bluuebunny/crossref_metadata_2025 huggingface dataset:
Skin Darkening, A Potential Social Signal in Subordinate Arctic Charr (Salvelinus Alpinus): The Regulatory Role of Brain Monoamines and Pro-Opiomelanocortin-Derived Peptides
Authors: Höglund Erik , Balm Paul H. M. , winberg Svante
Published: April 2021

Arctic charr were allowed to interact in groups of three for 5 days. Skin darkness was quantified by measuring the mean brightness of individual fish before and after social interaction. Brain levels of monoamines and monoamine metabolites and plasma concentrations of cortisol, adrenocorticotropic hormone (ACTH), N-acetyl-β-endorphin and α-melanocyte-stimulating hormone (α-MSH) were analysed. The results show that social subordination resulted in a significant skin darkening. Furthermore, plasma concentrations of α-MSH, ACTH and cortisol were elevated in subordinates, and these fish also displayed elevated levels of 5-hydroxyindoleacetic acid (5-HIAA) in the telencephalon. The ratio of [5-HIAA] to serotonin [5-HT] was increased in several brain areas. In addition, the ratio of 3-methoxy-4-hydroxyphenylglycol (MHPG) to norepinephrine (NE) concentrations was significantly increased in the optic tectum of subordinate fish. Skin darkness following social interaction showed a significant positive correlation with plasma levels of α-MSH. Plasma levels of ACTH and α-MSH were both positively correlated with that of cortisol. Brain [5-HIAA]/[5-HT] ratios were positively correlated with circulating plasma levels of ACTH, and a similar positive correlation was seen between [MHPG]/[NE] ratios in the optic tectum and plasma levels of ACTH, α-MSH and N-acetyl-β-endorphin. In contrast, hypothalamic [MHPG]/[NE] ratios displayed a negative correlation with plasma α-MSH concentrations. The present study demonstrates that social stress induces skin darkening in Arctic charr and that this effect could be mediated by a stress-induced increase in the levels of α-MSH in the circulation. Furthermore, the results suggest that 5-HT and NE in the central nervous system could be factors regulating the pituitary release of ACTH and α-MSH.
Physiological Variability in Neonatal Armadillo Quadruplets: Within- and Between-Litter Differences
Authors: Bagatto B. , Crossley D. A. , Burggren W. W.
Published: April 2021

The role of genetics on neonatal physiological variability was examined in the nine-banded armadillo (Dasypus novemcinctus). Since armadillos give birth to only monozygous quadruplets, the genetic variation within litters is essentially zero. Quadruplets born in captivity were isolated a.nd weighed within 8 h of birth. Oxygen consumption was measured in resting neonates by flow-through respirometry, heart rate obtained from an electrocardiogram and ventilation was measured by impedance techniques. Following the measurements, neonates were returned to the mother. Measurements were repeated at 4 and 8 days after birth. Mean heart rate significantly increased from 132 beats min−1 on the day of birth to 169 beats min−1 on day 8. Mean ventilation rate significantly decreased from 81 breaths min−1 on the day of birth to 54 breaths min−1 on day 8. During this same developmental period, mean mass significantly increased from 100 g to 129 g, and mean mass-specific oxygen consumption significantly decreased from ml O2 kg−1 min−1 to 28.6 ml O2 kg−1 min−1. For all variables measured, within-litter variability was always significantly less than between-litter variability, confirming a ‘sibling effect’ that we attribute to the genetic components determining physiological characters.
Developmental Dimorphism And Expression of Chemosensory-Mediated Behavior: Habitat Selection By A Specialist Marine Herbivore
Authors: Krug Patrick J. , Zimmer Richard K.
Published: April 2021

Developmental dimorphisms provide an opportunity to compare sensory systems and behavior patterns between different forms of a single species. Alternative morphs differing in dispersal ability often show behavioral differences that mediate life-history trade-offs. We measured the behavioral responses of both long-lived, feeding larvae and short-lived, non-feeding larvae of the specialist marine herbivore Alderia modesta during habitat selection. Larvae immediately responded to waterborne cues from the adult host algae by increasing their turning rate, by changing their swimming speed in the water and by moving in rapid hops or spiraling along the bottom. These behavior patterns retained larvae in areas where the dissolved cue was initially perceived, and prolonged exposure to the cue increased the percentage of larvae that initiated metamorphosis. Despite their differences in life span and trophic mode, both larval morphs displayed similar behavior patterns when stimulated by the waterborne cue. Long-lived larvae had a stronger response, however, suggesting that settlement behavior may offset the costs of a prolonged larval life. This is the first study to examine the effects of dimorphic development on chemosensory-mediated behavior.
The Functional Morphology of the Avian Flight Muscle M. Coracobrachialis Posterior
Authors: Woolley J. D.
Published: April 2021

The extensive range of movement of the avian glenohumeral joint makes functional interpretation of any muscle that crosses the joint difficult. Multiple functional roles for the M. coracobrachialis posterior (CBP), an architecturally complex muscle that lies deep to the M. pectoralis, have been assigned on the basis of its anatomical position. The mechanical properties, neuromotor pattern during flight and the biochemical properties of the CBP in pigeons (Columba livia) were studied by in situ length/active tension and length/passive tension measurements, in vivo electromyography and muscle histochemistry. The action of the muscle was studied directly through in situ stimulation and measurement of humeral excursion in non-reduced preparations.
Cops and Robbers: Putative Evolution of Copper Oxygen-Binding Proteins
Authors: Decker Heinz , Terwilliger Nora
Published: April 2021

