bluuebunny/crossref_metadata_2025_split huggingface dataset:
The aerodynamics of revolving wings I. Model hawkmoth wings
Authors: Usherwood James R. , Ellington Charles P. 
Published: April 2021

SUMMARYRecent work on flapping hawkmoth models has demonstrated the importance of a spiral `leading-edge vortex' created by dynamic stall, and maintained by some aspect of spanwise flow, for creating the lift required during flight. This study uses propeller models to investigate further the forces acting on model hawkmoth wings in `propeller-like' rotation (`revolution'). Steadily revolving model hawkmoth wings produce high vertical (≈ lift) and horizontal (≈ profile drag) force coefficients because of the presence of a leading-edge vortex. Both horizontal and vertical forces, at relevant angles of attack, are dominated by the pressure difference between the upper and lower surfaces; separation at the leading edge prevents `leading-edge suction'. This allows a simple geometric relationship between vertical and horizontal forces and the geometric angle of attack to be derived for thin, flat wings. Force coefficients are remarkably unaffected by considerable variations in leading-edge detail, twist and camber. Traditional accounts of the adaptive functions of twist and camber are based on conventional attached-flow aerodynamics and are not supported. Attempts to derive conventional profile drag and lift coefficients from `steady' propeller coefficients are relatively successful for angles of incidence up to 50° and, hence, for the angles normally applicable to insect flight.
The aerodynamics of revolving wings II. Propeller force coefficients from mayfly to quail
Authors: Usherwood James R. , Ellington Charles P. 
Published: April 2021

SUMMARYHigh force coefficients, similar to those observed for revolving model hawkmoth wings in the accompanying paper (for which steady leading-edge vortices are directly observed), are apparent for revolving model (mayfly,bumblebee and quail) and real (quail) animal wings ranging in Reynolds number(Re) from 1100 to 26000. Results for bumblebee and hawkmoth wings agree with those published previously for Drosophila(Re≈200). The effect of aspect ratio is also tested with planforms based on hawkmoth wings adjusted to aspect ratios ranging from 4.53 to 15.84 and is shown to be relatively minor, especially at angles of incidence below 50°.The normal force relationship introduced in the accompanying paper is supported for wings over a large range of aspect ratios in both `early' and`steady' conditions; local induced velocities appear not to affect the relationship.
Regulation of cardiac contractility in a cold stenothermal fish, the burbotLota lotaL.
Authors: Tiitu Virpi , Vornanen Matti 
Published: April 2021

SUMMARYIn the present study, burbot (Lota lota L.) was used as a model to study the effects of acute temperature changes on cardiac contractility in a cold stenothermal fish. The burbot were captured in the breeding season(February) and were maintained for 4 weeks at 1-2 °C in the laboratory before the contractile properties of the heart were measured. Both isometric force and the pumping capacity of in vitro perfused hearts were maximum at the acclimation temperature (1 °C) and declined markedly when the temperature increased. At 1 °C heart rate was 25 beats min-1 and increased to a maximum of 72 beats min-1 at 18°C, above which atrio—ventricular block was observed. Ryanodine (10μmol l-1), an inhibitor of sarcoplasmic reticulum (SR)Ca2+ release channels, reduced the maximum developed force of paced atrial and ventricular preparations at 1 °C by 32±8 % and 16±3 %, respectively. At 7 °C, ryanodine-induced inhibition of force increased to 52±3 % and 44±5 % in the atrium and ventricle, respectively. At 1 °C, ryanodine abolished rest-potentiation and turned it into rest-decay in both atrial and ventricular muscle. Ryanodine, however, had no effect on the mechanical refractory period or on the rate constants of mechanical and relaxation restitution in either preparation at 1 °C. The activity of myofibrillar Ca2+Mg2+-ATPase was higher in atrial than ventricular muscle and the temperature optimum of the ATPase in vitro was approximately 10 °C in both preparations. Our results indicate a significant dependence on SR Ca2+ stores for contractile activation in the burbot heart at temperatures that are known to inhibit SR function in mammalian heart. This suggests that the ryanodine receptors of the teleost heart, unlike those of the endotherms, are not leaky as temperatures approach 0 °C. Reliance on SR Ca2+ stores in both cold stenothermal burbot and cold-acclimated eurythermal teleosts suggests that enhanced SR Ca2+-release is a common characteristic of cold-living fish and may improve cardiac contractility in the cold.
Mammalian spinal biomechanics: postural support in seated macaques
Authors: Gal Julianna 
Published: April 2021

