bluuebunny/crossref_metadata_2025_split huggingface dataset:
Supercontracting muscle: producing tension over extreme muscle lengths
Authors: Herrel Anthony , Meyers Jay J. , Timmermans Jean-Pierre , Nishikawa Kiisa C. 
Published: April 2021

SUMMARYMuscle mechanics dictates a trade-off between the ability of a muscle to generate isometric force and its length. This intrinsic trade-off is the result of the need for overlap between thick and thin filaments upon extension of the sarcomere and of the limitations imposed by the physical interference between the thin filaments and the thick filaments with the Z-disk upon contraction. However, previously published data indicate that chameleons are able to produce a nearly constant tongue retraction force over a wide range of tongue extension lengths, made possible by the presence of supercontracting muscle in the tongue retractors. Investigation of the length/tension properties and ultrastructure of the tongue retractor in a closely related agamid lizard (Pogona vitticeps) indicates that the ability to generate tension at extreme elongation is probably a derived feature for chameleons. Whereas chameleons are unique among vertebrates in possessing supercontracting muscle, this seems to be a common phenomenon in invertebrates. However, the presence of supercontracting muscle in chameleons and in several invertebrate groups seems to be coupled to the need to generate tension over large changes in muscle length and might be a more general solution for this problem.
Phylogenetic implications of the superfast myosin in extraocular muscles
Authors: Schachat Fred , Briggs Margaret M. 
Published: April 2021

SUMMARYExtraocular muscle exhibits higher-velocity and lower-tension contractions than other vertebrate striated muscles. These distinctive physiological properties are associated with the expression of a novel extraocular myosin heavy chain (MYH). Encoded by the MYH13 gene, the extraocular myosin heavy chain is a member of the fast/developmental MYH gene cluster on human chromosome 17 and the syntenic MYH cluster on mouse chromosome 11. Comparison of cDNA sequences reveals that MYH13 also encodes the atypical MYH identified in laryngeal muscles, which have similar fast contractile properties. Comparing the MYH13 sequence with the other members of the fast/developmental cluster, the slow/cardiac MYH genes and two orphan skeletal MYH genes in the human genome provides insights into the origins of specialization in striated muscle myosins. Specifically, these studies indicate (i) that the extraocular myosin is not derived from the adult fast skeletal muscle myosins, but was the first member of the fast/developmental MYH gene cluster to diverge and specialize, (ii) that the motor and rod domains of the MYH13 have evolved under different selective pressures and (iii) that the MYH13 gene has been largely insulated from genomic events that have shaped other members of the fast/developmental cluster. In addition, phylogenetic footprinting suggests that regulation of the extraocular MYH gene is not governed primarily by myogenic factors, but by a hierarchical network of regulatory factors that relate its expression to the development of extraocular muscles.
Lift and power requirements of hovering flight inDrosophila virilis
Authors: Sun Mao , Tang Jian 
Published: April 2021

SUMMARYThe lift and power requirements for hovering flight in Drosophila virilis were studied using the method of computational fluid dynamics. The Navier-Stokes equations were solved numerically. The solution provided the flow velocity and pressure fields, from which the unsteady aerodynamic forces and moments were obtained. The inertial torques due to the acceleration of the wing mass were computed analytically. On the basis of the aerodynamic forces and moments and the inertial torques, the lift and power requirements for hovering flight were obtained.For the fruit fly Drosophila virilis in hovering flight (with symmetrical rotation), a midstroke angle of attack of approximately 37°was needed for the mean lift to balance the insect weight, which agreed with observations. The mean drag on the wings over an up- or downstroke was approximately 1.27 times the mean lift or insect weight (i.e. the wings of this tiny insect must overcome a drag that is approximately 27 % larger than its weight to produce a lift equal to its weight). The body-mass-specific power was 28.7 W kg-1, the muscle-mass-specific power was 95.7 W kg-1 and the muscle efficiency was 17 %.With advanced rotation, larger lift was produced than with symmetrical rotation, but it was more energy-demanding, i.e. the power required per unit lift was much larger. With delayed rotation, much less lift was produced than with symmetrical rotation at almost the same power expenditure; again, the power required per unit lift was much larger. On the basis of the calculated results for power expenditure, symmetrical rotation should be used for balanced, long-duration flight and advanced rotation and delayed rotation should be used for flight control and manoeuvring. This agrees with observations.
Respiratory airflow in a wingless dung beetle
Authors: Duncan Frances D. , Byrne Marcus J. 
Published: April 2021

