bluuebunny/crossref_metadata_2025 huggingface dataset:
The biomechanics of fast-starts during ontogeny in the common carp cyprinus carpio
Authors: Wakeling James M. , Kemp Kirsty M. , Johnston Ian A.
Published: April 2021

Common carp Cyprinus carpio L. were reared a constant temperature of 20 °C from the larval (7 mm total length) to the juvenile (80 mm) stage. Body morphology and white muscle mass distribution were measured. Fast-start escape responses were recorded using high-speed cinematography from which the velocities, accelerations and hydrodynamic power requirements were estimated. All three measures of fast-start performance increased during development. White muscle contraction regimes were calculated from changes in body shape during the fast-starts and used to predict the muscle force and power production for all longitudinal positions along the body. Scaling arguments predicted that increases in body length would constrain the fish to bend less rapidly because the cross-sectional muscle area, and hence force production, does not increase at the same rate as the inertial mass that resists bending. As predicted, the increases in body length resulted in decreases in muscle shortening velocity, and this coincided with increases in both the force and power produced by the muscles. The hydrodynamic efficiency, which relates the mechanical power produced by the muscles to the inertial power requirements in the direction of travel, showed no significant change during ontogeny. The increasing hydrodynamic power requirements were thus met by increases in the power available from the muscles. The majority of the increases in fast-start swimming performance during ontogeny can be explained by size-dependent increases in muscle power output. For all sizes, there was a decrease in muscle-mass-specific power output and an increase in muscle stress in a posterior direction along the body due to systematic variations in fibre strain. These changing strain regimes result in the central muscle bulk producing the majority of the power requirements during the fast-start, and this power is transmitted to the tail region of the fish and ultimately to the water via muscle in the caudal myotomes.
The sites of respiratory gas exchange in the planktonic crustacean daphnia magna: an in vivo study employing blood haemoglobin as an internal oxygen probe
Authors: Pirow R. , Wollinger F. , Paul R. J.
Published: April 2021

Recent studies on Daphnia magna have revealed that the feeding current is important for uptake of oxygen from the ambient medium. Respiratory gas exchange should therefore mainly occur within the filtering chamber, whose boundaries are formed by the trunk and the extended carapace shell valves. The precise site of gas exchange in the genus Daphnia is, however, a matter of conjecture. We have developed a method of imaging the haemoglobin oxygen-saturation in the circulatory system of transparent animals, which provides an opportunity to localize oxygen uptake from the environment and oxygen release to the tissues. Experiments were carried out at 20 °C on 2.8–3.0 mm long parthenogenetic females maintained in hypoxic culturing conditions, which had resulted in an increased haemoglobin content in the haemolymph. In lateral views of D. magna, the highest values of haemoglobin oxygen-saturation occurred near the posterior margin of the carapace and, surprisingly, in the rostral part of the head. The ambient oxygen partial pressures at which haemoglobin was half-oxygenated were 15 mmHg (2.0 kPa) for the posterior carapace region and 6 mmHg (0.8 kPa) for the rostrum. Although not all parts of the circulatory system could be analyzed using this technique, the data obtained from the accessible regions suggest that the inner wall of the carapace is a major site of respiratory gas exchange. Taking the circulatory pattern and the flow pattern of the medium in the filtering chamber into consideration, it becomes clear that the haemolymph, after passing from the limbs to the carapace lacuna, becomes oxygenated while flowing through the ventral part of the double-walled carapace in a posterior direction. The laterally flattened rostral region, where sensory and central nervous system structures are located, seems to have direct diffusive access to ambient oxygen, which could be especially advantageous during severe hypoxia when the convective transport systems fail to supply enough oxygen to that region.
Morphological basis of kinematic diversity in feeding sunfishes
Authors: Wainwright Peter C. , Shaw Samantha S.
Published: April 2021

The effects of differences among species in the scaling of lower jaw levers on the scaling of prey-capture kinematics are explored in three species of centrarchid fishes. We consider the jaw opening and closing lever systems and calculate the consequences of differences in the scaling of the in-levers for the scaling of the time taken to open the mouth (To) and the time taken to close the mouth (Tc) during prey capture. Predictions of To and Tc, based on differences in the scaling of jaw in-levers, are compared with the observed scaling of To and Tc in three centrarchid fishes. Video recordings (200 and 400 images s−1) were made of prey capture in largemouth bass Micropterus salmoides (33–206 mm standard length, SL), spotted sunfish Lepomis punctatus (24–145 mm SL) and bluegill sunfish Lepomis macrochirus (24–220 mm SL), and the fastest values of To and Tc were taken from the fastest recorded feeding event for each fish. The scaling exponents of To and Tc regressed on fish SL for largemouth bass were 0.592 and 0.572, respectively. Exponents observed for sunfishes were not significantly different from predicted values, based on scaling exponents in largemouth bass and interspecific differences in jaw lever proportions. Two conclusions are emphasized. First, between 25 and 220 mm SL, the time taken to open and close the mouth during the strike increases with body size in all three species, suggesting a general pattern for this family. Second, evolutionary changes in jaw lever mechanics are a major determinant of the diversity of prey-capture kinematics in this sample of centrarchid fishes.
Shear stress experienced by echinoderm eggs in the oviduct during spawning: potential role in the evolution of egg properties
Authors: Thomas Florence I. M. , Bolton Toby F.
Published: April 2021

