bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound production by abdominal tymbal organs in two moth species: the green silver-line and the scarce silver-line (Noctuoidea: Nolidae: Chloephorinae)
Authors: Skals Niels , Surlykke Annemarie
Published: April 2021

Male moths of the chloephorine species Pseudoips prasinana and Bena bicolorana produce clicks (approximately 100 dB peSPL at 10 cm) using ventral tymbal organs located in a cleft in the second abdominal sternite. Large muscles insert on the dorsal part of the tymbal frame and rhythmically flex a thin sheet of cuticle. Normally, each sound-production cycle contains four clicks, the left and right tymbals producing clicks both on active buckling caused by muscle contraction and on the passive elastic return from buckling. Histochemical staining indicated the presence of elastic resilin-like proteins in the tymbals. Obvious differences between the click patterns of the two species reflect differences in their tymbal morphology. P. prasinana has smooth tymbals and produces a single click (300 μs, 40 kHz) for each tymbal buckling. In contrast, B. bicolorana has striae on the medial part of the tymbals. Accordingly, it produces many clicks per buckling. The click pattern is a heterogeneous mixture of large clicks at 52 kHz, resembling those of P. prasinana, interspersed with series of broad-band clicks (20–100 kHz) of lower intensity (15–20 dB). Thus, in chloephorine moths, there is a correlation between the structure and function of the smooth and striated tymbals that is strikingly similar to that in arctiid moths, although the two types of tymbals have evolved independently. The hearing of P. prasinana is tuned to its own sounds with lowest threshold (38 dB SPL) at 40–60 kHz. We suggest that sound production in male chloephorines plays a part in sexual acoustic communication.
Colour vision of domestic chicks
Authors: Osorio D. , Vorobyev M. , Jones C. D.
Published: April 2021

The colour vision of domestic chicks (Gallus gallus) was investigated by training them to small food containers decorated with tilings of grey and coloured rectangles. Chicks learn to recognise the colour quickly and accurately. Chicks have four types of single-cone photoreceptor sensitive to ultraviolet, short-, medium- or long-wavelength light. To establish how these receptors are used for colour vision, stimuli were designed to be distinguished only by specific combinations of receptors. We infer (1) that all four single cones are used, and (2) that their outputs are encoded by at least three opponency mechanisms: one comparing the outputs of ultraviolet- and short-wavelength-sensitive receptors, one comparing the outputs of medium- and long-wavelength receptors and a third comparing of the outputs of short- and long- and/or medium-wavelength receptors. Thus, the chicks have tetrachromatic colour vision. These experiments do not exclude a role for the fifth cone type, double cones, but other evidence suggests that these cones serve luminance-based tasks, such as motion detection, and not colour recognition.
Processing of proprioceptive signals by ascending interneurones in the terminal abdominal ganglion of the crayfish
Authors: Aonuma Hitoshi , Newland Philip L. , Nagayama Toshiki
Published: April 2021

Intersegmental interneurones are crucial for the appropriate coordination of the activity of local circuits located in different body segments. We have analysed the synaptic inputs to ascending intersegmental interneurones from a proprioceptor in the tailfan of the crayfish. Twenty identified interneurones responded during stimulation of the exopodite–endopodite chordotonal organ. Of these 20 interneurones, three were excited phaso-tonically, nine were excited phasically and eight were inhibited. All received convergent exteroceptive inputs from water-motion- or touch-sensitive hairs on the uropods. The effects of simultaneous exteroceptive and proprioceptive stimulation depended upon the identity of an interneurone. For interneurones that were inhibited by proprioceptive stimulation, suprathreshold exteroceptive responses were reduced to a subthreshold level by simultaneous proprioceptive stimulation. In contrast, for interneurones that were excited by proprioceptive stimulation, the simultaneous application of subthreshold proprioceptive and exteroceptive stimulation elicited action potentials.

Two of the interneurones that receive proprioceptive input (NE-1 and RC-8) are known to be presynaptic to giant interneurones that mediate and coordinate the tail-flip. Many of the other interneurones that receive proprioceptive inputs in the tailfan are known to excite abdominal extensor motor neurones. Thus, proprioceptive input to these intersegmental interneurones could serve two roles: first, to extend the abdomen during postural movements or prior to escape and, second, to drive the tail-flip escape response.
Placental nutrition in the viviparous lizard Niveoscincus metallicus: the influence of placental type
Authors: Thompson Michael B. , Speake Brian K. , Stewart James R. , Russell Kylie J. , McCartney Ruth J. , Surai Peter F.
Published: April 2021

