efficiently than other lizards. To test this hypothesis, we compared the efficiency of the nocturnal gecko Coleonyx variegatus (average body mass 4.2 g) and the diurnal skink Eumeces skiltonianus (average body mass 4.8 g) when they performed vertical work during uphill locomotion. We measured the rate of oxygen consumption when each species walked on the level and up a 50 ˚ slope over a range of speeds. For Coleonyx variegatus, the energetic cost of traveling a unit distance (the minimum cost of transport, Cmin) increased from 1.5 to 2.7 ml O2 kg−1 m−1 between level and uphill locomotion. For Eumeces skiltonianus, Cmin increased from 2.5 to 4.7 ml O2 kg−1 m−1 between level and uphill locomotion. By taking the difference between Cmin for level and uphill locomotion, we found that the efficiency of performing vertical work during locomotion was 37 % for Coleonyx variegatus and 19 % for Eumeces skiltonianus. The similarity between the 1.9-fold difference in vertical efficiency and the 1.7-fold difference in the cost of transport on level ground is consistent with the hypothesis that nocturnal geckos have a lower cost of locomotion than other lizards because they can perform mechanical work during locomotion more efficiently.
Peripheral Control of the Gain of a Central Synaptic Connection Between Antagonistic Motor Neurones in the Locust
Authors: Jellema T. , Heitler W. J.
Published: April 2021

The metathoracic fast extensor tibiae (FETi) motor neurone of locusts is unusual amongst insect motor neurones because it makes output connections within the central nervous system as well as in the periphery. It makes excitatory chemical synaptic connections to most if not all of the antagonist flexor tibiae motor neurones. The gain of the FETi–flexor connection is dependent on the peripheral conditions at the time of the FETi spike. This dependency has two aspects. First, sensory input resulting from the extensor muscle contraction can sum with the central excitatory postsynaptic potential (EPSP) to augment its falling phase if the tibia is restrained in the flexed position (initiating a tension-dependent reflex) or is free to extend (initiating a movement-dependent resistance reflex). This effect is thus due to simple postsynaptic summation of the central EPSP with peripheral sensory input. Second, the static tibial position at the time of the FETi spike can change the amplitude of the central EPSP, in the absence of any extensor muscle contraction. The EPSP can be up to 30 % greater in amplitude if FETi spikes with the tibia held flexed rather than extended. The primary sense organ mediating this effect is the femoral chordotonal organ. Evidence is presented suggesting that the mechanism underlying this change in gain may be specifically localised to the FETi–flexor connection, rather than being due to general position-dependent sensory feedback summing with the EPSP. The change in the amplitude of the central EPSP is probably not caused by general postsynaptic summation with tonic sensory input, since a diminution in the amplitude of the central EPSP caused by tibial extension is often accompanied by overall tonic excitation of the flexor motor neurone. Small but significant changes in the peak amplitude of the FETi spike have a positive correlation with changes in the EPSP amplitude, suggesting a likely presynaptic component to the mechanism of gain control. The change in amplitude of the EPSP can alter its effectiveness in producing flexor motor output and, thus, has functional significance. The change serves to augment the effectiveness of the FETi–flexor connection when the tibia is fully flexed, and thus to increase its adaptive advantage during the co-contraction preceding a jump or kick, and to reduce the effectiveness of the connection when the tibia is partially or fully extended, and thus to reduce its potentially maladaptive consequences during voluntary extension movements such as thrusting.
Characterization of a Basolateral Electroneutral Na+/H+ Antiporter in Atlantic Lobster (Homarus Americanus) Hepatopancreatic Epithelial Vesicles
Authors: Duerr Jeffrey M. , Ahearn Gregory A.
Published: April 2021

