bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rapid Cold-Hardening of Drosophila Melanogaster (Diptera: Drosophilidae) During Ecologically Based Thermoperiodic Cycles
Authors: Kelty Jonathan D. , Lee Richard E. 
Published: April 2021

ABSTRACT
In contrast to most studies of rapid cold-hardening, in which abrupt transfers to low temperatures are used to induce an acclimatory response, the primary objectives of this study were to determine (i) whether rapid cold-hardening was induced during the cooling phase of an ecologically based thermoperiod, (ii) whether the protection afforded was lost during warming or contributed to increased cold-tolerance during subsequent cycles and (iii) whether the major thermally inducible stress protein (Hsp70) or carbohydrate cryoprotectants contributed to the protection afforded by rapid cold-hardening. During the cooling phase of a single ecologically based thermoperiod, the tolerance of Drosophila melanogaster to 1 h at −7 °C increased from 5±5 % survival to 62.5±7.3 % (means ± S.E.M., N=40–60), while their critical thermal minima (CTmin) decreased by 1.9 °C. Cold hardiness increased with the number of thermoperiods to which flies were exposed; i.e. flies exposed to six thermoperiods were more cold-tolerant than those exposed to two. Endogenous levels of Hsp70 and carbohydrate cryoprotectants were unchanged in rapidly cold-hardened adults compared with controls held at a constant 23 °C. In nature, rapid cold-hardening probably affords subtle benefits during short-term cooling, such as allowing D. melanogaster to remain active at lower temperatures than they otherwise could.
Passerinesversusnonpasserines: so far, no statistical differences in the scaling of avian energetics
Authors: Rezende Enrico L. , Swanson David L. , Novoa F. Fernando , Bozinovic Francisco 
Published: April 2021

SUMMARYWe analyzed and compared the scaling of both basal and maximal thermogenic metabolic rates in passerine and nonpasserine birds using conventional and phylogenetic methods. In spite of the presumed adaptive importance of both metabolic traits, few studies concerning both their relationships and their ecological and evolutionary constraints have been conducted. We found no statistical differences in the scaling of maximal metabolic rate between passerines and nonpasserines; hence, we suggest the use of a single allometric regression for this trait in birds. In addition, basal and maximal metabolic rates were indeed correlated after removing the effects of body mass and phylogeny. The apparent generality of this correlation within both birds and mammals reinforces the need for general ecological and physiological explanations for the evolution of endothermy.
Unsteady aerodynamic force generation by a model fruit fly wing in flapping motion
Authors: Sun Mao , Tang Jian 
Published: April 2021

SUMMARY
A computational fluid-dynamic analysis was conducted to study the unsteady aerodynamics of a model fruit fly wing. The wing performs an idealized flapping motion that emulates the wing motion of a fruit fly in normal hovering flight. The Navier–Stokes equations are solved numerically. The solution provides the flow and pressure fields, from which the aerodynamic forces and vorticity wake structure are obtained. Insights into the unsteady aerodynamic force generation process are gained from the force and flow-structure information.
Considerable lift can be produced when the majority of the wing rotation is conducted near the end of a stroke or wing rotation precedes stroke reversal (rotation advanced), and the mean lift coefficient can be more than twice the quasi-steady value. Three mechanisms are responsible for the large lift: the rapid acceleration of the wing at the beginning of a stroke, the absence of stall during the stroke and the fast pitching-up rotation of the wing near the end of the stroke.
When half the wing rotation is conducted near the end of a stroke and half at the beginning of the next stroke (symmetrical rotation), the lift at the beginning and near the end of a stroke becomes smaller because the effects of the first and third mechanisms above are reduced. The mean lift coefficient is smaller than that of the rotation-advanced case, but is still 80 % larger than the quasi-steady value. When the majority of the rotation is delayed until the beginning of the next stroke (rotation delayed), the lift at the beginning and near the end of a stroke becomes very small or even negative because the effect of the first mechanism above is cancelled and the third mechanism does not apply in this case. The mean lift coefficient is much smaller than in the other two cases.
Estimates of circulation and gait change based on a three-dimensional kinematic analysis of flight in cockatiels (Nymphicus hollandicus)and ringed turtle-doves (Streptopelia risoria)
Authors: Hedrick Tyson L. , Tobalske Bret W. , Biewener Andrew A. 
Published: April 2021

