bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoregulation of the Intra-Abdominal Testes of the Bottlenose Dolphin (Tursiops Truncatus) During Exercise
Authors: Pabst D. A. , Rommel S. A. , McLellan W. A. , Williams T. M. , Rowles T. K.
Published: April 2021

Dolphins possess a vascular countercurrent heat exchanger (CCHE) that functions to cool their intra-abdominal testes. Spermatic arteries in the posterior abdomen are juxtaposed to veins returning cooled blood from the surfaces of the dorsal fin and tail flukes. In this study, we investigated the effect of exercise on CCHE function in the bottlenose dolphin. The CCHE flanks a region of the bowel in the posterior abdomen and influences colonic temperatures. A rectal probe housing a linear array of seven copper–constantan thermocouples was designed to measure colonic temperatures simultaneously at positions anterior to, within and posterior to the region of the colon flanked by the CCHE. Immediately after vigorous swimming, temperatures at the CCHE decreased relative to resting and pre-swim values: post-swim temperatures at the CCHE were maximally 0.5 °C cooler than pre-swim temperatures. These data suggest that the CCHE has an increased ability to cool the arterial blood supply to the testes when the dolphin is swimming. This ability could offset the increased thermal load on the testes in an exercising dolphin. To the best of our knowledge, this is the first report of deep body cooling in an exercising mammal that is not undertaking a dive.
Oxygen Availability and Embryonic Development in Sand Snail (Polinices Sordidus) Egg Masses
Authors: Booth David T.
Published: April 2021

The oxygen transport physiology of sand snail Polinices sordidus egg masses was investigated using oxygen microelectrodes and open-flow respirometry. P. sordidus eggs are laid in a jelly matrix that rapidly absorbs water and swells into a horseshoe-shaped sausage. The average diameter of these sausages is 37 mm. Eggs are enclosed in capsules that are distributed throughout the jelly matrix, but 65 % of the eggs are located within 3 mm of the outer surface. There is no circulatory or canal system within the matrix so all gas exchange between developing embryos and the environment must occur by diffusion through the jelly matrix.

Oxygen tension in the outer layer remains moderately high throughout incubation but decreases rapidly in more centrally located regions, so that by day 4 embryos in this region are exposed to extremely hypoxic conditions . This hypoxia limits oxygen consumption of embryos to low levels and appears to slow embryonic development or even to arrest it. From day 4 onwards, the central region gradually become less hypoxic because the hatching of peripherally located embryos causes the outer layers of the jelly matrix to disintegrate and thus reduces the diffusion distance for oxygen between the centrally located embryos and the surrounding sea water. As the oxygen tension rises, development accelerates and the embryos eventually hatch as viable veligers, apparently unharmed by their prolonged exposure to hypoxia.
Immunocytochemical Localization Of Multiple Cholecystokinin-Like Peptides In The Stomatogastric Nervous System Of The Crab Cancer Borealis
Authors: Christie Andrew E. , Baldwin David , Turrigiano Gina , Graubard Katherine , Marder Eve
Published: April 2021

Three anti-cholecystokinin antibodies were used to label the stomatogastric nervous system of the crab Cancer borealis. Labeled tissues were examined as whole mounts using laser scanning confocal microscopy. Although each of the anti-cholecystokinin antibodies labeled a variety of structures within the stomatogastric nervous system (including somata, fibers and neuropil), the pattern of labeling produced by each antibody was distinct. These results indicate that there is a family of cholecystokinin-like molecules that are differentially distributed among a subpopulation of the neurons in the stomatogastric nervous system of Cancer borealis.
Evolutionary Adaptation of Contractile Performance in Muscle of Ectothermic Winter-Flying Moths
Authors: Marden James H.
Published: April 2021

temperature-sensitivity of muscle performance in a winter-flying ecotothermic moth (Operophtera bruceata) was examined and compared with that of a summer-flying endothermic hawkmoth (Manduca sexta). O. bruceata muscle contracted over a temperature range of 1–28 °C, whereas M. sexta muscle contracted at temperatures of 13–42.5 °C. Maximum (unloaded) contraction velocity (Vmax) was greater in O. bruceata over most of the range of temperatures where muscle from both species was excitable (3–4 lengths s−1versus 0.6–3.6 lengths s−1 at 13–28 °C), but M. sexta muscle achieved a much higher Vmax at the temperature that this species maintains during flight (10 lengths s−1 at 40–42.5 °C). The capacity of O. bruceata muscle to generate tension was approximately twice that of M. sexta muscle (peak tetanic tension of 13.9 versus 7.0N cm−2). This greater force-generating capacity in O. bruceata largely offset its lower shortening velocity, such that maximum instantaneous power output was equivalent in both species at temperatures below 35 °C (approximately 100–120 W kg−1). M. sexta muscle achieved instantaneous power outputs of up to 202 W kg−1 at temperatures of 40–42.5 °C. Muscle activation and deactivation (measured by times to peak tension and to half-relaxation during isometric twitches) were most rapid for O. bruceata at temperatures of 15–30 °C and for M. sexta at temperatures of 30–40 °C.

