bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reaction to Disturbances of a Walking Leg During Stance
Authors: Bartling Christian , Schmitz Josef 
Published: April 2021

ABSTRACT
The ground reaction forces exerted by the legs of freely walking stick insects, Carausius morosus, were recorded during normal and perturbed locomotion. The animals walked along a path into which a three-dimensional force transducer was integrated. The transducer registered all three components of the forces produced by a single leg when, by chance, it walked on the force platform. The stiffness of the walking surface was found to be a critical variable affecting the forces and the trajectories of leg movements during undisturbed walking. The forces produced by a leg were considerably smaller and the trajectories were closer to the body during walking on soft versus stiff surfaces. Perturbations during stance were generated by moving the platform in various directions within the horizontal plane and at two different rates.
Perturbations were applied either immediately after leg contact or after a delay of 300 ms. The reactions to these disturbances were compatible with the hypothesis that the velocity of leg movement is under negative feedback control. This interpretation is also supported by comparison with simulations based upon other control schemes. We propose a model circuit that provides a combination of negative and positive feedback control mechanisms to resolve the apparent discrepancies between our results and those of previous studies.
Limits of human lung function at high altitude
Authors: Schoene Robert B. 
Published: April 2021

SUMMARY
This paper will review the function of the lung at high altitude in humans. As the first interface between the environment and the body, the lung serves a vital role in the transfer of oxygen from the air to the blood. I will describe the limits of response and adaptation of the lung to this hypoxic stress, both at rest and during exercise when oxygen and carbon dioxide flux from the tissues is greater. First, ventilation will be described in terms of the hypoxic stimulus that causes an increase in breathing (ventilatory drives) and the metabolic cost from the respiratory muscles incurred by this increase. Individuals at high altitude also have a substantial sense of dyspnea which, in and of itself, may limit exercise tolerance. The final function of the lung is to exchange oxygen and carbon dioxide, which it does at the alveolar–capillary interface. Here, important limitations are encountered because the driving pressure for oxygen from the air to the blood is lower and the more rapid transit time of blood across the pulmonary capillary allows less time for equilibration of oxygen with the blood. Both these phenomena lead to a limitation of diffusion of oxygen across the alveolar–capillary membrane and, thus, more accentuated hypoxemia. In spite of these restrictions, humans still do remarkably well in times of great stress from the hypoxic environment.
The home team advantage: reproduction in women indigenous to high altitude
Authors: Vitzthum V. J. 
Published: April 2021

SUMMARYAlthough there is substantial evidence that environmental conditions disrupt reproductive function among newcomers to hypoxic settings, it is not certain that low oxygen pressure reduces fertility among those indigenous to high altitude. Even when fertility does appear to be relatively lower, numerous behavioral and sociocultural factors may be responsible. These are best examined within demographic frameworks that delineate a finite list of the proximate determinants of fertility. The findings presented here are based on several studies of indigenous Andean populations (Peruvian Quechua at 4000m, Bolivian Quechua at 3100m, Bolivian Aymara at 4000m). Data on ovarian function suggest that neither progesterone levels nor menstrual cycle length or regularity are significantly different from those of women at lower altitudes. Data on two behavioral factors that determine fertility levels, coital frequency and infant feeding practices, suggest that the former is not likely to be of significance in co-habitating couples, but that variation in breastfeeding patterns has probably made a substantial contribution to differences in fertility among at least some populations at high altitude.
Sensorimotor adaptations to microgravity in humans
Authors: Edgerton V. R. , McCall G. E. , Hodgson J. A. , Gotto J. , Goulet C. , Fleischmann K. , Roy R. R. 
Published: April 2021