SUMMARYBirds and bats are known to employ two different gaits in flapping flight,a vortex-ring gait in slow flight and a continuous-vortex gait in fast flight. We studied the use of these gaits over a wide range of speeds (1-17 ms-1) and transitions between gaits in cockatiels (Nymphicus hollandicus) and ringed turtle-doves (Streptopelia risoria)trained to fly in a recently built, variable-speed wind tunnel. Gait use was investigated via a combination of three-dimensional kinematics and quasi-steady aerodynamic modeling of bound circulation on the distal and proximal portions of the wing. Estimates of lift from our circulation model were sufficient to support body weight at all but the slowest speeds (1 and 3 ms-1). From comparisons of aerodynamic impulse derived from our circulation analysis with the impulse estimated from whole-body acceleration,it appeared that our quasi-steady aerodynamic analysis was most accurate at intermediate speeds (5-11 ms-1). Despite differences in wing shape and wing loading, both species shifted from a vortex-ring to a continuous-vortex gait at 7 ms-1. We found that the shift from a vortex-ring to a continuous-vortex gait (i) was associated with a phase delay in the peak angle of attack of the proximal wing section from downstroke into upstroke and (ii) depended on sufficient forward velocity to provide airflow over the wing during the upstroke similar to that during the downstroke. Our kinematic estimates indicated significant variation in the magnitude of circulation over the course the wingbeat cycle when either species used a continuous-vortex gait. This variation was great enough to suggest that both species shifted to a ladder-wake gait as they approached the maximum flight speed (cockatiels 15 ms-1, doves 17 ms-1) that they would sustain in the wind tunnel. This shift in flight gait appeared to reflect the need to minimize drag and produce forward thrust in order to fly at high speed. The ladder-wake gait was also employed in forward and vertical acceleration at medium and fast flight speeds.
Temporal determinants of long-term retention of olfactory memory in the cricket Gryllus bimaculatus
Authors: Matsumoto Yukihisa , Mizunami Makoto 
Published: April 2021

SUMMARY
Temporal determinants of olfactory long-term memory retention in the cricket Gryllus bimaculatus were studied. Elementary appetitive and aversive conditioning procedures, as well as a differential conditioning procedure, were applied. In appetitive conditioning, peppermint odour was paired with a water reward. In aversive conditioning, vanilla odour was paired with saline solution. In differential conditioning, an appetitive conditioning trial was followed by an aversive conditioning trial. The odour preference of crickets was tested before and 2 h, 1 day and 4 days after training by allowing the crickets to choose between peppermint or vanilla sources. Differential conditioning or appetitive conditioning alone led to long-lasting memory retention with no significant decay from 2 h to 4 days after training,but retention after aversive conditioning was absent 1 day after training. Studies using differential conditioning have shown (i) that four trials are sufficient to cause a saturated level of acquisition, (ii) that conditioning is successful when the conditioned stimulus is presented immediately or 5 s before the onset of presentation of the unconditioned stimulus, (iii) that the optimal interval between trials is 2-5 min, and (iv) that anaesthetic treatment with CO2 given immediately after training results in memory disruption but that anaesthetic-resistant memory develops fully 20 min after training. This study demonstrates that a differential conditioning procedure is particularly effective for the formation of long-term memory.
Fertilization in the sea
Authors: Riffell Jeffrey A. , Krug Patrick J. , Zimmer Richard K. 
Published: April 2021

