bluuebunny/crossref_metadata_2025 huggingface dataset:
Similarity in Flight Behaviour Between the Honeybee Apis Mellifera (Hymenoptera: Apidae) and its Presumed Mimic, the Dronefly Eristalis Tenax (Diptera: Syrphidae)
Authors: Golding Yvonne C. , Ennos A. Roland , Edmunds Malcolm
Published: April 2021

It is generally accepted that the dronefly Eristalis tenax is a Batesian mimic of the honeybee Apis mellifera. Previous work has established that the foraging behaviour of droneflies is more similar to that of its model than to that of other more closely related flies, suggesting that behaviour may be important in the mimicry. Locomotor mimicry has been demonstrated in mimetic Heliconius butterflies but not in hoverflies. This study therefore investigated aspects of the flight behaviour of Eristalis tenax, Apis mellifera and two other flies, Syrphus ribesii and a Musca sp. Insects were filmed foraging on Helichrysum bracteum flowers, and flight sequences were analysed to determine flight velocities, flight trajectories and the percentage of time spent hovering. It was found that the flight behaviour of droneflies was more similar to that of honeybees than to that of the other flies. This suggests that the flight behaviour of Eristalis tenax may be mimetic.
Muscle tissue adaptations to hypoxia
Authors: Hoppeler Hans , Vogt Michael
Published: April 2021

This review reports on the effects of hypoxia on human skeletal muscle tissue. It was hypothesized in early reports that chronic hypoxia, as the main physiological stress during exposure to altitude, per se might positively affect muscle oxidative capacity and capillarity. However, it is now established that sustained exposure to severe hypoxia has detrimental effects on muscle structure. Short-term effects on skeletal muscle structure can readily be observed after 2 months of acute exposure of lowlanders to severe hypoxia, e.g. during typical mountaineering expeditions to the Himalayas. The full range of phenotypic malleability of muscle tissue is demonstrated in people living permanently at high altitude (e.g. at La Paz, 3600–4000m). In addition, there is some evidence for genetic adaptations to hypoxia in high-altitude populations such as Tibetans and Quechuas, who have been exposed to altitudes in excess of 3500m for thousands of generations. The hallmark of muscle adaptation to hypoxia in all these cases is a decrease in muscle oxidative capacity concomitant with a decrease in aerobic work capacity. It is thought that local tissue hypoxia is an important adaptive stress for muscle tissue in exercise training, so these results seem contra-intuitive. Studies have therefore been conducted in which subjects were exposed to hypoxia only during exercise sessions. In this situation, the potentially negative effects of permanent hypoxic exposure and other confounding variables related to exposure to high altitude could be avoided. Training in hypoxia results, at the molecular level, in an upregulation of the regulatory subunit of hypoxia-inducible factor-1 (HIF-1). Possibly as a consequence of this upregulation of HIF-1, the levels mRNAs for myoglobin, for vascular endothelial growth factor and for glycolytic enzymes, such as phosphofructokinase, together with mitochondrial and capillary densities, increased in a hypoxia-dependent manner. Functional analyses revealed positive effects on V̇O2max (when measured at altitude) on maximal power output and on lean body mass. In addition to the positive effects of hypoxia training on athletic performance, there is some recent indication that hypoxia training has a positive effect on the risk factors for cardiovascular disease.
Mechanisms of cell survival in hypoxia and hypothermia
Authors: Boutilier R. G.
Published: April 2021

Most animals experience some degree of hypoxia and hypothermia during the course of their natural life history either as a consequence of ambient ‘exposure’ per se or through metabolic, respiratory and/or circulatory insufficiency. A prevailing experimental approach has been to probe tissues from natural models of hypoxia-tolerant and cold-tolerant vertebrates to look for common mechanisms of defence against O2 lack and hypothermia. The ability to sustain vital cellular functions in severe cases of either condition varies widely amongst the vertebrates. Like humans, the vast majority of mammals are unable to survive prolonged periods of hypothermia or O2 deprivation owing to irreversible membrane damage and loss of cellular ion homeostasis in vital organs such as the brain and heart. However, numerous hibernating endotherms, neonatal and diving mammals as well as many ectotherms can tolerate prolonged periods that would, in clinical terms, be called asphyxia or deep hypothermia. The key to their survival under such conditions lies in an inherent ability to downregulate their cellular metabolic rate to new hypometabolic steady states in a way that balances the ATP demand and ATP supply pathways.
Limits to sustainable human metabolic rate
Authors: Westerterp Klaas R.
Published: April 2021

There is a limit to the performance of an organism set by energy intake and energy mobilization. Here, the focus is on humans with unlimited access to food and for whom physical activity can be limited by energy mobilization. The physical activity level (PAL) in the general population, calculated as doubly-labelled-water-assessed average daily metabolic rate as a multiple of basal metabolic rate, has an upper limit of 2.2–2.5. The upper limit of sustainable metabolic rate is approximately twice as high in endurance athletes, mainly because of long-term exercise training with simultaneous consumption of carbohydrate-rich food during exercise. Endurance athletes have an increased fat-free mass and can maintain energy balance at a PAL value of 4.0–5.0. High altitude limits exercise performance as a result of combined effects on nutrient supply and the capacity to process nutrients. Thus, trained subjects climbing Mount Everest reached PAL values of 2.0–2.7, well below the observed upper limit at sea level.
Human aerobic performance: too much ado about limits to V̇O2
Authors: Lindstedt S. L. , Conley K. E.
Published: April 2021

