bluuebunny/crossref_metadata_2025 huggingface dataset:
An Analysis of the Relationship Between the Response Characteristics and Topography of Directional- and Non-Directional Auditory Neurons in the Torus Semicircularis of the Rainbow Trout
Authors: Wubbels R. J. , Schellart N. A. M.
Published: April 2021

The response characteristics of auditory neurons in the multimodal midbrain torus semicircularis of rainbow trout were analyzed to examine their topography and functional differences. This analysis included the localization of recording sites, the measurement of spontaneous activity, the ratio of transient/sustained activity, and the synchronization, latency, preferred direction and directional range of the response. On average, units with a directionally selective (DS) response are positioned 60 μm more dorsally than other auditory units. Directionally selective units usually have a higher response rate, a higher transient/sustained activity ratio and are better synchronized. Auditory units encountered within the same electrode track tend to be either all DS or all non-DS. Within a track, there is no uniformity of the response characteristics observed except that the preferred direction of DS units appears to be the same. The anatomical stratification of the torus, containing 66 000 somata (5–10 μm in diameter), does not match the electrophysiologically observed vertical distribution of functionally distinct units. On the basis of the topographical distribution of response characteristics, two types of well-synchronized DS units can be distinguished, hypothetically representing separate channels for the processing of acoustic motion and (mainly) pressure information. A third type of DS unit which receives input from both these channels and actually encodes the source direction uniquely for all directions is postulated.
Neural Modulation Of Salt Secretion In Teleost Opercular Epithelium By α2-Adrenergic Receptors And Inositol 1,4,5-Trisphosphate
Authors: Marshall W. S. , Duquesnay R. M. , Gillis J. M. , Bryson S. E. , Liedtke C. M.
Published: April 2021

Opercular epithelia from seawater-adapted killifish (Fundulus heteroclitus) were dissected with the nerve intact, mounted in Ussing-style membrane chambers and bathed in symmetrical saline solutions. Nerve stimulation rapidly inhibited transepithelial current (a measure of Cl− secretion rate) by 27.3±3.3 % (N=22), and the effect could be sustained for more than 10 min using intermittent pulse trains at 10 Hz. The effect was blocked in a dose-dependent manner by yohimbine, but not by propranolol, atropine or tubocurarine, indicating mediation by α2-adrenergic receptors. The effect was also present, but significantly diminished, in opercular membranes from animals that had been transferred to sea water for 48 h (18±8.6 % inhibition, N=14). The resting current and the effect were absent in membranes from freshwater-adapted animals. The addition of clonidine (1.0 μmol l−1 serosal side) started to inhibit Cl− current after 40–60 s; immediately before this, at 30 s, there was a significant rise (P<0.05, N=14) in tissue inositol 1,4,5,-trisphosphate (InsP3) level, but no change at later times, compared with LiCl-treated control membranes and measured by radiolabeled receptor assay. The results indicate that seawater-adapted killifish can decrease their Cl− secretion rate through the action of the sympathetic nervous system, a response appropriate for the entry of estuarine fish to fresh water, and that the effect is mediated by α2-adrenoceptors via InsP3. The results imply that euryhaline fish entering fresh water can undergo an autonomic reflex reduction in salt secretion that does not require a stress response.
Hearing In Mole Crickets (Orthoptera: Gryllotalpidae) At Sonic And Ultrasonic Frequencies
Authors: Mason Andrew C. , Forrest Timothy G. , Hoy Ron R.
Published: April 2021

We have studied auditory responses in two species of mole cricket (Scapteriscus borellii and S. abbreviatus) to determine (1) whether they show sensitivity to ultrasound, (2) whether their hearing (at both low and high frequencies) is based on the same neural circuitry as that of true crickets, and (3) whether ultrasound sensitivity in different mole cricket species varies with their ability to fly. S. borellii are sensitive to ultrasonic frequencies. There is evidence of a segregation of frequency bands in prothoracic auditory neurons. There are two pairs of omega neurons (ONs) with similar morphology to ON1 of true crickets. The two pairs of ONs differ in tuning. One pair has two sensitivity peaks: at the frequency of the calling song of this species (3 kHz), and in the ultrasonic range (25 kHz). The other pair lacks the high-frequency sensitivity and responds exclusively to frequencies in the range of the species song. These two types are not morphologically distinguishable. In S. abbreviatus, only one class of ON was found. S. abbreviatus ONs are narrowly tuned to the frequency of the species’ calls. A T-neuron had the best ultrasonic frequency sensitivity in S. borellii. This cell showed a broad tuning to ultrasonic frequencies and was inhibited by low-frequency stimuli. A morphologically similar neuron was also recorded in S. abbreviatus, but lacked the high-frequency sensitivity peak of that in S. borellii.

We also assessed the responses of flying S. borellii to ultrasound using field playbacks to free-flying animals. The attractiveness of broadcast calling song was diminished by the addition of an ultrasound signal, indicating that S. borellii avoid high-frequency sound.

