bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Graded Hypoxia on the Metabolic Rate and Buccal Activity of A Lungless Salamander (Desmognathus Fuscus)
Authors: Sheafor Elizabeth A. , Wood Stephen C. , Tattersall Glenn J. 
Published: April 2021

ABSTRACT
The hypothesis that the lungless salamander Desmognathus fuscus responds actively to hypoxia was tested. Patterns of buccal movements [apneic period duration, the duration (min h−1) of buccal pumping and buccal pumping frequency], heart rate and metabolic rate (rates of oxygen uptake and carbon dioxide output) were determined during a control period (21 % oxygen), a hypoxic period (2, 5, 6.5, 8 or 10 % oxygen) and a recovery period (21 % oxygen). Hypoxic salamanders maintained their rate of oxygen uptake at control levels until a critical oxygen level between 10 and 8 % oxygen was reached. The rate of carbon dioxide output remained constant across all oxygen levels, except for a significant increase during exposure to 5 % oxygen. The buccal activity of lungless salamanders was responsive to environmental hypoxia, with a significant stimulation during exposure to 6.5 % and 5 % oxygen. Buccal pumping frequency was inhibited at 2 % oxygen. Heart rate was stimulated at all hypoxic levels except 2 % O2. During recovery, metabolic rate and heart rate returned to control levels within 20 min after all hypoxic exposures. The durations of apneic periods increased significantly compared with the hypoxic value during recovery from exposure to 10 %, 6.5 % and 5 % oxygen. Overall, the animals responded actively to hypoxia by increasing the duration of buccal activity as oxygen levels decreased. The ability of these changes to facilitate oxygen uptake is not known. However, the response of the dusky salamander to low levels of oxygen is analogous to the hypoxic ventilatory response observed in lunged vertebrates.
Stomatopod Antennule Design: the Asymmetry, Sampling Efficiency and Ontogeny of Olfactory Flicking
Authors: Mead K. S. , Koehl M. A. R. 
Published: April 2021

ABSTRACT
Many crustaceans detect odors from distant sources using chemosensory sensilla (aesthetascs) on their antennules. The greater the flow of water through arrays of aesthetascs, the faster the access of odorant to receptors inside the aesthetascs. Stomatopods facilitate odorant access by flicking their antennules, thus increasing the relative velocity of the water reaching their aesthetascs. We used dynamically scaled physical models to investigate how aesthetasc size and spacing and antennule flicking velocity affect flow penetration into the simple aesthetasc arrays of the stomatopod Gonodactylaceus mutatus. Particle image velocimetry of flow fields near models of juvenile and adult antennules revealed that velocity gradients around the aesthetascs are steeper during the outward part of the flick than during the return stroke and that the velocity gradients are steeper at the aesthetasc tips than at their bases. More fluid per unit time flows between aesthetasc rows during the outward stroke than during the return stroke, ensuring that odor sampling is pulsatile. During flicking, velocity gradients are steeper near adult aesthetascs than near juvenile aesthetascs, and adults process more fluid per unit time than juveniles. The resulting differences in odorant access can be related to size- and age-dependent changes in stomatopod ecology.
The Electric Image in Weakly Electric Fish: Perception of Objects of Complex Impedance
Authors: Budelli Ruben , Caputi Angel A. 
Published: April 2021

ABSTRACT
Weakly electric fish explore the environment using electrolocation. They produce an electric field that is detected by cutaneous electroreceptors; external objects distort the field, thus generating an electric image. The electric image of objects of complex impedance was investigated using a realistic model, which was able to reproduce previous experimental data. The transcutaneous voltage in the presence of an elementary object is modulated in amplitude and waveform on the skin. Amplitude modulation (measured as the relative change in the local peak-to-peak amplitude) consists of a ‘Mexican hat’ profile whose maximum relative slope depends on the distance of the fish from the object. Waveform modulation depends on both the distance and the electrical characteristics of the object. Changes in waveform are indicated by the amplitude ratio of the larger positive and negative phases of the local electric organ discharge on the skin. Using the peak-to-peak amplitude and the positive-to-negative amplitude ratio of this discharge, a perceptual space can be defined and correlated with the capacitance and resistance of the object. When the object is moved away, the perceptual space is reduced but keeps the same proportions (homothetically): for a given object, the positive-to-negative amplitude ratio is a linear function of the peak-to-peak amplitude. This linear function depends on the electrical characteristics of the object. However, there are ‘families’ of objects with different electrical characteristics that produce changes in the parameters of the local electric organ discharge that are related by the same linear function. We propose that these functions code the perceptual properties of an object related to its impedance.
Rate-Dependent Changes in Cell Shortening, Intracellular Ca2+ Levels and Membrane Potential in Single, Isolated Rainbow Trout (Oncorhynchus Mykiss) Ventricular Myocytes
Authors: Harwood Claire L. , Howarth F. Chris , Altringham John D. , White Ed 
Published: April 2021