SUMMARYChemical communication between sperm and egg is a key factor mediating sexual reproduction. Dissolved signal molecules that cause sperm to orient and accelerate towards an egg could play pivotal roles in fertilization success,but such compounds are largely undescribed. This investigation considered the behavioral responses of red abalone (Haliotis rufescens) sperm to soluble factors released into sea water by conspecific eggs. Sperm in proximity to individual live eggs swam significantly faster and oriented towards the egg surface. Bioassay-guided fractionation was employed to isolate the chemoattractant, yielding a single pure, fully active compound after reversed-phase and size-exclusion high-performance liquid chromatography. Chemical characterization by nuclear magnetic resonance spectroscopy indicated that the free amino acid L-tryptophan was the natural sperm attractant in H. rufescens.Eggs released L-tryptophan at concentrations that triggered both activation and chemotaxis in sperm, exhibiting significant activity at levels as low as 10-8 mol l-1. The D-isomer of tryptophan was inactive,showing that the sperm response was stereospecific. Serotonin, a potent neuromodulator and tryptophan metabolite, had no effect on sperm swim speeds or on orientation. In experimental treatments involving an elevated, uniform concentration of tryptophan (10-7 mol l-1) or the addition of tryptophanase, an enzyme that selectively digests tryptophan,sperm failed to navigate towards live eggs. A natural gradient of L-tryptophan was therefore necessary and sufficient to promote recruitment of sperm to the surface of eggs in red abalone.
A three-dimensional computational study of the aerodynamic mechanisms of insect flight
Authors: Ramamurti Ravi , Sandberg William C. 
Published: April 2021

SUMMARY
A finite element flow solver was employed to compute unsteady flow past a three-dimensional Drosophila wing undergoing flapping motion. The computed thrust and drag forces agreed well with results from a previous experimental study. A grid-refinement study was performed to validate the computational results, and a grid-independent solution was achieved. The effect of phasing between the translational and rotational motions was studied by varying the rotational motion prior to the stroke reversal. It was observed that, when the wing rotation is advanced with respect to the stroke reversal,the peak in the thrust forces is higher than when the wing rotation is in phase with the stroke reversal and that the peak thrust is reduced further when the wing rotation is delayed. As suggested by previous authors, we observe that the rotational mechanism is important and that the combined translational and rotational mechanisms are necessary to describe accurately the force time histories and unsteady aerodynamics of flapping wings.
Jumping and kicking in the false stick insectProsarthria teretrirostris: kinematics and motor control
Authors: Burrows Malcolm , Wolf Harald 
Published: April 2021

SUMMARYThe false stick insect Prosarthria teretrirostris looks and behaves like a real stick insect but can jump and kick rapidly and powerfully like a locust, to which it is more closely related. It has an elongated body with slender hind legs that are some 2.5 times longer than the front and middle legs. A male with a body 67 mm long and weighing 0.28 g can jump 90 cm with a take-off angle of 40° and velocity of 2.5 ms-1,requiring an energy expenditure of 850 μJ. The body is accelerated at 165 ms-2 for only 30 ms. The larger and heavier females (mean body length 104 mm and weighing 1.5 g) can jump on average a distance of 49 cm.During jumping, the tibiae of the hind legs are extended in 30 ms with maximum rotational velocities of 11.5° per ms, but during kicking, when there is no body weight to support, extension is complete in 7 ms with rotational velocities as high as 48° per ms. The short time available to accelerate the body indicates that the movements are not powered by direct muscle contractions and that there must be storage of elastic energy in advance. The motor patterns responsible for generating the necessary forces in the hind legs for jumping and kicking are similar and consist of three phases;an initial flexion of the tibia is followed by a co-contraction of the small flexor and large extensor tibiae muscles lasting several hundred milliseconds while the tibia remains fully flexed. Finally, the flexor motor neurons stop spiking so that the tibia is able to extend rapidly. The small semi-lunar processes at the femoro-tibial joints are not distorted, so that they cannot act as energy stores. Some 7% of the energy is stored transiently by bending the thin tibiae during the initial acceleration phase of a jump and releasing it just before take-off.The jumping and kicking mechanisms of Prosarthria teretrirostrishave features in common with those used by locusts but also have their own characteristics. The evolution of jumping in Orthoptera is discussed in this context.
The locust tegula: kinematic parameters and activity pattern during the wing stroke
Authors: Fischer Hanno , Wolf Harald , Büschges Ansgar 
Published: April 2021