Two closely related copper proteins, phenoloxidase and haemocyanin, are known to be involved in different physiological functions such as the primary immune response and oxygen transport. Although the proteins differ structurally, they have the same active site by which dioxygen is bound. Recent results reveal that haemocyanin also exhibits phenoloxidase activity. A scenario is proposed for the evolutionary relationships among copper oxygen-binding proteins (COPs).
Activity Before Exercise Influences Recovery Metabolism in the Lizard Dipsosaurus Dorsalis
Authors: Scholnick David A. , Gleeson Todd T.
Published: April 2021

During recovery from even a brief period of exercise, metabolic rate remains elevated above resting levels for extended periods. The intensity and duration of exercise as well as body temperature and hormone levels can influence this excess post-exercise oxygen consumption (EPOC). We examined the influence of activity before exercise (ABE), commonly termed warm-up in endotherms, on EPOC in the desert iguana Dipsosaurus dorsalis. The rate of oxygen consumption and blood lactate levels were measured in 11 female D. dorsalis (mass 41.1±3.0 g; mean ± S.E.M.) during rest, after two types of ABE and after 5 min of exhaustive exercise followed by 60 min of recovery. ABE was either single (15 s of maximal activity followed by a 27 min pause) or intermittent (twelve 15 s periods of exercise separated by 2 min pauses). Our results indicate that both single and intermittent ABE reduced recovery metabolic rate. EPOC volumes decreased from 0.261 to 0.156 ml of oxygen consumed during 60 min of recovery when lizards were subjected to intermittent ABE. The average cost of activity (net during exercise and 60 min of recovery per distance traveled) was almost 40 % greater in lizards that exercised without any prior activity than in lizards that underwent ABE. Blood lactate levels and removal rates were greatest in animals that underwent ABE. These findings may be of particular importance for terrestrial ectotherms that typically use burst locomotion and have a small aerobic scope and a long recovery period.
TISSUE-SPECIFIC EXPRESSION OF ZEBRAFISH (DANIO RERIO) HEAT SHOCK FACTOR 1 mRNAS IN RESPONSE TO HEAT STRESS
Authors: Råbergh Christina M. I. , Airaksinen Susanna , Soitamo Arto , Björklund Harry V. , Johansson Tove , Nikinmaa Mikko , Sistonen Lea
Published: April 2021

All organisms respond to environmental, chemical and physiological stresses by enhanced synthesis of an evolutionarily conserved family of proteins known as heat shock proteins (HSPs) or stress proteins. Certain HSPs are also expressed constitutively during cell growth and development, and they function as molecular chaperones. The transcriptional regulation of hsp genes is mediated by the heat shock transcription factor (HSF). The stress response has been studied mostly in mammalian cell lines or organisms normally maintained under constant laboratory conditions. There is much less information on the regulation of the stress response of animals, such as fish, that have to tolerate large fluctuations in environmental and internal conditions. To characterize the regulation of the heat shock response in fish, we have cloned the first heat shock transcription factor from fish, zebrafish Danio rerio. Phylogenetic analysis confirms that the isolated zebrafish HSF belongs to the HSF1 family and is therefore designated zHSF1. Analysis by reverse transcriptase polymerase chain reaction (RT-PCR) shows the presence of two zHSF1 mRNA forms that are expressed in a tissue-specific fashion upon exposure to heat stress. Both forms are expressed in gonads under all conditions; in liver and to a lesser extent in the gills, the longer splice form of zHSF1 disappears upon heat shock. We present evidence for a unique tissue-specific regulation of HSF1 upon exposure to elevated temperature.
Behavioural Thermoregulation of Chum Salmon During Homing Migration in Coastal Waters
Authors: Tanaka Hideji , Takagi Yasuaki , Naito Yasuhiko
Published: April 2021

Homing Pacific salmon are suggested to utilise directional cues in shallow water while migrating in coastal waters. Since salmonids are typical cold-water fish, they may have to cope with warm surface water while gathering directional information. We studied behavioural thermoregulation of 31 free-ranging chum salmon Oncorhynchus keta using micro data loggers off the Sanriku coast from early October to December. The surface water temperature was approximately 20 °C in early October and decreased to approximately 12 °C in December. The seasonal change of water temperature transformed the behaviour of salmon markedly from deep diving to shallow swimming. In October, salmon frequently dived to depths exceeding 100 m. Duration of deep dives tended to be prolonged as the thermal difference between sea surface and bottom water increased. The results indicated that salmon sought the coolest thermal refuge that they could exploit by vertical movement. Thermal refuge could be a way for salmon to minimise metabolic energy cost; however, salmon repeatedly returned to the surface water column. We found a positive correlation between surface swimming of salmon and the presence of cool covering water, which could contain river waters. This suggests that salmon tend to be risk-prone when subjected to a high concentration of directional cues. Salmon in December spent most of their time in shallow water. These findings suggest that salmon adjusted their behavioural strategy with the hydrographic structure of the sea in order to achieve a balance between acquiring directional cues and behavioural thermoregulation.
Vocal Tract Function in Birdsong Production: Experimental Manipulation of Beak Movements
Authors: Hoese William J. , Podos Jeffrey , Boetticher Nicholas C. , Nowicki Stephen
Published: April 2021

