bluuebunny/crossref_metadata_2025 huggingface dataset:
Underwater Swimming At Low Energetic Cost By Pygoscelid Penguins
Authors: Culik Boris M. , Wilson Rory P. , Bannasch Rudolf
Published: April 2021

Energetic requirements of under-water swimming in pygoscelid penguins were studied in Antarctica, using respirometry together with a 21 m long swim canal and externally attached devices recording the swimming speed and dive duration of unrestrained animals. Field measurements were compared with measurements of the hydrodynamic properties of an Adélie penguin model in a circulating water tank. Minimium transport costs during underwater swimming in Adélie (Pygoscelis adeliae), chinstrap (P. antarctica) and gentoo (P. papua) penguins averaged 4.9, 3.7 and 7.6 J kg−1 m−1, respectively, at their preferred swimming speeds of 2.2, 2.4 and 1.8 m s−1, allowing the birds to dive aerobically for 110, 130 and 93 s, respectively. From the swim canal measurements, we calculated a drag coefficient (CD) of 0.0368 for a typical Adélie penguin at 2.2 m s−1. This value is significantly lower than the CDof 0.04 of an ideal spindle and the CD of 0.0496 measured on the model in the laboratory. The reasons for this difference are discussed.
The role of anion channels in osmotically activated taurine release from embryonic skate (Raja eglanteria) heart
Authors: Goldstein Leon , Davis-Amaral Erin M. , Blum Patricia C. , Luer Carl A.
Published: April 2021

Taurine, a major osmolyte of vertebrate hearts, is released from the skate heart at increased rates during hypotonic stress. We tested the hypothesis that this taurine release is mediated by chloride channels activated by swelling. Two inhibitors of the channels, NPPB and DIDS, inhibited the volume-activated release of taurine from embryonic skate hearts. These results support the hypothesis that swelling-activated chloride channels mediate the release of cardiac taurine.
Nitrogen Excretion: Three End Products, Many Physiological Roles
Authors: Wright Patricia A.
Published: April 2021

There are diverse physiological functions of nitrogen end products in different animal groups, including excretion, acid–base regulation, osmoregulation and buoyancy. Animals excrete a variety of nitrogen waste products, but ammonia, urea and uric acid predominate. A major factor in determining the mode of nitrogen excretion is the availability of water in the environment. Generally, aquatic animals excrete mostly ammonia, whereas terrestrial animals excrete either urea or uric acid. Ammonia, urea and uric acid are transported across cell membranes by different mechanisms corresponding to their different chemical properties in solution. Ammonia metabolism and excretion are linked to acid–base regulation in the kidney, but the role of urea and uric acid is less clear. Both invertebrates and vertebrates use nitrogen-containing organic compounds as intracellular osmolytes. In some marine invertebrates, NH4+ is sequestered in specific compartments to increase buoyancy.
Ca2+Versus Zn2+ Transport in the Gills of Freshwater Rainbow Trout and the Cost of Adaptation to Waterborne Zn2+
Authors: Hogstrand Christer , Reid Scott D. , Wood Chris M.
Published: April 2021

Previous work suggested that Ca2+ and Zn2+ share a common uptake pathway in rainbow trout gills. We here report on relationships between the kinetic variables for unidirectional Ca2+ influx and unidirectional Zn2+ influx during a 1 month exposure of freshwater rainbow trout to Zn2+ (150 μg l-1=2.3 μmol l-1 as total zinc, Zn). Initial exposure to Zn2+ caused a large competitive inhibition of Ca2+ influx, as indicated by a threefold increase in apparent Km for Ca2+ (measured in the presence of Zn2+). There was also a smaller non-competitive inhibition (50 % decrease in Jmax) of the Ca2+ transport system, which was abolished after 1–2 weeks of exposure. The Km, measured in the absence of Zn2+, decreased dramatically (i.e. elevated affinity) on days 1–4 but increased thereafter; both true and apparent Km finally stabilized significantly above control levels. However, the Km values for Ca2+ (<200 μmol l-1) were low relative to the Ca2+ level in the water (1000 μmol l-1), and therefore the changes did not influence the actual Ca2+ influx of the fish, which tracked Jmax. In contrast, water [Zn2+] (2.3 μmol l-1 as total Zn) was close to the reported apparent Km (3.7 μmol l-1) for Zn2+ influx in the presence of 1000 μmol l-1 Ca2+. Unidirectional Zn2+ influx increased during the first week of exposure to waterborne Zn2+, followed by a persistent reduction to about 50 % of control levels, effects that may be largely explained by the observed changes in true Km for Ca2+. We speculate that the initial response of the fish to elevated [Zn2+] is to compensate for a reduced availability of Ca2+ by markedly increasing the affinity of a dual Ca2+/Zn2+ transporter. Once the Ca2+ influx is ‘corrected’ by restoration of functional transport sites (Jmax), the system is tuned to limit the influx of Zn2+ by a persistent reduction in the affinities for both ions.