The ion, energy, lipid, nitrogen and fat-soluble vitamin contents of freshly ovulated eggs and neonates of the viviparous lizard Niveoscincus metallicus were measured to quantify uptake of nutrients across the placenta. This species is particularly interesting because it has a chorio–allantoic placenta that is intermediate in complexity compared to viviparous species that have been the focus of other studies. Newly ovulated eggs have a wet mass of 79.6±4.6 mg and a dry mass of 41.8±2.8 mg, compared to the neonates that have a wet mass of 224.2±8.2 mg and dry mass of 37.9±1.2 mg. Thus, there is no significant net uptake of dry matter across the placenta. Neonates have significantly less lipid (6.2±0.4 mg) than eggs (12.7±0.5 mg), but no significant difference in nitrogen (4.1±0.3 mg) compared to eggs (4.5±0.2 mg). Energy densities reflect the protein and lipid composition and the relative dry masses of the eggs and neonates. There is significantly more energy (1029.1±80.0 J) in the egg than in the neonate (858.2±38.6 J). The increase in the ash content of the neonates (2.9±0.2 mg) compared to fresh eggs (2.1±0.3 mg) was not significant, even though there was an approximately threefold increase in the amount of sodium (0.11±0.01 mg in neonates, 0.34±0.01 mg in eggs) and potassium (0.12±0.017 in neonates, 0.40±0.01 mg in eggs) in neonates compared to eggs. There was no significant uptake of calcium and magnesium during development. The egg lipids consisted of triacylglycerol (66.7±2.3 %), phospholipid (18.9±0.7 %), cholesteryl ester (4.9±1.6 %) and free cholesterol (5.6±1.5 %). The egg phospholipid contained comparatively high proportions of arachidonic and eicosapentanoic acids but low levels of docosahexaenoic acid (DHA), whereas the phospholipid of the neonate was greatly enriched in DHA. In the egg, the predominant vitamin E was α-tocopherol (62.6±3.4 mg g−1), although there was some γ-tocotrienol (3.5±0.3 mg g −1), and vitamin A was present (1.5±0.2 mg g−1). The ratio of neonate dry mass to egg dry mass of N. metallicus (0.91) lies between that of species with type I (0.78) and type III (1.70) chorio–allantoic placentae, confirming our conclusion that the placenta of N. metallicus is functionally intermediate, as well as intermediate in complexity, between these other two types.
Effects of zinc on L-[3H]proline uptake by lobster (Homarus americanus) hepatopancreatic brush-border membrane vesicles
Authors: Monteilh-Zoller Mahealani K. , Zonno Vincenzo , Storelli Carlo , Ahearn Gregory A.
Published: April 2021

Epithelial brush-border membrane vesicles (BBMVs) from the hepatopancreas of the lobster Homarus americanus were prepared using a magnesium precipitation technique and employed in transport experiments designed to demonstrate the effects of external and internal divalent cationic heavy metals on the uptake of L-[3H]proline. When BBMVs were exposed to a high external concentration (2.5 mmol l−1) of Cd2+, Cu2+, Fe2+, Mn2+ or Zn2+, L-[3H]proline (0.5 mmol l−1) uptake was significantly (P<0.05) decreased by each metal. However, if a 30 min pre-incubation period with each metal was used before incubation of the vesicles with amino acid and metal, a significant (P<0.05) enhancement of L-[3H]proline transport occurred. Zinc was the most stimulatory metal of those tested. Proline influxes (1.0 and 2.5 mmol l−1) were hyperbolic functions of bilateral [Zn2+], with a lower apparent zinc half-saturation constant (Km) at the higher amino acid concentration. L-[3H]proline influx was a hyperbolic function of external [L-proline] (Km=2.10±0.26 mmol l−1; Jmax=2290±600 pmol mg−1 protein 10 s−1) (means ± S.E.M., N=3), and bilateral exposure to zinc significantly (P<0.05) increased the maximal rate of influx, Jmax, of proline (Jmax=4890±250 pmol mg−1 protein 10 s−1), but had no effect (P>0.05) on apparent L-[3H]proline binding to the membranes (Km=1.66±0.23 mmol l−1) (means ± S.E.M., N=3). In the presence of 0.5 mmol l−1 l-pipecolate, bilateral zinc-stimulated, carrier-mediated, L-[3H]proline influx was abolished. At low external concentrations of zinc alone (e.g. below 1.0 mmol l−1), L-[3H]proline influx was enhanced by the metal. Enhanced amino acid uptake in the presence of external zinc alone was abolished by L-pipecolate. A model accounting for external and internal zinc enhancements of L-[3H]proline influx by the Na+-dependent L-pipecolate-sensitive IMINO transport system in these membranes is proposed.
The supramolecular organisation of fibrillin-rich microfibrils determines the mechanical properties of bovine zonular filaments
Authors: Wright D. M. , Duance V. C. , Wess T. J. , Kielty C. M. , Purslow P. P.
Published: April 2021

The zonular filaments from the eyes of cows are rich in microfibrils containing fibrillin. Tensile tests, stress-relaxation tests and X-ray diffraction studies were used to study the relationship between the mechanical behaviour of zonular filaments and the molecular packing and structure of the fibrillin-rich microfibrils. Zonular filaments show a non-linear (J-shaped) stress–strain curve and appreciable stress-relaxation. It is proposed that the non-linear properties are due to local variations in waviness in the microfibrils or assemblies of microfibrils, which straighten out and become more regularly aligned with strain. Previous and current X-ray diffraction results consistently show a partial ordering of microfibrils in zonular filaments into staggered aggregates which become more ordered and laterally aligned on stretching. Although the removal and re-addition of Ca2+ is known to change the molecular structure of fibrillin, no effect was observed on the tensile properties of the zonular filaments. It is hypothesised that strain-induced deformation in the supramolecular aggregate packing may not be Ca2+-sensitive but could dominate the mechanical behaviour of microfibrillar arrays in zonular filaments.
The hormonal coordination of behavior and physiology at adult ecdysis in Drosophila melanogaster
Authors: Baker James D. , McNabb Susan L. , Truman James W.
Published: April 2021

In insects, ecdysis is thought to be controlled by the interaction between peptide hormones; in particular between ecdysis-triggering hormone (ETH) from the periphery and eclosion hormone (EH) and crustacean cardioactive peptide (CCAP) from the central nervous system. We examined the behavioral and physiological functions of the first two of these peptides in Drosophila melanogaster using wild-type flies and knockout flies that lacked EH neurons. We used ETH from Manduca sexta (MasETH) to induce premature ecdysis and compared the responses of the two types of flies.

