bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flight and size constraints: hovering performance of large hummingbirds under maximal loading
Authors: Chai Peng , Millard David 
Published: April 2021

ABSTRACT
As the smallest birds, hummingbirds are the only birds capable of prolonged hovering. This suggests that hovering locomotion scales unfavourably with size. Is the hovering performance of larger hummingbird species more constrained by size than that of smaller ones? Maximal load-lifting capacities of the two largest species of hummingbirds found in the United States, the blue-throated (Lampornis clemenciae, 8.4 g) and magnificent (Eugenes fulgens, 7.4 g) hummingbird, as well as the two other local small species, the black-chinned (Archilochus alexandri, 3.0 g) and rufous (Selasphorus rufus, 3.3 g) hummingbird, were determined under conditions of short-burst performance. The power reserves of hummingbirds are substantial relative to normal hovering performance. The two large species lifted maximal loads close to twice their body mass for a very brief duration of over 0.4 s. The small species lifted maximal loads approximately equal to their own mass with a longer duration of over 0.6 s. For the two large species under maximal loading, estimates of burst muscle mass-specific mechanical power output assuming perfect elastic energy storage averaged 309 W kg−1, compared with 75 W kg−1 during free hovering without loading. For the two small species, these values were 228W kg−1 and 88 W kg−1, respectively. The differences in aerodynamic force production and power output between the large and small size classes occur despite their similar wing stroke velocity. This indicates that, during burst performance in these hummingbirds, the larger ones had a higher load-lifting capacity and generated more muscle power. In spite of the twofold difference in body mass, both large and small hummingbirds have evolved to become potent aerial competitors in order to exploit their common food resource, nectar. Both size classes have evolved to cope with the multi-dimensional effects of size constraining their aerodynamics, muscle mechanics, metabolism and ecology.
Mitochondrial arginine kinase in the midgut of the tobacco hornworm (Manduca sexta)
Authors: Chamberlin M. E. 
Published: April 2021

ABSTRACT
Mitochondria isolated from the posterior midgut of the tobacco hornworm (Manduca sexta) contain arginine kinase. The distribution of mitochondrial and cytoplasmic marker enzymes indicates that the presence of mitochondrial arginine kinase is not due to cytoplasmic contamination. Arginine is not oxidized by the midgut mitochondria but, when metabolic substrates and ATP are present, respiration can be initiated by the addition of arginine. Under these conditions, there is no return to State 4 respiration, indicating regeneration of ADP by the arginine kinase reaction. Respiration can be blocked, however, by atractyloside, an inhibitor of the adenine nucleotide translocator. These results indicate that arginine kinase resides outside the matrix. Mitochondrial arginine kinase is specific to L-arginine since analogs of L-arginine are ineffective in stimulating respiration in the presence of ATP. Coupling between the adenine nucleotide translocator and arginine kinase was investigated using kinetic and thermodynamic approaches. There were no differences in the activities of arginine kinase in respiring and non-respiring mitochondria when they were measured at different ATP or arginine concentrations. This result indicates that arginine kinase does not have preferential access to the ATP exported out of the matix. A comparison of the apparent equilibrium constant and the mass action ratio of the arginine kinase reaction also confirms that there is no microcompartmentation of the reaction.
Do Flatfish Feed Like Other Fishes? a Comparative Study of Percomorph Prey-Capture Kinematics
Authors: Gibb Alice C. 
Published: April 2021