SUMMARYMotor function is altered by microgravity, but little detail is available as to what these changes are and how changes in the individual components of the sensorimotor system affect the control of movement. Further, there is little information on whether the changes in motor performance reflect immediate or chronic adaptations to changing gravitational environments. To determine the effects of microgravity on the neural control properties of selected motor pools, four male astronauts from the NASA STS-78 mission performed motor tasks requiring the maintenance of either ankle dorsiflexor or plantarflexor torque. Torques of 10 or 50% of a maximal voluntary contraction (MVC) were requested of the subjects during 10° peak-to-peak sinusoidal movements at 0.5Hz. When 10% MVC of the plantarflexors was requested, the actual torques generated in-flight were similar to pre-flight values. Post-flight torques were higher than pre- and in-flight torques. The actual torques when 50% MVC was requested were higher in- and post-flight than pre-flight. Soleus (Sol) electromyographic (EMG) amplitudes during plantarflexion were higher in-flight than pre- or post-flight for both the 10 and 50% MVC tasks. No differences in medial gastrocnemius (MG) EMG amplitudes were observed for either the 10 or 50% MVC tasks. The EMG amplitudes of the tibialis anterior (TA), an antagonist to plantarflexion, were higher in- and post-flight than pre-flight for the 50% MVC task. During the dorsiflexion tasks, the torques generated in both the 10 and 50% MVC tasks did not differ pre-, in- and post-flight. TA EMG amplitudes were significantly higher in- than pre-flight for both the 10 or 50% MVC tasks, and remained elevated post-flight for the 50% MVC test. Both the Sol and MG EMG amplitudes were significantly higher in-flight than either pre- or post-flight for both the 10 and 50% MVC tests. These data suggest that the most consistent response to space flight was an elevation in the level of contractions of agonists and antagonists when attempting to maintain constant torques at a given level of MVC. Also, the chronic levels of EMG activity in selected ankle flexor and extensor muscles during space flight and during routine activities on Earth were recorded. Compared with pre- and post-flight values, there was a marked increase in the total EMG activity of the TA and the Sol and no change in the MG EMG activity in-flight. These data indicate that space flight, as occurs on shuttle missions, is a model of elevated activation of both flexor and extensor muscles, probably reflecting the effects of programmed work schedules in flight rather than a direct effect of microgravity.
Quantifying Nutrient Production by the Microbial Symbionts in an Aphid
Authors: Douglas A. E. , Minto L. B. , Wilkinson T. L. 
Published: April 2021

ABSTRACT
The symbiotic bacteria Buchnera sp. provide aphids with essential amino acids, nutrients in short supply in the aphid diet of plant phloem sap. The contribution of Buchnera-derived amino acids to net protein growth of the aphid Aphis fabae was quantified from the protein growth of aphids reared on chemically defined diets lacking individual amino acids. The amino acid production rates varied among the nine essential amino acids over the range 8–156 pmol μg−1 protein day−1 (for tryptophan and leucine, respectively), equivalent to 0.02–0.33 fmol Buchnera−1 day−1. In a complementary metabolic analysis, the aphids incorporated radioactivity from dietary [14C]glutamic acid into the essential amino acids isoleucine, lysine and threonine. Incorporation into isoleucine was significantly elevated by the omission of dietary isoleucine, indicating that dietary supply may affect the biosynthetic rates of certain amino acids by Buchnera. Aphids experimentally deprived of Buchnera did not synthesize essential amino acids from dietary glutamic acid. The mortality of aposymbionts was high over 7 days on the phenylalanine-free diet, and their assimilation of dietary leucine was depressed on the complete diet, suggesting that both the absence of bacteria-derived amino acids and the low rates of assimilation of certain dietary amino acids may contribute to the poor growth of these insects.
Hepatic Phosphoenolpyruvate Carboxykinase Gene Expression is not Repressed by Dietary Carbohydrates in Rainbow Trout (Oncorhynchus Mykiss)
Authors: Panserat S. , Plagnes-Juan E. , Bréque J. , Kaushik S. 
Published: April 2021