The changes in influx characteristics for Ca2+ and Zn2+ were correlated with internal physiological alterations indicative of adaptation to Zn2+ and increased metabolic cost. Depressed plasma [Ca] was corrected within 1 week, and there were no effects on whole-body [Ca] or [Zn]. A slight accumulation of Zn in the gills was associated with increased branchial metallothionein levels. Rates of protein synthesis and degradation in the gills were initially increased and whole-body growth was transiently impaired, effects which were reversed after 18 days of exposure. Sublethal challenge with Zn2+ (at 450 μg l-1=6.9 μmol l-1 as total Zn) always depressed plasma [Ca] in control fish, but by 1 month of exposure to Zn2+ at 150 μg l-1 (as total Zn), experimental fish were resistant to challenge. However, the fish did not acquire increased survival tolerance (LT50) to a lethal concentration of Zn2+ (4 mg l-1=61 μmol l-1 as total Zn).
Effects of Extreme pH on the Physiology of the Australian ‘Yabby’ Cherax Destructor: Acute and Chronic Changes in Haemolymph Carbon Dioxide, Acid–Base and Ionic Status
Authors: Ellis Bronwyn A. , Morris Stephen
Published: April 2021

Freshwater habitats throughout the world are becoming increasingly threatened by the likelihood of acidification, but little consideration has been given to the importance of severe alkalization. Acute and chronic fluctuations in haemolymph acid–base status , [Na+] and [Ca2+] were monitored for up to 504 h (21 days) in the Australian freshwater crayfish Cherax destructor exposed to low- and high-pH water. The importance of carapace [Ca2+] during acid exposure was assessed. Crayfish were exposed to pH 7.1, pH 4.5 and pH 8.0 water containing calcium at 500 μmol l−1while the effect of a lower calcium concentration (50 μmol l−1) was assessed in pH 4.5 water.

Cherax in acid water containing 50 μmol l−1Ca2+exhibited a significant decrease in CO2 content after 2 h (mean decrease 1.13 mmoll−1, venous; 1.57 mmoll−1, arterial) and large ranges in throughout the treatment (2.4–7.3 mmHg). The overall acid–base response was a metabolic acidosis compensated by a respiratory alkalosis. The haemolymph Na+concentration in both control (pH 7.1, 50 μmol l−1) and acid-exposed animals in lower-Ca2+water was up to 50 % reduced compared with that in animals in pH 7.1, 500 μmol l−1Ca2+water. Ion regulatory mechanisms, causing a subsequent increase in haemolymph [Na+] after 288 h, were implicated as an important component in acid–base homeostasis. Crayfish in acid, low-Ca2+water also exhibited a 3.2 mmoll−1increase in haemolymph [Ca2+] and showed a haemolymph alkalosis compared with animals in acid water with higher [Ca2+].

At higher water [Ca2+] in pH 4.5 water (500 μmol l−1 Ca2+), the haemolymph pH of Cherax was only 0.1 unit lower than that of animals in 50 μmol l−1 Ca2+ acid water after 96 h, and both and were unchanged compared with the initial condition. As with low-Ca2+ acid-exposure, the potential haemolymph acidosis appeared largely to be compensated by respiratory alkalosis. There was a transient 31 % reduction in haemolymph [Na+], although osmolality was unchanged (control 411±7.29 mosmol kg−1). Acid–base equilibrium recovered rapidly, probably in association with changes in ion flux and the re-establishment of normal haemolymph Na+ concentration.

Alkaline-exposed Cherax destructor exhibited a mixed respiratory alkalosis and metabolic acidosis. Whereas haemolymph [Ca2+] increased by 1.8 mmol l−1 after only 1 h, haemolymph Na+ levels increased by 36 % after 2 h, possibly as part of a net H+ loss from the haemolymph. Increased HCO3−/Cl− exchange could contribute to the 4.3 mmol l−1 decrease in haemolymph CO2 level after 0.5 h of alkaline exposure. The responses of Cherax to extreme pH are different from those of the European and North American crayfish species studied to date.
The Effect of Tendon Compliance on In Vitro/In Vivo Estimations of Sarcomere Length
Authors: James Rob S. , Young Iain S. , Altringham John D.
Published: April 2021

The errors likely to result from using excised rigor muscles to determine in vivo sarcomere length ranges were calculated for mouse extensor digitorum longus muscle (EDL). This muscle was chosen because its very long tendon makes it particularly susceptible to errors arising from tendon compliance. By placing dissected limbs into different locomotory stances, and allowing them to go into rigor, the range of sarcomere lengths over which muscles operate in vivo can be determined, but it is subject to errors due to tendon compliance. A tendon compliance of 0.24 GPa and a muscle rigor stress of 35 kPa were determined, and these were used to correct the estimates of in vivo sarcomere length, under worst case conditions. The error introduced was very small: a reduction in sarcomere length of less than 0.5 %.
Questioning Paradigms: Caste-Specific Ventilation in Harvester Ants, Messor Pergandei and M. Julianus (Hymenoptera: Formicidae)
Authors: Lighton John R. B. , Berrigan David
Published: April 2021