Kinematic analyses have demonstrated that the extent to which a songbird’s beak is open when singing correlates with the acoustic frequencies of the sounds produced, suggesting that beak movements function to modulate the acoustic properties of the vocal tract during song production. If motions of the beak are necessary for normal song production, then disrupting the ability of a bird to perform these movements should alter the acoustic properties of its song. We tested this prediction by comparing songs produced normally by white-throated sparrows and swamp sparrows with songs produced when the beak was temporarily immobilized. We also observed how temporarily loading the beak of canaries with extra mass affected vocal tract movements and song production. Disruption of vocal tract movements resulted in the predicted frequency-dependent amplitude changes in the songs of both white-throated sparrows and swamp sparrows. Canaries with mass added to their beak sang with their beak open more widely than normal and produced notes with greater harmonic content than those without weights. Both manipulations resulted in acoustic changes consistent with a model in which beak motions affect vocal tract resonances, thus supporting the hypothesis that dynamic vocal tract motions and post-production modulation of sound are necessary features of normal song production.
Responses Of Young Xenopus LaeviS TAdpoles To Light Dimming: Possible Roles For The Pineal Eye
Authors: Jamieson D. , Roberts Alan
Published: April 2021

When the light is dimmed, the pineal eye of hatchling Xenopus laevis tadpoles excites the central pattern generator for swimming, but the behavioural significance of pineal excitation is unclear. We show that tadpoles spend 99 % of their time hanging from the surface meniscus or solid objects using mucus secreted by a cement gland on the head. Attachment inhibits swimming, but unattached tadpoles swim spontaneously. Provided that their pineal eye is intact, they attach closer to the water surface in the dark than in the light and attach preferentially to the underside of floating objects that cast shadows. Dimming causes tadpoles swimming horizontally to turn upwards and is very effective in initiating upward swimming in unattached tadpoles. Similar pineal-dependent responses during swimming are present up to stage 44. Pinealectomy blocks responses to dimming at all stages. Recordings from immobilised tadpoles reveal that light dimming induces faster fictive swimming and that pineal activity is increased for up to 20 min during sustained light dimming. We suggest that the increase in pineal discharge during dimming increases the probability of upward swimming and, in this way, increases the probability of tadpoles attaching to objects higher in the water column that cast shadows.
Simple Mechanisms Organise Orientation of Escape Swimming in Embryos and Hatchling Tadpoles of Xenopus Laevis
Authors: Roberts Alan , Hill N. A. , Hicks Robin
Published: April 2021

Many amphibian tadpoles hatch and swim before their inner ears and sense of spatial orientation differentiate. We describe upward and downward swimming responses in hatchling Xenopus laevis tadpoles from stages 32 to 37/38 in which the body rotates about its longitudinal axis.

Tadpoles are heavier than water and, if touched while lying on the substratum, they reliably swim upwards, often in a tight spiral. This response has been observed using stroboscopic photography and high-speed video recordings. The sense of the spiral is not fixed for individual tadpoles. In ‘more horizontal swimming’ (i.e. in directions within ±30 ° of the horizontal), the tadpoles usually swim belly-down, but this position is not a prerequisite for subsequent upward spiral swimming.

Newly hatched tadpoles spend 99 % of their time hanging tail-down from mucus secreted by a cement gland on the head. When suspended in mid-water by a mucus strand, tadpoles from stage 31 to 37/38 tend to swim spirally down when touched on the head and up when touched on the tail. The three-dimensional swimming paths of stage 33/34 tadpoles were plotted using simultaneous video images recorded from the side and from above. Tadpoles spiralled for 70 % of the swimming time, and the probability of spiralling increased to 1 as swim path angles became more vertical.

Tadpoles were neutrally buoyant in Percoll/water mixtures at 1.05 g cm−3, in which anaesthetised tadpoles floated belly-down and head-up at 30 °. In water, their centre of mass was ventral to the muscles in the yolk mass.

A simple mathematical model suggests that the orientation of tadpoles during swimming is governed by the action of two torques, one of which raises the head (i.e. increases the pitch) and the other rotates (rolls) the body. Consequently, tadpoles (i) swim belly-down when the body is approximately horizontal because the body is ballasted by dense yolk, and (ii) swim spirally at more vertical orientations when the ballasting no longer stabilises orientation.

Measurements in tethered tadpoles show that dorsal body flexion, which could produce a dorsal pitch torque, is present during swimming and increases with tailbeat frequency.

We discuss how much of the tadpole’s behaviour can be explained by our mathematical model and suggest that, at this stage of development, oriented swimming responses may depend on simple touch reflexes, the organisation of the muscles and physical features of the body, rather than on vestibular reflexes.
Allometric Scaling Relationships of Jumping Performance in the Striped Marsh Frog Limnodynastes Peronii
Authors: Wilson Robbie S. , Franklin Craig E. , James Rob S.
Published: April 2021

We constructed a force platform to investigate the scaling relationships of the detailed dynamics of jumping performance in striped marsh frogs (Limnodynastes peronii). Data were used to test between two alternative models that describe the scaling of anuran jumping performance; Hill’s model, which predicts mass-independence of jump distance, and Marsh’s model, which predicts that jump distance increases as M0.2, where M is body mass. From the force platform, scaling relationships were calculated for maximum jumping force (Fmax), acceleration, take-off velocity (Umax), mass-specific jumping power (Pmax), total jumping distance (DJ) and total contact time for 75 L. peronii weighing between 2.9 and 38.4 g. Fmax was positively correlated with body mass and was described by the equation Fmax=0.16M0.61, while Pmax decreased significantly with body mass and was described by the equation Pmax=347M−0.46. Both DJ and Umax were mass-independent over the post-metamorph size range, and thus more closely resembled Hill’s model for the scaling of locomotion. We also examined the scaling relationships of jumping performance in metamorph L. peronii by recording the maximum jump distance of 39 animals weighing between 0.19 and 0.58 g. In contrast to the post-metamorphic L. peronii, DJ and Umax were highly dependent on body mass in metamorphs and were described by the equations DJ=38M0.53 and Umax=1.82M0.23, respectively. Neither model for the scaling of anuran jumping performance resembled data from metamorph L. peronii. Although the hindlimbs of post-metamorphic L. peronii scaled geometrically (body mass exponent approximately 0.33), the hindlimbs of metamorphs showed greater proportional increases with body mass (mass exponents of 0.41–0.42).
Catarrhine Photopigments are Optimized for Detecting Targets Against a Foliage Background
Authors: Sumner Petroc , Mollon J. D.
Published: April 2021

