bluuebunny/crossref_metadata_2025_split huggingface dataset:
A kinematic comparison of forward and backward swimming in the eel Anguilla anguilla
Authors: D’Août Kristiaan , Aerts Peter 
Published: April 2021

ABSTRACT
In addition to forward undulatory swimming, eels (and some other elongated swimmers) can swim backwards in a similar way. We compared the kinematics (wave speed, cycle frequency, amplitude, local bending and estimated muscle strain) of forward and backward swimming in the European eel Anguilla anguilla.
Both swimming modes are characterised by a wave of undulation that travels over the body in the direction opposite to that of swimming. We observe two major kinematic differences. First, the slope of wave frequency against swimming speed is significantly higher for backward than for forward swimming. Second, the amplitude profile along the body of the propulsive wave differs greatly. During forward swimming, the yaw at the head is minimal and the amplitude of the propulsive wave increases to approximately 15 % (left-to-right) of total body length towards the tail tip. During backward swimming, the amplitude profile is rather uniform along the body (with values similar to the tail-tip amplitude during forward swimming), resulting in considerable lateral head oscillation. Strikingly, the head remains approximately parallel to the swimming direction, which presumably enhances visual and acoustico-lateral perception. Furthermore, muscle strain is much higher in the rostral part of the body during backward swimming than during forward swimming. Values for stride length and propeller efficiency suggest that backward undulatory swimming is mechanically less efficient than forward swimming.
We suggest that the typical anguilliform body shape is an important feature that allows these animals to swim backwards using an undulatory mechanism that resembles the forward undulatory swimming mechanism. Most other fishes, if able to swim backwards at all, do so using fin oscillations or undulations.
Auditory sensory cells in hawkmoths: identification, physiology and structure
Authors: Göpfert Martin C. , Wasserthal Lutz T. 
Published: April 2021

ABSTRACT
The labral pilifers are thought to contain auditory sensory cells in hawkmoths of two distantly related subtribes, the Choerocampina and the Acherontiina. We identified and analysed these cells using neurophysiological and neuroanatomical techniques. In the death’s head hawkmoth Acherontia atropos, we found that the labral nerve carries the auditory afferent responses of a single auditory unit. This unit responds to ultrasonic stimulation with minimum thresholds of 49–57 dB SPL around 25 kHz. Ablation experiments and analyses of the neuronal activity in different regions of the pilifer revealed that the auditory afferent response originates in the basal pilifer region. The sensory organ was identified as a chordotonal organ that attaches to the base of the pilifer. This organ is the only sensory structure in the basal pilifer region and consists of a single mononematic scolopidium and a single sensory cell. In Choerocampina, a homologous scolopidium was also found and is probably the only sensory structure of the pilifer that might serve an auditory function. Since a pilifer chordotonal organ with only a single scolopidium has also been detected in a non-hearing hawkmoth species, hearing in the distantly related choerocampine and acherontiine hawkmoths presumably evolved from a single proprioceptive mechanoreceptor cell that is present in all hawkmoths.
Many-legged maneuverability: dynamics of turning in hexapods
Authors: Jindrich Devin L. , Full Robert J. 
Published: April 2021

ABSTRACT
Remarkable similarities in the vertical plane of forward motion exist among diverse legged runners. The effect of differences in posture may be reflected instead in maneuverability occurring in the horizontal plane. The maneuver we selected was turning during rapid running by the cockroach Blaberus discoidalis, a sprawled-postured arthropod. Executing a turn successfully involves at least two requirements. The animal’s mean heading (the direction of the mean velocity vector of the center of mass) must be deflected, and the animal’s body must rotate to keep the body axis aligned with the heading. We used two-dimensional kinematics to estimate net forces and rotational torques, and a photoelastic technique to estimate single-leg ground-reaction forces during turning. Stride frequencies and duty factors did not differ among legs during turning. The inside legs ended their steps closer to the body than during straight-ahead running, suggesting that they contributed to turning the body. However, the inside legs did not contribute forces or torques to turning the body, but actively pushed against the turn. Legs farther from the center of rotation on the outside of the turn contributed the majority of force and torque impulse which caused the body to turn. The dynamics of turning could not be predicted from kinematic measurements alone. To interpret the single-leg forces observed during turning, we have developed a general model that relates leg force production and leg position to turning performance. The model predicts that all legs could turn the body. Front legs can contribute most effectively to turning by producing forces nearly perpendicular to the heading, whereas middle and hind legs must produce additional force parallel to the heading. The force production necessary to turn required only minor alterations in the force hexapods generate during dynamically stable, straight-ahead locomotion. A consideration of maneuverability in the horizontal plane revealed that a sprawled-postured, hexapodal body design may provide exceptional performance with simplified control.
Modulatory effects of some amino acids and neuropeptides on luminescence in the brittlestar Amphipholis squamata
Authors: De Bremaeker N. , Baguet F. , Thorndyke M. C. , Mallefet J. 
Published: April 2021