Purified basolateral membrane vesicles (BLMVs) were prepared from Atlantic lobster (Homarus americanus) hepatopancreas using a Percoll density gradient technique. Enrichments of the Na+/K+-ATPase and alkaline phosphatase activities of these vesicles were 15.4-and 1.2-fold, respectively. The presence of amiloride-sensitive Na+/H+ exchange was demonstrated. Contrary to electrogenic 2Na+/1H+ exchange on apical membranes from the same tissue, kinetic studies of Na+ transport by these basolateral membranes indicate an electroneutral antiport with a Km of 28±1.7 mmol l−1 and a Jmax of 1.74±0.13 μmol mg−1 min−1. Amiloride interacted at a single binding site (Ki=39 μmol l−1) and external Li+ was shown to be an effective competitive inhibitor of the exchange process (Ki=493 μmol l−1). The presence of a membrane-potential-sensitive, Na+-accepting ion channel was also demonstrated. The basolateral Na+/H+ exchanger physiologically resembles members of the NHE family of Na+/H+ antiporters described in vertebrates and departs from the apical electrogenic system previously described in lobster. Whether or not the basolateral Na+/H+ antiporter is an NHE isoform remains to be determined.
Interneurones Involved in Stridulatory Pattern Generation in the Grasshopper Chorthippus Mollis (CHARP.)
Authors: Ocker W.-G. , Hedwig B.
Published: April 2021

In tethered grasshoppers, Chorthippus mollis, stridulatory leg movements were elicited by d.c. brain stimulation. Stridulatory chirps comprise both slow up-and-down movements and rapid oscillations of the hindlegs. Intracellular recording, stimulation and staining of interneurones within the metathoracic ganglion complex were performed simultaneously with recordings of leg movement.

Five interneurones were identified in the metathoracic ganglion complex. The branching patterns of these interneurones were typical of stridulatory interneurones. Three of these neurones had a structure very similar to stridulatory interneurones already characterized in the species Omocestus viridulus.

During stridulation, the spike activity of all interneurones was phasically coupled to the chirp rhythm; two interneurones additionally exhibited coupling to the rapid leg oscillations. Intracellular stimulation of interneurones A1-AC-2 and A1-AI-1 prolonged the duration of the rapid leg oscillations and influenced the generation of the chirp rhythm. Interneurones T3-LI-2 and T3-LC-4 decreased the amplitude of the slow up-and-down movement.

The data indicate that at least part of the metathoracic stridulatory network of C. mollis is organized in a structurally and functionally similar way to that of O. viridulus.
Maximum Cardiac Performance of Rainbow Trout (Oncorhynchus Mykiss) at Temperatures Approaching Their Upper Lethal Limit
Authors: Farrell A. P. , Gamperl A. K. , Hicks J. M. T. , Shiels H. A. , Jain K. E.
Published: April 2021

Numerous studies have examined the effect of temperature on in vivo and in situ cardiovascular function in trout. However, little information exists on cardiac function at temperatures near the trout’s upper lethal limit. This study measured routine and maximum in situ cardiac performance in rainbow trout (Oncorhynchus mykiss) following acclimation to 15, 18 and 22 °C, under conditions of tonic (30 nmol l-1), intermediate (60 nmol l-1) and maximal (200 nmol l-1) adrenergic stimulation. Heart rate increased significantly with both temperature and adrenaline concentration. The Q10 values for heart rate ranged from 1.28 at 30 nmol l-1 adrenaline to 1.36 at 200 nmol l-1 adrenaline. In contrast to heart rate, maximum stroke volume declined by approximately 20 % (from 1.0 to 0.8 ml kg-1) as temperature increased from 15 to 22 °C. This decrease was not alleviated by maximally stimulating the heart with 200 nmol l-1 adrenaline. Because of the equal and opposite effects of increasing temperature on heart rate and stroke volume, maximum cardiac output did not increase between 15 and 22 °C. Maximum power output decreased (by approximately 10–15 %) at all adrenaline concentrations as temperature increased. This reduction reflected a poorer pressure-generating ability at temperatures above 15 °C. These results, in combination with earlier work, suggest (1) that peak cardiac performance occurs around the trout’s preferred temperature and well below its upper lethal limit; (2) that the diminished cardiac function concomitant with acclimation to high temperatures was associated with inotropic failure; (3) that Q10 values for cardiac rate functions, other than heart rate per se, have a limited predictive value at temperatures above the trout’s preferred temperature; and (4) that heart rate is a poor indicator of cardiac function at temperatures above 15 °C.
The Uptake and Release of Serotonin and Dopamine Associated With Locust (Locusta Migratoria) Salivary Glands
Authors: Ali Declan W. , Orchard Ian
Published: April 2021