ABSTRACT
The effects of increasing stimulation frequency (from 0.2 to 1.4 Hz) on the contractility, intracellular Ca2+ concentration ([Ca2+]i) and membrane potential of single ventricular myocytes isolated from the heart of rainbow trout (Oncorhynchus mykiss) were measured. Cell shortening, expressed as a percentage of resting cell length, was our index of contractility. The fluorescent Ca2+ indicator Fura-2 was used to monitor changes in [Ca2+]i. Action potentials and L-type Ca2+ currents (ICa) were recorded using the whole-cell patch-clamp technique. Experiments were performed at 15 °C.
Increasing the stimulation frequency caused a significant increase in diastolic [Ca2+]i and a significant decrease in diastolic cell length and membrane potential. During systole, there was a significant fall in the amplitude of the [Ca2+]i transient, cell shortening and action potential with a decrease in the duration of the action potential at both 20 % and 90 % repolarisation. Caffeine was used to assess the Ca2+ content of the sarcoplasmic reticulum. We observed that sarcoplasmic reticulum Ca2+ load was greater at 1.0 Hz than at 0.6 Hz, despite a smaller electrically evoked [Ca2+]i transient. The amplitude of ICa was found to decrease with increased stimulation frequency. At 0.6 Hz, electrically evoked [Ca2+]i transients in the presence of 10 mmol l−1 caffeine or 10 μmol l−1 ryanodine and 2 μmol l−1 thapsigargin were reduced by approximately 15 %.
We have described the changes in contractility, [Ca2+]i and action potential configuration in a fish cardiac muscle system. Under the conditions tested (0.6 Hz, 15 °C), we conclude that the sarcoplasmic reticulum contributes at least 15 % of the Ca2+ associated with the [Ca2+]i transient. The rate-dependent decrease in contraction amplitude appears to be associated with the fall in the amplitude of the [Ca2+]i transient. This, in turn, may be influenced by changes in the action potential configuration via mechanisms such as altered Ca2+ efflux and Ca2+ influx. In support of our conclusions, we present evidence that there is a rate-dependent decrease in Ca2+ influx via ICa but that the Ca2+ load of the sarcoplasmic reticulum is not reduced at increased contraction frequencies.
Attachment Forces of Ants Measured With a Centrifuge: Better ‘Wax-Runners’ Have a Poorer Attachment to a Smooth Surface
Authors: Federle W. , Rohrseitz K. , Hölldobler B. 
Published: April 2021

ABSTRACT
The symbiotic ant partners of glaucous Macaranga ant-plants show an exceptional capacity to run on the slippery epicuticular wax crystals covering the plant stem without any difficulty. We test the hypothesis that these specialised ‘wax-runners’ have a general, superior attachment capacity. We compared attachment on a smooth surface for 11 ant species with different wax-running capacities. The maximum force that could be withstood before an ant became detached was quantified using a centrifuge recorded by a high-speed video camera. This technique has the advantage of causing minimum disruption and allows measurements in very small animals. When strong centrifugal forces were applied, the ants showed a conspicuous ‘freezing reflex’ advantageous to attachment. Attachment forces differed strongly among the ant species investigated. This variation could not be explained by different surface area/weight ratios of smaller and larger ants. Within species, however, detachment force per body weight (F/W) scaled with the predicted value of W−0.33, where W is body weight in newtons.
Surprisingly, our results not only disprove the hypothesis that ‘wax-runners’ generally attach better but also provide evidence for the reverse effect. Superior ‘wax-runners’ (genera Technomyrmex and Crematogaster) did not cling better to smooth Perspex, but performed significantly worse than closely related congeners that are unable to climb up waxy stems. This suggests an inverse relationship between adaptations to run on wax and to attach to a smooth surface.
Role of Prey-Capture Experience in the Development of the Escape Response in the Squid Loligo Opalescens: A Physiological Correlate in an Identified Neuron
Authors: Preuss Thomas , Gilly William F. 
Published: April 2021