ABSTRACT
Amphipholis squamata is a polychromatic luminescent ophiuroid. The effects of amino acids ( γ-aminobutyric acid, GABA, taurine, glycine and glutamate), N-methyl-D-aspartate (NMDA) and the invertebrate neuropeptides Antho-RFamide, FMRFamide and SALMFamides S1 and S2 were tested on acetylcholine-induced luminescence from isolated arms of clear and black specimens of Amphipholis squamata. The results showed that GABA, glycine and Antho-RFamide inhibited ACh-induced luminescence of clear specimens and had no significant effect on black specimens. Glutamic acid had no significant effect on ACh-induced luminescence, but triggered luminescence in the absence of ACh in both types of specimen. Taurine, NMDA and FMRFamide showed no significant effects on either clear or black specimens. S1 potentiated ACh-induced luminescence of clear and black specimens, while S2 had no clear modulatory effect on luminescence. These results suggest that, in addition to the previously described cholinergic system in Amphipholis squamata, there is also a modulatory component to luminescence control. Moreover, we observed a difference in modulation of luminescence between clear and black specimens.
Developmental analysis of Ganaspis xanthopoda, a larval parasitoid of Drosophila melanogaster
Authors: Melk Jonathan P. , Govind Shubha 
Published: April 2021

ABSTRACT
Ganaspis xanthopoda is a solitary larval parasitoid wasp of the fruit fly Drosophila melanogaster. The life cycle of Ganaspis xanthopoda in the wild-type and developmental mutant ecdysoneless strains of Drosophila melanogaster is described. The female infects a second-instar host larva. The parasitoid embryo hatches into a mobile first-instar (L1) larva. The L1 parasitoid has fleshy appendages and, while mobile, it remains confined within the wandering larval host. The second-instar larva (L2) is an endoparasite within the host prepupa and lacks appendages. The L2-to-L3 molt is dependent on pupation and marks the transition of the endoparasite into an ectoparasite. The third-instar larva (L3) is a sessile ectoparasite, develops an extensive tracheal system and consumes the host as it progresses through its prepupal and pupal stages. A single adult male or female emerges from the host puparium. The developmental analysis of Ganaspis xanthopoda reveals a tight synchrony between host and parasitoid development which is, at least in part, dependent on the ecdysone levels of the host.
The relationship of central and peripheral organ masses to aerobic performance variation in house sparrows
Authors: Chappell Mark A. , Bech Claus , Buttemer William A. 
Published: April 2021

ABSTRACT
We evaluated the relationship between organ mass and the limits to aerobic metabolism in house sparrows Passer domesticus. The results were used to test three models of performance limitation (the central limitation, peripheral limitation and symmorphosis concepts). Basal metabolic rate (BMR) was determined during the rest phase. The maximum rate of oxygen consumption during exercise was measured in an enclosed wheel that allowed limited hovering flight. Neither BMR nor was affected by gender, but adults had significantly higher and lower BMR than juveniles. The masses of most central organs (gut, gizzard, liver, heart, kidney and reproductive organs) differed significantly between ages. There were no gender differences in organ mass among juveniles, but liver mass differed between male and female adults. In the pooled data, BMR was positively correlated with the mass of three central organs (gut, liver and kidney) and with one peripheral effector (breast muscle); together, these explained more than half the variance in BMR (r2=0.57). In adults, BMR was positively correlated with the mass of reproductive tissue. The masses of one peripheral effector (breast muscle) and one central organ (the heart) were positively correlated with (r2=0.17 for the pooled data set). These results are consistent with a symmorphosis model of aerobic capacity. We found a significant positive relationship between BMR and in juveniles, but not in adults. Taken together, our data indicate that house sparrows can achieve elevated without paying a ‘penalty’ (fitness trade-off) in the form of an increased BMR.
Near-body flow dynamics in swimming fish
Authors: Wolfgang M. J. , Anderson J. M. , Grosenbaugh M. A. , Yue D. K. P. , Triantafyllou M. S. 
Published: April 2021