ABSTRACT
The kinematics of prey capture in two bilaterally asymmetrical pleuronectiform flatfish species (Pleuronichthys verticalis and Xystreurys liolepis) and two symmetrical percomorph species (Lepomis macrochirus, a centrarchid, and Cheilinus digrammus, a labrid) were compared to test the hypothesis that flatfish have distinct prey-capture kinematics from those quantified for other percomorph fishes. Size-matched individuals of both flatfish species were video-taped feeding using a high-speed video system. Cephalic displacement and timing variables were quantified and compared with data from similarly sized L. macrochirus and C. digrammus previously collected by other researchers using similar experimental methodology. Nested multivariate analyses of variance indicated that there was no significant difference in prey-capture kinematics between flatfish and non-flatfish taxa, but that prey-capture kinematics did differ among the four taxa. Multiple nested analyses of variance revealed that the taxa differed in 7 of 11 kinematic variables. Post-hoc tests and comparisons with other fish taxa suggest that individuals of P. verticalis possess an unusual combination of prey-capture kinematics including large hyoid depression, large neurocranial rotation, large upper jaw protrusion and small gape. Previous research has suggested that this combination of traits is associated with suction-based prey capture. Correspondingly, the ram–suction index calculated for P. verticalis is more negative (indicating a greater use of suction) than that calculated for the other taxa. When homologous kinematic variables are compared across these four taxa, flatfish do not appear to have similar prey-capture kinematics. However, both flatfish species are distinct from the two symmetrical percomorph species in their asymmetrical jaw movements.
Work and Power Output in the Hindlimb Muscles of Cuban Tree Frogs Osteopilus Septentrionalis During Jumping
Authors: Peplowski Matthew M. , Marsh Richard L. 
Published: April 2021

ABSTRACT
It has been suggested that small frogs use a catapult mechanism to amplify muscle power production during the takeoff phase of jumping. This conclusion was based on an apparent discrepancy between the power available from the hindlimb muscles and that required during takeoff. The present study provides integrated data on muscle contractile properties, morphology and jumping performance that support this conclusion. We show here that the predicted power output during takeoff in Cuban tree frogs Osteopilus septentrionalis exceeds that available from the muscles by at least sevenfold. We consider the sartorius muscle as representative of the bulk of the hindlimb muscles of these animals, because this muscle has properties typical of other hindlimb muscles of small frogs. At 25 °C, this muscle has a maximum shortening velocity (Vmax) of 8.77±0.62 L0 s−1 (where L0 is the muscle length yielding maximum isometric force), a maximum isometric force (P0) of 24.1±2.3 N cm−2 and a maximum isotonic power output of 230±9.2 W kg−1 of muscle (mean ± S.E.M.). In contrast, the power required to accelerate the animal in the longest jumps measured (approximately 1.4 m) is more than 800 W kg−1 of total hindlimb muscle. The peak instantaneous power is expected to be twice this value. These estimates are probably conservative because the muscles that probably power jumping make up only 85 % of the total hindlimb muscle mass. The total mechanical work required of the muscles is high (up to 60 J kg−1), but is within the work capacities predicted for vertebrate skeletal muscle. Clearly, a substantial portion of this work must be performed and stored prior to takeoff to account for the high power output during jumping. Interestingly, muscle work output during jumping is temperature-dependent, with greater work being produced at higher temperatures. The thermal dependence of work does not follow from simple muscle properties and instead must reflect the interaction between these properties and the other components of the skeletomuscular system during the propulsive phase of the jump.
Survival of Energy Failure in the Anoxic Frog Brain: Delayed Release of Glutamate
Authors: Lutz Peter L. , Reiners Raymond 
Published: April 2021

ABSTRACT
This study investigated the relationship between energy failure and neurotransmitter release in the frog (Rana pipiens) brain during 1–3 h of anoxia. Unlike truly anoxia-tolerant species, the frog does not defend its brain energy charge. When exposed to anoxia at 25 °C, there is an immediate fall in brain ATP levels, which reach approximately 20 % of normoxic levels in approximately 60 min. The frog, nevertheless, survives another 1–2 h of anoxia. At 100 min of anoxia, there is an increase in extracellular adenosine concentration, probably originating from the increased intracellular adenosine concentration caused by the breakdown of intracellular ATP. Increases in the levels of extracellular glutamate and
GABA do not occur until 1–2 h after ATP depletion. This response is quite unlike that recorded for other vertebrates, anoxia-tolerant or anoxia-intolerant, where energy failure quickly results in an uncontrolled and neurotoxic release of excitatory neurotransmitters. In the frog, the delay in excitotoxic neurotransmitter release may be one of the factors that allow a period of survival after energy failure. Clearly, energy failure by itself is not a fatal event in the frog brain.
Voltage Sensing in Jellyfish Shaker K+ Channels
Authors: Grigoriev Nikita G. , Spafford J. David , Gallin Warren J. , Spencer Andrew N. 
Published: April 2021