ABSTRACT
Although extensively used for biophysical studies, the squid giant axon system remains largely unexplored in regard to in vivo function and modulation in any biologically relevant context. Here we show that successful establishment of the recruitment pattern for the giant axon in the escape response elicited by a brief electrical stimulus depends on prey-capture experience early in life. Juvenile squid fed only slow-moving, easy-to-capture prey items (Artemia salina) develop deficits in coordinating activity in the giant axon system with that of a parallel set of non-giant motor axons during escape responses. These deficits are absent in cohorts fed fast-moving, challenging prey items (copepods). These results suggest that the acquisition of inhibitory control over the giant axon system is experience-dependent and that both prey-capture and escape behavior depend on this control.
The Control of Carrier Frequency in Cricket Calls: A Refutation of the Subalar–Tegminal Resonance/Auditory Feedback Model
Authors: Prestwich Kenneth N. , Lenihan Kristy M. , Martin Deborah M. 
Published: April 2021

ABSTRACT
The subalar–tegminal resonance/auditory feedback hypothesis attempts to explain how crickets control the carrier frequency (fC), the loudness and the spectral purity of their calls. This model contrasts with the ‘clockwork cricket’ or escapement model by proposing that fC is not controlled by the resonance of the cricket’s radiators (the harps) but is instead controlled neurally. It suggests that crickets are capable of driving their harps to vibrate at any frequency and that they use a tunable Helmholtz-like resonator consisting of the tegmina and the air within the subalar space to amplify and filter the fC. This model predicts that fC is variable, that call loudness is related to tegminal position (and subalar volume) and that low-density gases should cause fC to increase.
In Anurogryllus arboreus, fC is not constant and varied by as much as 0.8 % between pulses. Within each sound pulse, the average fC typically decreased from the first to the last third of a sound pulse by 9 %. When crickets called in a mixture of heliox and air, fC increased 1.07- to 1.14-fold above the value in air. However, if the subalar space were part of a Helmholtz-like resonator, then its resonant frequency should have increased by 40–50 %. Moreover, similar increases occurred in species that lack a subalar space (oecanthines). Experimental reduction of the subalar volume of singing crickets resulted neither in a change in fC nor in a change in loudness. Nor did crickets attempt to restore the subalar volume to its original value. These results disprove the presence of a subalar–tegminal resonator.
The free resonance of freshly excised Gryllus rubens tegmina shifted by 1.09-fold when moved between air and a mixture of helium and air. Auditory feedback cannot be the cause of this shift, which is similar to the fC shifts in intact individuals of other species.
Calculations show that the harp is 3.9–1.8 times more massive than the air that moves en masse with the vibrating harps. Replacing air with heliox-air lowers the mass of the vibrating system sufficiently to account for the fC shifts. These results re-affirm the ‘clockwork cricket’ (escapement) hypothesis. However, as realized by others, the harps should be viewed as narrow-band variable-frequency oscillators whose tuning may be controlled by factors that vary the effective mass.
The Distribution of Nadph-Diaphorase-Labelled Interneurons and the Role of Nitric Oxide in the Swimming System of Xenopus Laevis Larvae
Authors: Mclean David L. , Sillar Keith T. 
Published: April 2021