The results indicate that mole crickets process low-frequency auditory stimuli using mechanisms similar to those of true crickets. They show a negative behavioural response to high-frequency stimuli, as do true crickets, but the organization of ultrasound-sensitive auditory circuitry in mole crickets differs from that of true crickets.
Magnesium Transport in Freshwater Teleosts
Authors: Bijvelds Marcel J. C. , Van Der Velden Joan A. , Kolar Zvonimir I. , Flik Gert
Published: April 2021

The magnesium handling of freshwater teleost fish is discussed, with an emphasis on the role of branchial, intestinal and renal transport. In response to the eminent threat of constant diffusive losses of minerals such as magnesium, freshwater fish have developed efficient mechanisms for magnesium homeostasis. Magnesium losses are overcome by the uptake of magnesium from the food, making the intestine an important route for magnesium uptake. Some evidence suggests that intestinal magnesium uptake in fish is a regulated, cellular process. The ambient water is an additional magnesium source for fish, implicating the gills as a secondary route for magnesium uptake. Certainly, in some species, direct uptake from the water, probably via branchial routes, ameliorates the effects of a low-magnesium diet. The hard tissues, representing over 50 % of the total body magnesium pool, form a reservoir from which magnesium can be recruited to perform its functions in the cellular metabolism of soft tissues such as muscle. In fish, as in terrestrial vertebrates, the balance of a variety of elements becomes disturbed when the magnesium homeostasis of the soft tissues is disrupted. However, fish appear to be less sensitive than terrestrial vertebrates to these perturbations. Magnesium is reabsorbed in the kidneys to minimise losses. For renal cells, part of a cellular pathway has been elucidated that would allow absorptive magnesium transport (a magnesium conductive pathway in renal brush-border membranes). In some euryhaline teleosts, the kidneys appear to switch instantaneously to rapid magnesium secretion upon magnesium loading, a response common to marine fish that are threatened by diffusive magnesium entry. This enigmatic mechanism underlies the capacity of some euryhaline species to acclimate rapidly to sea water. Despite the progress made over the last decade, much of the cellular and molecular basis of magnesium transport in the gills, intestine and kidneys remains obscure. The application of fluorescent, radioactive and molecular probes, some of which have only recently become available, may yield rapid progress in the field of magnesium research.
Kinetic Analysis of a Signal-Transduction Pathway by Time-Resolved Somatic Complementation of Mutants
Authors: Starostzik Christine , Marwan Wolfgang
Published: April 2021

Sensory control of sporulation in Physarum polycephalum plasmodia is mediated by a branched signal-transduction pathway that integrates blue light, far-red light, heat shock and the starvation state. Mutants defective in the pathway were isolated and three phenotypes obtained: blue-blind, general-blind and light-independent sporulating. When plasmodia of the blue-blind mutant Blu1 were exposed to a pulse of blue light and subsequently fused to non-induced wild-type plasmodia, the resulting heterokaryons sporulated, indicating a functional blue-light photoreceptor in the mutant. When the general-blind mutant Nos1 was fused to a wild-type plasmodium which had been induced by light, sporulation of the heterokaryon was blocked. However, the dominant inhibition of sporulation by Nos1 was gradually lost with increasing time between induction by light and time of fusion, suggesting that Nos1 can be bypassed by the time-dependent formation of a downstream signal-transduction intermediate. Phenotype expression in constitutively sporulating (Cos) mutants depended on starvation. The Cos2 product was titrated by fusing mutant plasmodia of different sizes to wild-type plasmodia of constant size and analysing the sporulation probability of the resulting heterokaryon. The titration curve indicates that a small change in the amount of Cos2 product can cause sporulation. We conclude that somatic complementation analysis allows the time-resolved evaluation of the regulatory function of mutations in a signal-transduction pathway without prior cloning of the gene. This shortcut allows us to characterize many mutants quickly and to select those for molecular analysis that display a well-defined regulatory function.
Organic Matrix Synthesis in the Scleractinian Coral Stylophora Pistillata: Role in Biomineralization and Potential Target of the Organotin Tributyltin
Authors: Allemand Denis , Tambutté Éric , Girard Jean-Pierre , Jaubert Jean
Published: April 2021

The kinetics of organic matrix biosynthesis and incorporation into scleractinian coral skeleton was studied using microcolonies of Stylophora pistillata. [14C]Aspartic acid was used to label the organic matrix since this acidic amino acid can represent up to 50 mol % of organic matrix proteins. External aspartate was rapidly incorporated into tissue protein without any detectable lag phase, suggesting either a small intracellular pool of aspartic acid or a pool with a fast turn-over rate. The incorporation of 14C-labelled macromolecules into the skeleton was linear over time, after an initial delay of 20 min. Rates of calcification, measured by the incorporation of 45Ca into the skeleton, and of organic matrix biosynthesis and incorporation into the skeleton were constant. Inhibition of calcification by the Ca2+ channel inhibitor verapamil reduced the incorporation of organic matrix proteins into the skeleton. Similarly, organic matrix incorporation into the skeleton, but not protein synthesis for incorporation into the tissue compartment, was dependent on the state of polymerization of both actin and tubulin, as shown by the sensitivity of this process to cytochalasin B and colchicin. These drugs may inhibit exocytosis of organic matrix proteins into the subcalicoblastic space. Finally, inhibition of protein synthesis by emetin or cycloheximide and inhibition of N-glycosylation by tunicamycin reduced both the incorporation of macromolecules into the skeleton and the rate of calcification. This suggests that organic matrix biosynthesis and its migration towards the site of calcification may be a prerequisite step in the calcification process. On the basis of these results, we investigated the effects of tributyltin (TBT), a component of antifouling painting known to interfere with biomineralization processes. Our results have shown that this xenobiotic significantly inhibits protein synthesis and the subsequent incorporation of protein into coral skeleton. This effect was correlated with a reduction in the rate of calcification. Protein synthesis was shown to be the parameter most sensitive to TBT (IC50=0.2 µmol l−1), followed by aspartic acid uptake by coral tissue (IC50=0.6 µmol l−1), skeletogenesis (IC50=3 µmol l−1) and Ca2+ uptake by coral tissue (IC50=20 µmol l−1). These results suggest that the mode of action of TBT on calcification may be the inhibition of organic matrix biosynthesis.
Diving Speeds and Angles of a Gyrfalcon (Falco Rusticolus)
Authors: Tucker Vance A. , Cade Tom J. , Tucker Alice E.
Published: April 2021