The colour vision of many primates is trichromatic, whereas that of all other mammals is thought to be dichromatic or monochromatic. Moreover, the triplets of cone pigments in different catarrhines (Old World apes and monkeys) are strikingly similar in their spectral positions. We ask whether the selective advantage of trichromacy lies in an enhanced ability to find edible leaves or fruit. Further, we ask whether any factor in these two search tasks has constrained the particular set of cone spectral sensitivities observed in all catarrhines. We measured the spectral properties of the natural environments of six primate species in Uganda: Pan troglodytes, Cercopithecus mitis, Cercopithecus ascanius, Lophocebus albigena, Colobus guereza and Colobus badius. We concentrated on the fruit and leaves in their diets and the leaves of the trees that make up the background against which these diet items must be found. We plotted these measured stimuli in colour spaces appropriate for each primate species, and found that both frugivory and folivory are facilitated by the extra dimension of colour vision found in catarrhines but lacking in most other mammals. Furthermore, by treating the task of searching for food as a signal-detection task, we show that, of all possible combinations of cone sensitivities, the spectral positions of the actual primate pigments are optimal for finding fruit or young leaves against the background of mature leaves. This is because the variance of the chromaticities of the mature leaves is minimised in one channel of the primate’s colour vision, so allowing anything that is not a mature leaf to stand out.
Slow Muscle Function of Pacific Bonito (Sarda Chiliensis) During Steady Swimming
Authors: Ellerby D. J. , Altringham J. D. , Williams T. , Block B. A.
Published: April 2021

The Pacific bonito, Sarda chiliensis, is anatomically intermediate between mackerel and tuna. The specialisations exhibited by tuna are present in the bonito, but to a lesser degree. Slow-twitch muscle strain and activity patterns were determined during steady swimming (tailbeat frequency 1.2–3.2 Hz) at four locations on the body of Sarda chiliensis using sonomicrometry and electromyography. Both strain and the phase of electromygraphic activity were independent of tailbeat frequency. The strain of superficial slow-twitch muscle increased from ±3.1 % l0 at 0.35FL to ±5.8 % l0 at 0.65FL, where l0 is muscle resting length and FL is the body length from snout to tail fork. Between 0.35 and 0.65FL, there was a negative phase shift of 16 ° in the onset of electromygraphic activity in superficial slow-twitch muscle relative to the strain cycle. Muscle activity patterns are comparable with those of tuna. At 0.58FL, the onset of activity in deep slow-twitch muscle was approximately synchronous with the onset of activity in superficial muscle in the same myotome at 0.65FL. The distribution of slow-twitch muscle along the body of Sarda chiliensis and four additional fish species, Anguilla anguilla, Oncorhynchus mykiss, Scomber scombrus and Thunnus albacares, was also measured. Slow-twitch muscle appears to become more concentrated at approximately 0.5FL as swimming kinematics become more thunniform.
Effects of Catecholamines and Purines on Luminescence in the Brittlestar Amphipholis Squamata (Echinodermata)
Authors: Bremaeker N. De , Baguet F. , Mallefet J.
Published: April 2021

The effects of catecholamines (dopamine, adrenaline, noradrenaline and its derivatives), 5-hydroxytryptamine and purines (adenosine, ATP and their derivatives) on the acetylcholine-induced luminescence of isolated arms and dissociated photocytes of the luminescent ophiuroid Amphipholis squamata were tested. The results showed that catecholamines and 5-hydroxytryptamine (10−5 to 10−3 mol l−1) had a strong dose-dependent inhibitory effect on acetylcholine-induced luminescence. In contrast, purines (10−4 and 10−3 mol l−1) triggered luminescence in the absence of acetylcholine and/or potentiated acetylcholine-induced luminescence. The results with specific purinergic agonists and antagonists indicated the involvement of P1- and P2-like purinoceptors in the control of luminescence.

Our study suggests that, in addition to the previously described cholinergic system in Amphipholis squamata, there may be a purinergic system, acting in synergy with acetylcholine, and an inhibitory neuromodulatory catecholaminergic system, all associated with the control of luminescence.
Blood Pressure Control in a Larval Amphibian, Xenopus Laevis
Authors: Warburton Stephen J. , Fritsche Regina
Published: April 2021