ABSTRACT
The S4 segment of the jellyfish (Polyorchis penicillatus) Shaker channel jShak1 contains only six positively charged motifs. All other Shaker channels, including the jellyfish Shaker channel jShak2, have seven charges in this segment. Despite their charge differences, both these jellyfish channels produce currents with activation and inactivation curves shifted by approximately +40 mV relative to other Shaker currents.
Adding charge without changing segment length by mutating the N-terminal side of jShak1 S4 does not have a pronounced effect on channel activation properties. Adding the positively charged motif RIF on the N-terminal side of K294 (the homologue of K374 in Drosophila Shaker, which is a structurally critical residue) produced a large positive shift in both activation and inactivation without altering the slope of the activation curve of the channel. When IFR was added to the other side of K294, there was a small negative shift in activation and fast inactivation of the channel was prevented.
Our results demonstrate that K294 divides the S4 segment into functionally different regions and that the voltage threshold for activation and inactivation of the channel is not determined by the total charge on S4.
Cell Membrane Lipid Composition and Distribution: Implications for Cell Function and Lessons Learned From Photoreceptors and Platelets
Authors: Boesze-Battaglia Kathleen , Schimmel Richard J. 
Published: April 2021

ABSTRACT
Photoreceptor rod cells and blood platelets are remarkably different, yet both illustrate a similar phenomenon. Both are strongly affected by membrane cholesterol, and the distribution of cholesterol in the membranes of both cell types is determined by the lipid composition within the membranes. In rod cells, cholesterol strongly inhibits rhodopsin activity. The relatively higher level of cholesterol in the plasma membrane serves to inhibit, and thereby conserve, the activity of rhodopsin, which becomes fully active in the low-cholesterol environment of the disk membranes of these same cells. This physiologically important partitioning of cholesterol between disk membranes and plasma membranes occurs because the disk membranes are enriched with phosphatidylethanolamine, thus providing a thermodynamically unfavorable environment for the sterol. Cholesterol enrichment of platelets renders these cells more responsive to stimuli of aggregation. Stimuli for platelet aggregation cause a rapid transbilayer movement of cholesterol from the outer monolayer. This stimulus-dependent redistribution of cholesterol appears to result from the concomitant movement of phosphatidylethanolamine into the outer monolayer. The attractive, yet still unproven, hypothesis is that cholesterol translocation plays an important role in the overall platelet response and is intimately related to the sensitizing actions of cholesterol on these cells.
Behavioural Analysis of Olfactory Conditioning in the Moth Spodoptera Littoralis (Boisd.) (Lepidoptera: Noctuidae)
Authors: Fan Ruey-Jane , Anderson Peter , Hansson Bill S. 
Published: April 2021

ABSTRACT
We studied the associative learning capabilities for behaviourally relevant cues in the moth Spodoptera littoralis. The moths were trained to associate a conditioned stimulus (CS), geraniol odour, with an unconditioned stimulus (US), a sucrose solution. The occurrence of a proboscis extension reflex (PER) was tested. The PER performance during acquisition increased steadily with the number of training trials. Non-associative control procedures did not result in learning. PER conditioning was achieved when the CS was presented 1–3 s before the US. A wide range of inter-trial intervals was able to support conditioning. Males and females learned equally well. Moths could to some degree learn the CS–US association after a single trial. These results demonstrate that S. littoralis females and males have a good capability to associate an odour with a reward. The neural basis of olfactory coding in moths has been well studied; thus, the moth provides a powerful system in which to examine the neurobiology of olfactory learning.
L-Glutamate and Serotonin are Endogenous in Squid Chromatophore Nerves
Authors: Messenger J. B. , Cornwell C. J. , Reed C. M. 
Published: April 2021