An optical tracking device recorded the three-dimensional paths of 11 dives by a 1.02 kg gyrfalcon, trained to dive to a falconer. The dives started at altitudes up to 500 m above the ground and were inclined at angles of 17–62 ° from the horizontal. The falcon controlled its speed during the dives, rather than simply falling from the sky, and the dives had three phases. During the first (acceleration) phase, the falcon accelerated to speed limits between 52 and 58 m s−1 in the seven fastest dives, evidently with minimum drag, because its accelerations were close to those predicted from theory for minimum drag. The falcon then began a constant-speed phase by increasing drag by a factor of 1.3–4.8 while still 100–350 m above the ground in most dives. The constant-speed phase lasted no more than a few seconds, and the falcon then began a deceleration phase by increasing its drag further, this time by factors of 1.7–3.2, and decelerating with a mean value of −0.95 times gravitational acceleration.

During all three phases, the dive angle was nearly constant or increased during the deceleration phase, and the falcon made no changes in its body shape that were obvious through the tracking device telescope except to reduce its wing span as it accelerated. The falconer, however, was close to the falcon at the end of the dive and could see that, during the deceleration phase, the falcon held its wings in a cupped position, apparently with a high angle of attack and therefore high drag. At the end of the deceleration phase, the falcon dropped its legs, spread its toes and finally spread its wings as it approached the falconer.

Although the speeds reported here are the fastest ever measured with known accuracy in animals, the falcon could theoretically have reached more than 70 m s−1 if it had continued to accelerate with minimum drag until close to the ground. Even at this speed, it would have had enough altitude to pull out of the dive before crashing into the ground. Several authors have estimated that diving falcons reach speeds of more than 70 m s−1, and wild falcons may reach such speeds when they make long, steep dives upon birds flying high in the air.
Mechanics and Energetics of Human Locomotion on Sand
Authors: Lejeune T. M. , Willems P. A. , Heglund N. C.
Published: April 2021

Moving about in nature often involves walking or running on a soft yielding substratum such as sand, which has a profound effect on the mechanics and energetics of locomotion. Force platform and cinematographic analyses were used to determine the mechanical work performed by human subjects during walking and running on sand and on a hard surface. Oxygen consumption was used to determine the energetic cost of walking and running under the same conditions. Walking on sand requires 1.6–2.5 times more mechanical work than does walking on a hard surface at the same speed. In contrast, running on sand requires only 1.15 times more mechanical work than does running on a hard surface at the same speed. Walking on sand requires 2.1–2.7 times more energy expenditure than does walking on a hard surface at the same speed; while running on sand requires 1.6 times more energy expenditure than does running on a hard surface. The increase in energy cost is due primarily to two effects: the mechanical work done on the sand, and a decrease in the efficiency of positive work done by the muscles and tendons.
Effects of Buoyancy on the Diving Behavior of Northern Elephant Seals
Authors: Webb P. M. , Crocker D. E. , Blackwell S. B. , Costa D. P. , Boeuf B. J. Le
Published: April 2021

Marine mammals experience radical seasonal changes in body composition, which would be expected to affect their buoyancy in the water. The aim of this study was to examine the relationship between such changes in buoyancy and diving behavior in northern elephant seals Mirounga angustirostris. This was achieved by modifying the buoyancy of 13 juvenile elephant seals translocated from Año Nuevo State Reserve, CA, USA, and released at various sites in Monterey Bay, CA, USA. The buoyancy of each seal was calculated and was increased or decreased using syntactic foam or lead weights, and their diving behavior was recorded as they returned to Año Nuevo. The seals were divided into three groups: increased buoyancy (B+), reduced buoyancy (B−) and control seals (Bc). Mean descent rates were 0.77±0.3 m s−1 for the B+ seals, 0.82±0.2 m s−1 for the control seals and 0.87±0.3 m s−1 for the B-seals, and were significantly different. Mean ascent rates for the three treatments were 0.82±0.3 m s−1 for the B+ seals, 0.86±0.3 m s−1 for the control seals and 0.82±0.3 m s−1 for the B− seals. All the B+ seals ascended faster than they descended, while four of the five B− seals descended faster than they ascended. There was a significant negative correlation between buoyancy and descent rate, with less buoyant seals descending faster than more buoyant seals. There was, however, no correlation between ascent rate and buoyancy. This suggests that seals may use negative buoyancy to drift passively during descent, but that all seals may swim continuously during ascent. There was a significant correlation between buoyancy and the drift descent rate of C-type drift dives, including upwards drift in the most buoyant seal. Buoyancy was not correlated with diving depth, trip duration, dive duration or surface-interval duration. This study demonstrates that buoyancy plays a significant role in shaping diving behavior in northern elephant seals and that elephant seals may adjust their behavior to suit their buoyancy, rather than adjusting their buoyancy to suit a dive. This study also validated the truncated cones method of calculating body composition in this species by comparing it with body composition determined using tritium dilution.
Programmed Cell Death Specifically Eliminates one Part of a Locust Pleuroaxillary Muscle after the Imaginal Moult
Authors: Meuser Susanne , Pflüger Hans-Joachim
Published: April 2021

