bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Brood Size Manipulation on Offspring Physiology: An Experiment with Passerine Birds
Authors: Burness Gary P. , McClelland Grant B. , Wardrop Sharilynn L. , Hochachka Peter W.
Published: April 2021

The environment experienced during ontogeny has a significant impact on the physiological condition of offspring. This, in turn, forecasts survival probabilities and future reproductive potential. Despite the prominent role that the concept of condition plays in evolutionary studies, the physiological and biochemical characters that define it remain relatively unexplored. In this study, we quantified the impact of brood size manipulations on the physiology and biochemistry of nestling tree swallows (Tachycineta bicolor) shortly before they fledged. Over two breeding seasons, we either increased or decreased the number of individuals in a brood by a single nestling. Every 2–4 days, we determined the resting rate of oxygen consumption of individuals in each brood. Growth was followed until 16 days of age, at which time, to look for potential trade-offs in energy allocation, we measured total lipid mass, skeletal muscle and organ mass, indices of blood oxygen-carrying capacity and the activities of key metabolic enzymes in various tissues. Surprisingly, there was a minimal response of most characters to brood manipulation, suggesting that physiological and biochemical development is relatively invariant except perhaps under extreme conditions. Individuals reared in artificially enlarged broods, however., had a significantly lower body mass, body-size-adjusted , gizzard mass and total lipid mass. These individuals also had decreased activity of cardiac 3-hydroxyacyl CoA dehydrogenase, suggesting a decreased capacity for oxidation of fatty acids. How these characters affect survival or the future adult phenotype remains unknown.
The Transporter-Like Protein Inebriated Mediates Hyperosmotic Stimuli Through Intracellular Signaling
Authors: Chiu Chi-Sung , Ross Linda S. , Cohen Bruce N. , Lester Henry A. , Gill Sarjeet S.
Published: April 2021

We cloned the inebriated homologue MasIne from Manduca sexta and expressed it in Xenopus laevis oocytes. MasIne is homologous to neurotransmitter transporters but no transport was observed with a number of putative substrates. Oocytes expressing MasIne respond to hyperosmotic stimulation by releasing intracellular Ca2+, as revealed by activation of the endogenous Ca2+-activated Cl− current. This Ca2+ release requires the N-terminal 108 amino acid residues of MasIne and occurs via the inositol trisphosphate pathway. Fusion of the N terminus to the rat γ-aminobutyric acid transporter (rGAT1) also renders rGAT1 responsive to hyperosmotic stimulation. Immunohistochemical analyses show that MasIne and Drosophila Ine have similar tissue distribution patterns, suggesting functional identity. Inebriated is expressed in tissues and cells actively involved in K+ transport, which suggests that it may have a role in ion transport, particularly of K+. We propose that stimulation of MasIne releases intracellular Ca2+ in native tissues, activating Ca2+-dependent K+ channels, and leading to K+ transport.
Novel Aspects Of The Transport Of Organic Anions By The Malpighian Tubules OfDrosophila Melanogaster
Authors: Linton Stuart M. , O’donnell M. J.
Published: April 2021

Para-aminohippuric acid (PAH) is a negatively charged organic ion that can pass across the epithelium of Malpighian tubules. Its mode of transport was studied in Malpighian tubules of Drosophila melanogaster. PAH transport was an active process, with a Km of 2.74 mmol l−1 and a Vmax of 88.8 pmol min−1. Tubules had a low passive permeability to PAH, but PAH transport rates (832 nmol min−1 mm2) and concentrative ability ([PAH]secreted fluid:[PAH]bath=81.2) were the highest measured to date for insects. Competition experiments indicated that there were two organic anion transporters, one that transports carboxylate compounds, such as PAH and fluorescein, and another that transports sulphonates, such as amaranth and Indigo Carmine. PAH transport appears to be maximal in vivo because the rate of transport by isolated tubules is not increased when these are challenged with cyclic AMP, cyclic GMP, leucokinin I or staurosporine. Basolateral PAH transport was inhibited by ouabain and dependent on the Na+ gradient. The Malpighian tubules appeared not to possess an organic acid/α-keto acid exchanger because PAH accumulation was not affected by low concentrations (100 μmol l−1) of α-keto acids (α-ketoglutarate, glutarate, citrate and succinate) or the activity of phosphokinase C. PAH transport may be directly coupled to the Na+ gradient, perhaps via Na+/organic acid cotransport. Fluorescence microscopy showed that transport of the carboxylate fluorescein was confined to the principal cells of the main (secretory) segment and all the cells of the lower (reabsorptive) segment. Organic anions were transported across the cytoplasm of the principal cells both by diffusion and in vesicles. The accumulation of punctate fluorescence in the lumen is consistent with exocytosis of the cytoplasmic vesicles. Apical PAH transport was independent of the apical membrane potential and may not occur by an electrodiffusive mechanism.
Function Of The Heterocercal Tail In White Sturgeon: Flow Visualization During Steady Swimming And Vertical Maneuvering
Authors: Liao James , Lauder George V.
Published: April 2021