SUMMARYThe tegula is a complex, knob-shaped sense organ associated with the base of the locust wing. Despite a detailed knowledge of its role in flight motor control, little is known about the relationship between the stroke parameters of the wing, movement of the tegula organ and the pattern of tegula activity. In this study, therefore, the kinematic parameters of the fore- and hindwings were investigated with respect to the tegula activity pattern during tethered flight. The following results were obtained. (i) The tegula moves through a complex three-dimensional trajectory during the wing stroke, involving inclination and rotation about its longitudinal axis. (ii) The kinematic parameters of tegula movement are phase-locked to the wing stroke and vary in conjunction with wing stroke parameters such as amplitude and cycle period.(iii) In accordance with these phase-locked kinematics, both the onset of tegula activity with respect to the downstroke (latency) and the discharge of the organ (burst duration and amplitude) vary in conjunction with downstroke movement and cycle period, resulting in an (almost) constant phase of tegula activation during the stroke cycle. (iv) The pattern of tegula activity during flight is largely independent of stroke amplitude. (v) The latency, burst duration and amplitude of tegula activity are strongly related to the angular velocity of the wing during the downstroke, with latency reaching a steady minimum value at higher angular velocities. The data suggest that the tegula encodes the timing and velocity of the downstroke and that it may be involved in the control of the stroke's angular velocity.
The heart ofCiona intestinalis: eicosanoid-generating capacity and the effects of precursor fatty acids and eicosanoids on heart rate
Authors: Pope Edward C. , Rowley Andrew F. 
Published: April 2021

SUMMARYEicosanoids are a group of oxygenated fatty-acid derivatives formed from C20 polyunsaturated fatty acids including arachidonic and eicosapentaenoic acids. In mammals, these compounds have been shown to be key molecules in several physiological processes including regulation of the vascular system. This study determined whether eicosanoids or their precursors are involved in the regulation of heart rate in the sea squirt Ciona intestinalis. Eicosanoid generation by both heart and blood cells was measured. The major lipoxygenase products formed were both derivatives of eicosapentaenoic acid,namely 8- and 12-hydroxyeicosapentaenoic acids (8-HEPE and 12-HEPE). Smaller amounts of 8,15-dihydroxyeicosapentaenoic acid (8,15-diHEPE) were also formed. The cyclo-oxygenase product prostaglandin E was also found in small amounts in the heart. Isolated hearts were exposed either to these fatty acid precursors or to 8-HEPE, 12-HEPE or prostaglandin E3, and the effect on heart rate was recorded. Both eicosapentaenoic and arachidonic acids stimulated the heart rate at concentrations between 50 and 200 μmoll-1. 12-HEPE(5 μmoll-1) and prostaglandin E3 (50μmoll-1) caused a modest increase in heart rate, while 8-HEPE had no significant effects at any of the time periods studied (≤180 min). Overall, the results show that arachidonic and eicosapentaenoic acids have limited effects on heart rate and only at concentrations unlikely to be routinely liberated in vivo. Similarly, the eicosanoids tested had a minor stimulatory activity on heart rate. The potential mechanisms for this stimulation are discussed. Overall, these results suggest that such compounds are of limited importance in regulating the heart and vascular system of sea squirts.
Intracellular ion activities in Malpighian tubule cells ofRhodnius prolixus: evaluation of Na+-K+-2Cl-cotransport across the basolateral membrane
Authors: Ianowski Juan P. , Christensen Robert J. , O'Donnell Michael J. 
Published: April 2021

SUMMARYIntracellular ion activities (aion) and basolateral membrane potential (Vbl) were measured in Malpighian tubule cells of Rhodnius prolixus using double-barrelled ion-selective microelectrodes. In saline containing 103mmoll-1Na+, 6mmoll-1 K+ and 93mmoll-1Cl-, intracellular ion activities in unstimulated upper Malpighian tubules were 21, 86 and 32mmoll-1, respectively. In serotonin-stimulated tubules, aCl was unchanged, whereas aNa increased to 33mmoll-1 and aK declined to 71mmoll-1. Vbl was -59mV and -63mV for unstimulated and stimulated tubules, respectively. Calculated electrochemical potentials(Δμ/F) favour passive movement of Na+ into the cell and passive movement of Cl- out of the cell in both unstimulated and serotonin-stimulated tubules. Passive movement of K+ out of the cell is favoured in unstimulated tubules. In stimulated tubules, Δμ/F for K+ is close to 0 mV.The thermodynamic feasibilities of Na+-K+-2Cl-, Na+-Cl-and K+-Cl- cotransporters were evaluated by calculating the net electrochemical potential (Δμnet/F) for each transporter. Our results show that a Na+-K+-2Cl- or a Na+-Cl- cotransporter but not a K+-Cl- cotransporter would permit the movement of ions into the cell in stimulated tubules. The effects of Ba2+ and ouabain on Vbl and rates of fluid and ion secretion show that net entry of K+ through ion channels or the Na+/K+-ATPase can be ruled out in stimulated tubules. Maintenance of intracellular Cl- activity was dependent upon the presence of both Na+ and K+ in the bathing saline. Bumetanide reduced the fluxes of both Na+ and K+. Taken together, the results support the involvement of a basolateral Na+-K+-2Cl- cotransporter in serotonin-stimulated fluid secretion by Rhodnius prolixus Malpighian tubules.
Fertilization ecology of egg coats: physicalversuschemical contributions to fertilization success of free-spawned eggs
Authors: Podolsky Robert D. 
Published: April 2021