In the hemimetabolous insect Locusta migratoria, fundamental restructuring occurs at the transition from flightless nymph to flight-capable adult. This transition involves all components of the flight circuit, which is present but not used for flight in nymphs. The meso- and metathoracic pleuroaxillary muscles, M85 and M114 respectively, constitute one component of this circuit. In the adult locust, these are flight-steering muscles, but their function in the nymph is as yet unknown. Our study reveals that adult and nymphal metathoracic pleuroaxillary muscles M114 differ profoundly. The nymphal muscle contains the distinct part M114c in addition to parts M114a and M114b characteristic of the adult. The contractions of M114c are slow and long-lasting, corresponding to its long sarcomeres and slow form of ATPase, and contrast with the adult muscle parts M114a and M114b in all of these features. We demonstrate a hormone-dependent degeneration of M114c after the adult moult. This degeneration can be blocked by actinomycin D and cycloheximide. It may thus be termed genetically programmed cell death, triggered after the adult moult and, as demonstrated here, functioning via the ATP-dependent ubiquitin pathway. Given the defined onset of degeneration after the adult moult, it is possible that M114c may fulfil a specific function in nymphs, during or shortly after moulting.
Locust Dorsal Unpaired Median (Dum) Neurones Directly Innervate And Modulate Hindleg Proprioceptors
Authors: Bräunig Peter , Eder Matthias
Published: April 2021

A subgroup of the large efferent octopaminergic dorsal unpaired median (DUM) neurones of the third thoracic ganglion, the DUM3,4,5 neurones, directly innervates the tendons of certain proprioceptors of the locust hindleg, the so-called strand receptors. The terminals of the DUM neurones occur in regions of the strands that also contain the dendrites of the mechanoreceptive sensory cells. Both stimulation of the DUM3,4,5 neurones and bath application of octopamine change the responses of strand receptor units to mechanical stimulation. In both situations, most single strand receptor units show an increased response to mechanical stimulation. Some units, however, decrease their sensitivity to mechanical stimulation in response to octopamine application or DUM neurone stimulation.
Synaptic Activation Of Efferent Neuromodulatory Neurones In The Locust Schistocerca Gregaria
Authors: Baudoux Sylvie , Burrows Malcolm
Published: April 2021

The segmental ganglia of the locust contain efferent neuromodulatory neurones with cell bodies at the dorsal midline and axons that supply muscles and other tissue on both sides of the body. These are the dorsal unpaired median (DUM) neurones. Intracellular recordings were made from pairs of known metathoracic efferent DUM neurones in locusts in which all nerves were intact and in isolated metathoracic ganglia. The 19 metathoracic, efferent DUM neurones were identified according to the nerve roots through which their axons emerge from the ganglion. The synaptic potentials in these DUM neurones have been analysed to investigate how these neurones are activated and how their spikes are controlled.

The degree of correlation between the synaptic potentials in particular pairs of neurones was quantified using a correlation analysis. This allowed the population of DUM neurones to be divided into three subsets that also map onto an anatomical grouping based on the distribution of their axons in the lateral nerves: (i) DUM1 neurones (DUMDL and DUM1b); (ii) DUM3 and DUM3,4 neurones; and (iii) DUM3,4,5, DUM5b neurones and DUMETi. Individual neurones within each subset showed strong correlations between their synaptic potentials, in both intact locusts and isolated ganglia, and tended to spike at the same time. Neurones in different subsets had few synaptic potentials in common and tended to spike independently. The persistence of common synaptic potentials in neurones of the three subsets in isolated ganglia indicates that they are derived from neurones within the metathoracic ganglion.

The DUM neurones that had many common synaptic potentials in a quiescent locust responded in similar ways to mechanosensory stimulation of different parts of the body. DUM3,4,5 and DUM5 neurones gave the clearest and most consistent responses to stimulation of mechanoreceptors on either hind leg. DUM3 and DUM3,4 neurones responded variably, but usually with a hyperpolarisation. DUM1 neurones were rarely excited by mechanosensory stimuli but, like the preceding group, their responses were dependent upon whether the locust was moving its legs.