ABSTRACT
Phosphoenolpyruvate carboxykinase (PEPCK) is a rate-limiting enzyme in hepatic gluconeogenesis and therefore plays a central role in glucose homeostasis. The aim of this study was to analyse the nutritional regulation of PEPCK gene expression in rainbow trout (Oncorhynchus mykiss), which are known to use dietary carbohydrates poorly. A full-length hepatic PEPCK cDNA (2637 base pairs with one open reading frame putatively encoding a 635-residue protein) was cloned and found to be highly homologous to mammalian PEPCKs. The presence of a putative peptide signal specific to a mitochondrial-type PEPCK in the deduced amino acid sequence suggests that this PEPCK gene codes for a mitochondrial form. In gluconeogenic tissues such as liver, kidney and intestine, this PEPCK gene was expressed at high levels and, in the liver we found no regulation of PEPCK gene expression by dietary carbohydrates. These results suggest that the first step of the hepatic gluconeogenic pathway in rainbow trout is functional and highly active irrespective of the dietary carbohydrate supply.
Maturation of muscle properties and its hormonal control in an adult insect
Authors: Rose Uwe , Ferber Michael , Hustert Reinhold 
Published: April 2021

SUMMARYThe oviposition of female locusts requires longitudinal muscles to tolerate remarkable lengthening. Whether this ability together with concomitant properties develops during maturation or is present throughout life was investigated. The properties of the locust abdominal muscles involved in oviposition behaviour were investigated with respect to their maturation, segment- and gender-specificity and regulation by juvenile hormone (JH). Muscles from the sixth abdominal segment (an oviposition segment) of mature females (&gt;18 days old) were able to tolerate large extensions (&gt;8 mm). At this length, muscles were still able to generate considerable neurally evoked twitch tension. In contrast, muscle fibres from females less than 5 days old did not tolerate extension of more than 4 mm. At this length, tension generation was negligible. The maximum tension generated at different stimulus frequencies was significantly higher in muscles of females more than 18 days old than in females less than 5 days old. Furthermore, the cross-sectional area of muscle fibres increased significantly during reproductive development. Current-clamp recordings from denervated muscle fibres of females more than 18 days old revealed their ability to generate overshooting action potentials. The potentials were tetrodotoxin (TTX)-insensitive (0.5 μmol l–1 TTX), but were blocked by Cd2+ (50 μmol l–1) or nifedipine (50 μmol l–1), which suggests the involvement of L-type Ca2+ channels. Action potentials recorded from females less than 5 days old differed considerably in amplitude and shape from those recorded from females more than 18 days old, suggesting their maturation during the first 2 weeks of adult life. Inactivation of the corpora allata (CA) by precocene inhibited the maturation of these muscle properties, whereas injection of JH into precocene-treated females reversed this effect. Homologous muscles from the third abdominal segment (a non-oviposition segment, M169) and muscles from males (M214) revealed no comparable changes, although some minor changes occurred during reproductive development. The results suggest a gender- and segment-specific maturation of muscle properties that is related to reproductive behaviour and controlled by JH.
The mechanical power output of the pectoralis muscle of blue-breasted quail (Coturnix chinensis): thein vivolength cycle and its implications for muscle performance
Authors: Askew Graham N. , Marsh Richard L. 
Published: April 2021