Shear stresses experienced by eggs in the oviduct of the echinoid Arbacia punctulata during spawning were calculated using engineering equations that describe laminar flow through pipes. Shear stresses in the oviduct ranged from 0 to 58.7 Pa. Two properties of eggs were identified that have the potential either to minimize the shear stress in the oviduct or to reduce the damage experienced by eggs exposed to high shear stress. These properties are the viscosity of the eggs and the presence of extracellular layers on eggs of A. punctulata. The viscosity of eggs decreases with increasing shear rates, which reduces the magnitude of shear stress experienced in the oviduct, while the extracellular layers mitigate the effect of shear stress on the eggs. Eggs with intact extracellular layers were damaged less frequently than were those with the extracellular layers removed. The results of this research indicate that physical stresses may be important selective factors in the evolution of gamete properties.
Reactive oxygen intermediate production by oyster hemocytes exposed to hypoxia
Authors: Boyd John N. , Burnett Louis E.
Published: April 2021

Oysters are frequently exposed to severely hypoxic conditions, especially during summer months. During the summer, there are also large numbers of disease-related oyster mortalities. This research was conducted to determine whether exposure to environmental hypoxia reduces the ability of oyster hemocytes to produce reactive oxygen intermediates (ROIs), an important part of their defense system. Oysters of the species Crassostrea virginica were held in normoxic (, pH 7.8–8.0) and hypoxic conditions (, pH 7.1–7.4). In vivo hemolymph variables (and pH) were measured after both 1 hour and 2 days in each treatment to determine the appropriate environment for subsequent hemocyte experiments. Production of reactive oxygen intermediates by hemocytes was measured using luminol-enhanced chemiluminescence (CL). During CL tests, hemocytes were held under the following conditions: air (, pH 7.6), in vivo hemolymph conditions of normoxic oysters (, pH 7.6), and in vivo hemolymph conditions of hypoxic oysters (, pH 7.1). Production of ROIs under hypoxic conditions was 33 % of that under normoxia. This decrease was the result of specific and independent effects of lower oxygen levels and decreased pH. It was not due to any direct effect of CO2.
Ferromagnetic material in the eastern red-spotted newt notophthalmus viridescens
Authors: Brassart J. , Kirschvink J. L. , Phillips J. B. , Borland S. C.
Published: April 2021

Behavioral results obtained from the eastern red-spotted newt (Notophthalmus viridescens) led to the suggestion of a hybrid homing system involving inputs from both a light-dependent and a non-light-dependent mechanism. To evaluate the possible role of a receptor based on biogenic magnetite in this animal, we performed magnetometry experiments on a set of newts previously used in behavioral assays. The natural remanent magnetization (NRM) carried by these newts was strong enough to be measured easily using a direct-current-biased superconducting quantum interference device functioning as a moment magnetometer. Isothermal remanent magnetizations were two orders of magnitude higher than the NRM, suggesting that ferromagnetic material consistent with magnetite is present in the body of the newt. The NRM has no preferential orientation among the animals when analyzed relative to their body axis, and the demagnetization data show that, overall, the magnetic material grains are not aligned parallel to each other within each newt. Although the precise localization of the particles was not possible, the data indicate that magnetite is not clustered in a limited area. A quantity of single-domain magnetic material is present which would be adequate for use in either a magnetic intensity or direction receptor. Our data, when combined with the functional properties of homing, suggest a link between this behavioral response and the presence of ferromagnetic material, raising the possibility that magnetite is involved at least in the map component of homing of the eastern red-spotted newt.
Target organ specificity of major neuropeptide stimulants in locust excretory systems
Authors: Coast G. M. , Meredith J. , Phillips J. E.
Published: April 2021

The major stimulant of ileal fluid reabsorption in Locusta migratoria and Schistocerca gregaria corpora cardiaca, ion-transport peptide (ITP), had no stimulatory action on fluid secretion by isolated Malpighian tubules of S. gregaria, nor did it have a synergistic or antagonistic effect in combination with locustakinin (Lom-K) or Locusta-diuretic hormone (Locusta-DH). Stimulants of locust Malpighian tubules (Lom-K and Locusta-DH) had no action on either active transport of Cl− (measured as short-circuit current, Isc) or the rate of fluid reabsorption across S. gregaria ilea and recta in vitro. Thus, hormonal control of these major organs of the excretory system appears to be clearly separated.