ABSTRACT
We consider the motions and associated flow patterns of a swimming giant danio (Danio malabaricus). Experimental flow-visualization techniques have been employed to obtain the unsteady two-dimensional velocity fields around the straight-line swimming motions and a 60 ° turn of the fish in the centerline plane of the fish depth. A three-dimensional numerical method is also employed to predict the total velocity field through simulation. Comparison of the experimental and numerical velocity and vorticity fields shows good agreement. The fish morphology, with its narrow peduncle region, allows for smooth flow into the articulated tail, which is able to sustain a large load for thrust generation. Streamlines of the flow detail complex processes that enhance the efficiency of flow actuation by the tail. The fish benefits from smooth near-body flow patterns and the generation of controlled body-bound vorticity, which is propagated towards the tail, shed prior to the peduncle region and then manipulated by the caudal fin to form large-scale vortical structures with minimum wasted energy. This manipulation of body-generated vorticity and its interaction with the vorticity generated by the oscillating caudal fin are fundamental to the propulsion and maneuvering capabilities of fish.
Isolation of magnetic nanoparticles from Pachycondyla marginata ants
Authors: Acosta-Avalos Daniel , Wajnberg Eliane , Oliveira Paulo S. , Leal Inara , Farina Marcos , Esquivel Darci M. S. 
Published: April 2021

ABSTRACT
We report on the presence of magnetic iron oxides in the migratory ant Pachycondyla marginata. Magnetic particles were extracted from different parts of the ant (head, thorax and abdomen) using magnetic precipitation methods. Electron spectroscopic images for iron and oxygen were obtained from the extracted particles, and, by using the corresponding electron micrographs, histograms of size distribution were constructed. Selected area diffraction patterns were also obtained from the particles, and analysis of these showed the presence of a mixture of different iron oxides, including the magnetic oxides, magnetite and maghemite. The size distribution of the particles in the abdomen is different from that in the thorax and the head. In accordance with the hypothesis of magnetic orientation based on the presence of magnetic material within the body, two regions of the ant, the head and the abdomen, could be implicated in the detection of the geomagnetic field.
Directional hearing in grasshoppers: neurophysiological testing of a bioacoustic model
Authors: Schul Johannes , Holderied Marc , Helversen Dagmar Von , Helversen Otto Von 
Published: April 2021

ABSTRACT
A recently proposed biophysical model for directional hearing in grasshoppers was tested using complex stimulus situations, with two loudspeakers, one on either side of the animal, synchronously emitting sinusoids with defined phase and amplitude relationships. Hearing responses were determined from whole nerve recordings and compared with the predictions of the model. In Schistocerca gregaria, there were only minor differences between the predictions of the model and measurements and, by reducing the value of the gain of the internal sound path measured previously, a close agreement was achieved between model and measured hearing responses. In Chorthippus biguttulus, larger discrepancies between model calculations using the values measured previously and neuronal response functions were found in both shape and amplitude. A better fit between measurements and model predictions was achieved by increasing the values of the internal delay over those measured previously. The measurements presented here indicate high inter-individual variability of the parameters of the internal pathway, with a range of 60° for the internal phase delay. Calculating the directional characteristics using this range of values for the internal delay indicated that sufficient directional information was available down to 5 kHz. Increasing the value of the internal delay over that measured in an earlier study therefore provides an explanation for the discrepancy between the poor directional information attributed to C. biguttulus in that study and the excellent lateralization ability of males of this species at 5 kHz.
Control of abdominal extension in the freely moving intact crayfish Cherax destructor:: I. Activity of the tonic stretch receptor
Authors: McCarthy Bernard J. , Macmillan David L. 
Published: April 2021