The uptake and release characteristics of dopamine and serotonin in the salivary glands of the locust Locusta migratoria were examined. Cyclic AMP levels were determined in salivary glands in which the salivary nerve was stimulated under different experimental paradigms. Stimulation of the salivary nerve leads to time-and frequency-dependent elevations of cyclic AMP levels in the glands. The potent and specific D1 receptor antagonist SCH-23390 is capable of partially inhibiting the electrophysiologically induced elevations of cyclic AMP levels. The salivary glands appear to possess uptake transporters for serotonin and dopamine. [3H]serotonin uptake is Na+-dependent and is composed of high-and low-affinity components. [3H]dopamine uptake is Na+-independent and can be partially reduced by a challenge with high-K+ saline and by a challenge with ice-cold saline. Uptake inhibitors are capable of blocking the uptake of radiolabelled serotonin and dopamine. There is a Ca2+-dependent efflux of [3H]serotonin and [3H]dopamine from previously loaded salivary glands in response to stimulation of the salivary nerve and to treatment with a high-K+ saline.
Mechanical Design of Mussel Byssus: Material Yield Enhances Attachment Strength
Authors: Bell Emily C. , Gosline John M.
Published: April 2021

The competitive dominance of mussels in the wave-swept rocky intertidal zone is in part due to their ability to maintain a secure attachment. Mussels are tethered to the substratum by a byssus composed of numerous extracellular, collagenous threads secreted by the foot. Each byssal thread has three serially arranged parts: a corrugated proximal region, a smooth distal region and an adhesive plaque. This study examines the material and structural properties of the byssal threads of three mussel species: Mytilus californianus, M. trossulus, and M. galloprovincialis. Tensile tests in general reveal similar material properties among species: the proximal region has a lower initial modulus, a lower ultimate stress and a higher ultimate strain than the distal region. The distal region also yields at a stress well below its ultimate value. In whole thread tests, the proximal region and adhesive plaque are common sites of structural failure and are closely matched in strength, while the distal region appears to be excessively strong. We propose that the high strength of the distal region is the byproduct of a material designed to yield and extend before structural failure occurs. Experimental and theoretical evidence is presented suggesting that thread yield and extensibility provide two important mechanisms for increasing the overall attachment strength of the mussel: (1) the reorientation of threads towards the direction of applied load, and (2) the ‘recruitment’ of more threads into tension and the consequent distribution of applied load over a larger cross-sectional area, thereby reducing the stress on each thread. This distal region yield behavior is most striking for M. californianus and may be a key to its success in extreme wave-swept environments.
Dynamics of cyclic GMP levels in identified neurones during ecdysis behaviour in the locust Locusta migratoria
Authors: Truman James W. , Ewer John , Ball Eldon E.
Published: April 2021

A grasshopper hatches from its egg, which is laid in soil, as a vermiform larva. This larva continues the stereotyped hatching behaviour as it digs through the egg pod, which provides a passageway to the soil surface. Once at the surface, shedding, or ecdysis, of the vermiform cuticle is initiated. When this process is complete, the first-instar cuticle is expanded to assume the form of the first-instar hopper. We have demonstrated, using immunocytochemical techniques, that these behaviour patterns are associated with dramatic increases in intracellular levels of cyclic GMP in sets of identified neurones in the ventral central nervous system.

The most prominent cyclic-GMP-expressing cells are 34 neurones that appear to contain crustacean cardioactive peptide (CCAP). These CCAP cells show no detectable cyclic GMP at hatching or while the vermiform larva digs through the soil. Upon reaching the surface and freeing itself, the larva initiates ecdysis and associated air-swallowing and tracheal filling within about 1 min. These changes are immediately preceded by the appearance of cyclic GMP in the CCAP cells. Cyclic GMP levels in these neurones peak by 5 min and then decline back to basal levels by 20–30 min. Conditions that cause ecdysing animals to resume digging prolong the elevation of cyclic GMP levels. Once animals have assumed their ‘hopper’ form, however, external stimuli can no longer affect the time course of the cyclic GMP response. The neurones containing elevated cyclic GMP levels probably influence the air-swallowing, tracheal filling and circulatory changes that are associated with ecdysis behaviour.