These results lend further support to the idea that there is a subdivision of action amongst this population of DUM neurones, with those supplying the same targets being driven by the same presynaptic local neurones.
Hypoxia Elicits an Increase in Pulmonary Vasculature Resistance in Anaesthetised Turtles (Trachemys Scripta)
Authors: Crossley Dane , Altimiras Jordi , Wang Tobias
Published: April 2021

In mammals and birds, low oxygen levels in the lungs cause a constriction of the pulmonary vasculature. This response is locally mediated and is considered to be important for local matching of perfusion and ventilation. It is not known whether reptiles respond in a similar fashion. The present study describes the effects of altering lung oxygen levels (at a constant of 0.03) on systemic and pulmonary blood flows and pressures in anaesthetised (Nembumal, 50 mg kg−1) and artificially ventilated turtles Trachemys scripta. During severe hypoxia (1.5–3 kPa ), pulmonary blood flow decreased in all animals; systemic blood flow increased, resulting in an increased net right-to-left shunt blood flow. The redistribution of blood flows was associated with reciprocal changes in the vascular resistances within the pulmonary and the systemic circulations (Rpul and Rsys, respectively). At 1.5 kPa O2, Rpul increased from 0.09±0.01 to 0.15±0.03 kPa ml−1 min kg during normoxia (means ±1 S.E.M., N=5). Concurrently, Rsys tended to decrease from a normoxic value of 0.12±0.01 to 0.09±0.02 kPa ml−1 min kg (P=0.08). The effects of hypoxia on the haemodynamic variables persisted following atropinisation (1 mg kg−1) and cervical vagotomy, suggesting that the increased Rpul during hypoxia is locally mediated. This study therefore demonstrates that turtles exhibit hypoxic pulmonary vasoconstriction, although the threshold is low compared with that of mammals.
Roles of Eyes, Leg Proprioceptors and Statocysts in the Compensatory Eye Movements of Freely Walking Land Crabs (Cardisoma Guanhumi)
Authors: Paul Herbert , Barnes W. Jon P. , Varjú Dezsö
Published: April 2021

The compound eyes, the canal organs of the statocysts and proprioceptors in the legs all generate compensatory eye movements in the horizontal plane in the land crab Cardisoma guanhumi. Frequency analyses of the compensatory eye reflexes elicited by each of these inputs show that visual (V) and proprioceptive (P) reflexes respond best below 0.1 Hz, while statocyst (S) reflexes only achieve a high gain above this frequency. They thus increase the range of frequencies over which compensation can occur.

Eye and body movements were recorded in an arena under all possible combinations of crabs seeing or blind (V+ or V−), with or without statocysts (S+ or S−) and freely walking or passively transported on a trolley (P+ or P−). Intact crabs (V+S+P+) show good stabilisation of the eyes in space, the only movements with respect to external coordinates being saccadic resetting movements (fast phases of nystagmus). The eyes thus compensate well for body turns, but are unaffected by translatory movements of the body and turns that are not accompanied by a change in the orientation of the long axis of the body in space. In the absence of any one sense, compensation for rotation is significantly impaired, whether measured by the increase in the width of the histograms of changes in the angular positions of the eyes in space (ΔϕE), by the mean angular velocity of the eyes (slope of regression line, mE) with respect to the angular velocity of the body (mB) or by response gain plotted against angular acceleration of body turn (a). The absence of two senses reduces the crab’s ability to compensate still further, with the statocyst-only condition (V−S+P−) being little better than the condition when all three senses are absent (V−S−P−).

Such multisensory control of eye compensation for body rotation is discussed both in terms of making use of every available cue for reducing retinal slip and in making available the information content of the optic flow field.
Regulation of Muscle Mitochondrial Design
Authors: Moyes Christopher D. , Battersby Brendan J. , Leary Scot C.
Published: April 2021

Mitochondria are responsible for the generation of ATP to fuel muscle contraction. Hypermetabolic stresses imposed upon muscles can lead to mitochondrial proliferation, but the resulting mitochondria greatly resemble their progenitors. During the mitochondrial biogenesis that accompanies phenotypic adaptation, the stoichiometric relationships between functional elements are preserved through shared sensitivities of respiratory genes to specific transcription factors. Although the properties of muscle mitochondria are generally thought to be highly conserved across species, there are many examples of mitochondrial differences between muscle types, species and developmental states and even within single cells. In this review, we discuss (1) the nature and regulation of gene families that allow coordinated expression of genes for mitochondrial products and (2) the regulatory mechanisms by which mitochondrial differences can arise over physiological and evolutionary time.
Decay Of Ca2+ and Force Transients in Fast- and Slow-Twitch Skeletal Muscles from the Rat, Mouse and Etruscan Shrew
Authors: Wetzel Petra , Gros Gerolf
Published: April 2021

Isometric single-twitch force and intracellular Ca2+ transients were recorded simultaneously, using fura-2, from slow- and fast-twitch muscle fibres of the rat, mouse and Etruscan shrew Suncus etruscus. In the slow-twitch rat soleus, force half-relaxation time was three times longer than the 50 % decay time of the fura-2 signal. In contrast, in the fast-twitch extensor digitorum longus muscles of all three animals, muscle relaxation preceded Ca2+ decay. It is proposed that this surprising property of fast-twitch muscles is due to their pCa–tension curve, which is shifted to the right compared with that of slow-twitch muscle.
Gliding Flight: Speed and Acceleration of Ideal Falcons During Diving and Pull Out
Authors: Tucker Vance A.
Published: April 2021

Some falcons, such as peregrines (Falco peregrinus), attack their prey in the air at the end of high-speed dives and are thought to be the fastest of animals. Estimates of their top speed in a dive range up to 157 m s−1, although speeds this high have never been accurately measured. This study investigates the aerodynamic and gravitational forces on ‘ideal falcons’ and uses a mathematical model to calculate speed and acceleration during diving. Ideal falcons have body masses of 0.5–2.0 kg and morphological and aerodynamic properties based on those measured for real falcons.