SUMMARYThe sealed subelytral cavity of many flightless beetle species is widely acknowledged to be an adaptation to water saving in arid-habitat species. However, this hypothesis relies on the acceptance of two largely untested assumptions: (i) that the movement of respiratory gases is unidirectional from anterior to posterior and (ii) that the coordinated action of the spiracles directs this flow. We tested these assumptions by simultaneously measuring CO2 and O2 exchange at the anterior mesothorax,independently of gas exchange in the posterior body, which included the subelytral cavity, of a large apterous beetle, Circellium bacchus. Flow-through respirometry revealed a marked discontinuous gas-exchange cycle(DGC) pattern from the anterior half of the body. Very little CO2was released from the posterior body, where the DGC was not apparent. Labelled air was shown to flow forwards from the posterior to the anterior body. Individual sampling from the mesothoracic spiracles revealed that the right mesothoracic spiracle, lying outside the elytral cavity, is the primary route for respiratory gas exchange in C. bacchus at rest. This discovery necessitates a reassessment of the currently assumed role of the subelytral cavity in water conservation and is, to our knowledge, the first demonstration of forward airflow associated with the unilateral use of a single thoracic spiracle for respiration in an insect.
View-based navigation in insects: how wood ants (Formica rufaL.) look at and are guided by extended landmarks
Authors: Graham Paul , Collett Thomas S. 
Published: April 2021

SUMMARYBees, wasps and ants learn landmarks as views from particular vantage points, storing the retinal positions of landmark edges. By moving so as to minimise the difference between their stored and current view, they can return to the vantage point from which a view was taken. We have examined what wood ants learn about a laterally placed, extended landmark, a wall, while walking parallel to it to reach a feeder and how they use this stored information to guide their path. Manipulation of the height of the wall and the ant's starting distance from it reveals that ants maintain a desired distance from the wall by keeping the image of the top of the wall at a particular retinal elevation. Ants can thus employ image matching both for returning to a place and for following a fixed route.Unlike many flying insects, an ant's direction of motion while walking is always along its longitudinal body axis and, perhaps for this reason, it favours its frontal retina for viewing discrete landmarks. We find that ants also use their frontal retina for viewing a laterally placed wall. On a coarse scale, the ant's path along the wall is straight, but on a finer scale it is roughly sinusoidal, allowing the ant to scan the surrounding landscape with its frontal retina. The ant's side-to-side scanning means that the wall is viewed with its frontal retina for phases of the scanning cycle throughout its trajectory. Details of the scanning pattern depend on the scene. Ants scan further to the side that is empty of the wall than to the side containing the wall, and they scan further into the wall side when the wall is of a lower apparent height. We conclude that frontal retina is employed for image storage and for path control.
Conserved tyrosine-147 plays a critical role in the ligand-gated current of the epithelial cation/amino acid transporter/channel CAATCH1
Authors: Stevens Bruce R. , Feldman Daniel H. , Liu Zhilin , Harvey William R. 
Published: April 2021