Basal ray-finned fishes possess a heterocercal tail in which the dorsal lobe containing the extension of the vertebral column is longer than the ventral lobe. Clarifying the function of the heterocercal tail has proved elusive because of the difficulty of measuring the direction of force produced relative to body position in the aquatic medium. We measured the direction of force produced by the heterocercal tail of the white sturgeon (Acipenser transmontanus) by visualizing flow in the wake of the tail using digital particle image velocimetry (DPIV) while simultaneously recording body position and motion using high-speed video. To quantify tail function, we measured the vertical body velocity, the body angle and the path angle of the body from video recordings and the vortex ring axis angle and vortex jet angle from DPIV recordings of the wake downstream from the tail. These variables were measured for sturgeon exhibiting three swimming behaviors at 1.2 L s−1, where L is total body length: rising through the water column, holding vertical position, and sinking through the water column. For vertical body velocity, body angle and path angle values, all behaviors were significantly different from one another. For vortex ring axis angle and vortex jet angle, rising and holding behavior were not significantly different from each other, but both were significantly different from sinking behavior. During steady horizontal swimming, the sturgeon tail generates a lift force relative to the path of motion but no rotational moment because the reaction force passes through the center of mass. For a rising sturgeon, the tail does not produce a lift force but causes the tail to rotate ventrally in relation to the head since the reaction force passes ventral to the center of mass. While sinking, the direction of the fluid jet produced by the tail relative to the path of motion causes a lift force to be created and causes the tail to rotate dorsally in relation to the head since the reaction force passes dorsal to the center of mass. These data provide evidence that sturgeon can actively control the direction of force produced by their tail while maneuvering through the water column because the relationship between vortex jet angle and body angle is not constant.
Modulatory Effects of Nitric Oxide on Synaptic Depression in the Crayfish Neuromuscular System
Authors: Aonuma Hitoshi , Nagayama Toshiki , Takahata Masakazu
Published: April 2021

A characteristic physiological property of the neuromuscular junction between giant motor neurones (MoGs) and fast flexor muscles in crayfish is synaptic depression, in which repetitive electrical stimulation of the MoG results in a progressive decrease in excitatory junction potential (EJP) amplitude in flexor muscle fibres. Previous studies have demonstrated that L-arginine (L-Arg) modulates neuromuscular transmission. Since L-Arg is a precursor of nitric oxide (NO), we examined the possibility that NO may be involved in modulating neuromuscular transmission from MoGs to abdominal fast flexor muscles. The effect of a NO-generating compound, NOC7, was similar to that of L-Arg, reversibly decreasing the EJP amplitude mediated by the MoG. While NOC7 reduced the amplitude of the EJP, it induced no significant change in synaptic depression. In contrast, a scavenger of free radical NO, carboxy-PTIO, and an inhibitor of nitric oxide synthase, L-NAME, reversibly increased the EJP amplitude mediated by MoGs. Synaptic depression mediated by repetitive stimulation of MoGs at 1 Hz was partially blocked by bath application of L-NAME. Bath application of a NO scavenger, a NOS inhibitor and NO-generating compounds had no significant effects on the depolarisation of the muscle fibres evoked by local application of L-glutamate.

The opposing effects on EJP amplitude of NOC7 and of carboxy-PTIO and L-NAME suggest that endogenous NO presynaptically modulates neuromuscular transmission and that it could play a prominent role at nerve terminals in eliciting MoG-mediated synaptic depression in the crayfish Procambarus clarkii.
Hearing Threshold and Frequency Discrimination in the Purely Aquatic frogXenopus Laevis (Pipidae): Measurement by Means of Conditioning
Authors: Elepfandt Andreas , Eistetter Ilse , Fleig Andrea , Günther Elke , Hainich Michaela , Hepperle Susanne , Traub Burkhardt
Published: April 2021