Data for power output of flight muscle from these moths are combined with estimates of induced power required for flight in order to show how adaptations for thermal sensitivity of muscle power output interact with morphology (low wing-loading, high flight muscle ratio) to allow O. bruceata moths to fly at extremely low body temperatures, and to construct a model showing how the fecundity of flightless O. bruceata females would decline if they were to regain the ability to fly. Marginal flight over a narrow range of temperatures for O. bruceata females would require a 17 % reduction in fecundity; to fly over as large a range of temperatures as do males would require an 82 % reduction in fecundity.
The Thermal Acclimation of Burst Escape Performance in Fish: An Integrated Study of Molecular and Cellular Physiology and Organismal Performance
Authors: Johnson Timothy P. , Bennett Albert F.
Published: April 2021

Goldfish (Family Cyprinidae, Carassius auratus) and killifish (Family Cyprinodontidae, Fundulus heteroclitus) were acclimated to 10, 20 and 35 °C for 4 weeks. The thermal acclimation of C-start (escape swimming) performance and the physiological properties of fast twitch muscle fibres that underlie it were investigated in these species at the molecular (myosin isoform expression), biochemical (myofibrillar ATPase activity), cellular (contractile kinetics) and organismal levels of organisation. Peptide maps were obtained for fast muscle myosin heavy chains, isolated from 10 °C- and 35 °C-acclimated fish. Different myosin heavy chain isoforms were expressed in response to a change in acclimation temperature in goldfish, but myosin heavy chain isoform expression was unaffected by acclimation temperature in killifish. Compared with fish acclimated to 35 °C, acclimation to 10 °C increased the activity of fast muscle myofibrillar ATPase assayed at 10 °C fivefold in goldfish and only 50 % in killifish. Muscle twitch contraction time at 10 °C decreased significantly in response to acclimation to 10 °C in both species; however, the magnitude of this response was much greater in goldfish (100 %) than in killifish (30 % or less). In goldfish, these changes in the physiological properties of fast twitch fibres during 10 °C acclimation resulted in a six-to eightfold increase in the speed and turning velocity of fish performing C-starts at 10 °C. By comparison, the somewhat smaller acclimatory response of killifish fast muscle properties was accompanied by only a minor (50 % or less) adjustment in locomotor performance. Thermal acclimatory responses of fast muscle at the molecular, biochemical and cellular levels of organisation are clearly reflected in alterations in organismal escape performance.
Central Circuitry in the Jellyfish Aglantha Digitale: II. The Ring Giant and Carrier Systems
Authors: Mackie G. O. , Meech R. W.
Published: April 2021

The ring giant axon in the outer nerve ring of the jellyfish Aglantha digitale is a multinucleate syncytium 85 % of which is occupied by an electron-dense fluid-filled vacuole apparently in a Gibbs–Donnan equilibrium with the surrounding band of cytoplasmic cortex. Micropipette recordings show small (-15 to -25 mV) and large (−62 to -66 mV) resting potentials. Low values, obtained with a high proportion of the micropipette penetrations, are assumed to be from the central vacuole; high values from the cytoplasmic cortex. Background electrical activity includes rhythmic oscillations and synaptic potentials representing hair cell input caused by vibration. After the ring giant axon has been cut, propagating action potentials evoked by stimulation are conducted past the cut and re-enter the axon on the far side. The system responsible (the carrier system) through-conducts at a velocity approximately 25 % of that of the ring giant axon and is probably composed of small neurones running in parallel with it. Numerous small neurones are seen by electron microscopy, some making one-way and some two-way synapses with the ring giant. Despite their different conduction velocities, the two systems normally appear to fire in synchrony and at the velocity of the ring giant axon. We suggest that, once initiated, ring giant spikes propagate rapidly around the margin, firing the carrier neurones through serial synapses and giving them, in effect, the same high conduction velocity. Initiation of ring giant spikes can, however, require input from the carrier system. The spikes are frequently seen to be mounted on slow positive potentials representing summed carrier postsynaptic potentials. The carrier system fires one-for-one with the giant axons of the tentacles and may mediate impulse traffic between the latter and the ring giant axon. We suggest that the carrier system may also provide the pathways from the ring giant to the motor giant axons used in escape swimming. The findings show that the ring giant axon functions in close collaboration with the carrier system, increasing the latter’s effective conduction velocity, and that interactions with other neuronal sub-systems are probably mediated exclusively by the carrier system.
Electrosensory Stimulus-Intensity Thresholds in the Weakly Electric Knifefish Eigenmannia: Reduced Sensitivity at Harmonics of its own Organ Discharge
Authors: Kaunzinger Ivo , Kramer Bernd
Published: April 2021

The South American knifefish Eigenmannia sp. can detect the electric organ discharges (EODs; 250–600 Hz) of conspecifics when they are superimposed over its own EOD. This study investigates the minimum frequency difference necessary for such signal perception, using the application of sine-wave stimuli. Electrosensory stimulus-intensity thresholds were determined for trained fish using stimuli associated with food rewards. These sine-wave stimuli were ‘clamped’ to the EOD frequency of the fish. Electrosensory thresholds were also determined for the spontaneous jamming avoidance response (JAR; a change in EOD frequency evoked by a stimulus of sufficiently similar frequency), in this case using unclamped stimuli.