SUMMARYSonomicrometry and electromyographic (EMG) recordings were made for the pectoralis muscle of blue-breasted quail (Coturnix chinensis) during take-off and horizontal flight. In both modes of flight, the pectoralis strain trajectory was asymmetrical, with 70 % of the total cycle time spent shortening. EMG activity was found to start just before mid-upstroke and continued into the downstroke. The wingbeat frequency was 23 Hz, and the total strain was 23 % of the mean resting length.Bundles of fibres were dissected from the pectoralis and subjected in vitro to the in vivo length and activity patterns, whilst measuring force. The net power output was only 80 W kg–1 because of a large artefact in the force record during lengthening. For more realistic estimates of the pectoralis power output, we ignored the power absorbed by the muscle bundles during lengthening. The net power output during shortening averaged over the entire cycle was approximately 350 W kg–1, and in several preparations over 400 W kg–1. Sawtooth cycles were also examined for comparison with the simulation cycles, which were identical in all respects apart from the velocity profile. The power output during these cycles was found to be 14 % lower than during the in vivo strain trajectory. This difference was due to a higher velocity of stretch, which resulted in greater activation and higher power output throughout the later part of shortening, and the increase in shortening velocity towards the end of shortening, which facilitated deactivation.The muscle was found to operate at a mean length shorter than the plateau of the length/force relationship, which resulted in the isometric stress measured at the mean resting length being lower than is typically reported for striated muscle.
The mechanical power output of the flight muscles of blue-breasted quail (Coturnix chinensis) during take-off
Authors: Askew Graham N. , Marsh Richard L. , Ellington Charles P. 
Published: April 2021

SUMMARYBlue-breasted quail (Coturnix chinensis) were filmed during take-off flights. By tracking the position of the centre of mass of the bird in three dimensions, we were able to calculate the power required to increase the potential and kinetic energy. In addition, high-speed video recordings of the position of the wings over the course of the wing stroke, and morphological measurements, allowed us to calculate the aerodynamic and inertial power requirements. The total power output required from the pectoralis muscle was, on average, 390 W kg–1, which was similar to the highest measurements made on bundles of muscle fibres in vitro (433 W kg–1), although for one individual a power output of 530 W kg–1 was calculated. The majority of the power was required to increase the potential energy of the body. The power output of these muscles is the highest yet found for any muscle in repetitive contractions.We also calculated the power requirements during take-off flights in four other species in the family Phasianidae. Power output was found to be independent of body mass in this family. However, the precise scaling of burst power output within this group must await a better assessment of whether similar levels of performance were measured across the group. We extended our analysis to one species of hawk, several species of hummingbird and two species of bee. Remarkably, we concluded that, over a broad range of body size (0.0002–5 kg) and contractile frequency (5–186 Hz), the myofibrillar power output of flight muscles during short maximal bursts is very high (360–460 W kg–1) and shows very little scaling with body mass. The approximate constancy of power output means that the work output varies inversely with wingbeat frequency and reaches values of approximately 30–60 J kg–1 in the largest species.
Functional implications of supercontracting muscle in the chameleon tongue retractors
Authors: Herrel Anthony , Meyers Jay J. , Aerts Peter , Nishikawa Kiisa C. 
Published: April 2021

SUMMARYChameleons capture prey items using a ballistic tongue projection mechanism that is unique among lizards. During prey capture, the tongue can be projected up to two full body lengths and may extend up to 600 % of its resting length. Being ambush predators, chameleons eat infrequently and take relatively large prey. The extreme tongue elongation (sixfold) and the need to be able to retract fairly heavy prey at any given distance from the mouth are likely to place constraints on the tongue retractor muscles. The data examined here show that in vivo retractor force production is almost constant for a wide range of projection distances. An examination of muscle physiology and of the ultrastructure of the tongue retractor muscle shows that this is the result (i) of active hyoid retraction, (ii) of large muscle filament overlap at maximal tongue extension and (iii) of the supercontractile properties of the tongue retractor muscles. We suggest that the chameleon tongue retractor muscles may have evolved supercontractile properties to enable a substantial force to be produced over a wide range of tongue projection distances. This enables chameleons successfully to retract even large prey from a variety of distances in their complex three-dimensional habitat.
Aerobic respiratory costs of swimming in the negatively buoyant brief squidLolliguncula brevis
Authors: Bartol Ian K. , Mann Roger , Patterson Mark R. 
Published: April 2021