SUMMARYCAATCH1 functions both as an amino-acid-gated cation channel and as a cation-dependent, proline-preferring, nutrient amino acid transporter in which the two functions are thermodynamically uncoupled. This study focuses on the ionic channel aspect, in which a Tyr147 (wild type) to Phe147 (Y147F) site-directed mutation was investigated by steady-state electrophysiological measurements in the Xenopus laevisoocyte expression system. This tyrosine residue is conserved within the third transmembrane domain in members of the Na+:neurotransmitter transporter family (SNF), where it plays a role in binding pharmacological ligands such as cocaine to the serotonin (SERT), dopamine (DAT) and norepinephrine (NET) transporters. Epithelial CAATCH1 is a member of the SNF family. The results show that amino acid ligand-gating selectivity and current magnitudes in Na+- and K+-containing media are differentially altered in CAATCH1 Y147F compared with the wild type. In the absence of amino acid ligands, the channel conductance of Na+,K+ and Li+ that is observed in the wild type was reduced to virtually zero in Y147F. In the wild type, proline binding increased conductance strongly in Na+-containing medium and moderately in K+-containing medium, whereas in Y147F proline failed to elicit any cation currents beyond those of N-methyl-D-glucamine- or water-injected oocytes. In the wild type, methionine binding strongly inhibited inward Na+ currents, whereas in Y147F it strongly stimulated inward currents in both Na+ and K+-containing media. Indeed, in Na+-containing medium, the relative potency ranking for inward current inhibition in the wild type(Met&gt;Leu&gt;Gly&gt;Phe&gt;Thr) was similar to the ranking of ligand-permissive gating of large inward currents in Y147F. In Na+-containing medium, current/voltage relationships elicited by ligands in the wild type were complex and reversing, whereas in Y147F they were linear and inwardly rectifying. In K+-containing medium,current/voltage relationships remained non-linear in Y147F. Both wild-type and Y147F currents were Cl--independent. Together, these data demonstrate a critical role for Tyr147 in ligand-binding selectivity and modulation of the ionic channel conductance in CAATCH1. The results support the argument that inhibition of the CAATCH1 conductance by free methionine shares some properties in common with ligand inhibition of DAT, SERT, NET and the γ-aminobutyric acid transporter (GAT1).
Mutations in theDrosophilaglycoprotein hormone receptor,rickets, eliminate neuropeptide-induced tanning and selectively block a stereotyped behavioral program
Authors: Baker James D. , Truman James W. 
Published: April 2021

SUMMARYAdult insects achieve their final form shortly after adult eclosion by the combined effects of specialized behaviors that generate increased blood pressure, which causes cuticular expansion, and hormones, which plasticize and then tan the cuticle. We examined the molecular mechanisms contributing to these processes in Drosophila by analyzing mutants for the rickets gene. These flies fail to initiate the behavioral and tanning processes that normally follow ecdysis. Sequencing of rickets mutants and STS mapping of deficiencies confirmed that rickets encodes the glycoprotein hormone receptor DLGR2. Although rickets mutants produce and release the insect-tanning hormone bursicon, they do not melanize when injected with extracts containing bursicon. In contrast, mutants do melanize in response to injection of an analog of cyclic AMP, the second messenger for bursicon. Hence, rickets appears to encode a component of the bursicon response pathway, probably the bursicon receptor itself. Mutants also have a behavioral deficit in that they fail to initiate the behavioral program for wing expansion. A set of decapitation experiments utilizing rickets mutants and flies that lack cells containing the neuropeptide eclosion hormone, reveals a multicomponent control to the activation of this behavioral program.
Rapid patterning and zonal differentiation in a two-dimensionalDictyosteliumcell mass: the role of pH and ammonia
Authors: Sawai Satoshi , Hirano Takashi , Maeda Yasuo , Sawada Yasuji 
Published: April 2021