Human endurance performance is often evaluated on the basis of the maximal rate of oxygen uptake during exercise (V̇O2max). Methods for overcoming limits to V̇O2max are touted as means for increasing athletic endurance performance. Here, we argue that the respiratory system is well designed for delivering O2 to meet O2 demands and that no single factor is rate-determining for O2 uptake. We show that V̇O2max can vary 5000-fold among mammals, while any limitation to O2 delivery by a single component of the respiratory system affects V̇O2max by 10% or less. Attempts to increase O2 delivery by enhancing one step in the respiratory system are shown to have little effect. Blood doping, hyperoxia and O2 supplementation of high-altitude natives all raise O2 availability substantially to the working muscles, but these treatments increase V̇O2max only minimally. Finally, we argue that O2 uptake is only one of a number of properties important to human aerobic performance.
Functional and structural adaptations of skeletal muscle to microgravity
Authors: Fitts Robert H. , Riley Danny R. , Widrick Jeffrey J.
Published: April 2021

Our purpose is to summarize the major effects of space travel on skeletal muscle with particular emphasis on factors that alter function. The primary deleterious changes are muscle atrophy and the associated decline in peak force and power. Studies on both rats and humans demonstrate a rapid loss of cell mass with microgravity. In rats, a reduction in muscle mass of up to 37% was observed within 1 week. For both species, the antigravity soleus muscle showed greater atrophy than the fast-twitch gastrocnemius. However, in the rat, the slow type I fibers atrophied more than the fast type II fibers, while in humans, the fast type II fibers were at least as susceptible to space-induced atrophy as the slow fiber type. Space flight also resulted in a significant decline in peak force. For example, the maximal voluntary contraction of the human plantar flexor muscles declined by 20–48% following 6 months in space, while a 21% decline in the peak force of the soleus type I fibers was observed after a 17-day shuttle flight. The reduced force can be attributed both to muscle atrophy and to a selective loss of contractile protein. The former was the primary cause because, when force was expressed per cross-sectional area (kNm−2), the human fast type II and slow type I fibers of the soleus showed no change and a 4% decrease in force, respectively. Microgravity has been shown to increase the shortening velocity of the plantar flexors. This increase can be attributed both to an elevated maximal shortening velocity (V0) of the individual slow and fast fibers and to an increased expression of fibers containing fast myosin. Although the cause of the former is unknown, it might result from the selective loss of the thin filament actin and an associated decline in the internal drag during cross-bridge cycling. Despite the increase in fiber V0, peak power of the slow type I fiber was reduced following space flight. The decreased power was a direct result of the reduced force caused by the fiber atrophy. In addition to fiber atrophy and the loss of force and power, weightlessness reduces the ability of the slow soleus to oxidize fats and increases the utilization of muscle glycogen, at least in rats. This substrate change leads to an increased rate of fatigue. Finally, with return to the 1g environment of earth, rat studies have shown an increased occurrence of eccentric contraction-induced fiber damage. The damage occurs with re-loading and not in-flight, but the etiology has not been established.
Evidence that a central governor regulates exercise performance during acute hypoxia and hyperoxia
Authors: Noakes Timothy D. , Peltonen Juha E. , Rusko Heikki K.
Published: April 2021

An enduring hypothesis in exercise physiology holds that a limiting cardiorespiratory function determines maximal exercise performance as a result of specific metabolic changes in the exercising skeletal muscle, so-called peripheral fatigue. The origins of this classical hypothesis can be traced to work undertaken by Nobel Laureate A. V. Hill and his colleagues in London between 1923 and 1925. According to their classical model, peripheral fatigue occurs only after the onset of heart fatigue or failure. Thus, correctly interpreted, the Hill hypothesis predicts that it is the heart, not the skeletal muscle, that is at risk of anaerobiosis or ischaemia during maximal exercise. To prevent myocardial damage during maximal exercise, Hill proposed the existence of a ‘governor’ in either the heart or brain to limit heart work when myocardial ischaemia developed. Cardiorespiratory function during maximal exercise at different altitudes or at different oxygen fractions of inspired air provides a definitive test for the presence of a governor and its function. If skeletal muscle anaerobiosis is the protected variable then, under conditions in which arterial oxygen content is reduced, maximal exercise should terminate with peak cardiovascular function to ensure maximum delivery of oxygen to the active muscle. In contrast, if the function of the heart or some other oxygen-sensitive organ is to be protected, then peak cardiovascular function will be higher during hyperoxia and reduced during hypoxia compared with normoxia. This paper reviews the evidence that peak cardiovascular function is reduced during maximal exercise in both acute and chronic hypoxia with no evidence for any primary alterations in myocardial function. Since peak skeletal muscle electromyographic activity is also reduced during hypoxia, these data support a model in which a central, neural governor constrains the cardiac output by regulating the mass of skeletal muscle that can be activated during maximal exercise in both acute and chronic hypoxia.
Effects of High Extracellular [K+] and Adrenaline on Force Development, Relaxation and Membrane Potential in Cardiac Muscle From Freshwater Turtle And Rainbow Trout
Authors: Nielsen J. S. , Gesser H.
Published: April 2021