SUMMARYBecause of the inherent inefficiency of jet propulsion, squid are considered to be at a competitive disadvantage compared with fishes, which generally depend on forms of undulatory/oscillatory locomotion. Some squid, such as the brief squid Lolliguncula brevis, swim at low speeds in shallow-water complex environments, relying heavily on fin activity. Consequently, their swimming costs may be lower than those of the faster, more pelagic squid studied previously and competitive with those of ecologically relevant fishes. To examine aerobic respiratory swimming costs, O2 consumption rates were measured for L. brevis of various sizes (2–9 cm dorsal mantle length, DML) swimming over a range of speeds (3–30 cm s–1) in swim tunnel respirometers, while their behavior was videotaped. Using kinematic data from swimming squid and force data from models, power curves were also generated. Many squid demonstrated partial (J-shaped) or full (U-shaped) parabolic patterns of O2 consumption rate as a function of swimming speed, with O2 consumption minima at 0.5–1.5 DML s–1. Power curves derived from hydrodynamic data plotted as a function of swimming speed were also parabolic, with power minima at 1.2–1.7 DML s–1. The parabolic relationship between O2 consumption rate/power and speed, which is also found in aerial flyers such as birds, bats and insects but rarely in aquatic swimmers because of the difficulties associated with low-speed respirometry, is the result of the high cost of generating lift and maintaining stability at low speeds and overcoming drag at high speeds. L. brevis has a lower rate of O2 consumption than the squid Illex illecebrosus and Loligo opalescens studied in swim tunnel respirometers and is energetically competitive (especially at O2 consumption minima) with fishes, such as striped bass, mullet and flounder. Therefore, the results of this study indicate that, like aerial flyers, some negatively buoyant nekton have parabolic patterns of O2 consumption rate/power as a function of speed and that certain shallow-water squid using considerable fin activity have swimming costs that are competitive with those of ecologically relevant fishes.
Effects of hypoxia on egg capsule conductance inAmbystoma(Class Amphibia, Order Caudata)
Authors: Mills Nathan E. , Barnhart M. Christopher , Semlitsch R. D. 
Published: April 2021

SUMMARYAquatic amphibian eggs frequently encounter hypoxic conditions that have the potential to limit oxygen uptake and thereby slow embryonic development and hatching. Oxygen limitation might be avoided if egg capsule surface area and oxygen conductance increased in response to hypoxia. We investigated this possibility in two salamander species, Ambystoma annulatum and Ambystoma talpoideum. The effective surface area of egg capsules increased in response to hypoxia, which increased the conductance for oxygen and enhanced oxygen transport. The ability of amphibian eggs to adjust their conductance in response to oxygen availability may increase survival in hypoxic environments.
Chemolithoheterotrophy in a metazoan tissue: thiosulfate production matches ATP demand in ciliated mussel gills
Authors: Doeller Jeannette E. , Grieshaber Manfred K. , Kraus David W. 
Published: April 2021

SUMMARY
The ribbed mussel Geukensia demissa inhabits sulfide-rich coastal sediments with a distribution that suggests a preference for exposure to sulfide. Although sulfide is a respiratory poison, it is also a potent reductant. Geukensia demissa gill mitochondria can use sulfide as a respiratory substrate for ATP production, and the gills of this species exhibit sulfide-supported oxygen consumption that matches the energy demand of ciliary beating. Here, we demonstrate (i) that the major product of G. demissa gill sulfide oxidation is thiosulfate and (ii) that the rate of sulfide oxidation also matches the cellular energy demand, resulting in a ratio near unity of oxygen consumed to sulfide oxidized at both low and high ciliary beat frequencies. A value for this ratio of unity is consistent with electrons from sulfide oxidation entering the mitochondrial electron transport chain. In the gills of the blue mussel Mytilus edulis from sulfide-free conditions, this ratio is 3–5 times higher, indicating an uncoupling of oxygen consumption from sulfide oxidation. Whereas M. edulis gills exhibit anaerobic metabolism during sulfide exposure, G. demissa gills do not, indicating a difference in sulfide tolerance between the two mussel species.