Pairs of descending midline neurones in abdominal segments 2–4 also become cyclic-GMP-immunoreactive, but they show peak expression after cyclic GMP levels in the CCAP cells have declined. Also, neurones in the caudolateral region of the abdominal ganglia often become cyclic-GMP-immunoreactive when ecdysing animals are forced to resume digging for an extended period.
Seasonal Temperature Acclimatisation of Rainbow Trout: Cardiovascular and Morphometric Influences on Maximal Sustainable Exercise Level
Authors: Taylor S. E. , Egginton S. , Taylor E. W.
Published: April 2021

Adult rainbow trout (mass 600–1500 g; length 40–44 cm) were held in the laboratory for up to 28 days at seasonally appropriate temperatures. The maximal sustainable aerobic exercise level (involving slow-twitch muscle activity alone) was determined by following muscle recruitment patterns using electromyography. The mean (± S.E.M.) speeds recorded for maximal sustainable aerobic exercise were 0.52±0.02, 0.81±0.06 and 0.39±0.02 BL s−1 (body lengths per second) for animals swimming at their acclimatisation temperatures of 4, 11 and 18 °C, respectively. Thus, fish acclimatised to 11 °C reached the highest maximal sustainable (purely aerobic) levels of exercise. They had similar stride lengths to the 4 °C animals, but generated less thrust per stride, as indicated by increased tail-beat frequency. Acclimatisation to 4 °C led to an increased mass of slow muscle and more effective tail beats (greater stride length at lower frequencies), relative to animals at higher temperatures. Fish acclimatised to 18 °C had the lowest stride length and a reduced aerobic swimming capacity.

Sustainable levels of aerobic exercise were reflected in unchanged values for mean heart rate and arterial blood pressure between rest and imposed, graded exercise. Radiolabelled m.icrospheres were used to determine cardiac output and regional blood flow distribution simultaneously in fish, both at rest and while swimming, for each acclimatisation temperature. Fish acclima.tised to 11 °C had the greatest scope for increasing . This resulted in a significant hyperaemia in slow muscle upon exercise (10-fold increase), without an a.ctive redistribution of flow from other tissues. Maximum at 18 °C did not d.iffer significantly from that at 11 °C but, because resting was higher, the scope was reduced and was similar to that found at 4 °C. Specific blood flow to the active muscle was also reduced and this, together with decreased blood oxygen content and reduced slow muscle mass, may limit aerobic swimming performance at 18 °C.
The Peripheral Auditory Characteristics of Noctuid Moths: Information Encoding and Endogenous Noise
Authors: Waters Dean A.
Published: April 2021

The ability of the noctuid A1 cell acoustic receptor to encode biologically relevant information from bat echolocation calls is examined. Short-duration stimuli (less than approximately 6 ms) reduce the dynamic resolution of the receptor, making intensity, and hence range, estimates of foraging bats unreliable. This low dynamic range is further reduced by inaccurate encoding of stimulus intensity, reducing the real dynamic range of the A1 cell to 1 bit at stimulus durations below 3.1 ms. Interspike interval is also an unreliable measure of stimulus intensity at low stimulus levels and/or for short-duration stimuli. The quantity of information encoded per stimulus is reduced as the presentation rate of stimuli is increased. The spontaneous generation of A1 cell action potentials may reduce the ability of the moth to discriminate bat from non-bat signals. Even with a recognition criterion of three A1 cell spikes per call, the moth would regularly make wrong decisions about a bat being present in the immediate environment. Removing this noise would necessitate a considerable loss of information through filtering at the interneurone level. It is proposed that, for bats using short-duration calls, the moth would only be able to recognise an approaching bat from the repetitious nature of the incoming signal.
Active and Electrogenic Absorption of Na+ and Cl− Across Posterior Gills of Eriocheir Sinensis: Influence of Short-Term Osmotic Variations
Authors: Onken Horst
Published: April 2021