Lom-K and Locusta-DH acted synergistically to stimulate secretion by S. gregaria Malpighian tubules, and the diuretic response was more rapid than the response of the ileum and rectum to hindgut stimulants. Taken together, these data suggest that, in the initial phase of post-prandial diuresis, urine flow will exceed fluid uptake in the hindgut, thereby allowing excess water to be eliminated.
Methods for calculating factors of safety for plant stems
Authors: Niklas Karl J. , Spatz Hanns-Christof
Published: April 2021

The concept of a ‘factor of safety’ is used by biologists and engineers who generally agree that structures must be mechanically reliable, i.e. that structures must be capable of coping with unprecedented loads without failing. These factors can be calculated for individual structures or for a population of otherwise equivalent mechanical structures differing in their load capabilities. Objective methods for quantifying factors of safety for biological structures are nevertheless difficult to devise because (1) actual (working) loads are defined by environmental conditions that can vary widely, (2) breaking loads (capability) of otherwise mechanically equivalent structures can likewise vary as a result of developmental variation, and (3) specific criteria for failure must be determined a priori.

In this paper, we illustrate and discuss two methods for computing factors of safety for plants. One method works well for individual stems or entire plants, the other is useful when dealing with a population of conspecifics exhibiting a norm of reaction. Both methods require estimates of the actual and breaking bending (or torsional) moments experienced by stems, and both are amenable to dealing with any biologically reasonable criterion for failure. However, the two methods differ in terms of the assumptions made and the types of data that need to be gathered. The advantage of the first method is that it estimates the potential for survival of an individual stem or plant. The disadvantage is that it neglects natural variation among otherwise mechanically homologous individuals. The advantage of the second (statistical) approach is that it estimates the probability of survival of a population in a particular habitat. The disadvantage of this approach is that it sheds little light on the probability of an individual’s survival.
Mechanical design in arteries
Authors: Shadwick Robert E.
Published: April 2021

The most important mechanical property of the artery wall is its non-linear elasticity. Over the last century, this has been well-documented in vessels in many animals, from humans to lobsters. Arteries must be distensible to provide capacitance and pulse-smoothing in the circulation, but they must also be stable to inflation over a range of pressure. These mechanical requirements are met by strain-dependent increases in the elastic modulus of the vascular wall, manifest by a J-shaped stress–strain curve, as typically exhibited by other soft biological tissues. All vertebrates and invertebrates with closed circulatory systems have arteries with this non-linear behaviour, but specific tissue properties vary to give correct function for the physiological pressure range of each species. In all cases, the non-linear elasticity is a product of the parallel arrangement of rubbery and stiff connective tissue elements in the artery wall, and differences in composition and tissue architecture can account for the observed variations in mechanical properties. This phenomenon is most pronounced in large whales, in which very high compliance in the aortic arch and exceptionally low compliance in the descending aorta occur, and is correlated with specific modifications in the arterial structure.
Templates and anchors: neuromechanical hypotheses of legged locomotion on land
Authors: Full R. J. , Koditschek D. E.
Published: April 2021

Locomotion results from complex, high-dimensional, non-linear, dynamically coupled interactions between an organism and its environment. Fortunately, simple models we call templates have been and can be made to resolve the redundancy of multiple legs, joints and muscles by seeking synergies and symmetries. A template is the simplest model (least number of variables and parameters) that exhibits a targeted behavior. For example, diverse species that differ in skeletal type, leg number and posture run in a stable manner like sagittal- and horizontal-plane spring-mass systems. Templates suggest control strategies that can be tested against empirical data. Templates must be grounded in more detailed morphological and physiological models to ask specific questions about multiple legs, the joint torques that actuate them, the recruitment of muscles that produce those torques and the neural networks that activate the ensemble. We term these more elaborate models anchors. They introduce representations of specific biological details whose mechanism of coordination is of interest. Since mechanisms require controls, anchors incorporate specific hypotheses concerning the manner in which unnecessary motion or energy from legs, joints and muscles is removed, leaving behind the behavior of the body in the low-degree-of-freedom template. Locating the origin of control is a challenge because neural and mechanical systems are dynamically coupled and both play a role. The control of slow, variable-frequency locomotion appears to be dominated by the nervous system, whereas during rapid, rhythmic locomotion, the control may reside more within the mechanical system. Anchored templates of many-legged, sprawled-postured animals suggest that passive, dynamic self-stabilization from a feedforward, tuned mechanical system can reject rapid perturbations and simplify control. Future progress would benefit from the creation of a field embracing comparative neuromechanics.
Invertebrate paraxial locomotory appendages: design, deformation and control
Authors: Wootton Robin J.
Published: April 2021

Some principles governing the design of invertebrate paired propulsive appendages are discussed, with particular reference to the extent to which information encoded in their skeletal structure determines their instantaneous shape in locomotion. The hydrostatic paired fins of some cephalopods and marine gastropods, polychaete parapodia and onychophoran lobopodia rely entirely on musculature for shape control. The deformations of walking limbs, though still under muscular control, are strongly influenced by the nature and sequence of movement of the joints. Limbs adapted for walking in air are effectively point-loaded, and their rigid components need to resist axial forces as well as bending and torsional moments. Aquatic walking limbs have little axial loading, while swimming appendages and wings experience only bending and torsional moments, and can exploit these to assist in the deformations that are necessary to gain force asymmetry between half-strokes. Swimming appendages normally employ both muscles and drag, but the wings of insects lack internal muscles, and their changes in shape are largely complex aeroelastic responses to the constantly changing aerodynamic and inertial loads, moderated by muscles inserted at the base. For illustration, wings modelled as thin shells with flexible hinge-lines are used to investigate how transverse distal flexion, essential for controlling the angle of attack in the upstroke, is remotely controlled by the indirect flight muscles.
Resonators in insect sound production: how insects produce loud pure-tone songs
Authors: Bennet-Clark H. C.
Published: April 2021

In a resonant vibration, two reactive elements, such as a mass and a spring, interact: the resonant frequency depends on the magnitude of these two elements. The build-up and decay of the vibration depend on the way the resonator is driven and on the damping in the system.