Do developmental constraints in ant colonies limit gas exchange strategies to those displayed by female alates (presumptive queens)? In the xeric harvester ant genus Messor, we found that M. pergandei and M. julianus female alates ventilated highly discontinuously, as predicted, but M. julianus workers ventilated less discontinuously and M. pergandei workers (which occur in more xeric habitats) ventilated continuously. We present the salient characteristics of the discontinuous ventilation cycles of the species and the manner in which they are modulated by CO2 emission rates at a single temperature (24 °C). We demonstrate that, in M. julianus workers, open-spiracle phase CO2 emission rate only slightly exceeds overall CO2 emission rate, making discontinuous ventilation marginal, a state extrapolated in M. pergandei to continuous ventilation. However, workers are plainly capable of fargreater rates of CO2 emission than when inactive at 24 °C, so the lack of discontinuous ventilation in M. pergandei under normoxic conditions is not likely to be imposed by physiological constraints and may, in fact, be a response to its xeric environment. We hypothesize – aside from phylogenetic effects – that discontinuous ventilation occurs primarily in insects that may experience hypoxic and hypercapnic conditions, such as ant queens during claustral colony foundation and perhaps workers within the nest environment; that discontinuous ventilation is not necessarily essential to reduce respiratory water loss; and that it will not necessarily occur in castes or species routinely exposed to xeric but normoxic conditions.
Serotonin Immunoreactivity in the Ventral Nerve Cord of the Primitive Crustacean Anaspides Tasmaniae Closely Resembles that of Crayfish
Authors: Harrison Paul J. , Macmillan David L. , Young Heather M.
Published: April 2021

Syncarid crustaceans, of which only a few living species remain, have articulated segments with well-developed appendages along the length of the body, an arrangement thought to resemble that of the earliest malacostracan crustaceans. Decapod malacostracans have fused thoracic segments and reduced abdominal appendages. Modern representatives of the two groups are separated by at least 300 million years of evolutionary history. The serotonin immunoreactivity of ganglia and connectives from the ventral nerve cord of the syncarid Anaspides tasmaniae was compared with that of serially homologous ganglia of the crayfish Cherax destructor. Both species show the serotonin-immunoreactive longitudinal fibre bundles described from other decapods and thought to be part of a neuromodulatory network. They also have in common a number of the cell bodies associated with this system. Each species has some serotonergic cells in the region examined that are not present, or that do not stain, in the other species.
The Transfer of Signals From Photoreceptor Cells to Large Second-Order Neurones in the Ocellar Visual System of the Locust Locusta Migratoria
Authors: Simmons Peter J.
Published: April 2021

The operation of the first synapse in the ocellar pathway of the locust Locusta migratoria has been studied by making simultaneous intracellular recordings from photoreceptors and large, second-order L-neurones.

The transfer curve for the synapse, obtained by plotting the amplitudes of the initial peak responses by the two cells to pulses of light against each other, shows that L-neurones are extremely sensitive to changes in photoreceptor potential and that the connection is tonically active in darkness. Postsynaptic current in han L-neurone, produced when pulses of light are delivered from a dark background, saturates at a slightly brighter light intensity than does the postsynaptic potential. The signal-to-noise ratio improves with increases in light intensity in both cells, but the reduction in noise as signals are transmitted from photoreceptors to L-neurones is less than would be expected from the number of photoreceptors that probably converge on each L-neurone. In both cells, in the presence of different intensities of background illumination, the slope of the intensity–response curve is maintained as the curve moves along the light intensity axis. Adaptation is relatively slow so that, at least for several minutes after an increase in background illumination, both cells maintain a sustained response and the responses to stimuli of increased illumination are reduced in amplitude. During sustained background illumination, the transfer curve for the synapse between a photoreceptor and an L-neurone shifts along both axes without a change in its maximum slope. The slope of the synaptic transfer curve depends on the speed as well as the amplitude of changes in light. In response to injection of depolarising pulses of current into a photoreceptor, an L-neurone generates brief, hyperpolarising responses. The amplitude of the responses depends on the strength and speed of the depolarising stimuli. After an initial response by an L-neurone, subsequent responses are reduced in amplitude for 200 ms. 7.The amplitude of L-neurone responses to electrical stimulation of a photoreceptor increases when the hyperpolarising constant current is injected into the photoreceptor.
Speed Effects on Midline Kinematics During Steady Undulatory Swimming of Largemouth Bass, Micropterus Salmoides
Authors: Jayne Bruce C. , Lauder George V.
Published: April 2021

We used frame-by-frame analysis of high-speed videotapes to quantify midline kinematics during steady swimming in largemouth bass at five standardized speeds (0.7, 1.2, 1.6, 2.0 and 2.4 L s−1, where L is total length). By combining morphological data from X-ray photographs with mathematical reconstructions of the midline of each fish, we determined the amplitude and timing of lateral displacement (zmax), lateral flexion (βmax) and the angle between the midline and the axis of forward travel (θmax) for each vertebral joint, the hypural bones and four equally spaced segments of the caudal fin rays. Analysis of variance revealed pervasive significant effects of both swimming speed and longitudinal location on variables describing amplitude, phase and wavelength. The amplitudes of zmax, βmax and θmax generally increased in a non-linear fashion from approximately 25%L to the tip of the caudal fin, and the greatest speed-related increases occurred between 0.7 and 1.6 L s−1. For the snout, the first caudal vertebra and the trailing edge of the caudal fin, mean values of zmax increased with speed from 0.004 to 0.012 L, from 0.005 to 0.012 L and from 0.053 to 0.066 L, respectively. For joints between the skull and the first vertebra, between the trunk and the tail vertebrae, and among the most posterior caudal vertebrae, mean values of βmax increased with speed from 1.2 to 1.7 °, from 0.6 to 0.9 ° and from 1.4 to 2.2 °, respectively. Within each swimming speed, values of βmax of the distal caudal fin commonly exceeded twice those of the proximal caudal fin. Surprisingly, at a given longitudinal location, the times of maximum lateral displacement and bending did not occur simultaneously. Instead, the phase of zmax relative to βmax was commonly shifted by more than one-sixth of a cycle. Furthermore, the phase shift between zmax and βmax changed significantly with increased swimming speed. Angles of attack of the tail structures changed periodically from negative to positive values. Maximum angles of attack of the distal caudal fin ranged from 5 to 17 °, changed significantly with swimming speed and were less than those of the hypural bones of the tail. Mean tail-beat frequency increased significantly from 2.0 to 4.2 Hz with increased swimming speed. Estimated speeds of wave propagation showed considerable longitudinal variation, and the ratio of swimming speed to posterior wave speed increased from 0.59 to 0.83 with increased swimming speed.
The Ontogeny of Aquatic Feeding Behavior in Salamandra Salamandra: Stereotypy and Isometry in Feeding Kinematics
Authors: Reilly Stephen M.
Published: April 2021