Increases in extracellular K+ concentrations reduced the twitch force amplitude of heart muscle from the freshwater turtle (Trachemys scripta elegans) and rainbow trout (Oncorhynchus mykiss). Adrenaline augmented twitch force amplitude and reduced the relative influence of [K+]. In the absence of adrenaline, high [K+] had less effect in reducing twitch force in turtle than in trout, whereas the reverse was true in the presence of adrenaline. Under anoxic conditions, twitch force was lower in 10 mmol l−1 than in 2.5 mmol l−1 K+ in both preparations, but adrenaline removed this difference. A further analysis of turtle myocardium showed that action potential duration was shorter and resting potential more positive in high [K+] than in low [K+]. Adrenaline restored the duration of the action potential, but did not affect the depolarisation, which may attenuate Na+/Ca2+ exchange, participating in excitation/contraction coupling. The contractile responses in the presence of adrenaline were, however, similar in both high and low K+ concentrations when increases in extracellular Ca2+ were applied to increase the demand on excitation/contraction coupling. The possibilities that adrenaline counteracts the effects of high [K+] via the sarcoplasmic reticulum or sarcolemmal Na+/K+-ATPase were examined by inhibiting the sarcoplasmic reticulum with ryanodine (10 μmol l−1) or Na+/K+-ATPase with ouabain (0.25 or 3 mmol l−1). No evidence to support either of these possibilities was found. Adrenaline did not protect all aspects of excitation/contraction coupling because the maximal frequency giving regular twitches was lower at 10 mmol l−1 K+ than at 2.5 mmol l−1 K+.
Hydrobia Ulvae (Gastropoda: Prosobranchia): a New Model for Regeneration Studies
Authors: Gorbushin Alexander M. , Levakin Ivan A. , Panchina Nadejda A. , Panchin Yuri V.
Published: April 2021

Within 2 weeks of decapitation, Hydrobia ulvae was able to regenerate new head structures including buccal ganglia. It was also capable of regenerating propodial ganglia after anterior foot amputation. The functional regeneration of the buccal ganglia was demonstrated by behavioural observations and by electrophysiological experiments. The presence of the oesophagus was shown to be important for regeneration of the buccal complex. H. ulvae provides a new model for regeneration studies, so details of the topographic anatomy and biology of this species are described. To standardize experimental animals in future studies, the effects of age, sex and trematode infestation on the regeneration capacity of H. ulvae have been evaluated. The high capacity for regeneration together with the possibility of using electrophysiological techniques makes H. ulvae a favourable model in which to study neurogenesis in adult animals.
Structural Flexibility of the Intestine of Burmese Python in Response to Feeding
Authors: Starck J. Matthias , Beese Kathleen
Published: April 2021

The small intestine of Burmese pythons, Python molurus bivittatus, undergoes a remarkable size increase shortly after feeding. We studied the dynamics, reversibility and repeatability of organ size changes using noninvasive imaging techniques. We employed light and electron microscopy, flow cytometry and immunohistology to study the cytological mechanisms that drive the size changes of the small intestine. Within 2 days of feeding, the size of the small intestine increased to up to three times the fasting value. The size changes were fully reversible and could be elicited repeatedly by feeding. These enormous size changes were possible because the mucosal epithelium of the small intestine is a transitional epithelium that allows for considerable size changes without cell proliferation. Histological evidence suggested that a fluid pressure-pump system (lymphatic, blood pressure) was the driving force that inflated the intestinal villi. The rates of cell proliferation were not elevated immediately after feeding but peaked 1 week later when small intestine size was already declining. In contrast to the current paradigm, we suggest that the small intestine is not part of the previously proposed ‘pay-before-pumping’ model. Instead, the size of the python’s small intestine may be upregulated without major metabolic investment. It can occur even if the individual is energetically exhausted. An evolutionary perspective of the transitional epithelium mechanism suggests superior functionality compared with the pay-before-pumping model because it allows for long periods of fasting and depletion of energy reserves, while still enabling the snake to digest prey and absorb nutrients.
The kinematics and neural control of high-speed kicking movements in the locust
Authors: Burrows Malcolm , Morris Genevieve
Published: April 2021