Over the wide frequency range investigated (0.3–3.01 times EOD frequency), the lowest stimulus-intensity thresholds of 0.6 µV cm−1 (peak-to-peak) (0 dB) at a water conductivity of 100 µS cm−1 were found close to (but not exactly at) the EOD fundamental frequency. At exact frequency identity between the EOD and the stimulus, the stimulus-intensity response threshold rose abruptly by more than 10 dB compared with slightly higher or lower stimulus frequencies. A similar ‘needle-like’ threshold increase was found at exactly two and three times the EOD frequency, but neither at harmonic ratios between stimulus and EOD frequency that represent fractions (e.g. at 5:4=1.25, 4:3=1.33, 3:2=1.5 or 5:3=1.67 times EOD frequency) nor at subharmonics such as half or two-thirds of the EOD frequency. The steepest increase of stimulus-intensity response threshold was in the range 0.998–1.002 times EOD frequency, corresponding to a threshold change, or electrosensory filter slope, of 5000 dB per octave.

For the spontaneous JAR, a similar stimulus-intensity threshold increase was observed when EOD frequency equalled stimulus frequency. Because of the longer rise time for the stimulus amplitude (400 ms rather than 35 ms) the stimulus intensity threshold was higher (up to 32 dB; mean, 20 dB) than in the other experiments (up to 15 dB; mean, 13 dB).

A difference in frequency between the EOD and the applied stimulus as small as 1 Hz (that is, 0.2 % of the EOD frequency) was sufficient for good signal perception in Eigenmannia sp. The JAR appears to be useful in avoiding insensitivity at exact integer harmonics of the EOD frequency.
Matrix of neuromodulators in neurosecretory structures of the crab Cancer borealis
Authors: Christie Andrew E. , Skiebe Petra , Marder Eve
Published: April 2021

The crustacean stomatogastric ganglion, which is situated in the ophthalmic artery, can be modulated by both intrinsically released molecules and hormones. In the crab Cancer borealis, over a dozen neuroactive compounds have been identified in the input axons that project into the stomatogastric neuropil. However, little is known about the modulator content of the two major neurohemal organs, the sinus glands and the pericardial organs, in this crab. We now report the results of a series of immunocytochemical experiments designed to identify putative neurohormones in these tissues. We find that the majority of modulators present in the input axons of the stomatogastric ganglion are also present in at least one of the neurohemal organs. Specifically, allatostatin-like, buccalin-like, cholecystokinin-like, FLRFamide-like, GABA-like, locustatachykinin-like, myomodulin-like, proctolin-like, red pigment concentrating hormone-like and serotonin-like immunoreactivities are all present in both the stomatogastric neuropil and at least one of the neurohemal organs. Thus, these substances are likely to serve a dual role as both local and hormonal modulators of the stomatogastric network. Two other substances, β-pigment dispersing hormone and crustacean cardioactive peptide, are not present in the stomatogastric neuropil, but β-pigment dispersing hormone immunoreactivity is present in the sinus glands and crustacean cardioactive peptide immunoreactivity is present in the pericardial organs. It is likely that crustacean cardioactive peptide exerts its influence on the stomatogastric neural circuit via hormonal pathways. Double-labeling experiments show that the patterns of modulator co-localization present in the stomatogastric neuropil are different from those in the neurosecretory organs, suggesting that few rules of co-localization hold across these tissues.
Differential scanning calorimetry studies on the cysts of the potato-cyst nematode Globodera rostochiensis during freezing and melting
Authors: Wharton D. A. , Ramløv H.
Published: April 2021

Differential scanning calorimetry (DSC) was used to determine the thermal events associated with freezing and melting of the cysts of the potato-cyst nematode Globodera rostochiensis. There were no thermal events during the cooling of dry cysts from 5 to –60 °C and warming back to 5 °C, indicating the absence of water freezing in the dry cysts. During heating of dry cysts from 5 to 80 °C, two overlapping endothermic events were observed at 55 °C, indicating the irreversible destruction of the permeability barrier of the eggshell by the melting of the lipids which constitute the lipid layer.

The first exothermic event (T=–9 °C) during the cooling of hydrated cysts indicates the presence of an ice-nucleating agent. A broad exotherm at –38 °C is due to the freezing of eggs. DSC thus confirms that the eggshell prevents exogenous ice nucleation and allows the eggs to supercool in the presence of external ice. The enthalpy of the egg exotherm increased during hydration of the cysts. The temperature of the egg exotherm was elevated after heating of the sample to 70 °C. This is thought to be due to the loss of trehalose from the eggs following the destruction of the permeability barrier of the eggshell.

During melting, three endothermic events were observed. These became merged after the destruction of the permeability barrier of the eggshell by heating, and only two peaks were observed in isolated eggs. The sample is thus considered to consist of three freezable compartments: (1) the water surrounding the cyst, (2) the solution between the cyst wall and the eggs and (3) the egg contents.
The Young’s Modulus of Feather Keratin
Authors: Bonser Richard H. C. , Purslow Peter P.
Published: April 2021

The flexural stiffness of the rachis varies along the length of a primary feather, between primaries and between species; the possible contribution of variations in the longitudinal Young’s modulus of feather keratin to this was assessed. Tensile tests on compact keratin from eight species of birds belonging to different orders showed similar moduli (mean E=2.50 GPa) in all species apart from the grey heron (E=1.78 GPa). No significant differences were seen in the modulus of keratin from primaries 7–10 in any species. There was a systematic increase in the modulus distally along the length of the rachis from swan primary feathers. Dynamic bending tests on swan primary feather rachises also showed that the longitudinal elastic modulus increases with increasing frequency of bending over the range 0.1–10 Hz and decreases monotonically with increasing temperature over the range -50 to +50°C. The position-, frequency-and temperature-dependent variations in the modulus are, however, relatively small. It is concluded that, in the species studied, the flexural stiffness of the whole rachis is principally controlled by its cross-sectional morphology rather than by the material properties of the keratin.
A GabaB Receptor on an Identified Insect Motor Neurone
Authors: Bai Donglin , Sattelle David B.
Published: April 2021