To examine the extent to which aquatic prey-capture behavior in salamanders is stereotyped and how feeding kinematics scales with size, the ontogenetic variability of aquatic feeding behavior was examined in eight Salamandra salamandra. Feeding kinematics (seven duration and angular displacement variables), kinematic variance and capture performance were quantified and compared in the first several feedings after birth with a series of feedings 8 weeks later, just prior to metamorphosis. Analysis of variance revealed no statistically significant ontogenetic differences in the kinematic variables, and individual differences were found in only two variables (maximum gape angle and gape cycle time). A comparison of the relative kinematic variance within individuals revealed no significant differences in variance during ontogeny. In addition, capture success rate did not change. The strike is significantly faster than that of other salamanders. These results indicate that the initial prey-capture behavior remains unchanged throughout larval ontogeny. Thus, aquatic strike behavior in S. salamandra is developmentally fixed (innate) and does not appear to be influenced by learning or improvement in ‘skill’, supporting the hypothesis that aquatic salamander feeding is a highly stereotyped, unmodulated behavior. In addition, the lack of kinematic change through ontogeny indicates that feeding kinematics do not scale with body size, contrary to predictions that movements should be slower in larger animals.
Kinematics of Feeding in Bluegill Sunfish: is There a General Distinction Between Aquatic Capture and Transport Behaviors?
Authors: Gillis G. B. , Lauder G. V.
Published: April 2021

Despite numerous studies of food transport in terrestrial vertebrates, little is known about this aspect of the feeding repertoire in aquatic vertebrates. Previous work had predicted that the kinematics of aquatic prey capture by suction feeding should be similar to those of prey transport. However, recent analyses of aquatic prey capture and transport in the tiger salamander Ambystoma tigrinum have contradicted this hypothesis, and document numerous differences between these two behaviors. In this study, using high-speed video and statistical analyses, we compare prey capture and transport kinematics in a ray-finned fish (Lepomis macrochirus, the bluegill sunfish) to examine the generality of differences between capture and transport behaviors in aquatic vertebrates. Compared with prey capture, prey transport is significantly more rapid and tends to have reduced lower jaw excursions, while having similar hyoid movements. A nested analysis of variance was used to analyze six variables common to both this analysis of Lepomis macrochirus and a previous study of Ambystoma tigrinum; none of these six variables showed significant variation between taxa. These results indicate that aquatic prey transport is kinematically distinct from capture behavior and that the distinctions between these two behaviors are remarkably consistent in two phylogenetically divergent lower vertebrate taxa. Such consistent kinematic differences have not been found in amniote taxa studied to date, but may constitute a plesiomorphic feature of vertebrate feeding systems.
Subcellular Localization and Biochemical Properties of the Enzymes of Carbamoyl Phosphate and Urea Synthesis in the Batrachoidid Fishes Opsanus Beta, Opsanus Tau and Porichthys Notatus
Authors: Anderson Paul M. , Walsh Patrick J.
Published: April 2021

The subcellular localization and biochemical properties of the enzymes of carbamoyl phosphate and urea synthesis were examined in three representatives of fishes of the family Batrachoididae, the gulf toadfish (Opsanus beta), the oyster toadfish (Opsanus tau) and the plainfin midshipman (Porichthys notatus). The primary objective of the study was to compare the biochemical characteristics of these fishes, which represent a range between ammoniotelism and ureotelism (O. beta being facultatively ureotelic), with previous patterns observed for an ammoniotelic teleost (Micropterus salmoides, the largemouth bass) and an obligate ureogenic elasmobranch (Squalus acanthias, the dogfish shark). The present study documents the expression of mitochondrial carbamoyl phosphate synthetase (CPSase) III and cytosolic CPSase II (and its associated enzymes of pyrimidine synthesis, dihydro-orotase and aspartate carbamoyltransferase) in the livers of all three batrachoidid species. Both mitochondrial and cytosolic activities of arginase were present in the livers of all three species, as were cytosolic glutamine synthetase and argininosuccinate synthetase and lyase. However, O. beta also showed mitochondrial glutamine synthetase activity and higher total hepatic levels of glutamine synthetase than either O. tau or P. notatus. Taken together, these observations confirm that the arrangement of these enzymes in the batrachoidid fishes has greater similarity to that of M. salmoides than to that of S. acanthias. However, differences within the family appear to coincide with the different nitrogen excretion strategies. O. tau and P. notatus are primarily ammoniotelic and most closely resemble the ammoniotelic M. salmoides, whereas ureotelism in O. beta is correlated with the presence of a mitochondrial glutamine synthetase and the ability to induce higher total glutamine synthetase activities than O. tau or P. notatus. Additionally, isolated mitochondria from O. beta were able to generate citrulline from glutamine, whereas those from O. tau were not. Also in contrast to S. acanthias, glutamine synthetase activities in the mitochondria of O. beta are consistently lower than those of CPSase III. This and other kinetic observations lend support to the hypothesis that glutamine synthetase may be an important regulatory control point in determining rates of ureogenesis in O. beta.
Temperature And Myogenesis In Embryos Of The Atlantic Herring Clupea Harengus
Authors: Johnston Ian A. , Vieira Vera. L. A. , Abercromby Marguerite
Published: April 2021