SUMMARYRecently it was demonstrated that a rapidly forming, self-organizing pattern that emerges within two-dimensional Dictyostelium discoideumcell cultures could later give rise to stripes of distinct zones, each comprising different cell types. Here we report physiological aspects of the initial rapid patterning and its relationship to cell differentiation. We found that as the temperature is lowered the characteristic length of the pattern increases. From this we estimated the activation energy of the patterning kinetics. Fluorescence of fluorescein-conjugated dextran revealed that the cytosolic pH of cells in the inside zone becomes lower than that in the outer zone facing the air. The patterning could be inhibited by addition of the plasma-membrane proton pump inhibitors diethystilbestrol (DES) or miconazole. Preincubation of cells with weak acid delayed the timing of the patterning, whereas weak base hastened it. A pH-indicating dye revealed localized accumulation of ammonia in the extracellular space. These results suggest that gradients of secreted metabolites may be directly responsible for the rapid patterning and its consequence on cell differentiation in a confined geometrical situation. Possible diffusible candidate molecules and a reaction scheme coupled to the imposed oxygen gradient are discussed.
Dynamic stabilization of rapid hexapedal locomotion
Authors: Jindrich Devin L. , Full Robert J. 
Published: April 2021

SUMMARYTo stabilize locomotion, animals must generate forces appropriate to overcome the effects of perturbations and to maintain a desired speed or direction of movement. We studied the stabilizing mechanism employed by rapidly running insects by using a novel apparatus to perturb running cockroaches (Blaberus discoidalis). The apparatus used chemical propellants to accelerate a small projectile, generating reaction force impulses of less than 10 ms duration. The apparatus was mounted onto the thorax of the insect, oriented to propel the projectile laterally and loaded with propellant sufficient to cause a nearly tenfold increase in lateral velocity relative to maxima observed during unperturbed locomotion. Cockroaches were able to recover from these perturbations in 27±12 ms(mean ± S.D., N=9) when running on a high-friction substratum. Lateral velocity began to decrease 13±5 ms (mean ± S.D., N=11) following the start of a perturbation, a time comparable with the fastest reflexes measured in cockroaches. Cockroaches did not require step transitions to recover from lateral perturbations. Instead, they exhibited viscoelastic behavior in the lateral direction, with spring constants similar to those observed during unperturbed locomotion. The rapid onset of recovery from lateral perturbations supports the possibility that, during fast locomotion, intrinsic properties of the musculoskeletal system augment neural stabilization by reflexes.
Intensity control during target approach in echolocating bats;stereotypical sensori-motor behaviour in Daubenton's bats,Myotis daubentonii
Authors: Boonman Arjan , Jones Gareth 
Published: April 2021

SUMMARYWhen approaching a prey target, bats have been found to decrease the intensity of their emitted echolocation pulses, called intensity compensation. In this paper we examine whether intensity compensation in the echolocation of bats is flexible or stereotyped. We recorded the echolocation calls of Daubenton's bats (Myotis daubentonii) while the animals attacked targets of different dimensions. Myotis daubentonii reduced the peak sound pressure level emitted by about 4dB for each halving of distance,irrespective of the target presented (mealworms and two different sizes of spheres). The absolute sound pressure level emitted by the bat is not or only a little affected by target strength. Furthermore, the decrease in emitted intensity over distance shows less scatter than the same intensity over time for the last 20 cm of target approach. The bats matched the emitted intensity to target distance equally well for the spheres (aspect-invariant target strength) as for the mealworms (aspect-dependent echo strength). We therefore conclude that intensity compensation does not rely on feedback information from received intensity, but instead follows a stereotyped pattern.
Swimming in needlefish (Belonidae): anguilliform locomotion with fins
Authors: Liao James C. 
Published: April 2021