Hearing threshold and frequency discrimination for underwater sound were measured in the clawed frog Xenopus laevis by means of conditioning. A go/no go discrimination procedure was used in which the test tone was presented concurrently with a wave on the surface of the water. The tone signalled whether or not the frog should respond to the wave. The hearing range of X. laevis was 200–4000 Hz. Similar thresholds of 92–96 dB re 1 μPa were found at 600 Hz, 1400–1800 Hz and 3200–3600 Hz. A high threshold at 1000–1300 Hz suggested that this was the frequency range between the sensitivities of the amphibian and basilar papillae. Relative frequency discrimination was approximately 5 % at 400–800 Hz, 45 % at 1000 Hz and 2.4–6 % at 1600–2500 Hz. This last range encompasses the dominant frequencies of the advertisement call of this species. High discrimination acuity at these frequencies may be used in distinguishing between calling males. The threshold for a one-third-octave bandpass noise centred at 600 Hz was 27.6 dB lower than that for a pure tone of 600 Hz, suggesting that sound intensity was integrated within this bandwidth, possibly by a critical-band mechanism.
Thyroid Hormone Concentrations In Captive And Free-Ranging West Indian Manatees (Trichechus Manatus)
Authors: Ortiz Rudy M. , Mackenzie Duncan S. , Worthy Graham A. J.
Published: April 2021

Because thyroid hormones play a critical role in the regulation of metabolism, the low metabolic rates reported for manatees suggest that thyroid hormone concentrations in these animals may also be reduced. However, thyroid hormone concentrations have yet to be examined in manatees. The effects of captivity, diet and water salinity on plasma total triiodothyronine (tT3), total thyroxine (tT4) and free thyroxine (fT4) concentrations were assessed in adult West Indian manatees (Trichechus manatus). Free-ranging manatees exhibited significantly greater tT4 and fT4 concentrations than captive adults, regardless of diet, indicating that some aspect of a captive existence results in reduced T4 concentrations. To determine whether this reduction might be related to feeding, captive adults fed on a mixed vegetable diet were switched to a strictly sea grass diet, resulting in decreased food consumption and a decrease in body mass. However, tT4 and fT4 concentrations were significantly elevated over initial values for 19 days. This may indicate that during periods of reduced food consumption manatees activate thyroid-hormone-promoted lipolysis to meet water and energetic requirements. Alterations in water salinity for captive animals did not induce significant changes in thyroid hormone concentrations. In spite of lower metabolic rates, thyroid hormone concentrations in captive manatees were comparable with those for other terrestrial and marine mammals, suggesting that the low metabolic rate in manatees is not attributable to reduced circulating thyroid hormone concentrations.
Sound Production and Hearing in the Blue Cracker Butterfly Hamadryas Feronia (Lepidoptera, Nymphalidae) From Venezuela
Authors: Yack Jayne E. , Otero L. Daniel , Dawson Jeff W. , Surlykke Annemarie , Fullard James H.
Published: April 2021

Certain species of Hamadryas butterflies are known to use sounds during interactions with conspecifics. We have observed the behaviour associated with sound production and report on the acoustic characteristics of these sounds and on the anatomy and physiology of the hearing organ in one species, Hamadryas feronia, from Venezuela. Our observations confirm previous reports that males of this species will take flight from their tree perch when they detect a passing conspecific (male or female) and, during the chase, produce clicking sounds. Our analyses of both hand-held males and those flying in the field show that the sounds are short (approximately 0.5 s) trains of intense (approximately 80–100 dB SPL at 10 cm) and brief (2–3 ms) double-component clicks, exhibiting a broad frequency spectrum with a peak energy around 13–15 kHz. Our preliminary results on the mechanism of sound production showed that males can produce clicks using only one wing, thus contradicting a previous hypothesis that it is a percussive mechanism. The organ of hearing is believed to be Vogel’s organ, which is located at the base of the forewing subcostal and cubital veins. Vogel’s organ consists of a thinned region of exoskeleton (the tympanum) bordered by a rigid chitinous ring; associated with its inner surface are three chordotonal sensory organs and enlarged tracheae. The largest chordotonal organ attaches to a sclerite positioned near the center of the eardrum and possesses more than 110 scolopidial units. The two smaller organs attach to the perimeter of the membrane. Extracellular recordings from the nerve branch innervating the largest chordotonal organ confirm auditory sensitivity with a threshold of 68 dB SPL at the best frequency of 1.75 kHz. Hence, the clicks with peak energy around 14 kHz are acoustically mismatched to the best frequencies of the ear. However, the clicks are broad-banded and even at 1–2 kHz, far from the peak frequency, the energy is sufficient such that the butterflies can easily hear each other at the close distances at which they interact (less than 30 cm). In H. feronia, Vogel’s organ meets the anatomical and functional criteria for being recognized as a typical insect tympanal ear.
Functional Ureogenesis in the Gobiid Fish, Mugilogobius Abei
Authors: Iwata Katsuya , Kajimura Makiko , Sakamoto Tatsuya
Published: April 2021