ABSTRACT
Colour changes in cephalopods are controlled by complex organs termed chromatophores whose radial muscles are directly innervated from the brain. In the squids Alloteuthis subulata and Loligo vulgaris, light microscopy of silver- or Methylene-Blue-stained preparations shows that each muscle is innervated by 2–6 nerves running along its length. An electron microscope (EM) study shows that most of these nerves contain 50 nm diameter electron-lucent vesicles organised into numerous synapses along the muscle. Their size and appearance is consistent with their containing L-glutamate (L-Glu). Usually there is one nerve on each muscle containing 95 nm diameter electron-dense vesicles that are not organised into synapses. Such vesicles, whose appearance is consistent with their containing serotonin (5-HT), are never found co-localised with the small, clear vesicles.
Topically applied L-Glu causes the radial muscles to contract (and the chromatophore to expand), even after chronic denervation; this effect is blocked by the glutamate antagonists CNQX and DNQX. In contrast, topically applied 5-HT (or its agonists 8-OH-DOPAT and α-methyl 5-HT) induces relaxation of precontracted muscle. Incubation with antibodies to L-Glu (Lg-A), using peroxidase anti-peroxidase/diaminobenzidine visualisation, produces specific staining along the radial muscles like that seen with silver. Antibodies to 5-HT produce similar specific staining. When sections of skin that had stained positively with Lg-A in the light microscope are examined at the EM level, it is seen that such staining is confined to nerve axons.
These results, showing that L-Glu and 5-HT are endogenous in the nerves innervating squid chromatophores and that the radial muscles contain receptors for both substances, suggest that L-Glu is an excitatory transmitter at squid chromatophore muscles. The way in which 5-HT acts to relax the muscles, however, remains to be established.
The Effects of Length Trajectory on the Mechanical Power Output of Mouse Skeletal Muscles
Authors: Askew Graham N. , Marsh Richard L. 
Published: April 2021

ABSTRACT
The effects of length trajectory on the mechanical power output of mouse soleus and extensor digitorum longus (EDL) muscles were investigated using the work loop technique in vitro at 37 °C. Muscles were subjected to sinusoidal and sawtooth cycles of lengthening and shortening; for the sawtooth cycles, the proportion of the cycle spent shortening was varied. For each cycle frequency examined, the timing and duration of stimulation and the strain amplitude were optimized to yield the maximum power output. During sawtooth length trajectories, power increased as the proportion of the cycle spent shortening increased. The increase in power was attributable to more complete activation of the muscle due to the longer stimulation duration, to a more rapid rise in force resulting from increased stretch velocity and to an increase in the optimal strain amplitude. The power produced during symmetrical sawtooth cycles was 5–10 % higher than during sinusoidal work loops. Maximum power outputs of 92W kg−1 (soleus) and 247 W kg−1 (EDL) were obtained by manipulating the length trajectory. For each muscle, this was approximately 70 % of the maximum power output estimated from the isotonic force–velocity relationship.
We have found a number of examples suggesting that animals exploit prolonging the shortening phase during activities requiring a high power output, such as flying, jet-propulsion swimming and vocalization. In an evolutionary context, increasing the relative shortening duration provides an alternative to increasing the maximum shortening velocity (Vmax) as a way to increase power output.
The Effects of Walls, Paternity and Ageing on Sperm Motility
Authors: Gee Christopher C. , Zimmer-Faust Richard K. 
Published: April 2021

ABSTRACT
The measurement of sperm motility is critical when studying fertilization kinetics and chemotaxis. Analysis of motility has traditionally been carried out on cells in small fluid volumes on microscope slides. Several theoretical treatments suggest that drag forces significantly affect flagellar motion within 10 sperm body lengths of the slide surface. Understanding how sperm move in the absence of surface drag is crucial when considering natural locomotory patterns. To examine the effects of solid surfaces, motile sperm from sea urchins (Arbacia punctulata) were placed in a Plexiglas chamber (69 mm×45 mm×15.5 mm; length × width × height). A system was constructed to minimize convective flow by limiting temperature differences within the chamber to less than 0.1 °C. The movement of sperm was video-recorded at two levels:⩽100 μm (3 body lengths) and 5 mm (150 body lengths) below the chamber lid. When swimming speeds were measured using a computerized video motion-analysis system, a highly significant difference (P&lt;0.0001) between cells at the two depths was found. Cells nearest the lid swam at 174.6±5.9 μm s−1 (mean ± S.E.M.), whereas those farther away slowed to only 111.1±9.9 μm s−1 (mean ± S.E.M.). Swimming speed was also found to be significantly (P&lt;0.01) affected by paternity, but not by sperm age. We conclude that viscous wall effects must be carefully considered in studies of sperm motility and chemotaxis. The analysis of sperm on a microscope slide may substantially exaggerate swimming speed.
The Effect of Reduced Gravity on the Kinematics of Human Walking: A Test of the Dynamic Similarity Hypothesis for Locomotion
Authors: Donelan J. Maxwell , Kram Rodger 
Published: April 2021