The vertebrate GABAB receptor (GABABR) agonists 3-aminopropylphosphonous acid (3-APPA), SK&F97541 and 3-aminopropylphosphonic acid (3-APA) are able to induce a hyperpolarization on the cell body of motor neurone Df in the metathoracic ganglion of the cockroach (Periplaneta americana), although the classic vertebrate GABABR agonist L-baclofen fails to induce any responses on the same neurone. Consistent with the findings on vertebrate GABABRs, the 3-APPA-induced responses on Df were also insensitive to the GABAAR antagonists bicuculline and picrotoxin. However, the GABABR antagonists saclofen and CGP35348 also failed to block this GABAB-like response. These results indicate a novel pharmacology for the GABAB-like receptors on the Df neurone. The reversal potential indicates that these GABAB-like receptors may be coupled to K+ channels.
Effects of Oxygenation and the Stress Hormones Adrenaline and Cortisol on the Viscosity of Blood From the Trout Oncorhynchus Mykiss
Authors: Sørensen Bodil , Weber Roy E.
Published: April 2021

Although the concentrations of the stress hormones adrenaline and cortisol in rainbow trout (Oncorhynchus mykiss) blood increase upon hypoxic exposure, the combined effects of these hormones and O2 lack upon fish blood rheology have not been investigated. Deoxygenated blood taken by caudal puncture exhibited lower viscosities than oxygenated samples at low shear rates, whereas the opposite was true at high shear rates. However, blood from cannulated trout had similar viscosities in its deoxygenated and oxygenated states. In the deoxygenated state, addition of adrenaline lowered viscosity at low shear rates and increased it at high shear rates, resembling the effects of deoxygenation observed in blood taken by venepuncture. In oxygenated blood on the contrary, no marked adrenaline effects were observed. In deoxygenated blood, addition of cortisol lowered viscosity at all measured shear rates compared with blood without cortisol. In oxygenated blood, however, no cortisol effects were observed. The viscosity effects observed in the presence of cortisol could not be attributed to concomitant changes in haematological variables, However, the effects in the presence of adrenaline manifested in deoxygenated ‘cannula’ blood and in uncannulated blood without added hormones appear to result from parallel increases in haematocrit and cell volume.
Protein Synthesis and Degradation in the Flight Muscles of Adult Crickets (Gryllus Bimaculatus)
Authors: Gomi Tadashi , Okuda Takashi , Tanaka Seiji
Published: April 2021

The development and degeneration of the flight muscles in adult crickets, Gryllus bimaculatus, were studied (1) by determination of the total protein content, (2) by SDS one-dimensional polyacrylamide gel electrophoresis (SDS–PAGE) of muscle protein and (3) by in vitro culturing of the muscle. The total protein content of the dorso-longitudinal muscle (DLM) and metathoracic dorso-ventral muscle (DVM) increased during the early days of adult life in both sexes. This high protein content was maintained for at least a further 10 days in some individuals, while in others it declined to a low level. Mesothoracic DVMs in males also showed an increase in protein content after adult emergence but did not undergo histolysis, whereas those in females showed no significant temporal change in protein content. Removal of hind wings or artificial de-alation was found to be useful in inducing degeneration of DLMs and metathoracic DVMs. This treatment also stimulated ovarian development in females.

An analysis by SDS–PAGE provided no evidence for new protein synthesis prior to or during flight muscle degeneration. A high rate of [3H]-or [35S]methionine incorporation was observed in DLMs taken from newly emerged adults, but, in intact crickets, the rate declined rapidly during the first 3 days of adult life, a pattern consistent with that obtained from the measurement of total protein content. Compared with DLMs removed from intact crickets, DLMs taken from de-alated crickets showed reduced rates of protein synthesis during in vitro culturing. This, together with the onset of protein degradation, appears to cause the rapid decrease in total protein content of the muscle in de-alated crickets.
EmrE, the Smallest Ion-Coupled Transporter, Provides a Unique Paradigm for Structure–Function Studies
Authors: Schuldiner Shimon , Lebendiker Mario , Yerushalmi Hagit
Published: April 2021

EmrE is an Escherichia coli multidrug transporter which confers resistance to a wide variety of toxicants by actively removing them in exchange for hydrogen ions. EmrE is a highly hydrophobic 12 kDa protein which has been purified by taking advantage of its unique solubility in organic solvents. After solubilization and purification, the protein retains its ability to transport as judged from the fact that it can be reconstituted in a functional form. Hydrophobicity analysis of the sequence yielded four putative transmembrane domains of similar sizes. Results from transmission Fourier transform infrared measurements agree remarkably well with this hypothesis and yielded α-helical estimates of 78 % and 80 % for EmrE in CHCl3:MeOH and 1,2-dimyristoyl phosphocholine, respectively. Furthermore, the fact that most of the amide groups in the protein do not undergo amide–proton H/D exchange implies that most (approximately 80 %) of the residues are embedded in the bilayer. These observations are only consistent with four transmembrane helices. A domain lined by Cys41 and Cys95 accessible only to substrates such as the organic mercurial 4-(chloromercuri)benzoic acid has been identified. Both residues are asymmetric in their location with respect to the plane of the membrane, Cys95 being closer than Cys41 to the outside face of the membrane. In co-reconstitution experiments of wild-type protein with three different inactive mutants, negative dominance has been observed. This phenomenon suggests that EmrE is functional as a homo-oligomer.
Oxygen and Carbon Dioxide Transport in Vertebrate Erythrocytes: An Evolutionary Change in the Role of Membrane Transport
Authors: Nikinmaa Mikko
Published: April 2021