To examine the transition to ureogenesis, the gobiid fish Mugilogobius abei was immersed in 2 mmol l−1 NH4HCO3 or a 15N-labelled ammonia solution [1 mmol l−1 (15NH4)2SO4, pH 8.0] for 4–8 days. When exposed to 2 mmol l−1 NH4HCO3 or 15N-labelled ammonia solution for 4 days, the rate of urea excretion increased to seven times that of the control (in 20 % synthetic sea water) and remained at this level for 4 days. The proportion of nitrogen excreted as urea reached 62 % of total nitrogen excretion (ammonia-N + urea-N). 15N-enrichment of the amide-N in glutamine in the tissues of fish exposed to 15N-labelled ammonia was virtually the same as that of ammonia-N: i.e. approximately twice that of urea-N in the excreta and the tissues. Glutamine contents and glutamine synthetase activities in the liver and muscle increased greatly following exposure to ammonia. Urea and citrulline contents in the muscle and whole body of the exposed fish increased significantly, whereas uric acid contents remained unchanged. Carbamoyl phosphate synthetase III (CPSase III) mRNA expression and CPSase III activity were detected in the muscle, skin and gill, but levels were negligible in the liver. Furthermore, all other ornithine–urea cycle (O-UC) enzymes were also detected in muscle, skin and gill. Thus, M. abei clearly shows the transition from ammoniotely to ureotely under ammonia-loading condition and is able to produce urea mainly via the O-UC operating in multiple non-hepatic tissues as a means for ammonia detoxification.
Energetics of Surface Swimming in Brandt’s Cormorants (Phalacrocorax Penicillatus Brandt)
Authors: Ancel A. , Starke L. N. , Ponganis P. J. , Dam R. Van , Kooyman G. L.
Published: April 2021

The energy requirements of Brandt’s cormorants (Phalacrocorax penicillatus) during surface swimming were measured in birds swimming under a metabolic chamber in a water flume. From the oxygen consumption recordings, we extrapolated the metabolic rate and cost of transport at water speeds ranging from 0 to 1.3 m s−1. In still water, the birds’ mean mass-specific rate of oxygen consumption while floating at the surface was 20.2 ml O2 min−1 kg−1, 2.1 times the predicted resting metabolic rate. During stead.y-state voluntary swimming against a flow, their increased with water speed, reaching 74 ml O2 min−1 kg−1 at 1.3 m s−1, which corresponded to an increase in metabolic rate from 11 to 25 W kg−1. The cost of transport decreased with swimming velocity, approaching a minimum of 19 J kg−1 m−1 for a swimming speed of 1.3 m s−1. Surface swimming in the cormorant costs approximately 18 % less than sub-surface swimming. This confirms similar findings in tufted ducks (Aythya fuligula) and supports the hypothesis that increased energy requirements are necessary in these birds during diving to overcome buoyancy and heat loss during submergence.
Curved Flight Paths and Sideways Vision in Peregrine Falcons (Falco Peregrinus)
Authors: Tucker Vance A. , Tucker Alice E. , Akers Kathy , Enderson James H.
Published: April 2021

When diving at prey straight ahead from great distances at high speeds, a peregrine has a conflict between vision and aerodynamics: it must turn its head approximately 40 ° to one side to see the prey with maximum visual acuity at the deep fovea of one eye, but the head in this position increases aerodynamic drag and slows the falcon down. The falcon could resolve this conflict by holding its head straight and flying along a logarithmic spiral path that keeps the line of sight of the deep fovea pointed sideways at the prey. Wild peregrines, observed with binoculars, telescopes and a tracking device, did approach prey the size of American robins (Turdus migratorius) and smaller birds from distances of up to 1500 m by holding their heads straight and flying along curved paths that resembled the logarithmic spiral.
The Cardiovascular Responses of the Red-Eared Slider (Trachemys Scripta) Acclimated to Either 22 Or 5 °C: II. Effects of Anoxia on Adrenergic and Cholinergic Control
Authors: Hicks J. M. T. , Farrell A. P.
Published: April 2021

