bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical work for step-to-step transitions is a major determinant of the metabolic cost of human walking
Authors: Donelan J. Maxwell , Kram Rodger , Kuo Arthur D. 
Published: April 2021

SUMMARY
In the single stance phase of walking, center of mass motion resembles that of an inverted pendulum. Theoretically, mechanical work is not necessary for producing the pendular motion, but work is needed to redirect the center of mass velocity from one pendular arc to the next during the transition between steps. A collision model predicts a rate of negative work proportional to the fourth power of step length. Positive work is required to restore the energy lost, potentially exacting a proportional metabolic cost. We tested these predictions with humans (N=9) walking over a range of step lengths(0.4-1.1 m) while keeping step frequency fixed at 1.8 Hz. We measured individual limb external mechanical work using force plates, and metabolic rate using indirect calorimetry. As predicted, average negative and positive external mechanical work rates increased with the fourth power of step length(from 1 W to 38 W; r2=0.96). Metabolic rate also increased with the fourth power of step length (from 7 W to 379 W; r2=0.95), and linearly with mechanical work rate. Mechanical work for step-to-step transitions, rather than pendular motion itself, appears to be a major determinant of the metabolic cost of walking.
Stimulatory effects on Na+ transport in renal epithelia induced by extracts of Nigella arvensis are caused by adenosine
Authors: Atia Fatima , Mountian Irina , Simaels Jeannine , Waelkens Etienne , Van Driessche Willy 
Published: April 2021

SUMMARY
Effects of the extract of Nigella arvensis (NA) seeds on transepithelial Na+ transport were studied in cultured A6 toad kidney cells by recording short-circuit current (Isc),transepithelial conductance (GT), transepithelial capacitance (CT) and fluctuation in Isc. Apical application of NA extract had merely a small stimulatory effect on Na+ transport, whereas basolateral administration markedly increased Isc, GT and CT. A maximal effect was obtained at 500 μl l-1 of lyophilized NA extract. The increase in CT suggests that the activation of Isc occurs through the insertion of transport sites in the apical membrane. In experiments performed in the absence of Na+transport [apical Na+ was replaced by N-methyl-D-glucamine(NMDG+)], basolateral NA extract did not affect Isc and GT, indicating that Cl- conductance was not influenced. Noise analysis of Isc using 6-chloro-3,5-diaminopyrazine-2-carboxamide(CDPC) showed that NA extract reduced single-channel current(iNa) and decreased channel open probability(Po) but evoked a threefold increase in channel density(NT), which confirms the insertion of Na+channels. The separation of the compounds in the crude extract of NAwas performed by fast protein liquid chromatography (FPLC) on a Superdex 200 gel-filtration column and by reverse-phase high-pressure liquid chromatography(RPHPLC) on an μRPC C2/C18 SC2.1/10 column connected to a SMART system. Analysis of the purified active fraction by mass spectrometry demonstrated the presence of adenosine as the single organic compound in the extract that had a stimulatory effect on Na+ transport. In a separate series of experiments, we confirmed that 1 μmol l-1 adenosine had similar effects on the parameters of Na+ transport as did the NAextract. The action of adenosine was further identified by experiments in which NA extract was added after adenosine. In these experiments, NA extract did not affect Isc, GT or CT. These results clearly demonstrate an essential role of adenosine in the stimulatory action of NA extract.
Different colors reveal different information: how nutritional stress affects the expression of melanin- and structurally based ornamental plumage
Authors: McGraw Kevin J. , Mackillop Emiko A. , Dale James , Hauber Mark E. 
Published: April 2021