The development of axial muscles has been investigated in spring-spawning Atlantic herring (Clupea harengus L.) reared at 5, 8, 12 and 15 °C. In 1994, around 90 % of embryos hatched after 28 days at 5 °C, 16 days at 8 °C, 9 days at 12 °C and 8 days at 15 °C. The somites were formed from cells of the paraxial mesoderm in a rostral to caudal direction, starting at the neural plate stage. Somites were added at rates ranging from one every 3 h at 5 °C to one every 52 min at 15 °C. A small number of myoblasts, located adjacent and lateral to the notochord, elongated to span the somite to form mononuclear myotubes. The majority of muscle fibres were formed by the fusion of 2–5 myoblasts to produce multinucleated myotubes that subsequently differentiated into either superficial or inner fibre types. The timing of myogenesis with respect to somite stage and the initial appearance of the gut, pectoral fin buds and pronephric tubules was found to vary with development temperature. For rostral myotomes, the synthesis of contractile filaments and myofibril assembly were first observed at the 42-, 38-and 27-somite stages at 5, 8 and 12 °C, respectively. The differentiation of myotubes into morphologically recognisable muscle fibre types first occurred at the 62-somite stage at 5 °C, at the 48-somite stage at 8 °C and as early as the 40-somite stage at 12 °C. Cell proliferation experiments with 5-bromo-2′-deoxyuridine showed that another population of myoblasts was activated on the surface of muscle fibres just prior to hatching. Development temperature also affected muscle cellularity; there were 43 % more inner muscle fibres in the myotomes of 1-day-old larvae reared at 12 °C than at 5 °C (P<0.02).
Energy Substrates for Flight in the Blister Beetle Decapotoma Lunata (Meloidae)
Authors: Auerswald Lutz , Gäde Gerd
Published: April 2021

We investigated the substrates for flight in the blister beetle Decapotoma lunata by (a) establishing the patterns of maximum activities of enzymes of various metabolic pathways in the flight muscles, (b) measuring the respiratory rates of flight muscle mitochondria with various substrates and (c) determining metabolite concentrations in flight muscles and haemolymph during a flight period of up to 17 min and over a rest period of up to 2 h following 10 min of flight.

Activities of enzymes involved in proline metabolism (glutamate dehydrogenase, alanine aminotransferase, malic enzyme) were much higher in the blister beetle than in the migratory locust Locusta migratoria, whereas the activity of an enzyme responsible for fatty acid oxidation (-hydroxyacyl-CoA dehydrogenase) was much lower.

Mitochondria from flight muscles of D. lunata have a much higher capacity to oxidise proline than those from L. migratoria. The glycerophosphate shuttle, however, was equally active in both insects.

Whereas lipid levels in the haemolymph did not change significantly during flight, there was a continuous decrease in proline levels from 34.8 to 6.6 μmol ml-1 and a simultaneous increase in alanine concentration; carbohydrate levels dropped from 20.1 to 12.2 mg ml-1.

In the thorax (flight muscles), glycogen levels were diminished between 2 and 17 min of flight from 25.9 to 6.7 μmol glucose equivalents g-1 fresh mass. Proline concentration dropped continuously from an initial 49.5 to 10.1 μmol g-1 fresh mass, whereas alanine levels rose concomitantly from 2.9 to 17.3 μmol g-1 fresh mass.

After termination of a 10 min flight, pre-flight levels of proline in the haemolymph and flight muscles were only re-established after 2 h. In contrast, glycogen levels in the thorax were restored after 1 h.

Using the rates of utilisation of substrates during the first 10 min of flight to calculate rates of oxygen consumption during flight, it was shown that overall haemolymph substrates contribute 75 % and those of the flight muscles only 25 %. Although proline is an important substrate for flight in D. lunata, its role is secondary to that of carbohydrates. This type of substrate usage is different from that of the Colorado potato beetle Leptinotarsa decemlineata or the African fruit beetle Pachnoda sinuata, in which carbohydrates are of negligible or only slight importance, respectively.
Central Connections of Sensory Neurones From a Hair Plate Proprioceptor in the Thoraco-Coxal Joint of the Locust
Authors: Kuenzi F. , Burrows M.
Published: April 2021