Two major strategies are apparent for the regulation of gas transport by vertebrate blood except in the myxinoids, which seem to have little scope for such regulation. In lampreys and teleost fish, haemoglobins have low buffering capacities and large Bohr/Haldane effects. Na+/H+ exchange plays an important role in the control of haemoglobin oxygen-affinity in these vertebrate groups. The large Bohr/Haldane effect also facilitates carbon dioxide transport: the blood (or erythrocyte) pH increases upon deoxygenation, thus increasing the concentration of bicarbonate formed at a given carbon dioxide tension. In lampreys, the bicarbonate permeability of the erythrocyte membrane is low. As a consequence, extracellular acid loads cannot be buffered by haemoglobin. In contrast, teleost erythrocytes possess a functional anion exchange, allowing extracellular proton loads to be buffered by haemoglobin. However, because the buffering capacity of teleost haemoglobins is low, buffering of extracellular acid loads is less effective in teleost fish than in elasmobranch fish and in air-breathing vertebrates whose haemoglobins have a high buffering capacity. However, the high buffering capacity of the haemoglobins diminishes the possibility of regulating haemoglobin oxygen-affinity via secondarily active Na+/H+ exchange, because intracellular pH changes, caused by proton efflux, remain small.
Contrasting Strategies for Anoxic Brain Survival – Glycolysis Up or Down
Authors: Lutz Peter L. , Nilsson Göran E.
Published: April 2021

Anoxia-tolerant turtles and carp (Carassius) exhibit contrasting strategies for anoxic brain survival. In the turtle brain, the energy consumption is deeply depressed to the extent of producing a comatose-like state. Brain metabolic depression is brought about by activating channel arrest to reduce ion flux and through the release of inhibitory γ-aminobutyric acid (GABA) and the up-regulation of GABAA receptors. Key glycolytic enzymes are down-regulated during prolonged anoxia. The result is a suppression of neurotransmission and a substantial depression in brain electrical activity.

By contrast, Carassius remain active during anoxia, though at a reduced level. As in the turtle, there is an adenosine-mediated increase in brain blood flow but, in contrast to the turtle, this increase is sustained throughout the anoxic period. Key glycolytic enzymes are up-regulated and anaerobic glycolysis is enhanced. There is no evidence of channel arrest in Carassius brain. The probable result is that electrical activity in the brain is not suppressed but instead maintained at a level sufficient to regulate and control the locomotory and sensory activities of the anoxic carp.

The key adaptations permitting the continued high level of glycolysis in Carassius are the production and excretion of ethanol as the glycolytic end-product, which avoids self-pollution by lactate produced during glycolysis that occurs in other vertebrates.
The Influence of Surface Atmospheric Conditions on the Range and Area Reached by Animal Vocalizations
Authors: Larom David , Garstang Michael , Payne Katharine , Raspet Richard , Lindeque Malan
Published: April 2021

Low-level vertical changes in temperature and wind exert powerful and predictable influences on the area ensonified by animal vocalizations. Computer modelling of low-frequency sound propagation in measured atmospheric conditions predicts that the calls of the savanna elephant at these frequencies can have ranges exceeding 10 km and that the calls will be highly directional in the presence of wind shear. Calling area is maximized under temperature inversions with low wind speeds. Calling area changes substantially over 24 h periods; on any given day, the calling area undergoes an expansion and contraction which may be as large as one order of magnitude. This cycle is modulated by topography, regional weather patterns, seasonality and possibly by climate variation. Similar influences affect the somewhat higher-frequency calls of lions and may be a selective pressure towards their crepuscular and nocturnal calling behaviour. Coyotes and wolves, which also live in areas with strong and prevalent nocturnal temperature inversions, show similar calling patterns, maximizing their chances of being heard over the longest possible distances. The pronounced dawn and evening vocalization peaks in other animals including birds, frogs and insects may reflect the same influences in combination with other factors which selectively limit high-frequency sound propagation. Atmospheric conditions therefore need to be taken into account in many field studies of animal behaviour. A simplified method for estimating sound propagation during field studies is presented.
Ion Transport and Acid–Base Balance in Freshwater Bivalves
Authors: Byrne Roger A. , Dietz Thomas H.
Published: April 2021

Blood acid–base and ionic balance in freshwater bivalves is affected by the relative activities of epithelial Na+ and Cl− transporters. In the unionid Carunculina texasensis, the Na+/H+ exchanger is the predominant epithelial transporter that affects acid–base state, while Cl−/HCO3− exchange is of lesser importance. In the corbiculid Corbicula fluminea, Cl− and Na+ transport are both significant components affecting acid–base state. Serotonin (5-hydroxytryptamine, 5-HT) stimulates Na+ and Cl− transport in both species. In C. texasensis, the effect of exogenous serotonin is four times greater on Na+/H+ exchange than on Cl−/HCO3− transport, resulting in an increase in acid secretion and a rise in blood pH. In a Na+-free environment, serotonin had no effect on blood acid–base state in C. texasensis. In C. fluminea, the acid–base consequences of serotonin stimulation of Na+/H+ exchange were offset by similar increases in Cl−/HCO3− exchange and by alterations in blood in medium containing Na+. In Na+-free medium, stimulation of the Cl− transporter with 5-HT resulted in a decrease in blood pH. The differences between these two species are related to the reliance of C. fluminea on Cl− as the major anion in the blood, requiring high levels of epithelial Cl− transport. In C. texasensis, the anionic component of the blood consists of both Cl− and HCO3− and these ions are interchangeable over a wide concentration range. Extracellular acid–base balance in freshwater bivalves is governed, in part, by epithelial ion transporters.
Possible Mechanisms of Control of Vascular Resistance in the Lobster Homarus Americanus
Authors: Wilkens Jerrel L.
Published: April 2021

