bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coherent light scattering by nanostructured collagen arrays in the caruncles of the malagasy asities (Eurylaimidae: aves)
Authors: Prum Richard O. , Torres Rodolfo , Kovach Christopher , Williamson Scott , Goodman Steven M. 
Published: April 2021

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

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

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

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

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

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

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

ABSTRACT
Central vascular blood flows and ventilation were measured in conscious toads (Bufo marinus) at 15 and 25 °C. The animals were exposed to hypoxia ( and 0.05, where is the fractional oxygen concentration of inspired air) at both temperatures. In addition, the cardiorespiratory responses to hypercapnia and atropine injection (5mgkg−1; 7.4 μmol kg−1) were studied at 25 °C. At 25 °C, systemic blood flow (Q̇sys) exceeded pulmocutaneous blood flow (Q̇pc), indicating a large net right-to-left shunt (Q̇pc/Q̇sys was 0.39). Q̇pc/Q̇sys was reduced significantly to 0.22 at 15 °C. At both temperatures, Q̇pc increased significantly during hypoxia (from 26.2 to 50.8ml min−1 kg−1 at 25 °C and from 11.2 to 18.9 ml min−1 kg−1 at 15 °C), whereas Q̇sys changed little (from 77.2 to 66.2ml min−1 kg−1 at 25 °C and from 54.3 to 50.1 ml min−1 kg−1 at 15 °C). As a result, the net right-to-left shunt was greatly reduced, while total cardiac output remained almost unaffected. The ventilatory response was more pronounced during hypercapnia but, since Q̇pc and Q̇sys were affected similarly, there was no change in the shunt pattern. In undisturbed toads at 25 °C, atropine injection increased Q̇pc and eliminated the net right-to-left shunt. This is consistent with the known vagal innervation of the pulmonary artery.
The present study shows that the cardiac right-to-left shunt that prevails in undisturbed and resting toads is reduced with increased temperature and during hypoxia. These findings are consistent with the general view that the cardiac right-to-left shunt is regulated and reduced whenever oxygen delivery is compromised or metabolic rate is increased.
In vivo bafilomycin-sensitive Na+ uptake in young freshwater fish
Authors: Fenwick J. C. , Bonga S. E. Wendelaar , Flik G. 
Published: April 2021

ABSTRACT
In vivo treatment with external bafilomycin A1, a selective inhibitor of V-ATPase H+ pumps, reduced whole-body Na+ influx by up to 90 % in young tilapia and 70 % in young carp. The inhibition was rapidly reversible, with whole-body Na+ influx rebounding to 280 % of pre-treatment values within 20 min of removal from the bafilomycin. This rebound effect is consistent with the prior accumulation of protons during the period when the cells were exposed to bafilomycin. Bafilomycin also inhibited Cl− uptake, an effect that was still apparent 30 min after the removal of bafilomycin. These data provide circumstantial evidence for previous suggestions that Na+ uptake in freshwater fish is associated with a proton-motive force created by a proton pump and indirect evidence for the major significance of this mechanism in the branchial uptake of Na+ by freshwater fish.
Motor control of tongue movement during prey capture in plethodontid salamanders
Authors: Deban Stephen M. , Dicke Ursula 
Published: April 2021

ABSTRACT
Four species of salamander of the family Plethodontidae were examined using electromyographic (EMG) recording during prey-capture behavior to test the hypotheses that the tongue retractor, tongue protractor and jaw depressor muscles are activated simultaneously and in a stereotyped pattern, as was found in other salamanders, and to determine whether species with different tongue morphologies and tongue protraction abilities exhibit different motor control strategies. The results show that sequential activation was observed far more frequently than simultaneous activation; the jaw depressor muscle was activated first, followed by the tongue protractor and then the tongue retractor. Species with short, attached tongues (Desmognathus quadramaculatus and Plethodon jordani) showed simultaneous activation more often than species with long, free tongues (Pseudotriton ruber and Hydromantes supramontis), which showed strongly non-simultaneous activation. Most EMG variables showed no effect of prey-capture success, suggesting that sensory feedback is not involved in modulating the motor pattern during the prey-capture strike. Hydromantes supramontis was examined for modulation of its motor pattern in response to prey distance, and several EMG variables were found to be positively correlated with tongue protraction distance. The motor pattern of strongly non-simultaneous activation of antagonistic tongue muscles has evolved along with the evolution of long, free tongues in plethodontids. The variable motor patterns observed provide further evidence that amphibian feeding in general is not as highly stereotyped as has been previously thought.
Feeding kinematics of phelsuma madagascariensis (Reptilia: gekkonidae): testing differences between iguania and scleroglossa
Authors: Delheusy Veronique , Bels Vincent L. 
Published: April 2021