SUMMARYThe aim of this study was to investigate whether the ligamentous lumbar vertebral column of a macaque could potentially provide passive mechanical support to the weight of the head, upper body and forelimbs during upright sitting. The seated flexed curvature of the lumbar spine of Macaca sylvana was estimated from a photograph and was partitioned equally among the lumbar—lumbar intervertebral joints. This flexed curvature was compared with the hyper-extended profile of the unloaded excised ligamentous spine of a related species (Macaca fascicularis) and used to calculate changes in intervertebral angle from the unloaded excised state to the loaded in vivo state. Changes in intervertebral angle were then used to calculate the net flexion moment required to bend the spine from the unloaded curvature to the seated curvature. The moment arm of the ventrally displaced weight of the head, upper body and forelimbs was estimated and used to calculate a corresponding net force. It was found that this force corresponded to approximately 18 % of the total body weight of the 2.34 kg sample animal. This compares with a likely fractional body weight of approximately 30-40 % for the head, upper body and forelimbs of these primates. Therefore, approximately half of the ventral flexion moment associated with the combined weight of the head, upper body and forelimbs during sitting in these animals may be supported by the passive mechanical properties associated with the ligamentous lumbar spine. This represents a potential means of relieving muscular effort and saving metabolic energy.
High feeding costs limit dive time in the largest whales
Authors: Acevedo-Gutiérrez A. , Croll D. A. , Tershy B. R. 
Published: April 2021

SUMMARY
Large body size usually extends dive duration in air-breathing vertebrates. However, the two largest predators on earth, the blue whale (Balaenoptera musculus) and the fin whale (B. physalus), perform short dives for their size. Here, we test the hypothesis that the foraging behavior of these two species (lunge-feeding) is energetically expensive and limits their dive duration. We estimated the cost of lunge-feeding in both species using an approach that combined attaching time/depth recorders to seven blue whales and eight fin whales and comparing the collected dive information with predictions made by optimality models of dive behavior. We show that the rate at which whales recovered from a foraging dive was twice that of a non-foraging dive and that the cost of foraging relative to the cost of travel to and from the prey patch was 3.15 in blue whales (95 % CI 2.58-3.72) and 3.60 in fin whales(95 % CI 2.35-4.85). Whales foraged in small areas (&lt;1 km2) and foraging bouts lasted more than one dive, indicating that prey did not disperse and thus that prey dispersal could not account for the limited dive durations of the whales. Despite the enormous size of blue whales and fin whales, the high energetic costs of lunge-feeding confine them to short durations of submergence and to areas with dense prey aggregations. As a corollary, because of their limited foraging time under water, these whales may be particularly vulnerable to perturbations in prey abundance.
Orientation and lateralized cue use in pigeons navigating a large indoor environment
Authors: Prior Helmut , Lingenauber Frank , Nitschke Jörg , Güntürkün Onur 
Published: April 2021

SUMMARY
The pigeon's use of different visuo-spatial cues was studied under controlled laboratory conditions that simulated analogous aspects of a homing situation. The birds first learned the route to a goal that was not visible from the starting location, but became visible as it was approached. Birds could orientate within a mainly geometric global reference frame, using prominent landmarks within their range, or by `piloting' along local cues. After learning the route, the birds were tested from familiar and unfamiliar release points, and several aspects of the available cues were varied systematically. The study explored the contribution of the left and right brain hemispheres by performing tests with the right or left eye occluded. The results show that pigeons can establish accurate bearings towards a non-visible goal by using a global reference frame only. Furthermore, there was a peak of searching activity at the location predicted by the global reference frame. Search at this location and directedness of the bearings were equally high with both right and left eye, suggesting that both brain hemispheres have the same competence level for these components of the task. A lateralization effect occurred when prominent landmarks were removed or translated. While the right brain hemisphere completely ignored such changes,the left brain hemisphere was distracted by removal of landmarks. After translation of landmarks, the left but not the right brain hemisphere allocated part of the searching activity to the site predicted by the new landmark position. The results show that a mainly geometric global visual reference frame is sufficient to determine exact bearings from familiar and unfamiliar release points. Overall, the results suggest a model of brain lateralization with a well-developed global spatial reference system in either hemisphere and an extra capacity for the processing of object features in the left brain.
A comparison of propagated action potentials from tropical and temperate squid axons: different durations and conduction velocities correlate with ionic conductance levels
Authors: Rosenthal Joshua J. C. , Bezanilla Francisco 
Published: April 2021