The evidence for the existence of resonators in insect sound production is assessed. The mechanics of different types of sound-producing system found in insects is described. Mechanical frequency-multiplier mechanisms, which convert the relatively slow contraction of muscles to the higher frequency of the sound, are commonly used to convert the comparatively slow muscle contraction rate to the higher frequency of the sound. The phasing and rate of mechanical excitation may also affect the frequency and duration of the sound that is produced.

Although in many insects the song may appear to be produced by the excitation of a simple resonator, the song frequency may not be constant, suggesting that other factors, such as the mechanism of excitation, or variation of the effective mass or elasticity of the system during sound production, may be additional determinants of the song frequency.

Loud, and hence efficient, transduction of the energy of a mechanical resonator into sound may involve a second stage of transduction which, by damping the resonator, may compromise tonal purity. Some insect singers resolve this problem by tuning both stages of transduction to the same frequency, thereby maintaining tonal purity.
Scaling of echolocation call parameters in bats
Authors: Jones Gareth
Published: April 2021

I investigated the scaling of echolocation call parameters (frequency, duration and repetition rate) in bats in a functional context. Low-duty-cycle bats operate with search phase cycles of usually less than 20 %. They process echoes in the time domain and are therefore intolerant of pulse–echo overlap. High-duty-cycle (>30 %) species use Doppler shift compensation, and they separate pulse and echo in the frequency domain. Call frequency scales negatively with body mass in at least five bat families. Pulse duration scales positively with mass in low-duty-cycle quasi-constant-frequency (QCF) species because the large aerial-hawking species that emit these signals fly fast in open habitats. They therefore detect distant targets and experience pulse–echo overlap later than do smaller bats. Pulse duration also scales positively with mass in the Hipposideridae, which show at least partial Doppler shift compensation. Pulse repetition rate corresponds closely with wingbeat frequency in QCF bat species that fly relatively slowly. Larger, fast-flying species often skip pulses when detecting distant targets. There is probably a trade-off between call intensity and repetition rate because ‘whispering’ bats (and hipposiderids) produce several calls per predicted wingbeat and because batches of calls are emitted per wingbeat during terminal buzzes. Severe atmospheric attenuation at high frequencies limits the range of high-frequency calls. Low-duty-cycle bats that call at high frequencies must therefore use short pulses to avoid pulse–echo overlap. Rhinolophids escape this constraint by Doppler shift compensation and, importantly, can exploit advantages associated with the emission of both high-frequency and long-duration calls. Low frequencies are unsuited for the detection of small prey, and low repetition rates may limit prey detection rates. Echolocation parameters may therefore constrain maximum body size in aerial-hawking bats.
How muscles deal with real-world loads: the influence of length trajectory on muscle performance
Authors: Marsh Richard L.
Published: April 2021

The performance of skeletal muscles in vivo is determined by the feedback received when the muscle interacts with the external environment via various morphological structures. This interaction between the muscle and the ‘real-world load’ forces us to reconsider how muscles are adapted to suit their in vivo function. We must consider the co-evolution of the muscles and the morphological structures that ‘create’ the load in concert with the properties of the external environment. This complex set of interactions may limit muscle performance acutely and may also constrain the evolution of morphology and physiology.

The performance of skeletal muscle is determined by the length trajectory during movement and the pattern of stimulation. Important features of the length trajectory include its amplitude, frequency, starting length and shape (velocity profile). Many of these parameters interact. For example, changing the velocity profile during shortening may change the optimum values of the other parameters.

The length trajectory that maximizes performance depends on the task to be performed. During cyclical work, muscles benefit from using asymmetric cycles with longer shortening than lengthening phases. Modifying this ‘sawtooth’ cycle by increasing the velocity during shortening may further increase power by augmenting force output and speeding deactivation. In contrast, when accelerating an inertial load, as in jumping, the predicted ‘optimal’ velocity profile has two peak values, one early and one late in shortening.