The final release of EH normally occurs approximately 40 min before ecdysis. It is correlated with cyclic guanosine monophosphate (cGMP) production in selected neurons and tracheae, by an elevation in the heart rate and by the filling of the new tracheae with air. Injection of developing flies with MasETH causes all these events to occur prematurely. In EH cell knockouts, none of these changes occurs in response to MasETH, and these flies show a permanent failure in tracheal filling. This failure can be overcome in the knockouts by injecting them with membrane-permeant analogs of cGMP, the second messenger for EH.

The basis for the 40 min delay between EH release and the onset of ecdysis was examined by decapitating flies at various times relative to EH release. In flies that had already released EH, decapitation was always followed within 1 min by the start of ecdysis. Immediate ecdysis was never observed when the EH cell knockout flies were decapitated. We propose that EH activates both ventral central nervous system elements necessary for ecdysis (possibly the CCAP cells) and descending inhibitory neurons from the head. This descending inhibition establishes a delay in the onset of ecdysis that allows the completion of EH-activated physiological processes such as tracheal filling. A waning in the inhibition eventually allows ecdysis to begin 30–40 min later.
Primitive organization of cytosolic Ca2+ signals in hepatocytes from the little skate Raja erinacea
Authors: Nathanson Michael H. , O’Neill Allison Fa. , Burgstahler Angela D.
Published: April 2021

Cytosolic Ca2+ (Cai2+) signals begin as polarized, inositol 1,4,5-trisphosphate (InsP3)-mediated Cai2+ waves in mammalian epithelia, and this signaling pattern directs secretion together with other cell functions. To investigate whether Cai2+ signaling is similarly organized in elasmobranch epithelia, we examined Cai2+ signaling patterns and InsP3 receptor (InsP3R) expression in hepatocytes isolated from the little skate, Raja erinacea. Cai2+ signaling was examined by confocal microscopy, InsP3R expression by immunoblot, and the subcellular distribution of InsP3Rs by immunochemistry. ATP induced a rapid increase in Cai2+ in skate hepatocytes, as it does in mammalian hepatocytes. Unlike in mammalian hepatocytes, however, the Cai2+ increase in skate hepatocytes began randomly throughout the cell rather than in the apical region. In cells loaded with heparin ATP-induced Cai2+ signals were inhibited, but de-N-sulfated heparin was not inhibitory, suggesting that the increases in Cai2+ were mediated by InsP3. Immunoblot analysis showed that the type I but not the types II or III InsP3R was expressed in skate liver. Confocal immunofluorescence revealed that the InsP3R was distributed throughout the hepatocyte, rather than concentrated apically as in mammalian epithelia. These findings demonstrate that ATP-induced Cai2+ signals are mediated by InsP3 in skate hepatocytes, as they are in mammalian hepatocytes. However, in skate hepatocytes Cai2+ signals begin at loci throughout the cell rather than as an organized apical-to-basal Cai2+ wave, which is probably because the InsP3R is distributed throughout these cells. This primitive organization of Cai2+ signaling may in part explain the observation that Ca2+-mediated events such as secretion occur much less efficiently in elasmobranchs than in mammals.
The effects of intensity on the energetics of brief locomotor activity
Authors: Baker Emily J. , Gleeson Todd T.
Published: April 2021

The energetic costs associated with locomotion are often estimated only from the energy expended during activity and do not include the costs incurred during recovery. For some types of locomotion, this method overlooks important aspects of the metabolic costs incurred as a result of the activity. These estimates for energetic cost have also been predicted from long-duration, low-intensity activities that do not necessarily reflect all the behavior patterns utilized by animals in nature. We have investigated the effects of different activity intensities on the metabolic expenditure (per unit distance traveled) associated with brief exercise, and offer a more inclusive analysis of how the energetics of short-duration activities might be analyzed to estimate the costs to the animal. Mice ran on a treadmill for 15 or 60 s at 25 %, 50 % or 100 % of maximum aerobic speed (MAS) while enclosed in an open-flow respirometry system. Following the run, each mouse was allowed to recover while remaining enclosed in the respirometry chamber. Excess exercise oxygen consumption (EEOC), the excess volume of oxygen consumed during the exercise period, increased with the duration and increased linearly with the intensity of exercise. In contrast, the volume of oxygen consumed during the recovery period, or excess post-exercise oxygen consumption (EPOC), was independent of exercise intensity and duration and accounted for more than 90 % of the total metabolic cost. The net cost of activity (Cact), calculated by summing EEOC and EPOC and then dividing by the distance run, increased as both activity duration and intensity decreased. The values for Cact ranged from 553 ml O2 g−1 km−1 for a 15 s run at 25 % MAS to 43 ml O2 g−1 km−1 for a 60 s run at 100 % MAS. Combining these data with data from a companion paper, we conclude (1) that EPOC is independent of both the duration and intensity of activity when exercise duration is brief in mice, (2) that EPOC accounts for a majority of the oxygen consumed as a result of the activity when exercise durations are short, and (3) that animals can minimize their energy expenditure per unit distance by running faster for a longer period.
Precise monitoring of porpoising behaviour of Adelie penguins determined using acceleration data loggers
Authors: Yoda K. , Sato K. , Niizuma Y. , Kurita M. , Bost C.-A. , Maho Y. LE , Naito Y.
Published: April 2021