ABSTRACT
To gain insight into the basic principles that govern the biomechanics of locomotion, we investigated the effect of reduced gravity on walking kinematics. We hypothesized that humans walk in a dynamically similar fashion at combinations of speed and simulated gravity that provide equal values of the Froude number, v2/gLleg, where v is forward speed, g is gravitational acceleration and Lleg is leg length. The Froude number has been used to predict the kinematics and kinetics of legged locomotion over a wide range of animal sizes and speeds, and thus provides a potentially unifying theory for the combined effects of speed, size and gravity on locomotion biomechanics. The occurrence of dynamic similarity at equal Froude numbers has been attributed previously to the importance of gravitational forces in determining locomotion mechanics. We simulated reduced gravity using a device that applies a nearly constant upward force to the torso while subjects walked on a treadmill. We found that at equal Froude numbers, under different levels of gravity (0.25g–1.0g), the subjects walked with nearly the same duty factor (ratio of contact time to stride time), but with relative stride lengths (Ls/Lleg, where Ls is stride length) that differed by as much as 67 %, resulting in the rejection of our hypothesis. To understand the separate effects of speed and gravity further, we compared the mechanics of walking at the same absolute speed at different levels of gravity (0.25g–1.0g). In lower gravity, subjects walked with lower duty factors (10 %) and shorter relative stride lengths (16 %). These modest changes in response to the fourfold change in gravity indicate that factors other than gravitational forces are the primary determinants of walking biomechanics.
Comparison of Ca2+ Currents of Peptidergic Neurons Developing Differing Morphology with Time in Culture
Authors: Meyers Donald E. R. , Cooke Ian M. 
Published: April 2021

ABSTRACT
The whole-cell patch-clamp technique was used to examine Ca2+ currents (ICa) in mature neurons cultured in defined medium and derived from the principal neurosecretory system of decapod crustaceans, the X-organ–sinus gland. After 1 day in culture, X-organ neurons of the crab Cardisoma carnifex showed vigorous outgrowth characterized either by the production of broad lamellipodia (veils) or, from smaller somata, a branching morphology. The neurons developing veils (veilers) had a large ICa (approximately 650 pA) and ICa current density (approximately 5 μA cm−2) while other types of neuron had little or no ICa. This distinction between the two types was still present after 5–6 days in culture. However, morphologies observed after additional outgrowth, when correlated with the ICa responses, allowed four groups to be distinguished: (1) veilers and (2) branching veilers, which developed from veilers and had a similar ICa density (approximately 3 μA cm−2); and, developing from the 1 day branchers, (3) spiny branchers or (4) small cells (ICa density approximately 0.8 μA cm−2). Immunoreactivity indicative of the presence of crustacean hyperglycemic hormone was found in all veilers and branching veilers tested, while molt-inhibiting hormone reactivity, when observed, was seen in cells having a robust ICa density (≥:1.2 μA cm−2). Normalized average current–voltage curves for each morphological group were examined for changes with increasing time in culture. The curves were consistent with the ICa being produced by a population of high-voltage-activated Ca2+ channels whose properties are biophysically indistinguishable and unaffected by time in culture. The averaged peak current did not change, despite an increase in neuronal surface area as outgrowth proceeded, and this resulted in a reduction of ICa density. This indicated that net addition of Ca2+ channels did not match the addition of new membrane under our culturing conditions.