During level running at constant speed, muscles perform tasks other than producing work and power. Producing force to support the body weight is performed with nearly isometric contractions in some of the limb muscles of vertebrates. Muscles also play a key role in producing stability during running, and the intrinsic properties of the musculoskeletal system may be particularly important in stabilizing rapid running. Recently, muscles in running invertebrates and vertebrates have been described that routinely absorb large amounts of work during running. These muscles are hypothesized to play a key role in stability.
Fish swimming: patterns in muscle function
Authors: Altringham John D. , Ellerby David J.
Published: April 2021

Undulatory swimming in fish is powered by the segmental body musculature of the myotomes. Power generated by this muscle and the interactions between the fish and the water generate a backward-travelling wave of lateral displacement of the body and caudal fin. The body and tail push against the water, generating forward thrust. The muscle activation and strain patterns that underlie body bending and thrust generation have been described for a number of species and show considerable variation. This suggests that muscle function may also vary among species. This variation must be due in large part to the complex interactions between muscle mechanical properties, fish body form, swimming mode, swimming speed and phylogenetic relationships. Recent work in several laboratories has been directed at studying patterns of muscle power output in vitro under simulated swimming conditions. This work suggests that the way that fish generate muscle power and convert it into thrust through the body and caudal fin does indeed vary. However, despite the differences, several features appear to be common to virtually all species studied and suggest where future effort should be directed if muscle function in swimming fish is to be better understood.
A mechanical analysis of myomere shape in fish
Authors: Leeuwen Johan L. Van
Published: April 2021

An architectural analysis is offered of the trunk muscles in fish, which are arranged in a longitudinal series of geometrically complex myomeres. The myomeres are separated by myosepta, collagenous sheets with complex fibre patterns. The muscle fibres in the myomeres are also arranged in complex three-dimensional patterns. Previously, it has been proposed that the muscle fibre arrangement allows for a uniform strain distribution within the muscle. Physical constraints limit the range of shapes that fibre-reinforced materials such as muscles can adopt, irrespective of their genetic profile. The three-dimensional shapes of myosepta are predicted by mechanical modelling from the requirements for mechanical stability and prescribed muscle fibre arrangements. The model can also be used to study the force transmission and likely locations of ligaments and bones in the myosepta. The model shows that the dorsal and ventral fins are located such that unfavourable mechanical interactions with the trunk muscles are avoided. In bony fish, extensive muscular deformations (notably in the region of the horizontal septum) that would not contribute to bending are avoided by the mechanical support of the skin, intramuscular bones and ribs. In sharks, the skin plays a more prominent role in avoiding such deformations because of the absence of bony elements.
Aquatic vertebrate locomotion: wakes from body waves
Authors: Videler J. J. , Müller U. K. , Stamhuis E. J.
Published: April 2021

Vertebrates swimming with undulations of the body and tail have inflection points where the curvature of the body changes from concave to convex or vice versa. These inflection points travel down the body at the speed of the running wave of bending. In movements with increasing amplitudes, the body rotates around the inflection points, inducing semicircular flows in the adjacent water on both sides of the body that together form proto-vortices. Like the inflection points, the proto-vortices travel towards the end of the tail. In the experiments described here, the phase relationship between the tailbeat cycle and the inflection point cycle can be used as a first approximation of the phase between the proto-vortex and the tailbeat cycle. Proto-vortices are shed at the tail as body vortices at roughly the same time as the inflection points reach the tail tip. Thus, the phase between proto-vortex shedding and tailbeat cycle determines the interaction between body and tail vortices, which are shed when the tail changes direction. The shape of the body wave is under the control of the fish and determines the position of vortex shedding relative to the mean path of motion. This, in turn, determines whether and how the body vortex interacts with the tail vortex. The shape of the wake and the contribution of the body to thrust depend on this interaction between body vortex and tail vortex. So far, we have been able to describe two types of wake. One has two vortices per tailbeat where each vortex consists of a tail vortex enhanced by a body vortex. A second, more variable, type of wake has four vortices per tailbeat: two tail vortices and two body vortices shed from the tail tip while it is moving from one extreme position to the next. The function of the second type is still enigmatic.
The novel aerodynamics of insect flight: applications to micro-air vehicles
Authors: Ellington C. P.
Published: April 2021

The wing motion in free flight has been described for insects ranging from 1 to 100 mm in wingspan. To support the body weight, the wings typically produce 2–3 times more lift than can be accounted for by conventional aerodynamics. Some insects use the fling mechanism: the wings are clapped together and then flung open before the start of the downstroke, creating a lift-enhancing vortex around each wing. Most insects, however, rely on a leading-edge vortex (LEV) created by dynamic stall during flapping; a strong spanwise flow is also generated by the pressure gradients on the flapping wing, causing the LEV to spiral out to the wingtip. Technical applications of the fling are limited by the mechanical damage that accompanies repeated clapping of the wings, but the spiral LEV can be used to augment the lift production of propellers, rotors and micro-air vehicles (MAVs). Design characteristics of insect-based flying machines are presented, along with estimates of the mass supported, the mechanical power requirement and maximum flight speeds over a wide range of sizes and frequencies. To support a given mass, larger machines need less power, but smaller ones operating at higher frequencies will reach faster speeds.
Estimating power curves of flying vertebrates
Authors: Rayner Jeremy M. V.
Published: April 2021