SUMMARYTo determine which physiological properties contribute to temperature adaptation in the squid giant axon, action potentials were recorded from four species of squid whose habitats span a temperature range of 20°C. The environments of these species can be ranked from coldest to warmest as follows: Loligo opalescens&gt;Loligo pealei&gt;Loligo plei&gt;Sepioteuthis sepioidea. Action potential conduction velocities and rise times,recorded at many temperatures, were equivalent for all Loligospecies, but significantly slower in S. sepioidea. By contrast, the action potential's fall time differed among species and correlated well with the thermal environment of the species (`warmer' species had slower decay times). The biophysical underpinnings of these differences were examined in voltage-clamped axons. Surprisingly, no differences were found between the activation kinetics or voltage-dependence of Na+ and K+currents. Conductance levels, however, did vary. Maximum Na+conductance (gNa) in S. sepiodea was significantly less than in the Loligo species. K+ conductance (gK) was highest in L. pealei, intermediate in L. plei and smallest in S. sepiodea. The time course and magnitude of gK and gNa were measured directly during membrane action potentials. These data reveal clear species-dependent differences in the amount of gK and gNa recruited during an action potential.
Effects of temperature, epinephrine and Ca2+ on the hearts of yellowfin tuna (Thunnus albacares)
Authors: Blank Jason M. , Morrissette Jeffery M. , Davie Peter S. , Block Barbara A. 
Published: April 2021

SUMMARYTuna are endothermic fish with high metabolic rates, cardiac outputs and aerobic capacities. While tuna warm their skeletal muscle, viscera, brain and eyes, their hearts remain near ambient temperature, raising the possibility that cardiac performance may limit their thermal niches. We used an in situ perfused heart preparation to investigate the effects of acute temperature change and the effects of epinephrine and extracellular Ca2+ on cardiac function in yellowfin tuna (Thunnus albacares). Heart rate showed a strong temperature-dependence, ranging from 20 beats min-1 at 10 °C to 109 beats min-1 at 25 °C. Maximal stroke volume showed an inverse temperature-dependence,ranging from 1.4 ml kg-1 at 15 °C to 0.9 ml kg-1 at 25 °C. Maximal cardiac outputs were 27 ml kg-1 min-1at 10 °C and 98 ml kg-1 min-1 at 25 °C. There were no significant effects of perfusate epinephrine concentrations between 1 and 100 nmoll-1 at 20 °C. Increasing extracellular Ca2+ concentration from 1.84 to 7.36 mmoll-1 at 20°C produced significant increases in maximal stroke volume, cardiac output and myocardial power output. These data demonstrate that changes in heart rate and stroke volume are involved in maintaining cardiac output during temperature changes in tuna and support the hypothesis that cardiac performance may limit the thermal niches of yellowfin tuna.
The relationship between heart rate and rate of oxygen consumption in Galapagos marine iguanas (Amblyrhynchus cristatus)at two different temperatures
Authors: Butler Patrick J. , Frappell Peter B. , Wang Tobias , Wikelski Martin 
Published: April 2021