ABSTRACT
The kinematics of feeding in the gekkotan lizard Phelsuma madagascariensis (Scleroglossa) was investigated using high-speed cinematography (200–300 frames s−1 ) and X-ray films (64 frames s−1 ). Qualitative kinematic analysis of the head and jaw displacement of the prey to (capture) and within (reduction, transport, swallowing, licking) the buccal cavity are compared for two types of prey (crickets and mealworms) in 30 feeding sequences from four individuals. Maximal displacement of structures and timing of events are compared statistically to assess the differences among the phases and the prey using analysis of variance. P. madagascariensis uses its jaws only to capture the two types of prey item, and the capture jaw cycle is divided into fast-opening (FO), fast-closing (FC) and slow-closing (SC) stages only. As in iguanians and other scleroglossans, the reduction and transport cycles always involve a slow opening (SOI and SOII) stage before the FO stage, followed by FC and SC stages: this last stage was not easily identified in all feeding phase. Transport of the prey was followed by a large number of licking cycles. Our data show (i) that the capture profile in gekkotans is similar to that observed for other scleroglossans and different from that described for iguanians (e.g. the absence of an SO stage); (ii) that the kinematics of jaw and related hyo-lingual cycles of intraoral manipulation (reduction and transport) are similar in lizards with a very different hyo-lingual system (Iguania, Gekkota and Scincomorpha), suggesting a basic mechanism of feeding cycles in squamates, transformed in varanids and snakes; and (iii) that prey type affects the kinematics of capture and manipulation, although the high level of variation among lizards suggests a possible individual modulation of feeding mechanism. A principal components analysis was performed to compare capture and transport cycles in this study of P. madagascariensis (Gekkota) and a previous study of Oplurus cuvieri (Iguania). This analysis separated the capture cycle of each species, but the transport cycles were not completely separated. These results demonstrate the complexity of the modulation and evolution of feeding process in squamates.
Collagen-stimulated unidirectional translocation of cholesterol in human platelet membranes
Authors: Boesze-Battaglia Kathleen , Schimmel Richard J. 
Published: April 2021

ABSTRACT
When human platelets are stimulated with collagen or thrombin, the asymmetric distribution of membrane lipids is disrupted as phosphatidylserine and phosphatidylethanolamine translocate from the inner monolayer to the outer monolayer. Coincident with the stimulus-dependent rearrangement of membrane phospholipids is a rapid redistribution of cholesterol from the outer to the inner membrane monolayer. This redistribution of cholesterol was observed when the stimulus was collagen or ADP. The data presented here show that epinephrine stimulation does not promote cholesterol translocation but does potentiate collagen-promoted movement of cholesterol. To investigate the process of cholesterol translocation, experiments were performed to determine whether collagen stimulated reverse cholesterol movement; i.e. from the inner to the outer monolayer. For this study, the fluorescent sterol cholestatrienol (C-3) was incorporated into platelet membranes by exchange from cholesterol-containing phosphatidylcholine small unilamellar vesicles. C-3 was then removed selectively from the outer monolayer by treatment of the platelets with bovine serum albumin (BSA). During the subsequent incubation of BSA-treated platelets, C-3 moved spontaneously into the outer from the inner monolayer. This translocation had an apparent half-time of approximately 25 min and was unaltered by the presence of collagen. These results suggest that collagen treatment of platelets selectively facilitates the inward movement of the sterol. We have hypothesized that cholesterol translocation may be thermodynamically driven as a result of an unfavorable entropy, resulting in cholesterol translocation out of an environment becoming enriched in phosphatidylethanolamine. The unidirectional nature of collagen-promoted cholesterol movement from the phosphatidylethanolamine-rich outer monolayer is consistent with this interpretation.
Sexual behaviour in Euplotes raikovi is accompanied by pheromone-induced modifications of ionic currents
Authors: Stock Christian , Krüppel Thomas , Key Gundula , Lueken Wolfgang 
Published: April 2021

ABSTRACT
In the marine ciliate Euplotes raikovi, pheromone released by a complementary mating type (nonself pheromone) induces typical sexual behaviour, whereas self pheromone released by the same mating type generally has no effect. Nonself pheromone evokes a reduction of the mean walking speed by 66 %, a threefold increase in the frequency and duration of long-lasting rest phases and a doubling in the number of side-stepping reactions. Consequently, translocation is strongly reduced and the cells remain in a small area. This could increase the probability of finding a sexual partner for pair formation (conjugation). The usual pattern of rhythmic, spontaneous depolarizations controlling the walking rhythm is absent in nonself-pheromone-stimulated cells. The remaining depolarizations arise from a 4 mV hyperpolarized membrane potential and do not reach the usual amplitudes of 15–20 mV but only of 6–10 mV. In addition, the amplitudes of K+ currents are increased at depolarizations of more than 20 mV by at least 30 %. Hyperpolarization- and depolarization-activated Na+ current amplitudes are increased, whereas the Ca2+ current amplitude remains nearly unaffected.
Running, breathing and visceral motion in the domestic rabbit (Oryctolagus cuniculus): testing visceral displacement hypotheses
Authors: Simons Rachel S. 
Published: April 2021

ABSTRACT
The relative motion of the visceral mass may be important to ventilation during running. A visceral piston hypothesis predicts that, during galloping, cranial motion of the liver during expiration and caudal motion of the liver during inspiration may characterize efficient quadrupedal mammalian locomotion. Although a theoretical model based on vibration mechanics casts doubt on this prediction, only limited direct measurements of visceral mass motion during galloping have been reported. In the present study, mechanical interactions between running, breathing and liver oscillations in the domestic rabbit are recorded using synchronized videographic, cineradiographic and pneumotachographic techniques. The analysis focuses on the variation in locomotor–respiratory coupling (LRC) and on the relative position of the liver. Results from running rabbits show (1) variation in phase angle between the locomotor and respiratory periods that is inconsistent with the 1:1 LRC ratio that has been reported for other galloping mammals; (2) a tendency towards a 1:1 LRC ratio at higher speeds and stride frequencies; and (3) that the relative motion of the liver is caudal during expiration and cranial during inspiration, which is inconsistent with the visceral piston hypothesis. The data presented here are generally consistent with the theoretical vibration mechanics model for liver motion and with a pneumatic stabilization hypothesis that the lungs serve an important role in the stabilization of the thorax during locomotion.