A new method using acceleration data loggers enabled us to measure the porpoising behaviour of Adélie penguins (Pygoscelis adeliae), defined as a continuous rapid swimming with rhythmic serial leaps. Previous hydrodynamic models suggested that leaping would be energetically cheaper when an animal swims continuously at depths of less than three maximum body diameters below the water surface. In the present study, free-ranging Adélie penguins leapt at a mean speed of 2.8 m s−1 above the predicted threshold speed (0.18–1.88 m s−1). Wild penguins reduced drag by swimming deeper (0.91 m) and did not swim continuously within the high-drag layer while submerged. This indicates that previous calculations may be incomplete. Moreover, leaps represented an average of only 3.8 % of the total distance travelled during the porpoising cycle, which would make energy savings marginal. Among the six penguins used in our study, two did not porpoise and three porpoised for less than 7 min, also indicating that this behaviour was not important during travel to and from foraging sites, as has been previously suggested. Birds mainly porpoised at the start and end of a trip. One explanation of porpoising might be an escape behaviour from predators.
Accommodation in the cuttlefish (Sepia officinalis)
Authors: Schaeffel Frank , Murphy Christopher J. , Howland Howard C.
Published: April 2021

We have studied natural accommodation in the eye of six specimens of cuttlefish (Sepia officinalis) as they were fed with fish and shrimp. Using infrared photoretinoscopy, we observed (1) that the resting refractive state of the cuttlefish was emmetropic or slightly hyperopic, (2) that accommodation took place only a fraction of a second before a strike and (3) that accommodation focused selectively only in the frontal visual field while no change in refraction could be measured in the lateral field of view. Accommodation was bilateral and amounted to approximately 5 diopters (the reciprocal of the focal length expressed in meters). Simultaneously, the eyes converged. It appears that, as in most teleost fishes, accommodation in the cuttlefish involves a movement of the crystalline lens perpendicular to the axis of the eye. In histological sections, we observed the position and arrangement of the ciliary muscles, confirming earlier anatomical descriptions, and developed a model of how accommodation could be achieved.
Flight-muscle adenylate pool responses to flight demands and thermal constraints in individual Colias eurytheme (Lepidoptera, pieridae)
Authors: Kohane Michael J. , Watt Ward B.
Published: April 2021

We study here the connections among body temperature variation, flight performance and flight ‘fuel’ metabolism in Colias eurytheme butterflies, to begin re-examining the metabolic reasons for animal thermoregulation. Methods are presented for (a) stable extraction of adenylates (and other metabolites) from the flight muscles of individual Colias eurytheme, (b) automated separation and quantitative analysis of individual adenylate samples by high-pressure liquid chromatography and (c) reliable, low-variance assay of inorganic phosphate levels in the same extracts. Correlations among metabolite concentrations and two indices of muscle cytosol ATP maintenance occur as expected on general metabolic principles. [ATP] and [ATP]/[ADP] decline from resting levels to reach a plateau in the first minute of free, interrupted flight, while [AMP] increases at the same time; these concentrations do not vary further for up to 6 min total flight time. In an initial test of the alternative metabolic bases of the thermoregulation of Colias eurytheme, we find that [ATP]/[ADP] rises between a body temperature, Tb, of 31 and 35 °C, at the base of the behavioral thermal optimum for flight, but then decreases again at Tb=39 °C, at the top of the behavioral thermal optimum and well short of damaging temperatures. This is not consistent with the view that metabolic effectiveness increases monotonically up to the lower limits of thermal damage to enzymes, but supports an alternative hypothesis that the narrowness of thermoregulation results from a system-based constraint on the breadth of temperature over which maximal energy processing is possible.

‘Data on the biochemistry of insect thermoregulation are extremely scanty.’