SUMMARYTo enable the use of heart rate (fH) for estimating field metabolic rate (FMR) in free-ranging Galapagos marine iguanas Amblyrhynchus cristatus, we determined the relationships between fH and mass-specific rate of oxygen consumption(sV̇O2) in seven iguanas before and during exercise on a treadmill and during the post-exercise period. The experiments were conducted at 27 and 35°C, which are the temperatures that represent the lowest and highest average body temperatures of these animals in the field during summer. There were linear and significant relationships between fH and sV̇O2 at both temperatures (r2=0.86 and 0.91 at 27°C and 36°C,respectively). The slopes of the two regression lines did not differ, but there were significant differences in their intercepts. Thus, while heart rate can be used to predict FMR, the effects of temperature on the intercept of the regression must be taken into account when converting fH to sV̇O2. On the basis of our data, this can be achieved by applying the following formula: \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[\mathrm{s}{\dot{V}}_{\mathrm{o}_{2}}=0.0113f\mathrm{H}-0.2983\mathrm{Q}_{10}^{\frac{(T_{\mathrm{b}}-27)}{10}}.\] \end{document}The increase in sV̇O2 with elevated body temperature results from an increase in fH, with no significant change in mass-specific oxygen pulse (sO2 pulse;cardiac stroke volume times the difference in oxygen content between arterial and mixed venous blood). However, during exercise at both temperatures,increases in fH are insufficient to provide all of the additional O2 required and there are also significant increases in the sO2 pulses. This creates the situation whereby the same fH at the two temperatures can represent different values of sV̇O2.
Hypaxial muscle activity during running and breathing in dogs
Authors: Deban Stephen M. , Carrier David R. 
Published: April 2021

SUMMARYThe axial muscles of terrestrial vertebrates serve two potentially conflicting functions, locomotion and lung ventilation. To differentiate the locomotor and ventilatory functions of the hypaxial muscles in mammals, we examined the locomotor and ventilatory activity of the trunk muscles of trotting dogs under two conditions: when the ventilatory cycle and the locomotor cycle were coupled and when they were uncoupled. Patterns of muscle-activity entrainment with locomotor and ventilatory events revealed (i)that the internal and external abdominal oblique muscles performed primarily locomotor functions during running yet their activity was entrained to expiration when the dogs were standing, (ii) that the internal and external intercostal, external oblique thoracic and transversus abdominis muscles performed both locomotor and respiratory functions simultaneously, (iii) that the parasternal internal intercostal muscle performed a primarily respiratory function (inspiration) and (iv) that the deep pectoralis and longissimus dorsi muscles performed only locomotor functions and were not active while the dogs were standing still. We conclude that the dual function of many hypaxial muscles may produce functional conflicts during running. The redundancy and complexity of the respiratory musculature as well as the particular pattern of respiratory—locomotor coupling in quadrupedal mammals may circumvent these conflicts or minimize their impact on respiration.
Accumulation of the mitochondrial form of the sulphydryl oxidase Erv1p/Alrp during the early stages of spermatogenesis
Authors: Klissenbauer Monika , Winters Silke , Heinlein Uwe A. O. , Lisowsky Thomas 
Published: April 2021

SUMMARY
In this study, we investigated the expression of the mammalian FAD-dependent sulphydryl oxidase Erv1p/Alrp in the rat and mouse and during mouse spermatogenesis. Up to three forms of Alrp were identified in protein extracts from different tissues and organs, but very little enzyme was present in blood samples. The three forms of Alrp represent the full-length protein of 23 kDa and fragments of 21 kDa and 15 kDa. All forms of Alrp were assembled into dimers in vivo. In contrast to samples from other organs, the protein analysis of mouse testis identified predominantly full-length 23 kDa Alrp. This finding prompted us to investigate in more detail the expression of Alrp during spermatogenesis. Testis samples of individual mice from postnatal days 13-29 were probed with an antibody specific for mammalian Alrp. In addition, cells from whole testis preparations were fractionated on a bovine serum albumin column gradient. Protein expression of mouse Alrp was compared with those of testis-specific cyritestin, the cytoskeleton marker actin and mitochondrial subunit Vb of cytochrome oxidase and cytochrome c. These studies demonstrated a specific accumulation of full-length mouse Alrp during the early stages of spermatogenesis. The highest levels of Alrp were found in spermatogonia and primary spermatocytes. Levels of expression of Alrp did not correlate with the synthesis of components of the respiratory chain,indicating that full-length Alrp in the mitochondria of spermatogonia and spermatocytes has another function in addition to its role in oxidative phosphorylation.
Functional morphology of proximal hindlimb muscles in the frogRana pipiens
Authors: Kargo William J. , Rome Lawrence C. 
Published: April 2021