The power required for flight in any flying animal is a function of flight speed. The power curve that describes this function has become an icon of studies of flight mechanics and physiology because it encapsulates the accessible animal’s flight performance. The mechanical or aerodynamic power curve, describing the increase in kinetic energy of the air due to the passage of the bird, is necessarily U-shaped, for aerodynamic reasons, and can be estimated adequately by lifting-line theory. Predictions from this and related models agree well with measured mechanical work in flight and with results from flow visualization experiments. The total or metabolic power curve also includes energy released by the animal as heat, and is more variable in shape. These curves may be J-shaped for smaller birds and bats, but are difficult to predict theoretically owing to uncertainty about internal physiological processes and the efficiency of the flight muscles. The limitations of some existing models aiming to predict metabolic power curves are considered. The metabolic power curve can be measured for birds or bats flying in wind tunnels at controlled speeds. Simultaneous determination in European starlings Sturnus vulgaris of oxygen uptake, total metabolic rate (using labelled isotopes), aerodynamic power output and heat released (using digital video thermography) enable power curves to be determined with confidence; flight muscle efficiency is surprisingly low (averaging 15–18 %) and increases moderately with flight speed, so that the metabolic power curve is shallower than predicted by models. Accurate knowledge of the power curve is essential since extensive predictions of flight behaviour have been based upon it. The hypothesis that the power curve may not in fact exist, in the sense that the cost of flight may not be perceived by a bird as a continuous smooth function of air speed, is advanced but has not yet formally been tested. This hypothesis is considered together with evidence from variation in flight behaviour, wingbeat kinematics and flight gait with speed. Possible constraints on flight behaviour can be modelled by the power curves: these include the effect of a maximum power output and a constraint on maximum speed determined by downstroke wingbeat geometry and the relationship between thrust and lift.
Dominance hierarchy formation in juvenile crayfish procambarus clarkii
Authors: Issa Fadi A. , Adamson Daniel J. , Edwards Donald H.
Published: April 2021

The formation of social dominance hierarchies was studied in groups of five juvenile crayfish, 1.3–1.8 cm in length. Animals were grouped together in a small, featureless aquarium after having lived in isolation for more than a month. The occurrence of each of four behavior patterns (‘attack’, ‘approach’, ‘retreat’ and ‘escape’) was recorded for each animal, together with the frequency of encounters and the frequency of wins and losses. The frequencies of wins and losses were used to calculate the relative dominance value of each animal in the group. High levels of fighting developed immediately upon grouping the animals, and a positive feedback relationship between attacking and winning enabled one animal in each group to emerge quickly as the superdominant. If that animal was the largest, it remained as the superdominant; otherwise, it was replaced as superdominant within the first few days by the largest animal. This form of dominance hierarchy, with one superdominant and four subordinates, persisted throughout the duration of the grouping. Fighting declined over the first hour and by 24 h had dropped to low levels. After the first day, approaches were used together with attacks, and retreats replaced escapes. Attack and approach were the behavior patterns displayed most frequently by animals with high dominance values, whereas retreat and escape were performed by animals of low dominance. All these trends continued to develop over the next 2 weeks as the number of agonistic encounters declined to a low level.
Coherent light scattering by nanostructured collagen arrays in the caruncles of the malagasy asities (Eurylaimidae: aves)
Authors: Prum Richard O. , Torres Rodolfo , Kovach Christopher , Williamson Scott , Goodman Steven M.
Published: April 2021

We investigated the anatomy, nanostructure and biophysics of the structurally coloured facial caruncles of three species in a clade of birds endemic to Madagascar (Philepittinae, Eurylaimidae: Aves). Caruncle tissues of all species had reflectance spectra with prominent, peak hues between 403 and 528 nm. Dark blue Neodrepanis tissues had substantial reflectance in the near ultraviolet (320–400 nm), which is visible to birds but not to humans, providing the first evidence of ultraviolet skin colours in birds and the first indications of the possible function of ultraviolet skin colours in avian communication. These structural colours are produced by coherent scattering from arrays of parallel collagen fibres in the dermis. Tissues of Philepitta castanea were organized into hexagonal, crystal-like arrays, whereas Neodrepanis tissues were quasiordered. Predictions of the peak hues of reflectance (λmax) using Bragg’s law were relatively accurate, but Bragg’s law requires physical assumptions that are obviously violated by these structures. A two-dimensional discrete Fourier analysis of the spatial variation in refractive index within the tissues documented that all the tissues are substantially nanostructured at the appropriate spatial scale to scatter visible light coherently. Predicted reflectance spectra based on the two-dimensional Fourier power spectra are relatively accurate at predicting the hue and shape of the reflectance spectra of the tissues. These results confirm that the nanostructure of the collagen arrays determines the colours that are coherently scattered by these tissues. The evolution of the anatomy and nanostructure of asity caruncles is discussed.
Timing of elevator muscle activity during climbing in free locust flight
Authors: Fischer Hanno , Kutsch Wolfram
Published: April 2021