SUMMARYAvian plumage colors have emerged recently as model systems for investigating the types of information that can be signaled by showy sexual displays in animals. In many species, the brightness of carotenoid-based plumage reflects the health and condition of individuals and is used in mate selection. The information contained in melanin-based and structurally based ornamental colors in birds is less well resolved, however. We subjected male house sparrows Passer domesticus and brown-headed cowbirds Molothrus ater to stressful nutritional conditions during molt to test the hypothesis that melanin- and structurally based plumage colors are nutritionally condition-dependent. We restricted food access for treatment males during randomized 6 h periods on 4 days per week, while allowing control birds access to food ad libitum throughout the course of the molt. We found that the size and brightness of the melanin-based throat badges in male house sparrows were not affected by nutritional stress. Similarly, there were no differences between treatment and control male cowbirds in the size or brightness of the melanin-based brown hood. However, the structurally based iridescent plumage of cowbirds was indicative of the nutritional condition of males during molt. Nutritionally stressed cowbirds grew significantly less colorful plumage than did males with access to food ad libitum. These results are consistent with observations in other avian species that different types of plumage color communicate different sets of information. Melanin ornaments are less sensitive to nutritional conditions during molt and instead may reflect the hormonal status and/or competitive ability of males, whereas structural coloration appears to be an accurate signal of health and condition.
Rotational lift: something different or more of the same?
Authors: Walker Jeffrey A. 
Published: April 2021

SUMMARYThis paper addresses the question, do the rotational forces in the hovering fruit fly Drosophila melanogaster reflect something different (the Magnus effect) or more of the same (circulatory-and-attached-vortex force)?The results of an unsteady blade-element model using empirically derived force coefficients from translating (root-oscillating) wings are compared with recent results derived from both the measured forces on a dynamically scaled Drosophila wing and the computational fluid dynamic (CFD)-modeled forces on a virtual Drosophila wing. The behavior of the forces in all three models during wing rotation supports the hypothesis that rotational lift is not a novel aerodynamic mechanism but is caused by the same fluid-dynamic mechanism that occurs during wing translation. A comparison of the unsteady model with a quasi-steady model that employs empirically derived rotational coefficients further supports the hypothesis that rotational forces are more of the same. Finally, the overall similarity of the results between the unsteady model, the physical wing model and the CFD model suggests that the unsteady model can be used to explore the performance consequences of kinematic variation and to investigate locomotor control in freely moving animals.
TheDhgene ofDrosophila melanogasterencodes a diuretic peptide that acts through cyclic AMP
Authors: Cabrero Pablo , Radford Jonathan C. , Broderick Kate E. , Costes Laurence , Veenstra Jan A. , Spana Eric P. , Davies Shireen A. , Dow Julian A. T. 
Published: April 2021

SUMMARYDh, the gene that encodes a CRF-like peptide in Drosophila melanogaster, is described. The product of this gene is a 44-amino-acid peptide (Drome-DH44) with a sequence almost identical to the Musca domestica and Stomoxys calcitrans diuretic hormones. There are no other similar peptides encoded within the known Drosophila genomic sequence. Functional studies showed that the deduced peptide stimulated fluid production, and that this effect was mediated by cyclic AMP in principal cells only: there was no effect on the levels of either cyclic GMP or intracellular calcium. Stimulation also elevated levels of cyclic AMP (but not cyclic GMP) phosphodiesterase, a new mode of action for this class of hormone. The transcript was localised by in situhybridisation, and the peptide by immunocytochemistry, to two groups of three neurones in the pars intercerebralis within the brain. These cells also express receptors for leucokinin, another major diuretic peptide, implying that the cells may be important in homeostatic regulation.
The relationship between maximum jumping performance and hind limb morphology/physiology in domestic cats (Felis silvestris catus)
Authors: Harris Michelle A. , Steudel Karen 
Published: April 2021