Split lamellae of posterior gills of Chinese crabs (Eriocheir sinensis) acclimated to fresh water were mounted in a modified Ussing-type chamber, and the transepithelial short-circuit current and conductance were measured. The epithelium shows independent active and electrogenic absorption mechanisms for Na+ and Cl− that can be measured as positive and negative short-circuit currents, respectively, in the absence of the counter ion. Increasing the osmolarity of the haemolymph-side saline by addition of sucrose resulted in a marked decrease in active uptake of both Na+ and Cl−. In contrast, increasing the internal osmolarity by addition of urea or moderately decreasing the haemolymph-side osmolarity resulted in a marked increase in Na+ as well as Cl− transport. Circuit analysis revealed that Na+ current changes are mostly due to alterations in the apical amiloride-sensitive Na+ conductance, while Cl− current changes are caused not only by alterations in the transcellular conductance but also by changes in the electromotive force for Cl− absorption. Osmotic perturbations in the external bath induced current changes in the same directions, but the magnitudes of the effects were smaller than those after internal osmotic variations, indicating that the external barrier has a lower water permeability than the internal barrier. Short-term osmotic perturbations did not significantly affect the leak conductance, which is not associated with active transport and which may mostly reflect the paracellular conductance.
Squid (Lolliguncula Brevis) Life in Shallow Waters: Oxygen Limitation of Metabolism and Swimming Performance
Authors: Finke E. , Pörtner H. O. , Lee P. G. , Webber D. M.
Published: April 2021

Squid (Lolliguncula brevis) were exercised in a tunnel respirometer during a stepwise increase in water velocity in order to evaluate the anaerobic threshold, i.e. the critical swimming speed above which anaerobic metabolism contributes to energy production. The average anaerobic threshold was found at speeds of 1.5–2 mantle lengths s−1. Above this velocity, α-glycerophosphate, succinate and octopine started to accumulate in the mantle tissue. ATP levels fell and phospho-L-arginine was progressively depleted, while the levels of glucose 6-phosphate and inorganic phosphate rose. The finding of a simultaneous onset of anaerobic metabolism in the cytosol and the mitochondria indicates that a limited oxygen supply to the mitochondria elicits anaerobic energy production. This finding is opposite to the situation found in many other vertebrate and invertebrate species, in which energy requirements in excess of aerobic energy production are covered by anaerobic metabolism, with mitochondria remaining aerobic. In L. brevis, swimming at higher speeds is associated with a small factorial increase in metabolic rate based on a high resting rate of oxygen consumption. Pressure recordings in the mantle cavity support this finding, indicating a high basal level of spontaneous activity at rest and a small rise in mean pressure at higher swimming velocity. Bursts of higher pressures from the jet support elevated swimming speeds and may explain the early transition to anaerobic energy production which occurs when pressure amplitudes exceed 1.2–1.5 kPa or when mean pressure rises above 0.22–0.25 kPa.

The finding of mitochondrial hypoxia at a low critical speed in these squid is interpreted to be related to their life in shallow coastal and bay waters, which limits the necessity to maintain high swimming velocities. At increased swimming velocities, the animals oscillate between periods of high and low muscular activity. This behaviour is interpreted to reduce transport cost and to permit a longer-term net use of anaerobic resources when speed exceeds the critical value or when the squid dive into hypoxic waters. The simultaneous onset of anaerobic metabolism in the cytosol and the mitochondria emphasizes that squid generally make maximal use of available oxygen under resting conditions, when their energy requirements are the highest among marine invertebrates.
Pharmacological Properties of Voltage-Gated Na+ Currents in Motor Neurones from a Hydrozoan Jellyfish Polyorchis Penicillatus
Authors: Spafford J. David , Grigoriev Nikita G. , Spencer Andrew N.
Published: April 2021