ABSTRACT
The possible involvement of the free radical gas nitric oxide (NO) in the modulation of spinal rhythm-generating networks has been studied using Xenopus laevis larvae. Using NADPH-diaphorase histochemistry, three putative populations of nitric oxide synthase (NOS)-containing cells were identified in the brainstem. The position and morphology of the largest and most caudal population suggested that a proportion of these neurons is reticulospinal. The possible contribution of nitrergic neurons to the control of swimming activity was examined by manipulating exogenous and endogenous NO concentrations in vivo with an NO donor (SNAP, 100–500 μmol l−1) and NOS inhibitors (L-NAME and L-NNA, 0.5–5 mmol l−1), respectively. In the presence of SNAP, swim episode duration decreased and cycle period increased, whereas the NOS inhibitors had the opposite effects. We conclude from these data that the endogenous release of NO from brainstem neurons extrinsic to the spinal cord of Xenopus laevis larvae exerts a continuous modulatory influence on swimming activity, functioning like a ‘brake’. Although the exact level at which NO impinges upon the swimming rhythm generator has yet to be determined, the predominantly inhibitory effect of NO suggests that the underlying mechanisms of NO action could involve modulation of synaptic transmission and/or direct effects on neuronal membrane properties.
Kinematics and Mechanics of Ground Take-Off in the Starling Sturnis Vulgaris and the Quail Coturnix Coturnix
Authors: Earls Kathleen D. 
Published: April 2021

ABSTRACT
The mechanics of avian take-off are central to hypotheses about flight evolution, but have not been quantified in terms of whole-body movements for any species. In this study, I use a combination of high-speed video analysis and force plate recording to measure the kinematics and mechanics of ground take-off in the European starling Sturnis vulgaris and the European migratory quail Coturnix coturnix. Counter to hypotheses based on the habits and morphology of each species, S. vulgaris and C. coturnix both produce 80–90 % of the velocity of take-off with the hindlimbs. S. vulgaris performs a countermovement jump (peak vertical force four times body weight) followed by wing movement, while C. coturnix performs a squat jump (peak vertical force 7.8 times body weight) with simultaneous wing movement. The wings, while necessary for continuing the movement initiated by the hindlimbs and thereafter supporting the body weight, are not the primary take-off accelerator. Comparison with one other avian species in which take-off kinematics have been recorded (Columba livia) suggests that this could be a common pattern for living birds. Given these data and the fact that running take-offs such as those suggested for an evolving proto-flier are limited to large or highly specialized living taxa, a jumping model of take-off is proposed as a more logical starting point for the evolution of avian powered flight.
Head-Bobbing in Pigeons: How Stable is the Hold Phase?
Authors: Troje Nikolaus F. , Frost Barrie J. 
Published: April 2021

ABSTRACT
The head movement of a walking pigeon Columba livia is characterized by two alternating phases, a thrust phase and a hold phase. While the head is rapidly thrust forward during the thrust phase, it has been shown repeatedly that it remains virtually motionless with respect to translation along a horizontal axis (roll axis) during the hold phase. It has been shown that the stabilization during the hold phase is under visual control. This has led to the view that the pigeon’s head-bobbing is an optokinetic response to stabilize the retinal image during the hold phase. However, it has never been shown explicitly that the head is really held stable in space with respect to other translatory or rotatory dimensions. Using videography, we show here that this is in fact the case: except for a small but systematic slip that presumably serves as an error signal for retinal image stabilization, the head of the pigeon remains locked in space not only with respect to the horizontal (roll) axis but also with respect to vertical translation (along the yaw axis) and with respect to rotation around the pitch and yaw axes.
Mechanics of Lung Ventilation in a Post-Metamorphic Salamander, Ambystoma Tigrinum
Authors: Simons Rachel S. , Bennett Wallace O. , Brainerd Elizabeth L. 
Published: April 2021