In Homarus americanus, the resistance to fluid flow through each of the arteries leaving the heart, including the complete hemocoelic return pathways, can be controlled. Each of the five arterial types (anterior median, paired anterior lateral, paired hepatic, sternal and dorsal abdominal) exhibits a unique spectrum of responses to a battery of neurotransmitters (acetylcholine, glutamic acid, γ-aminobutyric acid) and neurohormones (dopamine, octopamine, 5-hydroxytryptamine, crustacean cardioactive peptide, FLRFamide-related peptides F1 and F2, and proctolin). Acetylcholine causes increases in resistance in all arteries except the anterior median artery; in the dorsal abdominal artery, this increase is antagonized by γ-aminobutyric acid. All neurohormones that are effective in a particular artery cause increases in resistance to flow. The sites of action of these compounds in the dorsal abdominal artery are valves located at major branch points; the sites of control in the other arteries are not known. It is concluded that the control of arterial resistance is a mechanism which the animal can exploit to produce different flow patterns among the various arteries.
Cyclic-Amp-Induced Water Uptake in A Moth Ovary: Inhibition by Bafilomycin and Anthracene-9-Carboxylic Acid
Authors: Wang Yuren , Telfer William H.
Published: April 2021

The ion physiology of osmotic swelling and a consequent loss of epithelial patency was examined in the ovaries of the moth Hyalophora cecropia. After 30 min in the presence of an activator of cyclic-AMP-dependent protein kinase (PKA), the membrane potentials of both oocyte and follicle cells had hyperpolarized by approximately 30 %, cytoplasmic pH had dropped from 7.26 to 7.06, a normally low Cl− conductance had increased and the follicle cells had begun to swell. Since ion distribution studies have indicated that conductance increases should depolarize membranes in this system, it is proposed that hyperpolarization may be effected by an azide-inhibitable component of the membrane potential. Nanomolar levels of bafilomycin, an inhibitor of H+ V-ATPase, blocked the active component and prevented osmotic swelling in response to PKA activation. Under a variety of circumstances, correlations were seen between membrane potential and cytoplasmic pH, suggesting that substrate availability to the proton pump may contribute to hyperpolarization. H+ V-ATPases are known to energize ion and water transport across many epithelia, but in this case they generate water absorption by the epithelium. The increase in Cl− conductance was also required for the swelling response: the Cl− channel blocker anthracene-9-carboxylic acid prevented both swelling and hyperpolarization, as did Cl− substitution in the medium. Differences in isotope loading rates between 36Cl− and 86Rb+ suggested that, after PKA activation, Cl− functions other than as a counterion for K+ uptake.
Proline Powers Pre-Flight Warm-Up In The African Fruit Beetle Pachnoda Sinuata (Cetoniinae)
Authors: Auerswald Lutz , Schneider Peter , Gäde Gerd
Published: April 2021

We investigated thoracic temperatures (Tth) during different activities of the endothermic fruit beetle Pachnoda sinuata and analysed which energy substrates are used for the pre-flight warm-up of its flight muscles.

Pachnoda sinuata elevates its Tth prior to take-off either by basking in the sun or by warming endothermically to a narrow range around 34 °C. During lift-generating tethered flight at low ambient temperatures (Ta=25 °C), Tth of P. sinuata decreases steadily until it reaches 28 °C, which is not sufficiently high to sustain flight. Tth remains stable during lift-generating tethered flight at high Ta (31 °C). Wingbeat frequency (fw) is dependent on Tth: when Tth declines, fw decreases in a linear manner.

The proline concentrations in the haemolymph and flight muscles decrease during warm-up. In contrast, the carbohydrate levels in the haemolymph and flight muscles are not affected by the warm-up process, while the glycogen level of the flight muscles declines significantly during the first 10 s of lift-generating tethered flight. This suggests that the energy for endothermic warm-up is produced solely by the oxidation of proline.