ABSTRACT
Electrical recordings were made from the sensory neurone of the tonic muscle receptor organ in the abdomen of the intact, freely behaving crayfish Cherax destructor. Slow extensions of the abdomen were evoked by lowering a platform from beneath the suspended crayfish, and the movements and tonic sensory neurone activity were video-recorded simultaneously. The recordings showed that the tonic sensory neurone was active when the abdomen was fully flexed prior to the extension. When the extension began, however, the sensory neurone ceased firing shortly after movement was detected, irrespective of the load applied to the abdomen. When the abdomen was physically blocked from extending fully, the sensory neurone did not fire. The tonic muscle receptor organ is considered to be the length-detecting sensor for a load-compensating servo-loop, but the results demonstrate that its activity pattern during extensions evoked by a platform-drop in C. destructor are not consistent with that role.
The anterior and posterior ‘stomach’ regions of larval Aedes aegypti midgut: regional specialization of ion transport and stimulation by 5-hydroxytryptamine
Authors: Clark Thomas M. , Koch Alan , Moffett David F. 
Published: April 2021

ABSTRACT
The ‘stomach’ region of the larval mosquito midgut is divided into histologically distinct anterior and posterior regions. Anterior stomach perfused symmetrically with saline in vitro had an initial transepithelial potential (TEP) of −66 mV (lumen negative) that decayed within 10–15 min to a steady-state TEP near −10 mV that was maintained for at least 1 h. Lumen-positive TEPs were never observed in the anterior stomach. The initial TEP of the perfused posterior stomach was opposite in polarity, but similar in magnitude, to that of the anterior stomach, measuring +75 mV (lumen positive). This initial TEP of the posterior stomach decayed rapidly at first, then more slowly, eventually reversing the electrical polarity of the epithelium as lumen-negative TEPs were recorded in all preparations within 70 min. Nanomolar concentrations of the biogenic amine 5-hydroxytryptamine (5-HT, serotonin) stimulated both regions, causing a negative deflection of the TEP of the anterior stomach and a positive deflection of the TEP of the posterior stomach. Phorbol 12,13-diacetate also caused a negative deflection of the TEP of the anterior stomach, but had no effect on the TEP of the posterior stomach. These data demonstrate that 5-HT stimulates region-specific ion-transport mechanisms in the stomach of Aedes aegypti and suggest that 5-HT coordinates the actions of the Malpighian tubules and midgut in the maintenance of an appropriate hemolymph composition in vivo.
Glycerol and fatty acid kinetics in rainbow trout: effects of endurance swimming
Authors: Bernard S. F. , Reidy S. P. , Zwingelstein G. , Weber J.-M. 
Published: April 2021

ABSTRACT
Continuous infusions of 2-[3H]glycerol and 1-[14C]palmitate were performed in vivo in rainbow trout to measure the effects of prolonged swimming on (1) the rate of appearance of glycerol (Ra glycerol or lipolytic rate), (2) the rate of appearance of non-esterified fatty acids (Ra NEFA) and (3) the rate of triacylglycerol:fatty acid cycling (TAG:FA cycling or re-esterification). Our goals were to test the hypothesis that sustained exercise for up to 4 days causes the progressive mobilization of triacylglycerol reserves to supply fuel to contracting muscles, and to assess whether TAG:FA cycling plays a role in the regulation of NEFA availability in teleosts. Contrary to expectation, the rates of lipolysis and fatty acid release in resting trout are not affected by endurance exercise. Unlike mammals, which increase the rate of lipolysis by two-to fourfold during submaximal exercise, these active teleosts do not mobilize triacylglycerol reserves beyond resting levels to supply more NEFAs to working muscles. Furthermore, they maintain Ra glycerol and Ra NEFA well in excess of oxidative fuel requirements even at rest. More than two-thirds of the NEFAs produced are re-esterified, but the results show that TAG:FA cycling is not involved in the regulation of NEFA availability during or after swimming. We propose that the observed high rates of re-esterification represent an important feature of ectothermic metabolism that allows the restructuring of membrane phospholipids to be synchronized with frequent changes in body temperature.
Single-cell analyses of nitrergic neurons in simple nervous systems
Authors: Moroz Leonid L. , Gillette Rhanor , Sweedler Jonathan V. 
Published: April 2021