SUMMARYThe Atlantic needlefish (Strongylura marina) is a unique anguilliform swimmer in that it possesses prominent fins, lives in coastal surface-waters, and can propel itself across the surface of the water to escape predators. In a laboratory flow tank, steadily swimming needlefish perform a speed-dependent suite of behaviors while maintaining at least a half wavelength of undulation on the body at all times. To investigate the effects of discrete fins on anguilliform swimming, I used high-speed video to record body and fin kinematics at swimming speeds ranging from 0.25 to 2.0 Ls-1 (where L is the total body length). Analysis of axial kinematics indicates that needlefish are less efficient anguilliform swimmers than eels, indicated by their lower slip values. Body amplitudes increase with swimming speed, but unlike most fishes, tail-beat amplitude increases linearly and does not plateau at maximal swimming speeds. At 2.0 Ls-1, the propulsive wave shortens and decelerates as it travels posteriorly, owing to the prominence of the median fins in the caudal region of the body. Analyses of fin kinematics show that at 1.0 Ls-1 the dorsal and anal fins are slightly less than 180° out of phase with the body and approximately 225° out of phase with the caudal fin. Needlefish exhibit two gait transitions using their pectoral fins. At 0.25 L s-1, the pectoral fins oscillate but do not produce thrust, at 1.0 L s-1 they are held abducted from the body,forming a positive dihedral that may reduce rolling moments, and above 2.0 L s-1 they remain completely adducted.
Differential scaling of locomotor performance in small and large terrestrial mammals
Authors: Iriarte-Díaz José 
Published: April 2021

SUMMARYIt has been observed that the relationship between locomotor performance and body mass in terrestrial mammals does not follow a single linear trend when the entire range of body mass is considered. Large taxa tend to show different scaling exponents compared to those of small taxa, suggesting that there would be a differential scaling between small and large mammals. This pattern, noted previously for several morphological traits in mammals, has been explained to occur as a result of mechanical constraints over bones due to the differential effect of gravity on small and large-sized forms. The relationship between maximum relative running speed (body length s-1) and body mass was analysed in 142 species of terrestrial mammals, in order to evaluate whether the relative locomotor performance shows a differential scaling depending on the range of mass analysed, and whether the scaling pattern is consistent with the idea of mechanical constraints on locomotor performance. The scaling of relative locomotor performance proved to be non-linear when the entire range of body masses was considered and showed a differential scaling between small and large mammals. Among the small species,a negative, although nearly independent, relationship with body mass was noted. In contrast, maximum relative running speed in large mammals showed a strong negative relationship with body mass. This reduction in locomotor performance was correlated with a decrease in the ability to withstand the forces applied on bones and may be understood as a necessary stress reduction mechanism for assuring the structural integrity of the limb skeleton in large species.
Altitudinal variation in parental energy expenditure by white-crowned sparrows
Authors: Weathers Wesley W. , Davidson Charisse L. , Olson Christopher R. , Morton Martin L. , Nur Nadav , Famula Thomas R. 
Published: April 2021

SUMMARY
We used the doubly labeled water technique to measure daily energy expenditure (DEE) during the incubation and feeding nestling stages in two populations of white-crowned sparrows (Zonotrichia leucophrys)— one montane and migratory, the other coastal and sedentary —that differ in thermal environment and clutch size. We assessed the birds'thermal environment by continuously monitoring (among other variables)operative temperature and wind speed both in the open and within bushes and willow thickets occupied by sparrows. From these measurements, we derived several estimates of the birds' thermal environment, including standard operative temperature (Tes). Shade air temperature and Tes averaged 6.6 and 10.3°C lower, respectively, at the montane study site during DEE measurements. The montane population's DEE averaged 24% higher than that of the sea-level population (103.6±12.2 versus 83.7±9.6 kJ day-1; means ± S.D., N=31 and 22, respectively), reflecting both its larger brood size(3.7 versus 2.9) and the colder environment. The DEE:BMR ratio was lowest in the sea-level population (2.1 versus 2.6), but neither population worked to their physiological capacity to produce young. DEE was significantly correlated with temperature across populations, with Tes explaining 42% of the variation in DEE. Statistically removing the effect of temperature by adjusting DEE to a common temperature reduced the difference in DEE between populations by 34% to 87.7 and 100.8 kJ day-1, respectively, for sea-level and montane populations. Basal and resting metabolic rates were similar in both populations, implying that greater activity in the montane population accounted for its higher temperature-adjusted DEE. Our results indicate that the thermal context within which behavior occurs can significantly affect interindividual variation in DEE. Attempts to assess reproductive effort by measuring DEE should therefore account explicitly for the effect of temperature.