The Na+ current of ‘swimming motor neurones’ in the hydromedusan Polyorchis penicillatus was tetrodotoxin-insensitive. The local anaesthetics lidocaine and procainamide caused partial, non use-dependent blockade of the Na+ channel. Veratridine produced partial blockade of the Na+ channel without affecting inactivation. An order of blocking potency of di- and trivalent cations was established as: La3+ = Zn2+ = Cd2+ > Ni2+ > Mn2+ = Co2+ > Ca2+ > Ba2+ > Mg2+. All these cations, except Ba2+, produced depolarizing shifts in the conductance–voltage curves. Even at relatively high concentrations, the dihydropyridines nicardipine, nitrendipine and (+)Bay K 8644 produced only weak blockade of the Na+ current; while nimodipine, nifedipine and (−)Bay K 8644 were ineffective. Diltiazem and verapamil weakly blocked the Na+ current in a dose-dependent manner with no evidence of use-dependence. The calmodulin inhibitors W7 and calmidazolium were ineffective blockers of Na+ currents. Crude Conus venoms and the Conus peptides, μ-conotoxin GIIA, μO-conotoxin MrVIA, w-conotoxin GVIA and ω-conotoxin MVIIC, were without effect. Capsaicin produced rapid, reversable blockade of Na+ current.

It has been suggested that ‘primitive’ Na+ channels could be expected to have pharmacological properties that are intermediate between those of Na+ and Ca2+ channels. If such channels exist, the Na+ channel described here is clearly not one of them.
Temporal and Spatial Distribution of V-ATPase and its mRNA in the Midgut of Moulting Manduca Sexta
Authors: Jäger Dieter , Novak Frans J. S. , Harvey William R. , Wieczorek Helmut , Klein Ulla
Published: April 2021

The spatial and temporal distribution of the plasma membrane V-ATPase and its encoding mRNA in the midgut of Manduca sexta were investigated during the moult from the fourth to the fifth larval instar. Digoxigenin-labelled RNA probes were used for in situ hybridization of V-ATPase mRNA of both peripheral and integrated subunits; monoclonal antibodies to subunits of the peripheral sector of the purified plasma membrane V-ATPase were used for immunocytochemistry. Extensive mRNA labelling was found in both mature columnar and goblet cells of intermoult and moulting larvae. Hybridization screening in several tissues suggested that only cells with increased V-ATPase biosynthesis were labelled by our hybridization method. Mature goblet cells contain a large amount of V-ATPase in the apical plasma membrane and were therefore expected to contain V-ATPase mRNA. The intense mRNA signal found in mature columnar cells was unexpected. However, after refining the techniques of tissue preparation, immunolabelling in apical blebs of columnar cells was demonstrated. Since this immunoreactivity did not appear to be membrane-associated, it suggested a cytosolic localization of peripheral V1 subunits. The mRNA encoding subunit A of the peripheral V1 sector was distributed unevenly in columnar cells with a strong apical preference, whereas the mRNA for the proteolipid of the integral V0 sector was evenly distributed in the cytosol. This spatial pattern reflected the distribution of free ribosomes and rough endoplasmic reticulum in the cell, supporting the view that V1 subunits are synthesized at free ribosomes, whereas the V0 subunits are synthesized at the rough endoplasmic reticulum. All undifferentiated cells exhibited intense mRNA signals for V-ATPase subunits of both holoenzyme sectors from the start of proliferation and thus precursors of columnar and goblet cells could not be distinguished.
Stimulation Of Ciliary Beat Frequency By Serotonin Is Mediated By A Ca2+ Influx In Ciliated Cells Of Helisoma Trivolvis Embryos
Authors: Christopher Kimberley J. , Chang John P. , Goldberg Jeffrey I.
Published: April 2021