G. A. Bartholomew (1987)
Temperature-dependence of neuronal performance in the motion pathway of the blowfly calliphora erythrocephala
Authors: Warzecha Anne-Kathrin , Horstmann Wolfram , Egelhaaf Martin
Published: April 2021

Raising the head temperature within a behaviourally relevant range has strong effects on the performance of an identified neuron, the H1 neuron, in the visual motion pathway of blowflies. The effect is seen as an increase in the mean amplitude of the responses to motion under both transient and steady-state conditions, a considerable decrease in the response latency and an improvement in the reliability of the responses to motion. These temperature-dependent effects are independent of whether the animal is exposed to transient temperature changes or is maintained continuously at the same temperature for its entire life. The changes in the neuronal response properties with temperature may be of immediate functional significance for the animal under its normal operating conditions. In particular, the decrease in latency and the improvement in the reliability with increasing temperature may be relevant for the fly when executing its extremely virtuosic flight manoeuvres.
Phenotypic flexibility of the avian gizzard: rapid, reversible and repeated changes of organ size in response to changes in dietary fibre content
Authors: Starck J. Matthias
Published: April 2021

Evolutionary biology presumes that organ capacities match their natural loads. Therefore, in fluctuating conditions, organ systems are expected to show a reversible, repeatable and rapid phenotypic response that is directional and scaled. In this study, phenotypic responses of the gizzard of adult Japanese quail (Coturnix japonica) to experimental mismatches of load and capacity were tested by a series of diet-switching experiments, involving an increased content of non-digestable fibre (NDF) in the diet. The results of all experiments were in accordance with the predictions of the hypothesis that there is matching between loads and capacities. (1) The observed phenotypic responses are directional and scaled to the demands, i.e. increasing NDF elicits an increase in gizzard size. When the proportion of NDF in the diet was raised from 1 % to 45 %, the gizzard was more than twice as large as in the control group. (2) Size responses were reversible, and reduced NDF was followed by a decrease of gizzard size. (3) Phenotypic responses could be elicited repeatedly in three successive trials. (4) Excess capacities were downregulated and insufficient capacities were upregulated. (5) The responses followed changes of loads with almost no time lag, with size changes measurable within 24 h.
The scaling of acceleratory aquatic locomotion: body size and tail-flip performance of the california spiny lobster panulirus interruptus
Authors: Nauen Jennifer C. , Shadwick Robert E.
Published: April 2021

Tail-flipping is a crucial escape locomotion of crustaceans which has been predicted to be limited by increased body mass (Mb). Given isometric growth, one may predict that with growth event duration will decrease as Mb−1/3, translational distances will increase as Mb1/3, translational velocity will be independent of Mb, translational acceleration will decrease as Mb−1/3, angular displacement will be independent of Mb and angular velocity and angular acceleration will decrease as Mb−1/3. We tested these hypotheses by examining the scaling of 12 morphological variables, five kinematic variables and six performance variables of tail-flipping by the California spiny lobster Panulirus interruptus.

Growth approximated isometry, which validated the use of the proposed scaling hypotheses. For animals from 1 to 1000 g Mb, the predicted scaling relationships for tail-flip duration and translational distance and velocity variables were supported; however, translational acceleration performance was much better than predicted. Predictions for rotation and rotational velocity variables were not supported, while the rotational acceleration data closely matched the predicted relationship.

The increase in tail-flip duration as predicted suggests that muscle shortening velocity decreases with growth; the sustained acceleration performance (similar to findings for shrimp and fish fast-starts) suggests that muscle force output may increase at a greater rate than predicted by isometry. The scaling of rotational acceleration indicates that the torque produced during the tail-flip scales with a mass exponent greater than 1. Comparison of the tail-flip performance of Panulirus interruptus with those of other crustacean species reveals a wide range in performance by animals of similar body size, which suggests that the abdominal muscle may show interesting differences in contractile properties among different species.
Cardiorespiratory response to progressive hypoxia and hypercapnia in the turtle trachemys scripta
Authors: Herman Jay K. , Smatresk Neal J.
Published: April 2021

The ventilatory responses of chelonian reptiles to hypoxic and hypercapnic stress have been fairly well described. As turtles are capable of large cardiac shunts, changes in pulmonary perfusion may be an equally viable and potent response to these stressors. To test this hypothesis, conscious unrestrained turtles were unidirectionally ventilated while blood flow in the left pulmonary artery (Q̇LPA) and left aortic arch (Q̇LAo) was monitored. Turtles were exposed to step changes (2.5 h step−1) in O2 tension (30, 15, 5, 2.5 or 0 % O2; CO2 inflow maintained constant) on day 1 followed by step changes in CO2 tension (0, 2, 4, 8 % CO2; O2 inflow maintained constant) on day 2. Steady-state cardiorespiratory variables were recorded for the last 30 min of each step change in gas tension.

Progressive hypoxia resulted in progressive increases in ventilation, Q̇LPA and Q̇LAo and a small, but non-significant, increase in heart rate. Progressive hypercapnia resulted in a progressive increase in ventilation, while Q̇LPA and Q̇Lao did not change at any level of CO2. These results suggest that information from the O2-sensitive chemoreceptors appears to be stimulatory to both the cardiovascular and ventilatory control systems, while CO2 chemoreception appears to affect primarily the ventilatory control system. These results also suggest that, in animals capable of intracardiac shunting, increasing pulmonary perfusion may be an integral component of the reflex response to hypoxia.
Contractile properties of muscles used in sound production and locomotion in two species of gray tree frog
Authors: Marsh Richard L.
Published: April 2021