The top speeds reached during a dive depend on the mass of the bird and the angle and duration of the dive. Given enough time, ideal falcons can reach top speeds of 89–112 m s−1 in a vertical dive, the higher speed for the heaviest bird, when the parasite drag coefficient has a value of 0.18. This value was measured for low-speed flight, and it could plausibly decline to 0.07 at high speeds. Top speeds then would be 138–174 m s−1.

An ideal falcon diving at angles between 15 and 90 ° with a mass of 1 kg reaches 95 % of top speed after travelling approximately 1200 m. The time and altitude loss to reach 95 % of top speed range from 38 s and 322 m at 15 ° to 16 s and 1140 m at 90 °, respectively.

During pull out at top speed from a vertical dive, the 1 kg ideal falcon can generate a lift force 18 times its own weight by reducing its wing span, compared with a lift force of 1.7 times its weight at full wing span. The falcon loses 60 m of altitude while pulling out of the dive, and lift and loss of altitude both decrease as the angle of the dive decreases.

The 1 kg falcon can slow down in a dive by increasing its parasite drag and the angle of attack of its wings. Both lift and drag increase with angle of attack, but the falcon can cancel the increased lift by holding its wings in a cupped position so that part of the lift is directed laterally. The increased drag of wings producing maximum lift is great enough to decelerate the falcon at −1.5 times the acceleration of gravity at a dive angle of 45 ° and a speed of 41 m s−1 (0.5 times top speed).

Real falcons can control their speeds in a dive by changing their drag and by choosing the length of the dive. They would encounter both advantages and disadvantages by diving at the top speeds of ideal falcons, and whether they achieve those speeds remains to be investigated.
Tissue-Specific Effects of Hypothyroidism On Postnatal Muscle Development In The Barnacle Goose
Authors: Deaton Katie E. , Bishop Charles M. , Butler Patrick J.
Published: April 2021

The hypothesis that tissue-specific levels of thyroid hormones may be required for normal locomotor muscle development was investigated in the barnacle goose Branta leucopsis. Hypothyroidism was induced in goslings by treatment with methimazole from either 3 days or 2 weeks of age, and birds were killed at 7 weeks of age. The masses of the pectoralis, iliofibularis, semimembranosus and cardiac ventricle muscles were measured, and samples from these tissues were analysed for the mass-specific activity of the mitochondrial enzyme citrate synthase (CS). An ultrastructural electron micrograph analysis of the pectoralis was also carried out. No significant differences were found between the two hypothyroid groups except for the effect on the relative mass of the iliofibularis muscle. Developmental responses to hypothyroidism were found to be tissue-specific. Hypothyroidism resulted in a significantly lower relative cardiac ventricle mass (by 17 %) and CS activity of the leg muscles (by 34 %), while absolute leg muscle mass was not affected. The relative mass of the pectoralis was significantly lower (by 57 %) in hypothyroid birds and showed a significant, uniformly lower CS activity (by 60–83 %) as a result of a lower mitochondrial fractional volume. Haematocrit and capillary-to-fibre ratio in the pectoralis were also significantly lower in hypothyroid birds, and skeletal growth and plumage development were affected.
Limits for Oxygen and Substrate Transport in Mammals
Authors: Hoppeler H. , Weibel E. R.
Published: April 2021

Environmental oxygen is transported by the respiratory cascade to the site of oxidation in active tissues. Under conditions of heavy exercise, it is ultimately the working skeletal muscle cells that set the aerobic demand because over 90% of energy is spent in muscle cells. The pathways for oxygen and substrates converge in muscle mitochondria. In mammals, a structural limitation of carbohydrate and lipid transfer from the microvascular system to the muscle cells is reached at a moderate work intensity (i.e. at 40–50% of ). At higher work rates, intracellular substrate stores must be used for oxidation. Because of the importance of these intracellular stores for aerobic work, we find larger intramyocellular substrate stores in ‘athletic’ species as well as in endurance-trained human athletes. The transfer limitations for carbohydrates and lipids at the level of the sarcolemma imply that the design of the respiratory cascade from lungs to muscle mitochondria reflects primarily oxygen demand. Comparative studies indicate that the oxidative capacity of skeletal muscle tissue, and hence maximal oxygen demand, is adjusted by varying mitochondrial content. At the level of microcirculatory oxygen supply, it is found that muscle tissue capillarity is adjusted to muscle oxygen demand but that the capillary erythrocyte volume also plays a role. Oxygen delivery by the heart has long been recognized to be a key link in the oxygen transport chain. In allometric variation it is heart rate and in adaptive variation it is essentially stroke volume, and hence heart size, that determines maximal cardiac output. Again, haematocrit is an important variable that allows the heart of athletic species to generate higher flux rates for oxygen. The pulmonary gas exchanger offers only a negligible resistance to oxygen flux to the periphery. However, in contrast to all other steps in the respiratory cascade, the lungs have only a minimal phenotypical plasticity and appear, therefore, to be built with considerable structural redundancy in all but the most athletic species. Because of the lack of malleability, the lungs may ultimately become limiting for when adaptive processes have maximized O2 flux through the malleable downstream elements of the respiratory system: the heart, microcirculation and muscle mitochondria.
Functional Adaptations of Oxygen-Transport Proteins
Authors: Terwilliger Nora B.
Published: April 2021