Measurements of the respiratory quotient (RQ) confirmed that P. sinuata uses a combination of carbohydrates and proline to power its flight. At rest and during lift-generating tethered flight, the RQ is approximately 0.9. During warm-up, the RQ is significantly lower at 0.82, which is close to the theoretical value of 0.8 for the partial oxidation of proline. The rate of oxygen consumption during endothermic warm-up is 45 % of that during lift-generating tethered flight
Oxygen-Sensitive Flight Metabolism in the Dragonfly Erythemis Simplicicollis
Authors: Harrison Jon F. , Lighton John R. B.
Published: April 2021

Insect flight metabolism is completely aerobic, and insect resting metabolism is quite insensitive to atmospheric oxygen level, suggesting a large safety margin in the capacity of the tracheal system to deliver oxygen during flight. We tested the sensitivity of flight initiation and metabolism to atmospheric oxygen level in the libellulid dragonfly Erythemis (Mesothemis) simplicicollis using flow-through res.pirometric measurements of the rate of CO2 emission . Flight initiations were unimpaired in atmospheric oxygen levels as low as 10 %. However, flight m. etabolic rate was affected by ambient oxygen level. Flight decreased in hypoxic mixtures (5 kPa or 10 kPa oxygen) and increased in hyperoxic atmospheres (30 kPa or 50 kPa oxygen), suggesting that ambient oxygen level influences flight muscle oxygen partial pressure and the vigour of flight. These are the first data to show oxygen-limitation of flight metabolism in a free-flying insect. A low safety margin for oxygen delivery during dragonfly flight is consistent with a previous hypothesis that atmospheric hyperoxia facilitated gigantism in Paleozoic protodonates. However, allometric studies of tracheal morphology, and mechanisms and capacity of gas exchange in extant insects are necessary in order to test the hypothesis that the oxygen-sensitivity of aerobic metabolism increases with body size in insects.
Development of Sensory Processes During Limb Regeneration in Adult Crayfish
Authors: Cooper Robin L.
Published: April 2021

The capacity of the crayfish Procambarus clarkii to regenerate its walking legs provides a system for studying the mechanisms of neural regeneration and repair. A set number of excitatory and inhibitory motor neurons innervate all the limb musculature throughout the normal development and regeneration of a limb. The cell bodies of the motor neurons reside within the segmental ganglion and, upon loss of the limb, their axons regrow from their severed distal ends. The cell bodies of the sensory neurons, in contrast, are located close to their sensory endings within the limb, and they are therefore lost, along with the limb, upon autotomy, leaving the severed, distal axonal stumps of the sensory neurons within the ganglionic root. During the regeneration of a limb, new sensory neurons develop within the limb, and their axons must then grow into the ganglionic root to make the appropriate connections for the new limb to become functional. Evidence is presented in the present paper that the sensory axonal stumps do not degenerate before the new sensory neurons appear within the root as the limb regenerates. These results also indicate a progressive advance of growth cones, presumably sensory in origin, towards the neuropil within the ganglion over time.
Tail-Flip Mechanism and Size-Dependent Kinematics of Escape Swimming in the Brown Shrimp Crangon Crangon
Authors: Arnott Stephen A. , Neil Douglas M. , Ansell Alan D.
Published: April 2021

Tail-flip escape swimming by the brown shrimp Crangon crangon has been investigated across a range of body lengths (11–69 mm) using high-speed video analysis. This has revealed several novel aspects of the tail-flip mechanism when compared with that of other decapod crustaceans that have been studied. (i) The pattern of body flexion in C. crangon produces movement of the cephalothorax as well as the abdomen about the centre of mass. (ii) Shrimps form a ‘head-fan’ with their antennal scales, in addition to the tail-fan formed by their uropods, apparently for generating thrust during tail-flips. (iii) Shrimps typically swim on their side rather than in an upright body position. It is suggested that these features may be interlinked and derive from habitat specialisation.

The kinematic properties of tail-flips were found to vary with shrimp size. As shrimp body length increased, the rate of body flexion and re-extension decreased whilst the duration of tail-flips increased. Mean (and maximum) velocity estimates ranged between 0.4 m s−1 (0.7 m s−1) and 1.1 m s−1 (1.8 m s−1) for shrimps of different sizes. The combined effects of escape behaviour and size-dependent variability in tail-flip kinematics will have important implications with regard to predation risk.
Natriuretic Peptide Binding Sites in the Gills of the Pouched Lamprey Geotria Australis
Authors: Toop T. , Grozdanovski D. , Potter I. C.
Published: April 2021

Iodinated atrial natriuretic peptide (ANP) binding sites were examined in the gills and ventral aorta of the adult upstream-migrating lamprey Geotria australis using tissue section autoradiography, in vitro competition analysis and affinity cross-linking, while guanylate cyclase assays were performed on gill membranes of both adult and juvenile lampreys. A partial natriuretic peptide (NP) receptor sequence was amplified using reverse transcription/ polymerase chain reaction (RT-PCR). The results indicated that there was specific NP binding to the aortic endothelium and to pillar cell regions in the axial plate and secondary lamellae. In competition studies, 50 % of NP binding was abolished by 4 nmol l−1 rat ANP, 35 nmol l−1 porcine C-type NP (CNP) and 45 nmol l−1 C-ANF (a truncated ANP). Affinity cross-linking followed by SDS–PAGE demonstrated two binding sites at 205 and 65 kDa under non-reducing conditions and at 85 and 65 kDa under reducing conditions. Guanylate cyclase assays demonstrated that, while no NP-stimulated GC activity occurred in adult lampreys, NP-stimulated enhancement of cyclic GMP accumulation was found in juveniles in fresh water and more particularly in salt water. RT-PCR amplified a 471 base pair fragment with 68 % amino acid sequence homology to the eel natriuretic peptide receptor D (NPR-D). This study suggests that NP binding sites in the adult gill and aorta are of an NPR-C/D type, whereas an additional GC-coupled site exists in juveniles.
The Electric Image in Weakly Electric Fish: Physical Images of Resistive Objects in Gnathonemus Petersii
Authors: Caputi A. A. , Budelli R. , Grant K. , Bell C. C.
Published: April 2021