Serotonin (5-HT) has been established as a regulator of ciliary beating in numerous systems. In early embryos of Helisoma trivolvis, a cilia-driven rotational movement is modulated by the release of endogenous serotonin from a pair of embryonic neurons, ENC1s, directly onto the ciliated epithelium. The present study was undertaken to examine the signal transduction mechanisms underlying serotonin-mediated cilio-excitation in Helisoma trivolvis embryos. Using time-lapse videomicroscopy, the ciliary beat frequency (CBF) of cultured embryonic ciliated cells was measured in response to various pharmacological manipulations. Serotonin increased CBF in a dose-dependent manner. Addition of 8-bromo-cyclic AMP, isobutylmethylxanthine (IBMX) or a combination of forskolin and IBMX, treatments that elevate the concentration of intracellular cyclic AMP, did not mimic the serotonin-induced increase in CBF. Thus, cyclic AMP does not appear to be involved in the regulation of CBF in this system. In contrast, depolarizing the cells with KCl or veratridine, and artificially raising the intracellular Ca2+ concentration with thapsigargin or A23187, caused a serotonin-like increase in CBF. Furthermore, the serotonin response was abolished in a Ca2+-depleted medium or in a medium containing the L-type Ca2+ channel blockers verapamil or nifedipine. These results suggest that serotonin-stimulated cilio-excitation in cultured Helisoma trivolvis cells involves an influx of Ca2+ to increase intracellular Ca2+ concentration. The link between serotonin–receptor binding and Ca2+ influx in these cells has yet to be determined.
The Metamorphosis of Feeding Kinematics in Salamandra Salamandra and the Evolution of Terrestrial Feeding Behavior
Authors: Reilly Stephen M.
Published: April 2021

The striking similarity between aquatic feeding behaviors in fishes and tetrapods and terrestrial prey transports in tetrapods and their contrasts to terrestrial tongue projection kinematics have led to a general hypothesis that terrestrial prey capture evolved from terrestrial prey transport, which, in turn, evolved from aquatic feeding behavior. This hypothesis is examined in Salamandra salamandra by comparing the kinematics of prey capture and transport before and after metamorphosis in the same group of eight individuals. Kinematics of aquatic and terrestrial strikes and transports are used to describe the metamorphosis of feeding behavior in S. salamandra and provide the first kinematic description of both aquatic and terrestrial feeding behaviors in the family Salamandridae. On the basis of the shared characteristics among the four behaviors, the two aquatic behaviors are most similar, and these are more similar to terrestrial transports than to terrestrial strikes. Given the ontogenetic polarity of these behaviors in salamanders, I suggest, on the basis of the shared similarities and functional shifts, that terrestrial transport is an intermediate behavior between aquatic feeding and terrestrial tongue projection. These results support the hypothesis that a shift from aquatic feeding to terrestrial transport to terrestrial tongue projection represents an evolutionary transformation series in the evolution of terrestrial feeding in early tetrapods.
Elastic and Length–Force Characteristics of the Gastrocnemius of the Hopping Mouse (Notomys Alexis) and the Rat (Rattus Norvegicus)
Authors: Ettema G. J. C.
Published: April 2021

The aim of this study was to compare the contractile and series elastic properties of terrestrial mammals that use bipedal versus quadrupedal gaits. The gastrocnemius muscle of the hopping mouse (body mass 30.2±2.4 g, mean ± S.D.) and the rat (313±10.7 g) were compared with data from the literature for the wallaby and the kangaroo rat to distinguish scaling effects and locomotion-related effects on muscle properties. Contractile length–force properties and series elastic stiffness were measured in situ during maximal tetanic contractions.

The rat had a larger muscle-fibre-to-tendon-length ratio. The rat and hopping mouse showed similar normalised length–force characteristics of the gastrocnemius. Normalised stiffness in the hopping mouse was higher. The hopping mouse showed a higher capacity to store elastic energy per unit of contractile work capacity, as well as per unit of body mass.

Accounting for body size differences, the rat had a smaller relative muscle mass and thus smaller work capacity than the three hopping animals considered. This is in agreement with a quadrupedal versus bipedal locomotion style.

The differences in contractile and elastic properties of the gastrocnemius of the rat and hopping mouse seem to be closely related to locomotion patterns. Small animals seem to be able to utilise the storage and release of elastic energy to a far lesser extent than larger animals. However, even in animals as small as hopping mice, the storage and utilisation of elastic energy during locomotion is of functional significance and probably depends on locomotor behaviour.