Oxygen-transport proteins are multisubunit, circulating molecules that provide an efficient supply of oxygen to metabolically active metazoans. Hemoglobins, hemerythrins and hemocyanins have evolved in both structural and functional diversity and exhibit functional repertoires beyond that of simple, monomeric tissue myoglobins. Their phylogenetic distribution is intriguing, especially with respect to those organisms that express more than one type of oxygen-transport protein. An animal can modify the delivery of oxygen to its tissues by varying the rate of synthesis of these proteins or by selective expression of individual subunits and/or molecules.

Changes in levels of allosteric modifiers that affect the protein’s oxygenation properties will also modify oxygen delivery; some organisms have more ability than others to control concentrations of modulators. Hemoglobins have assumed functions in addition to oxygen transport, while hemocyanins have diversified through multiple gene duplications and functional specializations. Understanding the mechanisms of regulation of expression, synthesis and modulator levels is a key focus of current investigations.
Intracellular Oxygen Diffusion: the Roles of Myoglobin and Lipid at Cold Body Temperature
Authors: Sidell Bruce D.
Published: April 2021

Cold temperature can constrain the rate of oxygen movement through muscle cells of ectothermic animals because the kinetic energy of the solvent–solute system decreases and the viscosity of the aqueous cytoplasm increases during cooling within the physiological range of body temperatures. These factors affect the movement of both dissolved oxygen and oxymyoglobin, the two predominant routes of intracellular oxygen diffusion in vertebrate oxidative muscles. In addition, reductions in temperature have been shown to increase the affinity of myoglobin for oxygen and to slow the rate of Mb O2-dissociation, compromising the ability of this oxygen-binding protein to facilitate intracellular oxygen diffusion. Experiments with both seasonally cold-bodied fishes and polar fish species suggest that several factors combine to overcome these limitations in delivery of oxygen from the blood to the mitochondria. First, reductions in body temperature induce increases in mitochondrial density of oxidative muscle cells, reducing the mean diffusional pathlength for oxygen between capillaries and mitochondria. Second, cold body temperature in both temperate-zone and polar fishes is frequently correlated with a high content of neutral lipid in oxidative muscles, providing an enhanced diffusional pathway for oxygen through the tissue. Third, recent data indicate that myoglobins from fish species bind and release oxygen more rapidly at cold temperature than do those from mammals. Data from both oxidative skeletal muscle and cardiac muscle of fishes suggest that these factors in various combinations contribute to enhance the aerobically supported mechanical performance of the tissues at cold cellular temperatures.
Oxygen Sensing, Hypoxia-Inducible Factor-1 and the Regulation of Mammalian Gene Expression
Authors: Ratcliffe Peter J. , O’rourke John F. , Maxwell Patrick H. , Pugh Christopher W.
Published: April 2021

A great many aspects of the anatomy and physiology of large animals are constrained by the need to match oxygen supply to cellular metabolism and appear likely to involve the regulation of gene expression by oxygen. Some insight into possible underlying mechanisms has been provided by studies of erythropoietin, a haemopoietic growth factor which stimulates red cell production in response to hypoxia. Studies of hypoxia-inducible cis-acting sequences from the erythropoietin gene have led to the recognition of a widespread transcriptional response to hypoxia based on the activation of a DNA-binding complex termed hypoxia-inducible factor-1 (HIF-1). Perturbation of the transcriptional response by particular transition metal ions, iron chelators and certain redox-active agents have suggested a specific oxygen sensing mechanism, perhaps involving a haem protein in a flavoprotein/cytochrome system. In addition to erythropoietin, HIF-1-responsive genes include examples with functions in cellular energy metabolism, iron metabolism, catecholamine metabolism, vasomotor control and angiogenesis, suggesting an important role in the coordination of oxygen supply and cellular metabolism. In support of this, we have demonstrated an important role for HIF-1 in tumour angiogenesis. HIF-1 itself consists of a heterodimer of two basic-helix–loop–helix proteins of the PAS family, termed HIF-1α and HIF-1β, although other closely related members of this family may also contribute to the response to hypoxia. We have fused domains of HIF-1 genes to heterologous transcription factors to assay for regulatory function. These experiments have defined several domains in HIF-1α which can independently confer the hypoxia-inducible property, and they suggest a mechanism of HIF-1 activation in which post-translational activation/derepression of HIF-1α is amplified by changes in HIF-1α abundance most probably arising from suppression of proteolytic breakdown. Pursuit of the mechanism(s) underlying these processes should ultimately lead to better definition of the oxygen-sensing process.
Multilayer Reflectors in Animals Using Green and Gold Beetles as Contrasting Examples
Authors: Parker Andrew R. , Mckenzie David R. , Large Maryanne C. J.
Published: April 2021