SUMMARYA critical role of functional morphology is to demonstrate form—function relationships that can then be used by evolutionary biologists to infer the evolutionary history of the structure in question. Tests of theoretical expectations about the effects of many aspects of morphology/physiology on locomotor performance have had very mixed results. If systems such as jumping can be shown to reliably predict performance from morphology, this would provide a foundation upon which hypotheses for the evolutionary origin of certain morphologies can be generated. The present study examined whether a relationship exists between maximum takeoff velocity(TOV) and several carefully chosen morphological and physiological traits in domestic cats (Felis silvestris catus). Based on the contributions of extensor muscle work to increasing the kinetic and potential energy of the center of mass (CM) during takeoff, we predicted that maximum TOV would be dependent upon relative limb length, relative extensor muscle mass, body mass and the percentage of fast-twitch muscle fibers. Both maximum TOV and this series of traits were measured in 18 cats. We found that variation in cat maximum TOV is significantly explained by both hind limb length and fat mass relative to lean body mass, but not by extensor muscle mass relative to lean mass or fast-twitch fiber content. The effect of body fat mass is pervasive because it reduces the proportion of muscle mass/body mass and thus increases the muscle work invested in increasing the CM potential energy as compared with kinetic energy during takeoff.
Landmark use and development of navigation behaviour in the weakly electric fishGnathonemus petersii(Mormyridae; Teleostei)
Authors: Cain Peter , Malwal Sapna 
Published: April 2021

SUMMARYAfrican mormyrids, such as Gnathonemus petersii, migrate:nocturnally, from daytime shelters to find food and return by morning, and seasonally, spawning in swamps flooded during the rainy season. The present study examined whether the fish use landmarks detected viaelectrolocation to locate an aperture, whether they detect changes in landmark size and respond appropriately, whether landmarks or hydrostatic pressure are the primary cues for navigation and whether fish of different developmental stages behave differently with respect to landmarks and navigation. The fish's task was to locate and swim through a circular aperture in a wall dividing an aquarium into two compartments. Two groups of fish were trained to find the aperture with a landmark present, while a control group had no such landmark. The water level remained constant throughout training. At the end of training,the fish's task was to locate the aperture after the landmark size had changed or the water level had increased. The results show that G. petersiiuse landmarks to orient and navigate. They can detect changes in landmark size and will modify their locomotor behaviour to integrate the change into an internal representation. If the water level changes, increasing hydrostatic pressure, the fish orient to a landmark, if present. If no landmark is present, the fish rely on an internal representation oriented to hydrostatic pressure. Larger, early-adult G. petersii located the aperture faster than smaller, sub-adult fish.
Oxygen uptake during post dive recovery in a diving birdAythya fuligula: implications for optimal foraging models
Authors: Parkes Roland , Halsey Lewis G. , Woakes Anthony J. , Holder Roger L. , Butler Patrick J. 
Published: April 2021

SUMMARYThe rate of oxygen uptake at the surface between dives was measured for four tufted ducks, Aythya fuligula, during bouts of foraging dives to a depth of 1.8 m. The ducks surfaced into a respirometer box after each dive so that the rate of oxygen uptake(V̇O2) could be measured. V̇O2decreased over time at the surface and there was a particularly rapid phase of oxygen uptake for approximately the first 3s. The specific shape of the oxygen uptake curve is dependent upon the duration of the preceding dive. The uptake curve after longer dives was significantly steeper during the first 3s at the surface than after shorter dives, although V̇O2 after the first 3s was not significantly different between these two dive duration bins. Thus, the mean total oxygen uptake (VO2) was higher after surface periods following longer dives. Due to the high V̇O2 during the initial part of the surface period, the curve associated with longer dives was statistically biphasic, with the point of inflection at 3.3s. The curve for shorter dives was not statistically biphasic. The birds may increase their respiratory frequency during the first 3s after longer dives, producing the increased V̇O2,which would enable the birds to resaturate their oxygen stores more rapidly in response to the increased oxygen depletion of the longer submergence time.
Implanted electrode recordings from a praying mantis auditory interneuron during flying bat attacks
Authors: Triblehorn Jeffrey D. , Yager David D. 
Published: April 2021