The hair plate proprioceptors at the thoraco-coxal joint of insect limbs provide information about the movements of the most basal joint of the legs. The ventral coxal hair plate of a middle leg consists of group of 10–15 long hairs (70 μm) and 20–30 short hairs (30 μm). The long hairs are deflected by the trochantin as the leg is swung forward during the swing phase of walking, and their sensory neurones respond phasically during an imposed deflection and tonically if the deflection is maintained. Selective stimulation of the long hairs elicits a resistance reflex that rotates the coxa posteriorly and is similar to that occurring at the transition from the swing to the stance phase of walking. The motor neurones innervating the posterior rotator and adductor coxae muscles are excited, and those to the antagonistic anterior rotator muscle are inhibited. By contrast, selective stimulation of the short hairs leads only to a weak inhibition of the anterior rotator. The excitatory effects of the long hairs are mediated, in part, by direct connections between their sensory neurones and particular motor neurones. A spike in a sensory neurone elicits a short-latency depolarising postsynaptic potential (PSP) in posterior rotator and adductor motor neurones whose amplitude is enhanced by hyperpolarising current injected into the motor neurone. When the calcium in the saline is replaced with magnesium, the amplitude of the PSP is reduced gradually, and not abruptly as would be expected if an interneurone were interposed in the pathway. Several sensory neurones from long hairs converge to excite an individual motor neurone, evoking spikes in some motor neurones. The projections of the sensory neurones overlap with some of the branches of the motor neurones in the lateral association centre of the neuropile. It is suggested that these pathways would limit the extent of the swing phase of walking and contribute to the switch to the stance phase in a negative feedback loop that relieves the excitation of the hairs by rotating the coxa backwards.
Tuning In To Fish Swimming Waves: Body Form, Swimming Mode And Muscle Function
Authors: Wardle C. S. , Videler J. J. , Altringham J. D.
Published: April 2021

Most fish species swim with lateral body undulations running from head to tail. These waves run more slowly than the waves of muscle activation causing them, reflecting the effect of the interaction between the fish’s body and the reactive forces from the water. The coupling between both waves depends on the lateral body shape and on the mechanical properties of the tail. During steady swimming, the length of each myotomal muscle fibre varies cyclically. The phase relationship between the strain (muscle length change) cycle and the active period (when force is generated) determines the work output of the muscle. The muscle power is converted to thrust either directly by the bending body or almost exclusively by the tail, depending upon the body shape of the species and the swimming kinematics. We have compared the kinematics and muscle activity patterns from seven species of fish with different body forms and swimming modes and propose a model which yields a consistent pattern, with at least three extremes. Subtle tuning of the phase relationship between muscle strain and activation cycles can lead to major changes in the way muscles function in different swimming modes.
Optical Scaling in Conspecific Cataglyphis Ants
Authors: Zollikofer Christoph P. E. , Wehner Rüdiger , Fukushi Tsukasa
Published: April 2021

This study examines the effects of body size variation on the optical properties of the compound eyes of visually guided desert ants belonging to the genus Cataglyphis. Although linear head size may vary by a factor of 2 within conspecific workers and most optical parameters change accordingly, the extent of the visual field remains constant. Comparative measurements carried out on workers of three species (C. albicans, C. bicolor and C. fortis) and on reproductive females and males of one species (C. bicolor) show that the form (size and shape) of the visual field is highly characteristic for each caste/species. A constant visual field is realised by reciprocal scaling rules for the number of ommatidia and the angular spacing of ommatidia. While larger ants have more ommatidia per compound eye, interommatidial angles are reduced accordingly, thus giving rise to a constant visual field. Among conspecific ant workers, the relationship between spatial visual acuity and eye size is similar to that found in interspecific comparisons and reflects optical constraints imposed on the design of the compound eye. Mapping of spatial visual directions onto the compound eye surface reveals a characteristic, inhomogeneous distribution of interommatidial spacing, particularly a foveal band with increased visual acuity in the vertical direction. This ‘visual stretch’ viewing the horizon is similar to that found in a variety of flying insects. Although, among conspecific workers, both the number of ommatidia and the interommatidial angles vary with varying head size, the overall pattern of interommatidial spacing is maintained so that corresponding positions on the compound eye of small and large individuals look in equivalent directions in space. These findings are in accordance with the observation that the shape of the compound eye surface, as expressed by the radius of curvature along cross sections, is similar in small and large ants.
Cage size and flight speed of the Tobacco Hawkmoth Manduca Sexta
Authors: Stevenson R. D. , Corbo Kathleen , Baca L. B. , Le Quang D.
Published: April 2021

Flight speeds and behaviors of the sphinx moth Manduca sexta were recorded in chambers of four different sizes (0.57, 8.5, 44 and 447 m3). Mean horizontal speed increased linearly with the cube root of chamber volume from 0.57 m s−1 in the smallest chamber to 3.4 m s−1 in the largest. The maximum horizontal speed observed was 5.3 m s−1 in the largest chamber. Speeds decreased linearly with the logarithm of hawkmoth proximity to the wall. In a tunnel chamber (the third largest), moths often flew in a scalloped-shaped path. At the top of the scallop, they glided for 1–5 wing beats. In the largest chamber, moths could be recorded flying at angles other than horizontal (0°). At flight angles greater or less than 0 °, mean speed decreased linearly with angle until ±40 °. At greater angles, speeds remained between 1 and 2 m s−1. Moths also flew closer to the wall at flight angles deviating from the horizontal. An allometric analysis of the flight speeds of insects and birds suggests that M. sexta may be able to fly at 7–10 m s−1. We conclude that chamber size limits the flight speed and modifies the flight behavior of the tobacco hawkmoth.
Pulsatile Urea Excretion in the Ureagenic Toadfish Opsanus Beta: an Analysis of Rates and Routes
Authors: Wood Chris M. , Hopkins Todd E. , Hogstrand Christer , Walsh Patrick J.
Published: April 2021