The tibiae of locust hind legs can be extended fully in a kick in 3 ms with peak angular velocities of at least 80° ms–1. If the mass of the distal part of the leg is halved, then the extension is complete in less than 1 ms with angular velocities of more than 200° ms–1. The high velocities and the associated power are generated by a preceding storage of energy and its sudden release produced by a specific motor pattern and specialisations of the femoro-tibial joints. To understand the dynamics of these rapid movements and the interrelations between joint mechanics and the motor pattern, kicks were analysed with high-speed video images coupled to simultaneous intracellular recordings from identified leg motor neurones. The first movement is a full tibial flexion followed by co-contraction of the extensor and flexor tibiae muscles for 0.3–1 s, during which the distal end of the femur is flattened dorso-ventrally and expanded laterally. The two semi-lunar processes on the distal femur are bent when the fast extensor tibiae motor neurone spikes so that their tips move ventrally by up to 0.6 mm. The inward projections of these processes into the femur form the proximal part of the hinge joint with the tibia, so that the pivot of the joint also changes and the tibia therefore moves proximally and ventrally, widening the gap between it and the femur. Extension of the tibia begins on average 34 ms after the flexor motor neurones are inhibited at the end of the co-contraction phase. The tibia then begins to extend slowly, reaching peak velocities only when it has extended by 60–70°. The semi-lunar processes do not start to unfurl until the tibia has extended by 55°, so they cannot provide the initial energy for extension. An audible click is produced when the semi-lunar processes unfurl. The peak velocity of tibial extension is correlated with the amount of bending of the semi-lunar processes and with the number of fast extensor motor spikes, but the same amount of semi-lunar bending can be produced by both short and long co-contractions. When the tibia reaches full extension, inertial forces may cause it to bend by as much as 33° at a plane of weakness in the proximal tibia, thus allowing further extension of the distal end.
Slow ATP loss and the defense of ion homeostasis in the anoxic frog brain
Authors: Knickerbocker Debra L. , Lutz Peter L.
Published: April 2021

For most vertebrates, cutting off the oxygen supply to the brain results in a rapid (within minutes) loss of ATP, the failure of ATP-dependent ion-transport process, subsequent anoxic depolarization of neuronal membrane potential and consequential neuronal death. The few species that survive brain anoxia for days or months, such as the freshwater turtle Trachemys scripta, avoid anoxic depolarization and maintain brain ATP levels through a coordinated downregulation of brain energy demand processes. The frog Rana pipiens represents an intermediate in anoxia-tolerance, being able to survive brain anoxia for hours. However, the anoxic frog brain does not defend its energy stores. Instead, anoxia-tolerance appears to be related to a retarded rate of ATP depletion. To investigate the relationship between this slow ATP depletion and the loss of ionic homeostasis, cerebral extracellular K+ concentrations were monitored and ATP levels measured during anoxia, during the initial phase of anoxic depolarization and during complete anoxic depolarization. Extracellular K+ levels were maintained at normoxic levels for at least 3 h of anoxia, while ATP content decreased by 35 %. When ATP levels reached 0.33±0.06 mmol l–1 (mean ± s.e.m., N=5), extracellular K+ levels slowly started to increase. This value is thought to represent a critical ATP concentration for the maintenance of ion homeostasis. When extracellular [K+] reached an inflection value of 4.77±0.84 mmol l–1 (mean ± s.e.m., N=5), approximately 1 h later, the brain quickly depolarized. Part of the reduction in ATP demand was attributable to an approximately 50 % decrease in the rate of K+ efflux from the anoxic frog brain, which would also contribute to the retarded rate of increase in extracellular [K+] during the initial phase of anoxic depolarization. However, unlike the anoxia-tolerant turtle brain, adenosine did not appear to be involved in the downregulation of K+ leakage in the frog brain. The increased anoxia-tolerance of the frog brain is thought to be a matter more of slow death than of enhanced protective mechanisms.
The influence of locomotion on air-sac pressures in little penguins
Authors: Boggs D. F. , Baudinette R. V. , Frappell P. B. , Butler P. J.
Published: April 2021

Air-sac pressures have been reported to oscillate with wing beat in flying magpies and with foot paddling in diving ducks. We sought to determine the impact on air-sac pressure of wing beats during swimming and of the step cycle during walking in little penguins (Eudyptula minor). Fluctuations averaged 0.16±0.06 kPa in the interclavicular air sacs, but only 0.06±0.04 kPa in the posterior thoracic sac, generating a small differential pressure between sacs of 0.06±0.02 kPa (means ± s.e.m., N=4). These fluctuations occurred at approximately 3 Hz and corresponded to wing beats during swimming, indicated by electromyograms from the pectoralis and supracoracoideus muscles. There was no abdominal muscle activity associated with swimming or exhalation, but the abdominal muscles were active with the step cycle in walking penguins, and oscillations in posterior air-sac pressure (0.08±0.038 kPa) occurred with steps. We conclude that high-frequency oscillations in differential air-sac pressure enhance access to and utilization of the O2 stores in the air sacs during a dive.
Characterization of theDrosophila melanogasteralkali-metal/proton exchanger (NHE) gene family
Authors: Giannakou Maria E. , Dow Julian A. T.
Published: April 2021

The NHE family of Na+/H+ exchangers is believed to play an essential role in animals, but may play an additional, specialised epithelial role in insects. The pharmacological sensitivity of the Drosophila melanogaster Malpighian tubule to a range of amiloride derivatives was shown to be consistent with an effect on an exchanger, rather than a Na+ channel. Consistent with this, no degenerin/epithelial Na+ channel (ENaC) genes could be detected in Malpighian tubules by reverse transcriptase/polymerase chain reaction (RT-PCR). Using a low-stringency homology searching, three members of the NHE family were identified in the genomic sequence of Drosophila melanogaster, although only two genes were represented as expressed sequence tags. All three genes (DmNHE1 at cytological position 21B1, DmNHE2 at 39B1 and DmNHE3 at 27A1) were found by RT-PCR to be widely expressed, and one (DmNHE2) was shown to have multiple transcripts. The putative translations of the three genes mark them as distantly related members of the family, inviting the possibility that they may serve distinct roles in insects.
Intestinal iron uptake in the European flounder (Platichthys flesus)
Authors: Bury N. R. , Grosell M. , Wood C. M. , Hogstrand C. , Wilson R. W. , Rankin J. C. , Busk M. , Lecklin T. , Jensen F. B.
Published: April 2021