The regulation of arterial pressure in early vertebrate embryos and larvae with non-innervated hearts is poorly understood. We used nanoliter intravascular injections in anaesthetized Xenopus laevis larvae (stage 49–51) to assess their ability to maintain arterial pressure in the face of a volume load. Injections of saline and hetastarch (a volume expander) were made into the ventricle. Arterial pressure, end-diastolic ventricular volume, end-systolic ventricular volume and heart rate were measured. Injection of 800 nl caused a rapid rise in arterial pressure and stroke volume. There were no changes in heart rate, indicating the absence of an arterial baroreflex. Blood pressure in saline-injected animals recovered quickly (within 5 min), whereas hetastarch injections caused hypertension to be maintained for much longer, for over 40 min in the most extreme case. We surmise that Starling forces at the capillary play an important role in pressure regulation but are not adequate to explain the entire response. Finally, there was ample evidence for a Frank–Starling relationship in the ventricle.
The Mechanistic Basis of Aerobic Performance Variation in Red Junglefowl
Authors: Hammond Kimberly A. , Chappell Mark A. , Cardullo Richard A. , Lin Ruei-Shiuan , Johnsen Torgeir S.
Published: April 2021

We examined aerobic performance, organ and muscle mass and enzymatic activity in red junglefowl (Gallus gallus). We tested three models of performance limitation (central limits, peripheral limits, symmorphosis) and explored relationships between basal metabolic rate (BMR), aerobic capacity and social rank. Males had a lower BMR, a higher and a greater aerobic scope than females. Females possessed larger peritoneal and reproductive organs, while males had larger hearts, lungs and leg muscles. In females, BMR was correlated with spleen mass and was correlated with hematocrit and large intestine mass. Male BMR was correlated with intestinal tract and lung mass, and was correlated with heart and pectoralis mass. Male citrate synthase activity averaged 57 % higher than that of females and was correlated with (this correlation was not significant in females). Female social status was not correlated with any variable, but male dominance was associated with higher aerobic scope, larger heart and lungs, smaller peritoneal organs and greater leg citrate synthase activity. We conclude that aerobic capacity is controlled by system-wide limitations (symmorphosis) in males, while in females it is controlled by central organs.

In neither sex is elevated aerobic capacity associated with increased maintenance costs
Effect of Temperature On pH and Electrolyte Concentration in Air-Breathing Ectotherms
Authors: Stinner J. N. , Hartzler L. K.
Published: April 2021

The aim of this study was to determine the effects of temperature upon pH, protein charge and acid–base-relevant ion exchange in air-breathing ectotherms. Plasma and skeletal muscles in cane toads (Bufo marinus) and bullfrogs (Rana catesbeiana) were examined at 30, 20 and 10 °C. In addition, skeletal muscle ion concentrations were examined in black racer snakes (Coluber constrictor) at 30 and 10 °C. Cooling the amphibians produced a reduction in most of the plasma ion concentrations (Na+, K+, Ca2+, Cl−, SO42−) and in protein concentration because of increased hydration. Between 30 and 10 °C, total plasma osmolality fell by 14 % in the toads and by 5 % in the frogs. Plasma protein charge, calculated using the principle of electroneutrality, was unaffected by temperature, except possibly for the toads at 10 °C. The in vivo skeletal muscle ΔpHi/ΔT ratio, where pHi is intracellular pH and T is temperature, between 30 and 20 °C averaged −0.014 °C−1 in the toads and −0.019 °C−1 in the frogs. Between 20 and 10 °C, there was no change in pHi in the toads and a −0.005 °C−1 change in the frogs. The in vitro skeletal muscle ΔpHi/ΔT averaged −0.011 °C−1 in both toads and frogs. In all three species, skeletal muscle inulin space declined with cooling. Intracellular ion concentrations were calculated by subtracting extracellular fluid ion concentrations from whole-muscle ion concentrations. In general, temperature had a large effect upon intracellular ion concentrations (Na+, K+, Cl−) and intracellular CO2 levels. The relevance of the changes in intracellular ion concentration to skeletal muscle acid–base status and protein charge and the possible mechanisms producing the adjustments in intracellular ion concentration are discussed. It is concluded that ion-exchange mechanisms make an important contribution to adjusting pH with changes in temperature.
Lipid Compositional Correlates of Temperature-Adaptive Interspecific Differences in Membrane Physical Structure
Authors: Logue James A. , De Vries Art L. , Fodor Elfrieda , Cossins Andrew R.
Published: April 2021

Teleost species from cold environments possess more disordered brain synaptic membranes than species from warm habitats, thereby providing equivalent physical structures at their respective habitat temperatures. We have related this adaptive interspecific biophysical response to the fatty acid composition of brain membranes from 17 teleost species obtained from Antarctic, temperate and semi-tropical waters, as well as from rat and turkey as representative homeotherms. Cold-adaptive increases in membrane disorder (determined by fluorescence anisotropy with diphenylhexatriene as probe) were correlated with large and linear increases in the proportion of unsaturated fatty acids, from 35 to 60 % in phosphatidylcholine (PtdCho) and from 55 to 85 % in phosphatidylethanolamine (PtdEth). For PtdCho, the cold-adaptive increase in unsaturation was associated almost entirely with increased proportions (from 7 to 40 %) of polyunsaturated fatty acids (PUFAs), with mono-unsaturates (MUFAs) providing an approximately constant proportion in all species. Exactly opposite effects were evident for phosphatidylethanolamine (PtdEth). Thus, the compositional adaptation for PtdCho occurred largely by exchange of polyunsaturated and mono-unsaturated fatty acid in the sn-2 position, whilst for PtdEth it involved exchanges between saturates and mono-unsaturates at the sn-1 position. This difference may be related to the different molecular shapes of the two phosphoglycerides and the need to maintain the balance between bilayer-stabilising and -destabilising tendencies. This comparative study provides a more comprehensive view of the compositional adjustments that accompany and perhaps account for temperature-adaptive interspecific differences in membrane physical structure.
The Visually Controlled Prey-Capture Behaviour of the European Mantispid Mantispa Styriaca
Authors: Kral Karl , Vernik Martin , Devetak Dušan
Published: April 2021