SUMMARYFree-spawned eggs are typically enclosed within accessory structures that are shed early in development. Most research on the role of these structures in fertilization has focused on chemical constituents and their influence on sperm—egg interaction. Here I test an alternative hypothesis that accessory structures play an important physical role in fertilization by increasing the size and buoyancy of the egg, making it a better target for sperm. In the sand dollar Dendraster excentricus, the jelly coat increases egg target size sixfold. At nonsaturating sperm concentrations,fertilization declined consistently following jelly coat removal by two independent methods. Regression analysis using a standard fertilization kinetics model found that 54-73% of this decline on average was predicted by changes in the rate of sperm—egg collision, resulting from changes in egg target size and density. Sperm swimming speed, a key parameter in the model, did not vary as a function of sperm concentration or exposure to egg-water. The organic cost of jelly is a fraction of that of the ovum,providing an efficient means of extending target size beyond the ovum size that is optimal for larval or juvenile development. These results support the hypothesis that physical attributes of jelly coats can account for a significant portion of their contribution to fertilization, and may help to explain why coats and other accessory structures are often substantially larger than expected from the nature of chemical interactions between egg and sperm.
Hydrodynamics of caudal fin locomotion by chub mackerel,Scomber japonicus(Scombridae)
Authors: Nauen Jennifer C. , Lauder George V. 
Published: April 2021

SUMMARYAs members of the derived teleost fish clade Scombridae, mackerel exhibit high-performance aquatic locomotion via oscillation of the homocercal forked caudal fin. We present the first quantitative flow visualization of the wake of a scombrid fish, chub mackerel Scomber japonicus (20-26cm fork length, FL), swimming steadily in a recirculating flow tank at cruising speeds of 1.2 and 2.2FLs-1. Thrust was calculated from wake measurements made separately in the horizontal (frontal) plane and vertical (parasagittal) planes using digital particle image velocimetry (DPIV)and compared with drag measurements obtained by towing the same specimens of S. japonicus post mortem.Patterns of flow indicated that the wake consisted of a series of linked elliptical vortex rings, each with central jet flow. The length of the minor axis (height) of the vortex rings was approximately equal to caudal fin span;the length of the major ring axis was dependent on swimming speed and was up to twice the magnitude of ring height. Profiles of wake velocity components were similar to theoretical profiles of vortex rings.Lift, thrust and lateral forces were calculated from DPIV measurements. At 1.2FLs-1, lift forces measured relative to the Xaxis were low in magnitude (-1±1mN, mean ± S.D., N=20)but oriented at a mean angle of 6° to the body axis. Reaction forces tend to rotate the fish about its center of mass, tipping the head down. Thus, the homocercal caudal fin of S. japonicus functions asymmetrically in the vertical plane. Pitching moments may be balanced anteriorly via lift generation by the pectoral fins. Thrust estimates for the two smallest fish based on DPIV analysis were not significantly different from drag measurements made by towing those same animals. At a speed of 1.2FLs-1,thrust magnitude was 11±6mN (mean ± S.D, N=40). Lateral force magnitudes were approximately double thrust magnitudes (22±6mN,mean ± S.D., N=20), resulting in a mean mechanical performance ratio (thrust/total force) of 0.32 at 1.2FLs-1. An increase in speed by a factor of 1.8 resulted in a mean increase in thrust by a factor of 4.4, a mean increase in lateral forces by a factor of 3, no change in the magnitude of lift produced and an increase in mean mechanical performance to 0.42. The relatively high lateral forces generated during swimming may be a necessary consequence of force production viapropagated waves of bending.