Iron is an essential element because it is a key constituent of the metalloproteins involved in cellular respiration and oxygen transport. There is no known regulated excretory mechanism for iron, and homeostasis is tightly controlled via its uptake from the diet. This study assessed in vivo intestinal iron uptake and in vitro iron absorption in a marine teleost, the European flounder Platichthys flesus. Ferric iron, in the form 59FeCl3, was reduced to Fe2+ by ascorbate, and the bioavailability of Fe3+ and Fe2+ were compared. In vivo Fe2+ uptake was significantly greater than Fe3+ uptake and was reduced by the iron chelator desferrioxamine. Fe2+ was also more bioavailable than Fe3+ in in vitro studies that assessed the temporal pattern and concentration-dependency of iron absorption. The posterior region, when compared with the anterior and mid regions of the intestine, was the preferential site for Fe2+ uptake in vivo. In vitro iron absorption was upregulated in the posterior intestine in response to prior haemoglobin depletion of the fish, and the transport showed a Q10 value of 1.94. Iron absorption in the other segments of the intestine did not correlate with haematocrit, and Q10 values were lower. Manipulation of the luminal pH had no effect on in vitro iron absorption. The present study demonstrates that a marine teleost absorbs Fe2+ preferentially in the posterior intestine. This occurs in spite of extremely high luminal bicarbonate concentrations recorded in vivo, which may be expected to reduce the bioavailability of divalent cations as a result of the precipitation as carbonates (e.g. FeCO3).
Nitric oxide induces centrally generated motor patterns in the locust suboesophageal ganglion
Authors: Rast Georg F.
Published: April 2021

The stimulatory effects of nitric oxide (NO) on central motor pattern generation in isolated locust suboesophageal ganglia (SOGs) were studied using extracellular recordings from motor nerves. Different NO donor molecules and a specific inhibitor of soluble guanylyl cyclases were used to confirm that the observed motor pattern occurred in response to activation of the NO/cyclic GMP signalling pathway. Experiments with muscarinic agonists and antagonists showed that the NO-induced motor pattern is generated independently from the motor pattern induced by muscarinic agonists described previously. Staining for NADPH-diaphorase and an antiserum directed against cyclic GMP were used to identify neurones representing potential sources of NO and their target cells within the SOG. Using intracellular dye injection and backfilling of peripheral nerves in combination with anti-cGMP immunohistochemistry, it was shown that identified efferent neurones involved in the mandibular motor pattern are potential target cells of NO.
Platelet-activating-factor-hydrolyzing phospholipase C in the salivary glands and saliva of the mosquitoCulex quinquefasciatus
Authors: Ribeiro José M. C. , Francischetti Ivo M. B.
Published: April 2021

A phospholipase C activity specific for platelet-activating factor (PAF), named PAF phosphorylcholine hydrolase, was found in the salivary glands and saliva of the human-feeding mosquito Culex quinquefasciatus. The enzymatic activity was demonstrated by inhibition of PAF-induced platelet aggregation, and by identification of substrate consumption and production of diacyl glyceride by electrospray-ionisation mass spectrometry. The activity has a neutral optimal pH and an apparent molecular mass of 40–50 kDa. Two anthropophilic mosquito species, Aedes aegypti and Anopheles gambiae, do not have this salivary activity. The results are interpreted within the evolutionary context of the genera Culex, Aedes and Anopheles.
Swimming speeds and buoyancy compensation of migrating adult chum salmon Oncorhynchus keta revealed by speed/depth/acceleration data logger
Authors: Tanaka Hideji , Takagi Yasuaki , Naito Yasuhiko
Published: April 2021

Although the homing migration of Pacific salmon is well documented, the swimming behaviour of the returning salmon has been poorly described, principally as a result of the difficulties encountered in monitoring salmon behaviour in the sea. The present study describes the use of a recently developed electronic data logger to obtain simultaneous recordings of the swimming speed, depth, fin-beating activity and body angle of free-ranging chum salmon Oncorhynchus keta during their homing migration in coastal waters. Chum salmon migrated horizontally at speeds of 1.5–3.0 km h–1. The gross horizontal distance salmon moved during total recording periods were 1.24- to 19.0-fold greater than the net distance from the release site to the retrieval points. It is suggested that homing salmon did not drift passively but swam actively to the spawning grounds. Salmon preferred the surface water, but also made frequent vertical migrations. The travelled depth of each salmon ranged from 0.36 to 0.64 km per hour. Salmon descended at faster rates and steeper angles than they ascended. Both tailbeat frequency and tail thrust were higher during the ascent than the descent phase. These results suggest that chum salmon spent more energy during the ascent than the descent phase. Profiles of descent rate assumed an arched shape with respect to a change in hydrostatic pressure, while ascent rate increased with decreasing depth. High tailbeat frequencies were found during the course of ascent, which suggests that the salmon did not regulate the volume of air in the swim bladder during short-term vertical migrations.
Swimbladder gas gland cells cultured on permeable supports regain their characteristic polarity
Authors: Prem Caroline , Pelster Bernd
Published: April 2021