SUMMARYUsing an implanted electrode, we recorded the responses from the ultrasound-sensitive mantis interneuron 501-T3 during flying bat attacks in a large flight room where the mantis served as the target. 501-T3 responds to each vocalization emitted with multi-spike bursts when pulse repetition rates (PRRs) are below 55 pulses s–1. As PRR increases and pulse durations fall below 3 ms, 501-T3 ceases burst activity. On average, spike bursts cease 272 ms before contact (when the bat is 73 cm away from the preparation). The timing of cessation of activity in 501-T3 is similar to the latency for the diving portion of the response of the mantid (242 ms). Experiments using vocalizing stationary bats confirm that 501-T3 responds more reliably to longer pulse durations (⩾3 ms) when intensities are below 90 dB pe SPL. The cessation of 501-T3 activity is probably due both to the increasing PRR and to the decreasing pulse duration that occur in the terminal buzz phase of a bat attack. 501-T3 may be actively shut off at high PRRs and/or intensities to protect the interneuron from habituation while the mantis performs an escape response. The cessation of 501-T3 activity is consistent with the lack of a very late ultrasound-mediated evasive response by the mantis. However, cessation of 501-T3 activity may allow a true ‘last-chance’ response to be mediated by other neural systems.
Differences in behaviour between rainbow trout selected for high- and low-stress responsiveness
Authors: Øverli Øyvind , Pottinger Tom G. , Carrick Toby R. , Øverli Elisabeth , Winberg Svante 
Published: April 2021

SUMMARY
Two F1 lines of rainbow trout Oncorhynchus mykiss, divergent for plasma cortisol responsiveness, were generated by individual selection for post-stress cortisol values within the F0 generation. Adult females of the F1 generation were transferred to rearing in social isolation in observation tanks. After 6 days, locomotor activity in high-responding (HR) and low-responding (LR) individuals was quantified as time spent moving during a 20 min observation period. Behavioural observations were repeated the next day with a smaller conspecific intruder present in each observation tank. Differential hypothalamus–pituitary–interrenal axis activity in the two lines was subsequently confirmed by a standardised confinement stress test, which resulted in significantly higher plasma cortisol concentrations in HR than LR fish. HR fish displayed higher levels of locomotor activity than LR fish in the presence of an intruder, but not when in isolation. Aggressive behaviour towards the intruder was not seen, suggesting either a state-dependent lack of territorial aggression, or chronic stress in the experimental fish. A significantly higher incidence of feed intake was seen in LR trout when held in observation tanks (40 % versus 0 % of the fish took food when in isolation), suggesting that these fish acclimated more successfully to the experimental conditions than HR fish did. These results suggest that selection for stress responsiveness in salmonid fish leads to behavioural alterations, which are of potential importance to the performance of these fish in aquaculture rearing operations.
Copper transport by lobster (Homarus americanus) hepatopancreatic mitochondria
Authors: Chavez-Crooker Pamela , Garrido Nestor , Ahearn Gregory A. 
Published: April 2021

SUMMARYMechanisms of copper transport into purified mitochondrial suspensions prepared from the hepatopancreas of the Atlantic lobster Homarus americanus were investigated. Mitochondria were purified by combining methods of differential and Percoll-gradient centrifugation, and copper transport was studied using the copper-sensitive fluorescent dye Phen Green. Copper transport by this mitochondrial preparation was kinetically the sum of saturable and non-saturable transfer components. Addition of 500 μmol l–1 Ca2+ or 500 nmol l–1 Ruthenium Red abolished the non-saturable copper transport component, significantly (P&lt;0.01) reduced the apparent binding affinity of the saturable transport component, but was without effect (P&gt;0.05) on the apparent maximal transport velocity of the saturable transfer process. The antiport inhibitor diltiazem (500 μmol l–1) acted as a mixed inhibitor of the saturable transport mechanism, but had no effect on the non-saturable component of transfer. These results suggest that the non-saturable copper influx process was probably by way of the well-known Ruthenium-Red-sensitive Ca2+ uniporter and that the saturable transport component was probably due to a combination of both the Na+-dependent, diltiazem-sensitive 1Ca2+/2Na+ antiporter and the Na+-independent, diltiazem-insensitive 1Ca2+/2H+ antiporter. A model is discussed relating these mitochondrial copper uptake processes to the transfer of metal ions across the epithelial brush-border membrane.
Visual control of host pursuit in the parasitoid fly Exorista japonica
Authors: Yamawaki Yoshifumi , Kainoh Yooichi , Honda Hiroshi 
Published: April 2021