ABSTRACT
Understanding the role of the gaseous messenger nitric oxide (NO) in the nervous system is complicated by the heterogeneity of its nerve cells; analyses carried out at the single cell level are therefore important, if not critical. Some invertebrate preparations, most especially those from the gastropod molluscs, provide large, hardy and identified neurons that are useful both for the development of analytical methodologies and for cellular analyses of NO metabolism and its actions. Recent modifications of capillary electrophoresis (CE) allow the use of a small fraction of an individual neuron to perform direct, quantitative and simultaneous assays of the major metabolites of the NO–citrulline cycle and associated biochemical pathways. These chemical species include the products of NO oxidation (NO2−/NO3−), L-arginine, L-citrulline, L-ornithine, L-argininosuccinate, as well as selected NO synthase inhibitors and cofactors such as NADPH, biopterin, FMN and FAD. Diverse cotransmitters can also be identified in the same nitrergic neuron. The sensitivity of CE methods is in the femtomole to attomole range, depending on the species analysed and on the specific detector used. CE analysis can be combined with prior in vivo electrophysiological and pharmacological manipulations and measurements to yield multiple physiological and biochemical values from single cells. The methodologies and instrumentation developed and tested using the convenient molluscan cell model can be adapted to the smaller and more delicate neurons of other invertebrates and chordates.
P-type Ca2+ current in crayfish peptidergic neurones
Authors: García-Colunga Jesús , Valdiosera René , García Ubaldo 
Published: April 2021

ABSTRACT
Inward Ca2+ current through voltage-gated Ca2+ channels was recorded from freshly dissociated crayfish X-organ (XO) neurones using the whole-cell voltage-clamp technique. Changing the holding potential from —50 to —90 mV had little effect on the characteristics of the current–voltage relationship: neither the time course nor the amplitude of the Ca2+ current was affected. Inactivation of the Ca2+ current was observed over a small voltage range, between —35 and —10 mV, with half-inactivation at —20 mV. The activation of the Ca2+ current was modelled using Hodgkin–Huxley kinetics. The time constant of activation, τm, was 568±66 μs at —20 mV and decreased gradually to 171±23 μs at 40 mV (means ± S.E.M., N=5). The steady-state activation, m∞, was fitted with a Boltzmann function, with a half-activation voltage of —7.45 mV and an apparent threshold at —40 mV. The instantaneous current–voltage relationship was adjusted using the Goldman–Hodgkin–Katz constant-field equation, giving a permeation of 4.95×10−5 cm s−1. The inactivation of the Ca2+ current in XO neurones was dependent on previous entry of Ca2+. Using a double-pulse protocol, the inactivation was fitted to a U-shaped curve with a maximal inactivation of 35 % at 30 mV. The time course of the recovery from inactivation was fitted with an exponential function. The time constants were 17±2.6 ms for a prepulse of 10 ms and 31±3.2 ms for a prepulse of 20 ms. The permeability sequence of the Ca2+ channels was as follows: Ba2+&gt;Sr2+≈Ca2+Mg2+. Other divalent cations blocked the Ca2+ current, and their effects were voltage-dependent; the potency of blockage was Cd2+≈Zn2+Co2+≈Ni2+. The peptide ω-agatoxin-IVA, a selective toxin for P-type Ca2+ channels, blocked 85 % of the Ca2+ current in XO neurones at 200 nmol l−1, but the current was insensitive to dihydropyridines, phenylalkylamines, ω-conotoxin-GVIA and ω-conotoxin-MVIIC, which are blockers of L-, N- and Q-type Ca2+ channels, respectively. From the voltage- and Ca2+-dependent kinetics, the higher permeability to Ba2+ than to Ca2+ and the higher sensitivity of the current to Cd2+ than to Ni2+, we conclude that the Ca2+ current in XO neurones is generated by high-voltage-activated (HVA) channels. Furthermore, its blockage by ω-agatoxin-IVA suggests that it is mainly generated through P-type Ca2+ channels.