A cell culture system has been developed in which swimbladder gas gland cells from the European eel (Anguilla anguilla) were cultured on a permeable support. Cells seeded on Anodisc 13 (Whatman) or Costar Transwell 13 mm membranes form a confluent cell layer within the first 2 or 3 days of culture but, on the basis of measurements of transepithelial resistance, it is a ‘leaky’ cell layer. In a superfusion system, the apical and basal sides of the cells were superfused asymmetrically, with saline on the apical side and a glucose-containing cell culture medium on the basal side. Under these conditions, the cells continuously produced lactic acid, and approximately 60–70 % of this lactate was released at the basal side. To mimic the in vivo situation, the saline solution supplied to the apical side was replaced by humidified air in an additional series of experiments. Cells cultured in an air/liquid system produced even more lactate, and this lactate was only released to the basal side; there was no leakage of fluid to the apical side. After 4 or 5 days in the superfusion system, the cells were fixed for histological examination. The cells were columnar, similar to gas gland cells in vivo, and showed a clear polarity, with some small microvilli at the apical membrane and extensive membrane foldings at lateral and basal membranes. Immunohistochemical localization of Na+/K+-ATPase revealed that this ATPase was present mainly in the lateral membranes; it was never found in the apical membranes. Cells cultured in the air/liquid system showed a similar structure and polarity.
Postnatal development and control of the pulmonary surfactant system in the tammar wallaby Macropus eugenii
Authors: Miller Natalie J. , Orgeig Sandra , Daniels Christopher B. , Baudinette Russell V.
Published: April 2021

Marsupials are born at an early stage of development and are adapted for future development inside the pouch. Whether the pulmonary surfactant system is fully established at this altricial stage is unknown. This study correlates the presence of surfactant proteins (SP-A, SP-B and SP-D), using immunohistochemistry, with the ex-utero development of the lung in the tammar wallaby Macropus eugenii and also investigates the control of phosphatidylcholine (PC) secretion from developing alveolar type II cells. All three surfactant proteins were found at the site of gas exchange in the lungs of joeys at all ages, even at birth when the lungs are in the early stages of the terminal air-sac phase. Co-cultures of alveolar type II cells and fibroblasts were isolated from the lungs of 30- and 70-day-old joeys and incubated with the hormones dexamethasone (10 μmol l–1), prolactin (1 μmol l–1) or triiodothyronine (100 μmol l–1) or with the autonomic secretagogues isoproterenol (100 μmol l–1) or carbamylcholine chloride (100 μmol l–1). Basal secretion of PC was greater at 30 days of age than at 70 days. Co-cultures responded to all five agonists at 30 days of age, but only the autonomic secretagogues caused a significant increase in PC secretion at 70 days of age. This demonstrates that, as the cells mature, their activity and responsiveness are reduced. The presence of the surfactant proteins at the site of gas exchange at birth suggests that the system is fully functional. It appears that surfactant development is coupled with the terminal air-sac phase of lung development rather than with birth, the length of gestation or the onset of air-breathing.
Maneuvering in an arboreal habitat: the effects of turning angle on the locomotion of three sympatric ecomorphs ofAnolislizards
Authors: Higham Timothy E. , Davenport Matthew S. , Jayne Bruce C.
Published: April 2021

Although the maximal speeds of straight-ahead running are well-documented for many species of Anolis and other lizards, no previous study has experimentally determined the effects of turning on the locomotor performance of a lizard. Anolis lizards are a diverse group of arboreal species, and the discrete paths created by networks of perches in arboreal environments often force animals to turn in their natural habitats. For three species of Anolis with similar overall body size but different shape, we quantified the escape locomotor performance for arboreal locomotion on 4.8 cm diameter perches that were straight (0°) or had turning angles of 30° and 90°. The turning angle had widespread significant effects that were often species-dependent. This was shown by measuring the average gross velocity (including the times while the lizards paused) of the three species covering the middle 30 cm of a racetrack with either 30° or 90° turns. The results were expressed as a percentage of the gross velocity over the same distance on a straight racetrack. The values obtained for A. grahami (99 % for 30° turns and 79 % for 90° turns) showed a smaller effect of turning angle than for A. lineatopus (79 % for 30° turns and 50 % for 90° turns) and A. valencienni (74 % for 30° turns and 48 % for 90° turns). Consequently, the rank order of species based on speed depended on the angle of the turn. Some of the magnitudes of decreased locomotor speed associated with turning exceeded those reported previously for the effects of decreasing perch diameter for these species. For all species, more pausing occurred with increased turning angle, with the twig ecomorph (A. valencienni) pausing the most. Approximately half the individuals of each species jumped to traverse the 90° turn, but some of the potential benefits of jumping for increasing speed were offset by pauses associated with preparing to jump or recovering balance immediately after a jump. The tail of Anolis lizards may facilitate the substantial rotation (>60°) of the body that often occurred in the airborne phase of the jumps.
A snake venom phospholipase A2 blocks malaria parasite development in the mosquito midgut by inhibiting ookinete association with the midgut surface
Authors: Zieler Helge , Keister David B. , Dvorak James A. , Ribeiro José M. C.
Published: April 2021