Cardiovascular control in cold-acclimated freshwater turtles during chronic anoxic exposure is not well understood. We tested the hypothesis that the observed bradycardia in Trachemys scripta results from increased cholinergic inhibitory tone and reduced sympathetic activity. Cardiovascular status was measured in vivo in turtles acclimated to either 22 °C or 5 °C and either acutely exposed (6 h) to anoxia at 22 °C or chronically exposed (22 days) to anoxia at 5 °C. In 22 °C-acclimated turtles, injection of the cholinergic antagonist atropine induced a significant tachycardia under both normoxic and anoxic conditions. However, in 5 °C-acclimated turtles, atropine injection had little effect on heart rate. Therefore, cholinergic control of heart rate was suppressed during cold acclimation; instead, temperature effects are more important in bringing about bradycardia, while the intrinsic effects of anoxia and acidosis are probably important during chronic anoxia. Injection of adrenaline caused a pressor response through increased systemic resistance at both acclimation temperatures. This response was blunted by acute and chronic anoxic exposure, suggesting that systemic vasomotor control was altered independently of acclimation temperature. This anoxic blunting may be related in part to the anoxia-induced increase in systemic resistance. Injection of nadolol after atropine decreased systemic cardiac output. The tonic β-adrenergic cardiac stimulation was attenuated by acute and chronic anoxic exposure. Some of this attenuation of β-adrenergic control could be attributed to the 39–40 % reduction in cell surface β-adrenoreceptor density in the ventricles of these turtles that accompanied acute and chronic anoxic exposure. In conclusion and contrary to our original hypothesis, cholinergic and adrenergic control of the cardiovascular system in turtles was attenuated under cold anoxic conditions, perhaps assisting in the depressed physiological state of these animals.
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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Three-Dimensional Odor Tracking by Nautilus Pompilius
Authors: Basil Jennifer A. , Hanlon Roger T. , Sheikh Sarah I. , Atema Jelle
Published: April 2021

The ‘living fossil’ Nautilus pompilius is thought to use olfaction as its primary sensory system during foraging, yet neither the organs responsible for olfaction nor the mechanisms or behaviors associated with odor tracking have been subjected to experimentation. Flume testing under dark conditions revealed that Nautilus could consistently detect and follow turbulent odor plumes to the source over distances up to 10 m, exhibiting two types of orientation behavior while sampling in three dimensions. The paired rhinophores were necessary for orientation behavior: when they were temporarily blocked either uni-or bilaterally, Nautilus detected odor but could not track the plume and locate the source. Animals that were tested post-blockage were able to track and locate the source. The role of the 90 thin tentacles remains enigmatic; they seemed to be able to detect odor, but they were not capable of guiding orientation behavior towards a distant odor source. Bilateral chemical sensing by rhinophores in three dimensions may have been the Umwelt of ammonites and belemnites before the evolution of complex eyes and fast locomotion in modern coleoids.
In Search Of Molecular Dovetails in Mussel Byssus: From The Threads to The Stem
Authors: Coyne Kathryn J. , Waite J. Herbert
Published: April 2021

We recently described the cDNA sequence for a unique collagenous protein, preCol-P, in the byssal threads of the marine mussel Mytilus edulis. The translated amino acid sequence encodes an unprecedented block-copolymer-like sequence with a central collagenous domain flanked by elastin-like sequences. Here, we report on the presence of two additional variants of preCol-P. The distribution of these variants in M. edulis foot tissue was examined by reverse transcription followed by polymerase chain reaction (RT-PCR) and in situ hybridization techniques. One of the variants, P33, exhibits a graded distribution with decreasing concentrations along the longitudinal axis of the foot. The second variant, P22, is expressed only at the base of the mussel’s foot. In situ hybridization confirms the exclusive expression of preCol-P variant P22 in the stem gland. We propose that this variant may represent a molecular ‘dovetail’ between the proximal thread and the byssal stem, imparting extensibility and elastic recoil to the ring portion of the stem.
Way-Finding and Landmarks: The Multiple-Bearings Hypothesis
Authors: Kamil Alan C. , Cheng Ken
Published: April 2021

Clark’s nutcrackers (Nucifraga columbiana) are capable of very precise searching using the metric relationships between a goal and multiple landmarks to relocate the goal location. They can judge the direction more accurately than the distance to a landmark when the landmark is distant from the goal. On the basis of these findings, we propose that nutcrackers use a set of bearings, each a measure of the direction from the goal to a different landmark, when searching for that goal. The results of a simulation demonstrate that increasing the number of landmarks used results in increasingly precise searching. This multiple-bearings hypothesis makes a series of detailed predictions about how the distribution of searches will vary as a function of the geometry of the locations of the relevant landmarks and the goal. It also suggests an explanation for inconsistencies in the literature on the effects of clock-shifts on searching and on homing.