ABSTRACT
The mechanics of lung ventilation in frogs and aquatic salamanders has been well characterized, whereas lung ventilation in terrestrial-phase (post-metamorphic) salamanders has received little attention. We used electromyography (EMG), X-ray videography, standard videography and buccal and body cavity pressure measurements to characterize the ventilation mechanics of adult (post-metamorphic) tiger salamanders (Ambystoma tigrinum). Three results emerged: (i) under terrestrial conditions or when floating at the surface of the water, adult A. tigrinum breathed through their nares using a two-stroke buccal pump; (ii) in addition to this narial two-stroke pump, adult tiger salamanders also gulped air in through their mouths using a modified two-stroke buccal pump when in an aquatic environment; and (iii) exhalation in adult tiger salamanders is active during aquatic gulping breaths, whereas exhalation appears to be passive during terrestrial breathing at rest. Active exhalation in aquatic breaths is indicated by an increase in body cavity pressure during exhalation and associated EMG activity in the lateral hypaxial musculature, particularly the M. transversus abdominis. In terrestrial breathing, no EMG activity in the lateral hypaxial muscles is generally present, and body cavity pressure decreases during exhalation. In aquatic breaths, tidal volume is larger than in terrestrial breaths, and breathing frequency is much lower (approximately 1 breath 10 min−1versus 4–6 breaths min−1). The use of hypaxial muscles to power active exhalation in the aquatic environment may result from the need for more complete exhalation and larger tidal volumes when breathing infrequently. This hypothesis is supported by previous findings that terrestrial frogs ventilate their lungs with small tidal volumes and exhale passively, whereas aquatic frogs and salamanders use large tidal volumes and and exhale actively.
Energy Metabolism of Eucalyptus-Boring Beetles at Rest and During Locomotion: Gender Makes a Difference
Authors: Rogowitz Gordon L. , Chappell Mark A. 
Published: April 2021

ABSTRACT
We studied metabolic rates during rest, maximal running exercise and tethered flight in the long-horned eucalyptus-boring beetles Phoracantha recurva and P. semipunctata. Simultaneous measurement .of rates of O2 consumption and CO2 production indicated that closely approximated and hence was a good index of aerobic metabolic rate. The resting metabolic rate (RMR), peak during running-wheel locomotion (MRrun) and factorial scope during running (MRrun/RMR) are similar to published values for several other insect taxa. MRrun was repeatable for most test groups over intervals of 48–96 h. Studies of P. semipunctata show that MRrun is relatively insensitive to changes in ambient temperature (Ta) between 20 and 30 °C, whereas resting metabolic rate increases with Ta with a normal Q10 (2.4). Consequently, factorial scope declines at the higher Ta: mean factorial scopes for male and female P. semipunctata are 17.7 and 13.6 at 20 °C versus 8.9 and 5.5 at 30 °C, respectively. Flight activity requires a considerably greater metabolic rate than terrestrial activity: at Ta values of 20–30 °C, the mean factorial scope for flight activity of male P. semipunctata is 72 (range 36–110). Nevertheless, our measurements of flight metabolic rate in Phoracantha spp. are considerably lower than predicted from allometric equations for other insects. Our most interesting finding was that males of both species had a substantially and significantly higher MRrun and aerobic scope than females. The gender differences in MRrun are consistent with differences in activity levels of males and females during mate-seeking behavior.
Spectral and Ultraviolet-Polarisation Sensitivity in Juvenile Salmonids: A Comparative Analysis using Electrophysiology
Authors: Parkyn Daryl C. , Hawryshyn Craig W. 
Published: April 2021

ABSTRACT
Spectral and polarisation sensitivity were compared among juvenile (parr) rainbow trout (Oncorhynchus mykiss), steelhead (O. mykiss), cutthroat trout (O. clarki clarki), kokanee (O. nerka) and brook char (Salvelinus fontinalis) using multi-unit recording from the optic nerve. Although reared under the same conditions, differences in photopic spectral sensitivity were evident. Specifically, ON-responses were co-dominated by L- and M-cone mechanisms in all fish except O. nerka, consistent with an M-cone mechanism sensitivity. The sensitivity of OFF-responses was dominated by the M-cone mechanism for all fish, but O. mykiss appeared to show an additional contribution from the L-cone mechanism. Using chromatic adaptation, an independent ultraviolet-sensitive mechanism is described for the first time for the salmonid genus Salvelinus. In addition, this ultraviolet-cone mechanism was present in the members of the genus Oncorhynchus that were examined. Thus, ultraviolet sensitivity appears to be common to the major extant clades of the subfamily Salmoninae. All species showed differential sensitivity to both vertical and horizontal linearly polarised light. This sensitivity differed between ON- and OFF-responses. The ON-responses were maximally sensitive to both vertically and horizontally polarised light, whereas the OFF-responses displayed maximal sensitivity to horizontally polarised light in all species, with reduced sensitivity to vertically polarised light compared with ON-responses. Because of the similarity in the physiological characteristics of polarisation sensitivity among the salmonid species examined, no relationship between the degree of migratory tendency and the ability to detect polarised light could be identified.