This study focused on the rates and routes of urea-N and ammonia-N excretion in the ureagenic toadfish and on the possibility that urea-N excretion occurs in pulses. Experimental approaches included the following: confinement in small individual containers with automated hourly sampling of water to follow temporal excretion patterns; divided chambers to separate excretion from the anterior and posterior parts of the fish; collection of urine and rectal fluid via chronic indwelling catheters; and gavage with [14C]-labelled polyethylene glycol 4000 to detect regurgitation of gastrointestinal fluids. When a standardized ‘crowding’ pre-treatment was employed to induce ureotelic behaviour, the fish exhibited significant elevations in the activity of glutamine synthetase in liver, kidney and gills, elevated plasma and bile urea-N levels, but unchanged ammonia-N and urea-N levels in most other body fluids. Unencumbered ureotelic fish confined in small containers excreted 82 % of their waste-N as urea-N and 18 % as ammonia-N; almost all (94 %) of this urea-N excretion occurred in a single pulse of less than 3 h duration about once every 24 h. This daily pulse did not occur by regurgitation of gut fluids, by excretion through prominent pores behind the pectoral fins or by discharge of rectal fluid or urine. Intestinal and urinary excretion accounted for less than 10 % of whole-body urea-N excretion and a negligible fraction of ammonia-N excretion. Pulsatile urea-N excretion occurred at the head end across the gills and/or body surface. Ammonia-N excretion, which was not pulsatile, also occurred largely through the head end. However, once the toadfish had been placed in divided chambers, urea-N excretion became continuous rather than pulsatile, and ammonia-N excretion increased greatly. A severe stress response was indicated by high levels of plasma cortisol, and the skin, which lacks scales, became a significant route of both ammonia-N and urea-N excretion. We speculate that the normal adaptive significance is that ureotelism facilitates cryptic behaviour, allowing the toadfish to virtually eliminate N-waste excretion during long periods while it remains sheltered in burrows. However, during severe stress, the effects of extremely high cortisol levels overwhelm the ammonia and urea retention mechanisms, and both substances leak across the general body surface.
Directional Sound Processing and Interaural Sound Transmission in a Small and a Large Grasshopper
Authors: Michelsen Axel , Rohrseitz Kristin
Published: April 2021

Physical mechanisms involved in directional hearing are investigated in two species of short-horned grasshoppers that differ in body length by a factor of 3–4. The directional cues (the effects of the direction of sound incidence on the amplitude and phase angle of the sounds at the ears) are more pronounced in the larger animal, but the scaling is not simple.

At high frequencies (10–20 kHz), the sound pressures at the ears of the larger species (Schistocerca gregaria) differ sufficiently to provide a useful directionality. In contrast, at low frequencies (3–5 kHz), the ears must be acoustically coupled and work as pressure difference receivers. At 3–5 kHz, the interaural sound transmission is approximately 0.5 (that is, when a tympanum is driven by a sound pressure of unit amplitude at its outer surface, the tympanum of the opposite ear receives a sound pressure with an amplitude of 0.5 through the interaural pathway). The interaural transmission decreases with frequency, and above 10 kHz it is only 0.1–0.2. It still has a significant effect on the directionality, however, because the directional cues are large.

In the smaller species (Chorthippus biguttulus), the interaural sound transmission is also around 0.5 at 5 kHz, but the directionality is poor. The reason for this is not the modest directional cues, but rather the fact that the transmitted sound is not sufficiently delayed for the ear to exploit the directional cues. Above 7 kHz, the transmission increases to approximately 0.8 and the transmission delay increases; this allows the ear to become more directional, despite the still modest directional cues.
Functional Expression of a Cloned Drosophila Muscarinic Acetylcholine Receptor in a Stable Drosophila Cell Line
Authors: Millar Neil S. , Baylis Howard A. , Reaper Carolann , Bunting Richard , Mason William T. , Sattelle David B.
Published: April 2021

A cloned Drosophila muscarinic acetylcholine receptor (mAChR) has been stably expressed in a Drosophila cell line (S2) under the control of an inducible Drosophila metallothionein promoter. A clonal cell line (S2–Dm1-1) has been isolated which, after induction of mAChR expression with CuSO4, exhibits high-affinity, saturable, specific binding of the muscarinic antagonist N-methyl scopolamine (NMS). The apparent molecular mass of the expressed protein, calculated by sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE), is in good agreement with the apparent molecular mass of mAChRs purified from Drosophila brain. Functional expression of the cloned mAChR in this stable cell line has been demonstrated by quantitative fluorescence ratio-imaging of Fura-2-loaded cells. We have observed transient, agonist-induced elevations in intracellular Ca2+ levels which can be completely blocked by atropine, whereas AFDX-116, a muscarinic antagonist which binds preferentially to the vertebrate mAChR M2 subtype, has little effect at 100 μmol l−1. The suitability of this stable Drosophila expression system for the characterization of neurotransmitter receptors is discussed.
How Fish Power Predation Fast-Starts
Authors: Johnston Ian A. , Van Leeuwen Johan L. , Davies Melissa L. F. , Beddow Toni
Published: April 2021