The sound-producing muscles of frogs and toads are interesting because they have been selected to produce high-power outputs at high frequencies. The two North American species of gray tree frog, Hyla chrysoscelis and Hyla versicolor, are a diploid–tetraploid species pair. They are morphologically identical, but differ in the structure of their advertisement calls. H. chrysoscelis produces very loud pulsed calls by contracting its calling muscles at approximately 40 Hz at 20 °C, whereas, H. versicolor operates the homologous muscles at approximately 20 Hz at this temperature. This study examined the matching of the intrinsic contractile properties of the calling muscles to their frequency of use. I measured the isotonic and isometric contractile properties of two calling muscles, the laryngeal dilator, which presumably has a role in modulating call structure, and the external oblique, which is one of the muscles that provides the mechanical power for calling. I also examined the properties of the sartorius as a representative locomotor muscle. The calling muscles differ greatly in twitch kinetics between the two species. The calling muscles of H. chrysoscelis reach peak tension in a twitch after approximately 15 ms, compared with 25 ms for the same muscles in H. versicolor. The muscles also differ significantly in isotonic properties in the direction predicted from their calling frequencies. However, the maximum shortening velocities of the calling muscles of H. versicolor are only slightly lower than those of the comparable muscles of H. chrysoscelis. The calling muscles have similar maximum shortening velocities to the sartorius, but have much flatter force–velocity curves, which may be an adaptation to their role in cyclical power output. I conclude that twitch properties have been modified more by selection than have intrinsic shortening velocities. This difference corresponds to the differing roles of shortening velocity and twitch kinetics in determining power output at differing frequencies.
Power output of sound-producing muscles in the tree frogs Hyla versicolor and Hyla chrysoscelis
Authors: Girgenrath Mahasweta , Marsh Richard L.
Published: April 2021

Sound-producing muscles provide the opportunity of studying the limits of power production at high contractile frequencies. We used the work loop technique to determine the power available from the external oblique muscles in two related species of North American gray tree frog, Hyla chrysoscelis and Hyla versicolor. These trunk muscles contract cyclically, powering high-intensity sound production in anuran amphibians. The external oblique muscles in H. chrysoscelis have an in vivo operating frequency of 40–55 Hz at 20–25 °C, whereas in H. versicolor these muscles contract with a frequency of 20–25 Hz at these temperatures. In vivo investigations have shown that these muscles use an asymmetrical sawtooth length trajectory (with a longer shortening phase compared with the lengthening phase) during natural cycles. To study the influence of this particular length trajectory on power output, we subjected the muscles to both sinusoidal and sawtooth length trajectories. In both species, the sawtooth trajectory yielded a significantly higher power output than the sinusoidal length pattern. The maximum power output during sawtooth cycles was similar in both species (54W kg−1 in H. chrysoscelis and 58 W kg−1 in H. versicolor). These values are impressive, particularly at the operating frequencies and temperatures of the muscle. The sinusoidal length trajectory yielded only 60 % of the total power output compared with the sawtooth trajectory (34W kg−1 for H. chrysoscelis and 36 W kg−1 for H. versicolor). The optimum cycle frequencies maximizing the power output using a sawtooth length pattern were approximately 44 Hz for H. chrysoscelis and 21 Hz for H. versicolor. These frequencies are close to those used by the two species during calling. Operating at higher frequencies, H. chrysoscelis maximized power at a strain amplitude of only 8 % compared with a value of 12 % in H. versicolor. These strains match those used in vivo during calling. The stimulus timing observed in vivo during calling was also similar to that yielding maximum power at optimal frequency in both species (6 ms and 8 ms before the start of shortening in H. chrysoscelis and H. versicolor, respectively). As expected, twitch duration in H. chrysoscelis is much shorter than that in H. versicolor (23 ms and 37 ms, respectively). There was a less remarkable difference between their maximum shortening velocities (Vmax) of 13.6 L0 s−1 in H. chrysoscelis and 11.1 L0 s−1 in H. versicolor, where L0 is muscle length. The force–velocity curves are very flat, which increases power output. At the myofibrillar level, the flat force–velocity curves more than compensate for the lower peak isometric force found in these muscles. The data presented here emphasize the importance of incorporating in vivo variables in designing in vitro studies.
From cellulose to cell
Authors: Vincent Julian F. V.
Published: April 2021

The cell wall is often pictured as a more-or-less random feltwork of cellulose microfibrils in association with other polysaccharide and protein complexes. There is evidence from morphology, morphogenesis and mechanics that the structures in the cell wall are far more regular and that their interactions are driven by their chemical and morphological properties. In particular, a model based on liquid crystal structures has more than morphological implications.
Mechanical behaviour of plant tissues: composite materials or structures?
Authors: Spatz H.-Ch. , Köhler L. , Niklas K. J.
Published: April 2021

The mechanical characteristics of the strengthening tissue of young axes of Aristolochia macrophylla were studied in successive loading–unloading cycles in tension. Elastic, viscoelastic and plastic deformations could be distinguished. After the first cycle, the material was in a state different from its original state, to which it returned only partially and/or slowly. Internal ‘microstructural’ prestresses are considered as an explanation for the mechanical behaviour seen in Aristolochia macrophylla and several other plants.
The aerodynamics and hydrodynamics of plants
Authors: Ennos A. R.
Published: April 2021