Mantispids (Mantispa styriaca) are predatory insects; on bright sunny days, they wait in ambush for insect prey. The prey is captured as soon as it is within reach by means of lightning-speed strikes with the powerful forelegs. The strikes can take less than 60 ms. The mantispid accomplishes this almost as effectively as the larger praying mantis, which occupies a similar habitat, even though the praying mantis has apposition eyes with a high-resolution fovea, whereas the mantispid has unspecialized optical superposition eyes. Mantispa styriaca reacts to an item of prey when the latter covers a critical visual angle. The detection of prey immediately triggers adjustment reactions in the mantispid, which attempts to position the prey item in the visual field of both eyes and in the capture zone. Irrespective of the size of the prey, the capture reaction of the mantispid is always triggered if the distance to the prey falls below a certain critical value. As indicated by the analysis of individual video frames, immediately before an aimed strike, the item of prey is always positioned exactly in the centre of the binocular field of vision in the extended midsagittal plane of the mantispid’s head. The strike may be triggered by the ommatidia of the left and right eyes, the lines of sight of which converge precisely on this region. The principal conclusion to be drawn is that the prey-capture behaviour of the mantispid appears to be based on a triangulation mechanism.
The Development of Fatigue Quality in High- and Low-Stressed Tendons of Sheep (Ovis Aries)
Authors: Pike Anna V. L. , Ker Robert F. , Alexander R. Mcneill
Published: April 2021

The time taken to rupture in cyclic fatigue tests, to a stress of 45 MPa, was used to compare the fatigue quality of tendons from sheep of varying ages. Muscle and tendon cross-sectional areas were used to calculate the stress-in-life of each tendon. For any given age, high-stressed plantaris tendons were of a higher fatigue quality than low-stressed extensor tendons. Both fatigue quality and stress-in-life increased with age for each tendon type. High-stressed tendons are subjected to large increases in stress-in-life during growth, and fatigue quality increased significantly with this stress. This relationship was not seen, however, in low-stressed tendons, which are not subjected to a comparable range of stresses over time. It is possible that cells modify tendon fatigue quality in response to tendon loading history. Whilst Young’s modulus was seen to increase with age, no difference was detected between high- and low-stressed tendons.
Evidence for the Role of a Na+/HCO3−Cotransporter in Trout Hepatocyte pHi Regulation
Authors: Furimsky M. , Moon T. W. , Perry S. F.
Published: April 2021

The mechanisms of intracellular pH (pHi) regulation were examined in hepatocytes of the rainbow trout Oncorhynchus mykiss. pHi was monitored using the pH-sensitive fluorescent dye BCECF, and the effects of various media and pharmacological agents were examined for their influence on baseline pHi and recovery rates from acid and base loading. Rates of Na+ uptake were measured using 22Na, and changes in membrane potential were examined using the potentiometric fluorescent dye Oxonol VI. The rate of proton extrusion following acid loading was diminished by the blockade of either Na+/H+ exchange (using amiloride) or anion transport (using DIDS). The removal of external HCO3− and the abolition of outward K+ diffusion by the channel blocker Ba2+ also decreased the rate of proton extrusion following acid load. Depolarization of the cell membrane with 50 mmol l−1 K+, however, did not affect pHi. The rate of recovery from base loading was significantly diminished by the blockade of anion transport, removal of external HCO3− and, to a lesser extent, by blocking Na+/H+ exchange. The blockade of K+ conductance had no effect. The decrease in Na+ uptake rate observed in the presence of the anion transport blocker DIDS and the DIDS-sensitive hyperpolarization of membrane potential during recovery from acid loading suggest that a Na+-dependent electrogenic transport system is involved in the restoration of pHi after intracellular acidification. The effects on baseline pHi indicate that the different membrane exchangers are tonically active in the maintenance of steady-state pHi. This study confirms the roles of a Na+/H+ exchanger and a Cl−/HCO3− exchanger in the regulation of trout hepatocyte pHi and provides new evidence that a Na+/HCO3− cotransporter contributes to pHi regulation.
The Resting Membrane Potential of White Muscle from Brown Trout (Salmo Trutta) Exposed to Copper in Soft, Acidic Water
Authors: Beaumont M. W. , Taylor E. W. , Butler P. J.
Published: April 2021

Previously, the distribution of ammonia between the intracellular and extracellular compartments has been used to predict a significant depolarisation of the resting membrane potential (EM) of white muscle from brown trout (Salmo trutta) exposed to a sub-lethal combination of copper and low pH. However, this prediction is based upon two assumptions (i) a relatively high membrane permeability for the ammonium ion with respect to that for ammonia gas and (ii) that this is unaltered by exposure to copper and low pH. Since there is conflicting evidence in the literature of the validity of these assumptions, in the present study EM was directly measured in white muscle fibres of trout exposed to copper and low pH (EM=−52.2±4.9 mV) and compared with that of unexposed, control animals (EM=−86.5±2.9 mV) (means ± S.E.M., N=6). In confirming the predicted depolarisation, these data support the hypothesis of electrophysiological impairment as a factor in the reduction in the swimming performance of trout exposed to these pollutants. In addition, the results of this study support the role of a significant permeability of the muscle membrane to NH4+ in determining the distribution of ammonia in fish.
Locomotion in Scombrid Fishes: Morphology and Kinematics of the Finlets of the Chub Mackerel Scomber Japonicus
Authors: Nauen Jennifer C. , Lauder George V.
Published: April 2021

Finlets are small non-retractable fins located on the dorsal and ventral margins of the body between the second dorsal and anal fins and the tail of scombrid fishes. The morphology of the finlets, and finlet kinematics during swimming in a flow tank at speeds of 0.8–3.0 fork lengths s−1, were examined in the chub mackerel Scomber japonicus. Functionally, S. japonicus has five dorsal and anal triangular finlets (the fifth finlet is a pair of finlets acting in concert). Slips of muscle that insert onto the base of each finlet indicate the potential for active movement. In animals of similar mass, finlet length and area increased posteriorly. Finlet length, height and area show positive allometry in animals from 45 to 279 g body mass. Summed finlet area was approximately 15 % of caudal fin area.