Short-horned sculpin (Myoxocephalus scorpius L.) were acclimated for 6–8 weeks to either 5#x00B0;C or 15#x00B0;C (12 h dark: 12 h light). Fast-starts elicited by prey capture were filmed from above in silhouette using a high-speed video camera (200 frames s−1). Outlines of the body in successive frames were digitised and changes in strain for the dorsal fast muscle calculated from a knowledge of backbone curvature and the geometrical arrangement of fibres. For 15#x00B0;C-acclimated fish at 15#x00B0;C, muscle strain amplitude (peak-to-peak) during the first tail-beat was approximately 0.16 at 0.32L, 0.19 at 0.52L and 0.15 at 0.77L, where L is the total length of the fish. Fast muscle fibres were isolated and subjected to the strains calculated for the first tail-beat of the fast-start (abstracted cycle). Preparations were electrically stimulated at various times after the initiation of the fast-start using an in vivo value of duty cycle (27 %). Prior to shortening, muscle fibres at 0.52L and 0.77L were subjected to a pre-stretch of 0.055l0 and 0.085l0 respectively (where l0 is resting muscle length). The net work per cycle was calculated from plots of fibre length and tensile stress. For realistic values of stimulus onset, the average power output per abstracted cycle was similar at different points along the body and was in the range 24–31 W kg−1 wet muscle mass. During shortening, the instantaneous power output reached 175–265 W kg−1 wet muscle mass in middle and caudal myotomes. At the most posterior position examined, the muscle fibres produced significant tensile stresses whilst being stretched, resulting in an initially negative power output. The fibres half-way down the trunk produced their maximum power at around the same time that caudal muscle fibres generated significant tensile stress. Fast muscle fibres at 0.37–0.66L produced 76 % of the total work done during the first tail-beat compared with only 14 % for fibres at 0.67–0.86L, largely reflecting differences in muscle mass. The effect of temperature acclimation on muscle power was determined using the strain fluctuations calculated for 0.52L. For 5#x00B0;C-acclimated fish, the average power per cycle (± S.E.M.; W kg−1 wet muscle mass) was 21.8±3.4 at 5#x00B0;C, falling to 6.3±1.8 at 15#x00B0;C. Following acclimation to 15#x00B0;C, average power per cycle increased to 23.8±2.8 W kg−1 wet muscle mass at 15#x00B0;C. The results indicate near-perfect compensation of muscle performance with temperature acclimation.
Feeding Behavior in the Nocturnal Moth Manduca Sexta is Mediated Mainly by Blue Receptors, but where are they Located in the Retina?
Authors: Cutler Dianne E. , Bennett Ruth R. , Stevenson Robert D. , White Richard H.
Published: April 2021

The spectral sensitivity of nectar feeding by adults of the tobacco hawkmoth Manduca sexta was measured in free-choice experiments. The action spectrum displayed a narrow peak at 450 nm and a low secondary maximum at 560 nm. Thus, the feeding response is mediated primarily by blue-sensitive receptors containing the Manduca sexta photopigment P450, while green-sensitive receptors containing P520 play a minor role. A minimum at 500 nm separating the two peaks suggests mutual inhibition between green and blue receptors or negative interaction more proximally in the visual system. The action spectrum drops off abruptly at 400 nm, in accordance with an earlier finding that ultraviolet wavelengths, discerned by receptors containing P357, obstruct the feeding response.

The spectral sensitivity of the Manduca sexta compound eye, determined by electroretinogram recordings, and earlier visual pigment measurements indicate that approximately 75 % of the receptors are green-sensitive, with the remainder divided between blue-and ultraviolet-sensitive cells. The distribution of receptor types in small areas of the retina was measured by their ultrastructural response to light. Green and ultraviolet receptors were found, but not the blue receptors that dominate the feeding response. Possibly they are concentrated in a particular region of the retina that has not yet been found.
Evidence That Calcium-Dependent Cellular Processes are Involved in the Stiffening Response of Holothurian Dermis and That Dermal Cells Contain an Organic Stiffening Factor
Authors: Trotter John A. , Koob Thomas J.
Published: April 2021

Although previous investigations have shown that experimental increases and decreases of the concentration of extracellular Ca2+ produce correlated changes in the stiffness of holothurian dermis, they have failed to determine whether the Ca2+-correlated changes were due to Ca2+-dependent cellular events or to direct effects of Ca2+ on the viscosity of the extracellular matrix. We have addressed this question by testing two explicit predictions of the latter hypothesis: that dermal stiffness should be correlated with the Ca2+ concentration in the absence of viable cells; and that, in the presence of a normal extracellular Ca2+ concentration, drugs that inhibit cellular pathways dependent on Ca2+ should not affect dermal stiffness. Our results are inconsistent with the hypothesis and support the alternative hypothesis that Ca2+ is important only in the cellular regulation of dermal stiffness. In addition, we have extracted from dermal cells an organic factor that stiffens the extracellular matrix.
Remodelling of an Intact Neurone in the Central Nervous System of the Leech
Authors: Calabrese B. , Pellegrino M.
Published: April 2021

The regeneration pattern of two identified central neurones was studied in the leech Hirudo medicinalis. Anterior pagoda (AP) and mechanosensory touch-sensitive (T) neurones were stained in adult segmental ganglia, maintained in culture for 6–10 days. AP neurones, which normally project only to the contralateral nerve roots, sprouted extensively in all the available nerve paths during regeneration. Mechanosensory T cells, in the same experimental conditions, showed only a moderate growth and did not change their normal pattern of axonal projections. The observed differences in the growth pattern might account for the different electrophysiological responses to axotomy exhibited by the two types of neurone. Interruption of interganglionic connectives induced a moderate and stereotyped remodelling of the morphology of intact AP neurones, which was reminiscent of that transiently exhibited during embryonic development. This response was observed in 25 % of the AP neurones we examined.