The present study describes a measurement-based model of electric image generation in the weakly electric mormyrid fish Gnathonemus petersii. Measurements of skin impedance, internal resistivity and fish body dimensions have been used to generate an electrical-equivalent model of the fish and to calculate electrical images and equivalent dipole sources for elementary resistive objects. These calculations allow us to understand how exafferent and reafferent signals are sensed by electroreceptors. An object’s electric image consists of the modulation of the transcutaneous voltage profile generated by the fish’s own discharge. The results suggest a set of rules for electrolocation: (1) the side of the fish where modulation is larger indicates the side on which the object is situated; (2) the object’s position in the electroreceptive field is indicated by the point of maximum modulation of the transcutaneous voltage; (3) the degree of focus of the image indicates the distance to the object. In addition, center–surround opposition originating at pre-receptor level is proposed.

Both experimental measurements and modeling indicate that fish skin impedance is relatively low (400–11 000 Ω cm2) and mainly resistive. This low skin impedance appears to enhance the local electric organ discharge modulation, the center–surround effect, the signal-to-noise ratio for electrolocation and the active space for electrocommunication.
Cold Inhibition of Cell Volume Regulation During the Freezing of Insect Malpighian Tubules
Authors: Neufeld Douglas S. , Leader John P.
Published: April 2021

Cells in freeze-tolerant tissues must survive substantial shrinkage during exposure to the hyperosmolarity that results as solutes are excluded from extracellular ice. We investigated the possibility that this hyperosmotic shock elicits an acute regulatory volume increase (RVI) by monitoring the response of epithelial cell volume in the Malpighian tubules of the New Zealand alpine weta (Hemideina maori) during exposure to low temperature/hyperosmolarity (mimicking freezing conditions) or during an actual freeze/thaw cycle. The cross-sectional area of cells in isolated Malpighian tubules was measured using differential interference contrast microscopy. At 20 °C, cells held in saline containing 400 mmol l−1 glucose exhibit an RVI in response to hyperosmotic shock. Cross-sectional area decreased by 30 % immediately after a change from iso-osmotic (0.7 osmol l−1) to hyper-osmotic saline (2.1 osmol l−1, equal to the osmotic shock encountered during freezing to −4 °C) and then returned to 21 % below the control value 30 min after the exposure. Although substantial cellular function of Malpighian tubules was retained at low temperature (the rate of fluid secretion by isolated tubules at 4 °C was 72 % of that measured at 20 °C), no RVI was observed at 0 °C; cross-sectional area was 39 % below the control value immediately after the hyperosmotic exposure and 36 % below the control value 30 min after hyperosmotic exposure. Dibutyryl cyclic AMP potentiated the RVI observed at 20 °C, but failed to elicit an RVI at 0 °C. A substantial RVI was also absent when the saline contained trehalose rather than glucose, regardless of whether the tubules were held at 20 °C or 0 °C. The cross-sectional area of cells in saline containing glucose remained at approximately 30 % below the control value during an entire 30 min period of actual freezing to −4 °C, suggesting that an acute volume regulatory response was in fact inhibited during mild freezing. The inhibition of an acute RVI during mild freezing may serve to avoid the energetic expenditure associated with volume regulation at a time when the normal defence of cell volume appears to be unnecessary.
The Effect of the Neuropeptide FMRFamide on Aplysia Californica Siphon Motoneurons Involves Multiple Ionic Currents That Vary Seasonally
Authors: Belkin Kira J. , Abrams Thomas W.
Published: April 2021

The molluscan neuropeptide FMRFamide has a number of inhibitory actions on the sensory neurons and motoneurons mediating the defensive gill and siphon withdrawal reflex pathway of Aplysia californica. Exogenous application of FMRFamide has a biphasic, dual-polarity effect on the majority of LFS siphon motoneurons, causing a transient depolarization followed by a prolonged hyperpolarization. FMRFamide induces this response in LFS neurons by causing an increase in multiple ionic currents, including a transient Na+ current, a slow prolonged Na+ current, a 4-aminopyridine (4-AP)-sensitive K+ current and a 4-AP-insensitive K+ current. We have found that a subset of LFS neurons exhibits an exclusively excitatory, biphasic response to FMRFamide, consisting of a transient depolarization followed by a prolonged depolarization of reduced magnitude. Over a period of 29 months, we consistently observed an increase in the incidence of the exclusively excitatory response during the summer months (June to September). From October to May, we observed an exclusively excitatory response to FMRFamide in 19 % of LFS neurons; yet, in the summer months, 51 % of LFS neurons exhibited this response pattern. We compared the ionic basis of the exclusively excitatory response to FMRFamide with the ionic mechanisms mediating the more frequently observed excitatory/inhibitory response. The exclusively excitatory response involves three of the same ionic components as the more typical excitatory/inhibitory response, including the activation of a transient Na+ current, a slow prolonged Na+ current and a 4-AP-insensitive K+ current. The principal difference between the two response types is that FMRFamide fails to activate a 4-AP-sensitive K+ current in those LFS neurons that exhibit an exclusively excitatory response to the peptide. In addition, LFS neurons with an exclusively excitatory response tend to show a coordinated increase in the magnitude of the inward current component of the FMRFamide response. Together, these changes during the summer months may enable this modulatory peptide to bring LFS neurons to suprathreshold levels of activity for eliciting a siphon withdrawal and should substantially alter the neuromodulatory effects of the peptide.