The light reflectors in the beetles Calloodes grayanus and Anoplognathus parvulus are examined. Contrasting multilayer reflectors are revealed. Calloodes grayanus appears a weak green colour, matching its background leaves, while A. parvulus is strongly metallic-gold coloured. The former reflection is diffuse, as the result of a structure causing scattering that overlies the multilayer reflector, whereas the latter reflection is strongly directional. The green colour of C. grayanus is achieved by a multilayer reflector with a fixed spatial periodicity, here termed ‘regular’, which is far removed from the quarterwave, or physically ‘ideal’, condition. The gold colour of A. parvulus is achieved by a type of reflector which involves systematically changing optical thicknesses of the component layers with depth in the structure. A layer of melanin underlies the reflector of C. grayanus to absorb the transmitted portion of light and prevent its back-reflectance, which would otherwise alter the green colour. The resultant structural reflectance from C. grayanus effectively matches green pigments, which are rare in beetles.
Visual Pigments, Oil Droplets and Cone Photoreceptor Distribution in the European Starling (Sturnus Vulgaris)
Authors: Hart N. S. , Partridge J. C. , Cuthill I. C.
Published: April 2021

Microspectrophotometric measurements of retinal photoreceptors from the European starling (Sturnus vulgaris) revealed four classes of single cone, containing visual pigments with wavelengths of maximum absorbance (λmax) at 563, 504, 449 and close to 362 nm. The two longer-wave-sensitive single cones contained brightly coloured oil droplets which cut off light below 572 and 514 nm, respectively. The 449 nm λmax pigment was associated with a ‘colourless’ oil droplet with peak measured absorptance below 400 nm. The ultraviolet-sensitive visual pigment was paired with a transparent oil droplet which showed no significant absorption above 350 nm. A single class of double cone was identified, both members of which contained the longwave-sensitive (λmax 563 nm) visual pigment. The principal member of the double cone contained an oil droplet with a topographically variable cut-off wavelength below 471 nm; the oil droplet found in the accessory member was only measured in the ventral retina and displayed three distinct peaks of absorption at approximately 430, 450 and 480 nm. Rod photoreceptors had a λmax at 503 nm. A new polynomial for fitting visual pigment templates to ultraviolet-sensitive visual pigment data is given. Topographic density measurements of the different cone classes were made using Nitroblue-tetrazolium chloride to label selectively bleached photoreceptors. The two classes of shortwave-sensitive single cone were more abundant in the dorsal retina, and longwave-sensitive single cones were notably less abundant in the dorso-temporal region of the retina, which subserves binocular vision.
Prey capture in the weakly electric fish Apteronotus albifrons: sensory acquisition strategies and electrosensory consequences
Authors: Nelson Mark E. , Maciver Malcolm A.
Published: April 2021

Sensory systems are faced with the task of extracting behaviorally relevant information from complex sensory environments. In general, sensory acquisition involves two aspects: the control of peripheral sensory surfaces to improve signal reception and the subsequent neural filtering of incoming sensory signals to extract and enhance signals of interest. The electrosensory system of weakly electric fish provides a good model system for studying both these aspects of sensory acquisition. On the basis of infrared video recordings of black ghost knifefish (Apteronotus albifrons) feeding on small prey (Daphnia magna) in the dark, we reconstruct three-dimensional movement trajectories of the fish and prey. We combine the reconstructed trajectory information with models of peripheral electric image formation and primary electrosensory afferent response dynamics to estimate the spatiotemporal patterns of transdermal potential change and afferent activation that occur during prey-capture behavior. We characterize the behavioral strategies used by the fish, with emphasis on the functional importance of the dorsal edge in prey capture behavior, and we analyze the electrosensory consequences. In particular, we find that the high-pass filter characteristics of P-type afferent response dynamics can serve as a predictive filter for estimating the future position of the prey as the electrosensory image moves across the receptor array.
Design features for electric communication
Authors: Hopkins Carl D.
Published: April 2021

How do the communication discharges produced by electric fish evolve to accommodate the unique design features for the modality? Two design features are considered: first, the limited range of signaling imposed on the electric modality by the physics of signal transmission from dipole sources; and second, the absence of signal echoes and reverberations for electric discharges, which are non-propagating electrostatic fields.

Electrostatic theory predicts that electric dicharges from fish will have a short range because of the inverse cube law of geometric spreading around an electrostatic dipole. From this, one predicts that the costs of signaling will be high when fish attempt to signal over a large distance. Electric fish may economize in signal production whenever possible. For example, some gymnotiform fish appear to be impedance-matched to the resistivity of the water; others modulate the amplitude of their discharge seasonally and diurnally.

The fact that electric signals do not propagate, but exist as electrostatic fields, means that, unlike sound signals, electric organ discharges produce no echoes or reverberations. Because temporal information is preserved during signal transmission, receivers may pay close attention to the temporal details of electric signals. As a consequence, electric organs have evolved with mechanisms for controlling the fine structure of electric discharge waveforms.