SUMMARY
The tachinid fly Exorista japonica is a parasitoid of many kinds of lepidopterous larvae. After encountering a suitable host, the fly pursues the crawling larva on foot using visual cues to guide it. To investigate the visual control of host pursuit, we observed and videotaped pursuits of a host, the common armyworm Mythimna separata, for frame-by-frame analysis. Observation was performed in sunlight and under illumination from a fluorescent lamp. The fly pursued hosts discontinuously with a repeated stop-and-run motion. During a run, its movements consisted of rotation, forward translation and sideways translation. Rotation during a run was positively correlated with the angular position of the host’s head. The direction of translation depended on the angular position of the host’s head. Forward translation was negatively correlated with the visual angle subtended by the host. These results suggest that the fly orients and walks towards the leading edge of a moving target. There was little difference in the results between sunlight and illumination from a fluorescent lamp.
Myofibrillar protein isoform expression is correlated with synaptic efficacy in slow fibres of the claw and leg opener muscles of crayfish and lobster
Authors: Mykles Donald L. , Medler Scott , Koenders Annette , Cooper Robin 
Published: April 2021

SUMMARYIn the crayfish and lobster opener neuromuscular preparations of the walking legs and claws, there are regional differences in synaptic transmission even though the entire muscle is innervated by a single excitatory tonic motor neuron. The innervation of the proximal fibres produced larger excitatory postsynaptic potentials (EPSPs) than those of the central fibres. The amplitudes of the EPSPs in the distal fibres were intermediate between those of the proximal and central regions. These differences in EPSP amplitudes were correlated with differences in short-term facilitation between the three regions. When given a 10- or 20-pulse train of stimuli, the proximal fibres showed greater short-term facilitation initially, often followed by a maximization of short-term facilitation towards the end of a train. In contrast, the central fibres showed a linear increase in short-term facilitation throughout a stimulus train. The distal fibres showed intermediate short-term facilitation compared with the other two regions. Analysis of myofibrillar isoforms showed that levels of troponin-T1 (TnT1), a 55 kDa isoform expressed in slow-tonic (S2) fibres, were correlated with synaptic properties. Proximal fibres had the highest levels of TnT1, with lower levels in distal fibres; central fibres lacked TnT1, which is characteristic of slow-twitch (S1) fibres. In addition, differences in troponin-I isoforms correlated with TnT1 levels between the proximal, central and distal regions. The correlation between slow fibre phenotype and strength of innervation suggests a relationship between synaptic structure and expression of troponin isoforms.
Mechanics of the respiratory system in the newborn tammar wallaby
Authors: MacFarlane P. M. , Frappell P. B. , Mortola J. P. 
Published: April 2021

SUMMARYWe investigated whether the mechanical properties of the respiratory system represent a major constraint to spontaneous breathing in the newborn tammar wallaby Macropus eugenii, which is born after a very short gestation (approximately 28 days, birth mass approximately 380 mg). The rate of oxygen consumption (V̇O2) through the skin was approximately 33 % of the total V̇O2 at day 1 and approximately 14 % at day 6. The mass-specific resting minute ventilation (V̇e) and the ventilatory equivalent (V̇e/V̇O2) were approximately the same at the two ages, with a breathing pattern significantly deeper and slower at day 1. The mass-specific compliance of the respiratory system (Crs) did not differ significantly between the two age groups and was close to the values predicted from measurements in eutherian newborns. Mass-specific respiratory system resistance (Rrs) at day 1 was higher than at day 6, and also higher than in eutherian newborns. Chest distortion, quantified as the degree of abdominal motion during spontaneous breathing compared with that required to inflate the lungs passively, at day 1 was very large, whereas it was modest at day 6. We conclude that, in the tammar wallaby at birth, the high resistance of the respiratory system and the distortion of the chest wall greatly reduce the mechanical efficiency of breathing. At this age, gas exchange through the skin is therefore an important complement to pulmonary ventilation.