During steady swimming, the finlets typically oscillated symmetrically in the horizontal and vertical planes. Finlet excursions in the x, y and z directions ranged from 1 to 5 mm, increased posteriorly and were independent of speed. The timing of the maximum amplitude of oscillation was phased posteriorly; the phase lag of the maximum amplitude of oscillation was independent of speed. During some periods of gliding, a finlet occasionally moved independently of the body and the other finlets, which indicated active control of finlet movement.

The angle of attack of the finlets averaged approximately 0 ° over a tailbeat, indicating no net contribution to thrust production via classical lift-based mechanisms. However, the timing of finlet movement relative to that of the tail suggests that more posterior finlets may direct some flow longitudinally as the tail decelerates and thereby contribute flow to the developing caudal fin vortex.

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Immunolocalization of Ion-Transport Proteins to Branchial Epithelium Mitochondria-Rich Cells in the Mudskipper (Periophthalmodon Schlosseri)
Authors: Wilson Jonathan M. , Randall David J. , Donowitz Mark , Vogl A. Wayne , Ip Alex K.-Y.
Published: April 2021

The branchial epithelium of the mudskipper Periophthalmodon schlosseri is densely packed with mitochondria-rich (MR) cells. This species of mudskipper is also able to eliminate ammonia against large inward gradients and to tolerate extremely high environmental ammonia concentrations. To test whether these branchial MR cells are the sites of active ammonia elimination, we used an immunological approach to localize ion-transport proteins that have been shown pharmacologically to be involved in the elimination of NH4+(Na+/NH4+exchanger and Na+/NH4+-ATPase). We also investigated the role of carbonic anhydrase and boundary-layer pH effects in ammonia elimination by using the carbonic anhydrase inhibitor acetazolamide and by buffering the bath water with Hepes, respectively. In the branchial epithelium, Na+/H+exchangers (both NHE2- and NHE3-like isoforms), a cystic fibrosis transmembrane regulator (CFTR)-like anion channel, a vacuolar-type H+-ATPase (V-ATPase) and carbonic anhydrase immunoreactivity are associated with the apical crypt region of MR cells. Associated with the MR cell basolateral membrane and tubular system are the Na+/K+-ATPase and a Na+/K+/2Cl−cotransporter. A proportion of the ammonia eliminated by P. schlosseri involves carbonic anhydrase activity and is not dependent on boundary-layer pH effects. The apical CFTR-like anion channel may be serving as a HCO3−channel accounting for the acid–base neutral effects observed with net ammonia efflux inhibition.
Heat-Shock Protein Expression is Absent in the Antarctic Fish Trematomus Bernacchii (Family Nototheniidae)
Authors: Hofmann Gretchen E. , Buckley Bradley A. , Airaksinen Susanna , Keen John E. , Somero George N.
Published: April 2021

The heat-shock response, the enhanced expression of one or more classes of molecular chaperones termed heat-shock proteins (hsps) in response to stress induced by high temperatures, is commonly viewed as a ‘universal’ characteristic of organisms. We examined the occurrence of the heat-shock response in a highly cold-adapted, stenothermal Antarctic teleost fish, Trematomus bernacchii, to determine whether this response has persisted in a lineage that has encountered very low and stable temperatures for at least the past 14–25 million years. The patterns of protein synthesis observed in in vivo metabolic labelling experiments that involved injection of 35S-labelled methionine and cysteine into whole fish previously subjected to a heat stress of 10 °C yielded no evidence for synthesis of any size class of heat-shock protein. Parallel in vivo labelling experiments with isolated hepatocytes similarly showed significant amounts of protein synthesis, but no indication of enhanced expression of any class of hsp. The heavy metal cadmium, which is known to induce synthesis of hsps, also failed to alter the pattern of proteins synthesized in hepatocytes. Although stress-induced chaperones could not be detected under any of the experimental condition used, solid-phase antibody (western) analysis revealed that a constitutively expressed 70 kDa chaperone was present in this species, as predicted on the basis of requirements for chaperoning during protein synthesis. Amounts of the constitutively expressed 70 kDa chaperone increased in brain, but not in gill, during 22 days of acclimation to 5 °C. The apparent absence of a heat-shock response in this highly stenothermal species is interpreted as an indication that a physiological capacity observed in almost all other organisms has been lost as a result of the absence of positive selection during evolution at stable sub-zero temperatures. Whether the loss of the heat-shock response is due to dysfunctional genes for inducible hsps (loss of open reading frames or functional regulatory regions), unstable messenger RNAs, the absence of a functional heat-shock factor or some other lesion remains to be determined.
Cortisol Increases Na+/K+-ATPase Density in Plasma Membranes of Gill Chloride Cells in the Freshwater Tilapia Oreochromis Mossambicus
Authors: Dang Zhichao , Balm Paul H. M. , Flik Gert , Wendelaar Bonga Sjoerd E. , Lock Robert A. C.
Published: April 2021