Because they grow away from their substratum to compete for light, plants have to withstand hydrodynamic or aerodynamic drag. Both water and land plants reconfigure in response to this drag, and this is presumed to reduce the risk of mechanical failure. However, there is little unequivocal evidence of drag reduction in large trees as a result of reconfiguration. Land plants must also transport water internally to their tissues, and many have developed xylem tracheids and vessels that help speed up this process. Recent evidence that tree height is limited by water supply suggests that water transport efficiency must be a crucial element in tree design. However, the resistance of many parts of the xylem is still unknown. More focused work is urgently required to shed light on the evolution and ecology of plants in relation to the flow of fluids.
The design of mineralised hard tissues for their mechanical functions
Authors: Currey John D.
Published: April 2021

Most hard tissues have as their primary purpose to be stiff. Outside the arthropods, mineralisation of a soft organic matrix is the almost universal method of producing high stiffness. However, stiffening brings with it the undesirable mechanical result of brittleness (lack of toughness). The mineralisation of some tissues, such as bone and dentine, can be modified rather easily, in evolutionary terms, to produce the optimum mix of stiffness with bending strength (which, except at the highest mineralisations, go together) on one hand and toughness on the other hand. However, in most other tissues, such as mollusc shell, echinoderm skeleton, brachiopod shell, barnacle shell and enamel, mineralisation is almost all-or-none, and no subtle gradations seem possible. In such cases, other features, such as architecture, must be modified to produce a useful skeleton.

Not only the mechanical properties of the skeletal tissue, but its cost, mass and time taken for production will, biologists tend to assume, be balanced by natural selection to produce a satisfactory result. However, such complexity makes it difficult to be sure that we understand the extent to which mineralised skeletal materials are the best possible solution to the problems facing the animals and that we are not just telling ‘Just-So’ stories. Furthermore, there are some skeletal materials that do not seem to make much sense at the moment, although no doubt all will become clear eventually.
The mechanical design of spider silks: from fibroin sequence to mechanical function
Authors: Gosline J. M. , Guerette P. A. , Ortlepp C. S. , Savage K. N.
Published: April 2021

Spiders produce a variety of silks, and the cloning of genes for silk fibroins reveals a clear link between protein sequence and structure–property relationships. The fibroins produced in the spider’s major ampullate (MA) gland, which forms the dragline and web frame, contain multiple repeats of motifs that include an 8–10 residue long poly-alanine block and a 24–35 residue long glycine-rich block. When fibroins are spun into fibres, the poly-alanine blocks form β-sheet crystals that crosslink the fibroins into a polymer network with great stiffness, strength and toughness. As illustrated by a comparison of MA silks from Araneus diadematus and Nephila clavipes, variation in fibroin sequence and properties between spider species provides the opportunity to investigate the design of these remarkable biomaterials.
The design of soft collagenous load-bearing tissues
Authors: Ker Robert F.
Published: April 2021

Tendon, articular cartilage and the human heel pad are all soft load-bearing collagenous tissues but are designed according to utterly different micromechanical principles. Tendon is (probably) a fibre-reinforced composite material. The mechanical properties of cartilage depend on osmotic pressure developed within an aqueous proteoglycan gel and resisted by tension in a collagenous network. The micromechanics of the heel pad have not previously been described quantitatively. Order-of-magnitude calculations are introduced to assess a model based on a fluid-filled cushion. The processes of biological design are illustrated by considering tendon. Structural design determines the tendon’s cross-sectional area relative to that of its muscle and, hence, the maximum stress to which the tendon may be subjected in life. Stress-in-life varies widely between tendons. Material design includes the development of compressive stiffness in the regions where transverse loads arise. More generally, the fatigue quality of each tendon is adjusted to suit its stress-in-life. The correlation between fatigue quality and stress-in-life means that every tendon is subject, on average, to a comparable rate of fatigue damage. Homeostasis requires that routine repair can keep up with this rate of damage.
Dynamics of muscle function during locomotion: accommodating variable conditions
Authors: Biewener Andrew A. , Gillis Gary B.
Published: April 2021

Much of what we know about animal locomotion is derived from studies examining animals moving within a single, homogeneous environment, at a steady speed and along a flat grade. As a result, the issue of how musculoskeletal function might shift to accommodate variability within the external environment has remained relatively unexplored. One possibility is that locomotor muscles are differentially recruited depending upon the environment in which the animal is moving. A second possibility is that the same muscles are recruited, but that they are activated in a different manner so that their contractile function differs according to environment. Finally, it is also possible that, in some cases, animals may not need to alter their musculoskeletal function to move under different external conditions. In this case, however, the mechanical behavior appropriate for one environmental condition may constrain locomotor performance in another. To begin to explore the means by which animals accommodate variable conditions in their environment, we present three case studies examining how musculoskeletal systems function to allow locomotion under variable conditions: (1) eels undulating through water and across land, (2) turkeys running on level and inclined surfaces, and (3) ducks using their limbs to walk and to paddle. In all three of these examples, the mechanical behavior of some muscle(s) involved in locomotion are altered, although to different degrees and in different ways. In the running turkeys, the mechanical function of a major ankle extensor muscle shifts from contracting isometrically on a flat surface (producing little work and power), to shortening actively during contraction on an uphill gradient (increasing the amount of work and power generated). In the ducks, the major ankle extensor undergoes the same general pattern of activation and shortening in water and on land, except that the absolute levels of muscle stress and strain and work output are greater during terrestrial locomotion. In eels, a transition to land elicits changes in electromyographic duty cycles and the relative timing of muscle activation, suggesting some alteration in the functional mechanics of the underlying musculature. Only by studying muscle function in animals moving under more variable conditions can we begin to characterize the functional breadth of the vertebrate musculoskeletal system and understand more fully its evolutionary design.
Animal movement, mechanical tuning and coupled systems
Authors: Daniel Thomas L. , Tu Michael S.
Published: April 2021