Oocyst formation is a critical stage in the development of the malaria parasite in the mosquito. We have discovered that the phospholipase A2 (PLA2) from the venom of the eastern diamondback rattlesnake (Crotalus adamanteus) inhibits oocyst formation when added to infected chicken blood and fed to mosquitoes. A similar transmission-blocking activity was demonstrated for PLA2s from the venom of other snakes and from the honeybee. This effect is seen both with the avian malaria parasite Plasmodium gallinaceum and with the human parasite Plasmodium falciparum developing in their respective mosquito hosts. The inhibition occurs even in the presence of an irreversible inhibitor of the active site of PLA2, indicating that the hydrolytic activity of the enzyme is not required for the antiparasitic effect. Inhibition is also seen when the enzyme is fed to mosquitoes together with ookinetes, suggesting that the inhibition occurs after ookinete maturation. PLA2 has no direct effect on the parasite. However, pretreatment of midguts with PLA2 (catalytically active or inactive) dramatically lowers the level of ookinete/midgut association in vitro. It appears, therefore, that PLA2 is acting by associating with the midgut surface and preventing ookinete attachment to this surface. Thus, PLA2 is an excellent candidate for expression in transgenic mosquitoes as a means of inhibiting the transmission of malaria.
Egocentric information helps desert ants to navigate around familiar obstacles
Authors: Bisch-Knaden Sonja , Wehner Rüdiger
Published: April 2021

Homing ants have been shown to associate directional information with familiar landmarks. The sight of these local cues might either directly guide the path of the ant or it might activate a landmark-based vector that points towards the goal position. In either case, the ants define their courses within allocentric systems of reference. Here, we show that desert ants, Cataglyphis fortis, forced to run along a devious path can use egocentric information as well. The ants were trained to deviate from their straight homebound course by a wide inconspicuous barrier that was placed between the feeding and nesting sites. At a distant test area, the ants were confronted with an identical barrier rotated through 45°. After passing the edge of the obstacle, the ants did not proceed in the trained direction, defined by the skylight compass, but rotated their courses to match the rotation of the barrier. Visual guidance could be excluded because, as soon as the ants turned around the end of the barrier, the visual cue it provided vanished from their field of view. Instead, the ants must have maintained a constant angle relative to their previous walking trajectory along the obstacle and, hence, must have determined their new vector course in an egocentric way.
Variations in respiratory muscle activity during echolocation when stationary in three species of bat (Microchiroptera: Vespertilionidae)
Authors: Lancaster Winston C. , Speakman J. R.
Published: April 2021

Echolocating bats use respiratory muscles to power the production of biosonar vocalisations. The physical characteristics of these calls vary among species of bat, and variations also exist in the timing and patterns of respiratory muscle recruitment during echolocation. We recorded electromyograms from the respiratory muscles of three species of bat (Family Vespertilionidae) while the animals vocalised from stationary positions. Activity was recorded consistently from the lateral abdominal muscles (internal abdominal oblique and transversus abdominis) from all calling bats, but we found much variation within and among species. Bats in the family Vespertilionidae devoted longer periods of expiratory muscle activity to each call than did the mormoopid bat Pteronotus parnellii. These differences correlate negatively with the duration of calls. We suggest that morphological adaptations in some bats may facilitate the economic production of echolocation calls at rest.
Geographic variation in thermal sensitivity of jumping performance in the frog Limnodynastes peronii
Authors: Wilson Robbie S.
Published: April 2021

I compared the thermal sensitivity of jumping performance of five populations of the striped marsh frog (Limnodynastes peronii) over a wide geographic range extending from the cool-temperate south to the tropical north of Australia. Maximum jumping performance of adult L. peronii was assessed for each population at eight temperatures between 5°C and 32°C using a custom-designed force platform. From force recordings for each individual jump, maximum jumping force (Fmax) and acceleration (Amax) and maximum power output (Pmax), take-off velocity (Umax), jump distance (DJ) and contact time on the platform (TC) were calculated. The body mass of adult L. peronii varied over their geographic range, from approximately 5 g for the lowland tropical population to more than 22 g for the cool-temperate populations. The thermal sensitivity of jumping performance varied over their geographic range, with the populations from the cooler climates generally performing better than those from the warmer climate populations at the cooler temperatures, and vice versa at the higher temperatures. However, not all parameters of jumping performance underwent parallel changes in thermal sensitivity amongst the populations of L. peronii. Only minor differences in the shape of the thermal sensitivity curves for Fmax and Amax were detected amongst the populations, while the thermal sensitivities of Umax, DJ and Pmax all displayed considerable variation amongst the populations. The optimal temperatures for Umax, DJ and Pmax were generally lower in the cool-temperate populations than in the tropical populations of L. peronii. To determine whether this geographic variation was due to genetic variation, or merely reflected phenotypic plasticity, I also compared the thermal sensitivity of jumping performance between metamorph L. peronii from two different populations raised under identical conditions in the laboratory. The maximum jumping distance of the metamorph L. peronii was assessed at seven temperatures between 8°C and 35°C for the two latitudinally extreme populations (i.e. lowland tropical Proserpine and cool-temperate Gippsland populations). Like adult L. peronii, the metamorphs from the cool-temperate population jumped further than those from the lowland tropical population at the lower temperatures, although no differences were detected at the higher temperatures. Thus, geographic variation in thermal sensitivity of jumping performance in L. peronii probably has a genetic component, and the different populations appear to have undergone genetic adaptation of their thermal sensitivity to the varied thermal environments.
Identification of myosin light chains in Rana pipiens skeletal muscle and their expression patterns along single fibres
Authors: Lutz Gordon J. , Bremner Shannon N. , Bade Michael J. , Lieber Richard L.
Published: April 2021