Despite detailed knowledge of the sensory–motor interactions during elevator muscle timing for the generation of a ‘functional’ flight motor pattern in flying locusts, there is little information about how a possible shift in the onset of elevator activity is correlated with changes in flight variables under closed-loop conditions (i.e. during free flight). Free-flight variables were investigated with respect to ascent angle during climbing flight in locusts Schistocerca gregaria. The motor pattern during free flight was examined by telemetric electromyography of particular antagonistic flight muscles in both ipsilateral hemisegments of the pterothorax while flight variables were recorded simultaneously on video. In the majority of the animals tested, the onset of elevator muscle activity within the wingbeat cycle is delayed when animals increase their ascent angle during climbing flight. In accordance with the motor pattern, the downstroke phase and the stroke amplitude of the wings increased with increasing the ascent angle. This suggests that the relative elevator timing during the wingbeat cycle may be related to the generation of the additional aerodynamic lift required for ascending flight and may, therefore, play a role in the regulation of ascent angle during free flight in the locust.
Comparative study on the metabolic responses of subterranean and surface-dwelling amphipods to long-term starvation and subsequent refeeding
Authors: Hervant Frédéric , Mathieu Jacques , Barré Hervé
Published: April 2021

The effects of long-term starvation and subsequent refeeding on intermediary and energy metabolism were investigated in two subterranean aquatic crustaceans, Niphargus rhenorhodanensis and Niphargus virei, and in a morphologically similar surface-dwelling species, Gammarus fossarum. The metabolic response to prolonged food deprivation was monophasic in G. fossarum, showing an immediate, linear and large decline in all of the energy reserves. In contrast, both subterranean organisms displayed successive periods of glucidic, proteo-glucidic then lipidic-dominant catabolism during food deprivation. In both subterranean species, lipids (51 % of the energy consumed during a 180-day starvation period) and proteins (44 %) were the most metabolized substrates in terms of total energy, whereas glycogen (5 %) contributed little energy. G. fossarum displayed a different energetic strategy: proteins comprised 56 % of the energy losses during a 28-day starvation period, total lipids some 39 % and glycogen reserves only 5 %. We propose an energy strategy for food-limited subterranean crustaceans involving the possession of (1) higher amounts of stored arginine phosphate, triglycerides and glycogen and (2) lower utilization rates of stored metabolites than G. fossarum and numerous other surface-dwelling crustaceans, making the fueling of food deprivation possible for a longer time. In addition, these species had a faster and more efficient assimilation of available nutrients during recovery from food deprivation, enabling preparation for a new nutritional stress. These specific adaptive responses might be considered, for N. virei and N. rhenorhodanensis, as an efficient energy-saving strategy for an environment where extended starvation periods alternate with sporadic feeding events, therefore improving their competitive advantages.
Trimethylamine oxide stabilizes teleost and mammalian lactate dehydrogenases against inactivation by hydrostatic pressure and trypsinolysis
Authors: Yancey Paul H. , Siebenaller Joseph F.
Published: April 2021

Trimethylamine N-oxide (TMAO) is an organic osmolyte present at high levels in elasmobranchs, in which it counteracts the deleterious effects of urea on proteins, and is also accumulated by deep-living invertebrates and teleost fishes. To test the hypothesis that TMAO may compensate for the adverse effects of elevated pressure on protein structure in deep-sea species, we studied the efficacy of TMAO in preventing denaturation and enhanced proteolysis by hydrostatic pressure. TMAO was compared to a common ‘compatible’ osmolyte, glycine, using muscle-type lactate dehydrogenase (A4-LDH) homologs from three scorpaenid teleost fish species and from a mammal, the cow. Test conditions lasted 1 h and were: (1) no addition, (2) 250 mmol l−1 TMAO and (3) 250 mmol l−1 glycine, in the absence and presence of trypsin. Comparisons were made at 0.1 and 101.3 MPa for the deeper occurring Sebastolobus altivelis, 0.1, 50.7 and 101.3 MPa for the moderate-depth congener S. alascanus, 0.1 and 25.3 MPa for shallow-living Sebastes melanops and 0.1 and 50.7 MPa for Bos taurus. Susceptibility to denaturation was determined by the residual LDH activity. For all the species and pressures tested, 250 mmol l−1 TMAO reduced trypsinolysis significantly. For all except S. altivelis, which was minimally affected by 101.3 MPa pressure, TMAO stabilized the LDH homologs and reduced pressure denaturation significantly. Glycine, in contrast, showed no ability to reduce pressure denaturation alone, and little or no ability to reduce the rate of proteolysis.
Antarctic fishes have a limited capacity for catecholamine synthesis
Authors: Whiteley N. M. , Egginton S.
Published: April 2021