SUMMARYMusculoskeletal models have become important tools in understanding motor control issues ranging from how muscles power movement to how sensory feedback supports movements. In the present study, we developed the initial musculotendon subsystem of a realistic model of the frog Rana pipiens. We measured the anatomical properties of 13 proximal muscles in the frog hindlimb and incorporated these measurements into a set of musculotendon actuators. We examined whether the interaction between this musculotendon subsystem and a previously developed skeleton/joint subsystem captured the passive behavior of the real frog's musculoskeletal system. To do this, we compared the moment arms of musculotendon complexes measured experimentally with moment arms predicted by the model. We also compared sarcomere lengths measured experimentally at the starting and take-off positions of a jump with sarcomere lengths predicted by the model at these same limb positions. On the basis of the good fit of the experimental data, we used the model to describe the multi-joint mechanical effects produced by contraction of each hindlimb muscle and to predict muscle trajectories during a range of limb behaviors (wiping, defensive kicking, swimming and jumping). Through these analyses, we show that all hindlimb muscles have multiple functions with respect to accelerating the limb in its three-dimensional workspace and that the balance of functions depends greatly on limb configuration. In addition, we show that muscles have multiple, task-specific functions with respect to the type of contraction performed. The results of this study provide important data regarding the multifunctional role of hindlimb muscles in the frog and form a foundation upon which additional model subsystems (e.g. neural) and more sophisticated muscle models can be appended.
Effect of increased calcium concentration in sea water on calcification and photosynthesis in the scleractinian coralGalaxea fascicularis
Authors: Marshall Alan T. , Clode Peta L. 
Published: April 2021

SUMMARYThe relationship between calcification and photosynthesis in coral was investigated using standard sea water with enhanced calcium concentration. In standard sea water at 23°C with the calcium concentration increased by 2.5 mmol l-1, incorporation of calcium into the skeleton increased by 30-61 %, depending on the method of data normalisation, and photosynthesis, measured as 14C incorporation into the tissues, also increased by 87 %. At 29 °C, calcium incorporation into the skeleton increased by 54-84 % and 14C incorporation increased by 32 % when sea water calcium concentration was increased by 5 mmol l-1. However, photosynthesis measured as net photosynthetic oxygen production did not increase. Similarly there was no change in respiration rate when coral polyps were incubated in high-calcium sea water. It is conjectured that an increase in photorespiration may be responsible for the latter observations. Bisphosphonate has been considered to inhibit calcification but not photosynthesis in corals. We show that bisphosphonate may not inhibit formation of amorphous calcium carbonate and that the inhibition of calcification is possibly illusory. The data are consistent with the trans-calcification model, which suggests that calcification is a source of CO2 for photosynthesis in corals.
Etruscan shrew muscle: the consequences of being small
Authors: Jürgens Klaus D. 
Published: April 2021

SUMMARYThe skeletal muscles of the smallest mammal, the Etruscan shrew Suncus etruscus, are functionally and structurally adapted to the requirements of an enormously high energy turnover. Isometric twitch contractions of the extensor digitorum longus (EDL) and soleus muscles are shorter than in any other mammal, allowing these muscles to contract at outstandingly high frequencies. The skeletal muscles of S. etruscus contract at up to 900 min-1 for respiration, up to 780 min-1 for running and up to 3500 min-1 for shivering. All skeletal muscles investigated lack slow-twitch type I fibres and consist only of fast-twitch type IID fibres. These fibres are optimally equipped with properties enabling a high rate of almost purely oxidative metabolism: they have a small diameter,their citrate synthase activity is higher and their lactate dehydrogenase activity is lower than in the muscles of any other mammal and they have a rapid shortening velocity. Differences in isometric twitch contraction times between different muscles are, at least in part, probably due to differences in cytosolic creatine kinase activities.