Over the past two decades, there has been a growing interest in developing predictive models of animal movement and force generation in fluids. In a departure from past studies that have asked how prescribed motions of a propulsor (wing or fin) generate lift and thrust during swimming and flying, we are increasingly interested in predicting the propulsor’s movement as well as the forces generated by it. This interest, motivated by a need to understand the control and dynamics of locomotion and its applications to robotics and animal physiology, requires that we develop integrative models and analyses of swimming and flying that incorporate neural control and muscle physiology into more traditional biomechanical studies of locomotion in fluids. This approach extends from whole-animal studies to the molecular basis of force generation. In this paper, we explore mechanical tuning from the level of the whole animal to the proteins driving force generation in muscle.
Are there mechanical limits to size in wave-swept organisms?
Authors: Denny Mark
Published: April 2021

Hydrodynamic forces imposed by ocean waves are thought to limit the size of nearshore plants and animals, but it has proved difficult to determine the mechanism. Explanations based on the scaling mismatch between hydrodynamic accelerational forces and the strength of organisms do not work. Mechanisms that incorporate the allometry of drag and strength accurately predict the maximal size of intertidal algae but not of animals, and internally imposed inertial forces may explain the limits to size in large kelps. The general question of size in wave-swept organisms remains open and intriguing.
Ecological biomechanics of benthic organisms: life history, mechanical design and temporal patterns of mechanical stress
Authors: Koehl M. A. R.
Published: April 2021

We can gain biomechanical insights if we couple knowledge of the environments, ecological roles and life history strategies of organisms with our laboratory analyses of their mechanical function or fluid dynamics, as illustrated by studies of the mechanical design of bottom-dwelling marine organisms. Obviously, measurements of the spatial and temporal distribution of loads on an organism in nature reveal the magnitudes and rates at which biomechanical tests should be performed in the laboratory. Furthermore, knowledge of the population biology and ecological interactions of the organisms being studied is crucial to determine when during the life of an individual particular aspects of mechanical performance should be measured; not only can the size, shape and material properties of an individual change during ontogeny, but so can its habitat, activities and ecological role. Such ecological information is also necessary to determine whether the aspects of mechanical performance being studied are biologically important, i.e. whether they affect the survivorship or fitness of the organisms. My point in raising these examples is to illustrate how ecological studies can enhance or change our understanding of biomechanical function.
Visual simulations, artificial animals and virtual ecosystems
Authors: Hokkanen J. E. I.
Published: April 2021

This review is about a field that does not traditionally belong to biological sciences. A branch of computer animation has its mission to create active self-powered objects living artificial lives in the theoretical biology zone. Selected work, of particular interest to biologists, is presented here. These works include animated simulations of legged locomotion, flexible-bodied animals swimming and crawling, artificial fish in virtual ecosystems, automated learning of swimming and the evolution of virtual creatures with respect to morphology, locomotion and behaviour. The corresponding animations are available for downloading via the Internet. I hope that watching these intriguing pieces of visual simulation will stimulate digitally oriented biologists to seize the interactive methods made possible by ever-increasing computing power.
In vivo sequential changes in chloride cell morphology in the yolk-sac membrane of mozambique tilapia (Oreochromis mossambicus) embryos and larvae during seawater adaptation
Authors: Hiroi Junya , Kaneko Toyoji , Tanaka Masaru
Published: April 2021

Changes in chloride cell morphology were examined in the yolk-sac membrane of Mozambique tilapia (Oreochromis mossambicus) embryos and larvae transferred from fresh water to sea water. By labelling chloride cells with DASPEI, a fluorescent probe specific for mitochondria, we observed in vivo sequential changes in individual chloride cells by confocal laser scanning microscopy. In embryos transferred from fresh water to sea water 3 days after fertilization, 75 % of chloride cells survived for 96 h, and cells showed a remarkable increase in size. In contrast, the cell size did not change in embryos and larvae kept in fresh water. The same rate of chloride cell turnover was observed in both fresh water and sea water. Using differential interference contrast (DIC) optics and whole-mount immunocytochemistry with anti-Na+/K+-ATPase, we classified chloride cells into three developmental stages: a single chloride cell without an apical pit, a single chloride cell with an apical pit, and a multicellular complex of chloride and accessory cells with an apical pit. DIC and immunofluorescence microscopy revealed that single chloride cells enlarged and were frequently indented by newly differentiated accessory cells to form multicellular complexes during seawater adaptation. These results indicate that freshwater-type single chloride cells are transformed into seawater-type multicellular complexes during seawater adaptation, suggesting plasticity in the ion-transporting functions of chloride cells in the yolk-sac membrane of tilapia embryos and larvae.