Isoforms of myosin heavy chain (MHC) and myosin light chain (MLC) influence contractile kinetics of skeletal muscle. We previously showed that the four major skeletal muscle fibre types in Rana pipiens (type 1, type 2, type 3 and tonic; amphibian nomenclature) contain four unique MHC isoforms. In the present study we defined the MLCs expressed in each of these R. pipiens fibre types. The MLC composition of single MHC-typed fibres was determined from western blots using a panel of monoclonal MLC antibodies. A total of seven MLCs were identified, including four types of MLC1, two of MLC2 and a single MLC3. Twitch fibre types (types 1, 2 and 3) expressed MLC1f and MLC2f, while tonic fibres contained a unique set of isoforms, MLC1Ta, MLC1Tb and MLC2T. MLC3 was expressed primarily in type 1, type 1-2 and type 2 fibres. Surprisingly, some frogs displayed a striking pattern of MLC expression where a unique isoform of MLC1 (MLC1x) was coexpressed along with the normal MLC1 isoform(s) in all fibre types. MLC1x was either expressed in all fibres of a given frog or was completely absent. The intraspecific polymorphism in MLC1 expression is likely to have a genetic basis, but is unlikely to be caused by allelic variation. The ratio of MLC3/MLC1 increased in direct proportion to the percentage of type 1 MHC, but was only weakly correlated. The variability in MLC3/MLC1 within a fibre type was extremely large. Both the MHC isoform and MLC3/MLC1 ratio varied significantly between 1 mm segments along the length of fibres. For all segments combined, MLC3/MLC1 increased with the percentage of type 1 MHC, but the correlation between segments was weaker than between fibres.
Molecular activity of Na+/K+-ATPase from different sources is related to the packing of membrane lipids
Authors: Wu Ben J. , Else Paul L. , Storlien Leonard H. , Hulbert A. J.
Published: April 2021

The activity of the ubiquitous Na+/K+-ATPase represents a substantial portion of the resting metabolic activity of cells, and the molecular activity of this enzyme from tissues of different vertebrates can vary several-fold. Microsomes were prepared from the kidney and brain of the rat (Rattus norvegicus) and the cane toad (Bufo marinus), and Na+/K+-ATPase molecular activity was determined. The membrane lipids surrounding this enzyme were isolated and phospholipids prepared. ‘Surface pressure/area’ isotherms were measured in monolayers for both membrane lipids and phospholipids using classic Langmuir trough techniques. Microsomal lipid composition was also measured. Whilst significant correlations were observed between membrane composition and Na+/K+-ATPase molecular activity, the strongest correlations were found between the molecular activity and parameters describing the packing of the surrounding membrane lipids and phospholipids. The influence of membrane lipid composition, especially membrane acyl composition, on the activity of a membrane protein mediated by physical properties of the lipids may represent a fundamental principle applicable to other membrane proteins.
Event-related potentials in an invertebrate: crayfish emit ‘omitted stimulus potentials’
Authors: Ramón Fidel , Hernández Oscar H. , Bullock Theodore H.
Published: April 2021

Electrical signs of neural activity correlated with stimuli or states include a subclass called event-related potentials. These overlap with, but can often be distinguished from, simple stimulus-bound evoked potentials by their greater dependence on endogenous (internal state) factors. Studied mainly in humans, where they are commonly associated with cognition, they are considered to represent objective signs of moderately high-level brain processing.

We tested the hypothesis that invertebrates lack such signs by looking in the crayfish Procambarus clarkii for a class of OFF-effects shown in humans to index expectancy. Disproving the hypothesis, we find, using chronic, implanted preparations, that a good omitted stimulus potential is reliably present. The system learns in a few cycles of a regularly repeated light flash to expect one on schedule. Omitted stimulus potentials are found in the protocerebrum, the circumesophageal connective and in the optic tract – perhaps arising in the retina, as in vertebrates. These potentials can be very local and can include loci with and without direct visual evoked potentials in response to each flash. In some loci, the omitted stimulus potential has a slow wave component, in others only a spike burst. Omitted stimulus potentials are more endogenous than visual evoked potentials, with little dependence on flash or ambient light intensity or on train duration. They vary little in size at different times of the day, but abruptly fail to appear if the ambient light is cut off. They can occur during walking, eating or the maintained defense posture but are diminished by ‘distraction’ and are often absent from an inert crayfish until it is aroused.

We consider this form of apparent expectation of a learned rhythm (a property that makes it ‘cognitive’ in current usage), to be one of low level, even though some properties suggest endogenous factors. The flashes in a train have an inhibitory effect on a circuit that quickly ‘learns’ the stimulus interval so that the omitted stimulus potential, ready to happen after the learned interval, is prevented by each flash, until released by a missing stimulus.