The effect of cortisol on Na+/K+-ATPase expression in the gill chloride cells of tilapia Oreochromis mossambicus was studied by immunocytochemistry at the light and electron microscope levels. One of three doses of cortisol (low, 125 mg kg−1food; middle, 375 mg kg−1food; high, 750 mg kg−1food) was administered via the food (at a ration of 1.5 % of body mass) and the fish were sampled after 5 days. Plasma osmolality and Na+levels were elevated in the middle- and high-dose groups, and plasma cortisol levels in the high-dose groups. Hematocrit values were not affected by the treatments. Opercular membrane chloride cell density increased by 94 % and 286 % in the middle- and high-dose fish, respectively, whereas the gill chloride cell frequency increased by up to 28 % maximally in the high-dose fish. Lamellar gill chloride cells were absent in the control and low-dose groups, but were observed in the middle- and high-dose groups. Cortisol increased the volume of the tubular membrane system in mature gill chloride cells. Quantification of immunogold-labelled Na+/K+-ATPase antigen (a 104 kDa protein species, as demonstrated by western blot) revealed that the high dose of cortisol increases the Na+/K+-ATPase density in the tubular system of chloride cells. This is the first direct evidence that cortisol not only increases chloride cell numbers but also Na+/K+-ATPase density in these cells.
Molecular Characterization of a Urea Transporter in the Gill of the Gulf Toadfish (Opsanus Beta)
Authors: Walsh Patrick J. , Heitz Molly J. , Campbell Catherine E. , Cooper Gordon J. , Medina Monica , Wang Yuxiang S. , Goss Greg G. , Vincek Vladimir , Wood Chris M. , Smith Craig P.
Published: April 2021

Urea excretion by the gulf toadfish (Opsanus beta) has been shown in previous studies to be a highly pulsatile facilitated transport, with excretion probably occurring at the gill. The present study reports the isolation of an 1800 base pair (kb) cDNA from toadfish gill with one open reading frame putatively encoding a 475-residue protein, the toadfish urea transporter (tUT). tUT, the first teleostean urea transporter cloned, has high homology with UTs (facilitated urea transporters) cloned from mammals, an amphibian and a shark, and most closely resembles the UT-A subfamily. When expressed in Xenopus laevis oocytes, tUT increased urea permeability (as measured by [14C]urea uptake) five- to sevenfold, and this permeability increase was abolished by phloretin, a common inhibitor of other UTs. Northern analysis using the 1.8 kb clone was performed to determine the tissue distribution and dynamics of tUT mRNA expression. Of six tissues examined (gill, liver, red blood cells, kidney, skin and intestine), only gill showed expression of tUT mRNA, with a predominant band at 1.8 kb and a minor band at 3.5 kb. During several points in the urea pulse cycle of toadfish (0, 4, 6, 12 and 18 h post-pulse), measured by excretion of [14C]urea into the water, gill mRNA samples were obtained. Expression of tUT mRNA was found to be largely invariant relative to expression of β-actin mRNA over the pulse cycle. These results further confirm the gill localization of urea transport in the toadfish and suggest that tUT regulation (and the regulation of pulsatile urea excretion) is probably not at the level of mRNA control. The results are discussed in the context of the mechanisms of vasopressin-regulated UT-A in mammalian kidney and morphological data for the toadfish gill.
Mechanisms of Gastrointestinal Copper Absorption in the African Walking Catfish: Copper Dose-Effects and a Novel Anion-Dependent Pathway in the Intestine
Authors: Handy R. D. , Musonda M. M. , Phillips C. , Falla S. J.
Published: April 2021

In mammals, copper (Cu) absorption occurs mostly in the small intestine, and some of the Cu transporters involved in its uptake have been characterised. In fish, however, the regions of the gut involved in Cu absorption and the membrane transport mechanisms responsible for gastrointestinal Cu uptake are unknown. Everted gut sacs and isolated perfused intestine of Clarias gariepinus were used to explore Cu absorption (at 22 °C). Gut sacs exposed to 100 μmol l−1mucosal solution Cu ([Cu]m) showed that Cu was mostly (70 %) absorbed in the middle and hind intestine. Most of the accumulated Cu was located in the mucosa. In perfused intestines, cumulative Cu absorption from the mucosal solution to the serosal perfusate was greatest at 10 μmol l−1[Cu]m and decreased at higher values of [Cu]m, while tissue accumulation of Cu showed a dose-dependent elevation. Absorption efficiency therefore declined with increasing Cu dose, and basolateral transport was the limiting factor in Cu uptake. Serosal applications of the P-type ATPase inhibitor vanadate (100 μmol l−1) or the anion transport inhibitor DIDS (100 μmol l−1) caused threefold increases in net Cu uptake (at [Cu]m=10 μmol l−1). The vanadate effect was explained by a reduction in transepithelial potential rather than inhibition of Cu-ATPase, but the DIDS effect was not. Transepithelial potential, water transport and tissue [Cu] were not affected by DIDS, but tissue [K+] was elevated. Removal of Cl−simultaneously from both the mucosal and serosal solutions caused a 10-fold reduction in the rate of Cu uptake, while removal of Cl−from the mucosal solution only completely abolished Cu absorption to the serosal perfusate. Transepithelial potential effects are discussed. We conclude that Cu absorption occurs mostly in the intestine and is normally driven by a basolateral Cu/anion symport that prefers Cl−.