To determine whether an attenuated stress response is a general feature of Antarctic fish or is dependent on ecotype, the capacity for catecholamine synthesis within the head kidney and plasma levels of the primary stress hormones (catecholamines and cortisol) were determined in species with a range of activity patterns. Tyrosine hydroxylase (TH) activities were similar in both sluggish (Gobionotothen gibberifons, 153±22 nmol g−1 h−1, mean ± S.E.M.) and active (Notothenia rossii, 185±39 nmol g−1 h−1, Dissostichus mawsoni, 128±31 nmol g−1 h−1 ) pelagic nototheniids, but only 30 % of those in Atlantic cod (Gadus morhua, 393±88 nmol g−1 h−1 ) at the same temperature. TH activities were even lower in white-blooded channichthyids (Chaenocephalus aceratus, 74±16 nmol g−1 h−1 and Champsocephalus gunnari, 53±17 nmol g−1 h−1 ), although values in Chionodraco rastrospinosus were similar to red-blooded species (178±45 nmol g−1 h−1 ). Circulating catecholamine levels were extremely high in all species after fishing stress, with adrenaline levels 3–4 times higher than noradrenaline levels. Cortisol levels remained low, ranging from 1.33±0.58 ng ml−1 in Champsocephalus gunnari to 44.9±25.0 ng ml−1 in Dissostichus mawsoni. These data suggest that depressed catecholamine synthesis is typical of Antarctic fish regardless of life style, although they are able to release extensive stores from the chromaffin tissue under conditions of extreme trauma. Cortisol does not appear to be an important primary stress hormone in these species.
Daphnia pulex swims towards the most strongly polarized light – a response that leads to ‘shore flight’
Authors: Schwind Rudolf
Published: April 2021

When Daphnia pulex are presented on one side of their visual field with diffuse, large-area linearly polarized light with a horizontal e-vector and on the other side of their visual field with large-area polarized light with a lower degree of polarization, they swim towards the place with the higher degree of polarization. The response is intensity-invariant: Daphnia pulex swim towards the place of maximal polarization regardless of which side of their visual field has the higher intensity of light. As a result of Rayleigh scattering in a pond, the light surrounding the Daphnia is polarized and has a horizontal e-vector. Near the shore, polarization is not homogeneous. The light seen in the direction of the open water has a higher degree of polarization than that seen in the direction towards the shore. Therefore, in a pond, swimming towards the place with the highest degree of polarization leads the Daphnia away from the shore. For Daphnia, this response explains a mechanism that underlies the well-known phenomenon of ‘shore flight’, the active departure of small pelagic crustaceans from shore zones.
Hypoxia accelerates the development of respiratory regulation in brine shrimp – but at a cost
Authors: Spicer J. I. , El-Gamal M. M.
Published: April 2021

The ability to regulate O2 uptake during exposure to acutely declining O2 tensions developed early (stage 6) in the brine shrimp Artemia franciscana and co-occurred with the appearance of a functional heart and gills. Culture under chronic hypoxia resulted in this regulation being brought forward both in development (to stage 3) and in time (hypoxia stimulated early growth), but still before heart and gill formation took place. Consequently, it was suggested that the hypoxia-related early appearance of respiratory regulation is most probably linked to an increase in haemoglobin concentration that occurred at this time. Brine shrimp cultured under conditions of intermittent hypoxia exposure (16 h of normoxia, 8 h of hypoxia) showed a pattern of regulation development intermediate between that of individuals reared in normoxic and chronically hypoxic culture. This occurrence of hypoxia-related, physiological ‘heterochrony’ in brine shrimp resulted in a decrease in Darwinian fitness (as indicated by a decrease in individual lifetime reproductive output), indicating that, in some cases at least, relatively small alterations in the expression of physiological traits may well have major ecological, and ultimately evolutionary, consequences.
Cardiorespiratory responses of the toad (Bufo marinus) to hypoxia at two different temperatures
Authors: Gamperl A. K. , Milsom W. K. , Farrell A. P. , Wang T.
Published: April 2021

Central vascular blood flows and ventilation were measured in conscious toads (Bufo marinus) at 15 and 25 °C. The animals were exposed to hypoxia ( and 0.05, where is the fractional oxygen concentration of inspired air) at both temperatures. In addition, the cardiorespiratory responses to hypercapnia and atropine injection (5mgkg−1; 7.4 μmol kg−1) were studied at 25 °C. At 25 °C, systemic blood flow (Q̇sys) exceeded pulmocutaneous blood flow (Q̇pc), indicating a large net right-to-left shunt (Q̇pc/Q̇sys was 0.39). Q̇pc/Q̇sys was reduced significantly to 0.22 at 15 °C. At both temperatures, Q̇pc increased significantly during hypoxia (from 26.2 to 50.8ml min−1 kg−1 at 25 °C and from 11.2 to 18.9 ml min−1 kg−1 at 15 °C), whereas Q̇sys changed little (from 77.2 to 66.2ml min−1 kg−1 at 25 °C and from 54.3 to 50.1 ml min−1 kg−1 at 15 °C). As a result, the net right-to-left shunt was greatly reduced, while total cardiac output remained almost unaffected. The ventilatory response was more pronounced during hypercapnia but, since Q̇pc and Q̇sys were affected similarly, there was no change in the shunt pattern. In undisturbed toads at 25 °C, atropine injection increased Q̇pc and eliminated the net right-to-left shunt. This is consistent with the known vagal innervation of the pulmonary artery.

The present study shows that the cardiac right-to-left shunt that prevails in undisturbed and resting toads is reduced with increased temperature and during hypoxia. These findings are consistent with the general view that the cardiac right-to-left shunt is regulated and reduced whenever oxygen delivery is compromised or metabolic rate is increased.