bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gliding Flight: Speed and Acceleration of Ideal Falcons During Diving and Pull Out
Authors: Tucker Vance A. 
Published: April 2021

ABSTRACT
Some falcons, such as peregrines (Falco peregrinus), attack their prey in the air at the end of high-speed dives and are thought to be the fastest of animals. Estimates of their top speed in a dive range up to 157 m s−1, although speeds this high have never been accurately measured. This study investigates the aerodynamic and gravitational forces on ‘ideal falcons’ and uses a mathematical model to calculate speed and acceleration during diving. Ideal falcons have body masses of 0.5–2.0 kg and morphological and aerodynamic properties based on those measured for real falcons.
The top speeds reached during a dive depend on the mass of the bird and the angle and duration of the dive. Given enough time, ideal falcons can reach top speeds of 89–112 m s−1 in a vertical dive, the higher speed for the heaviest bird, when the parasite drag coefficient has a value of 0.18. This value was measured for low-speed flight, and it could plausibly decline to 0.07 at high speeds. Top speeds then would be 138–174 m s−1.
An ideal falcon diving at angles between 15 and 90 ° with a mass of 1 kg reaches 95 % of top speed after travelling approximately 1200 m. The time and altitude loss to reach 95 % of top speed range from 38 s and 322 m at 15 ° to 16 s and 1140 m at 90 °, respectively.
During pull out at top speed from a vertical dive, the 1 kg ideal falcon can generate a lift force 18 times its own weight by reducing its wing span, compared with a lift force of 1.7 times its weight at full wing span. The falcon loses 60 m of altitude while pulling out of the dive, and lift and loss of altitude both decrease as the angle of the dive decreases.
The 1 kg falcon can slow down in a dive by increasing its parasite drag and the angle of attack of its wings. Both lift and drag increase with angle of attack, but the falcon can cancel the increased lift by holding its wings in a cupped position so that part of the lift is directed laterally. The increased drag of wings producing maximum lift is great enough to decelerate the falcon at −1.5 times the acceleration of gravity at a dive angle of 45 ° and a speed of 41 m s−1 (0.5 times top speed).
Real falcons can control their speeds in a dive by changing their drag and by choosing the length of the dive. They would encounter both advantages and disadvantages by diving at the top speeds of ideal falcons, and whether they achieve those speeds remains to be investigated.
Tissue-Specific Effects of Hypothyroidism On Postnatal Muscle Development In The Barnacle Goose
Authors: Deaton Katie E. , Bishop Charles M. , Butler Patrick J. 
Published: April 2021

ABSTRACT
The hypothesis that tissue-specific levels of thyroid hormones may be required for normal locomotor muscle development was investigated in the barnacle goose Branta leucopsis. Hypothyroidism was induced in goslings by treatment with methimazole from either 3 days or 2 weeks of age, and birds were killed at 7 weeks of age. The masses of the pectoralis, iliofibularis, semimembranosus and cardiac ventricle muscles were measured, and samples from these tissues were analysed for the mass-specific activity of the mitochondrial enzyme citrate synthase (CS). An ultrastructural electron micrograph analysis of the pectoralis was also carried out. No significant differences were found between the two hypothyroid groups except for the effect on the relative mass of the iliofibularis muscle. Developmental responses to hypothyroidism were found to be tissue-specific. Hypothyroidism resulted in a significantly lower relative cardiac ventricle mass (by 17 %) and CS activity of the leg muscles (by 34 %), while absolute leg muscle mass was not affected. The relative mass of the pectoralis was significantly lower (by 57 %) in hypothyroid birds and showed a significant, uniformly lower CS activity (by 60–83 %) as a result of a lower mitochondrial fractional volume. Haematocrit and capillary-to-fibre ratio in the pectoralis were also significantly lower in hypothyroid birds, and skeletal growth and plumage development were affected.
Limits for Oxygen and Substrate Transport in Mammals
Authors: Hoppeler H. , Weibel E. R. 
Published: April 2021

ABSTRACT
Environmental oxygen is transported by the respiratory cascade to the site of oxidation in active tissues. Under conditions of heavy exercise, it is ultimately the working skeletal muscle cells that set the aerobic demand because over 90% of energy is spent in muscle cells. The pathways for oxygen and substrates converge in muscle mitochondria. In mammals, a structural limitation of carbohydrate and lipid transfer from the microvascular system to the muscle cells is reached at a moderate work intensity (i.e. at 40–50% of ). At higher work rates, intracellular substrate stores must be used for oxidation. Because of the importance of these intracellular stores for aerobic work, we find larger intramyocellular substrate stores in ‘athletic’ species as well as in endurance-trained human athletes. The transfer limitations for carbohydrates and lipids at the level of the sarcolemma imply that the design of the respiratory cascade from lungs to muscle mitochondria reflects primarily oxygen demand. Comparative studies indicate that the oxidative capacity of skeletal muscle tissue, and hence maximal oxygen demand, is adjusted by varying mitochondrial content. At the level of microcirculatory oxygen supply, it is found that muscle tissue capillarity is adjusted to muscle oxygen demand but that the capillary erythrocyte volume also plays a role. Oxygen delivery by the heart has long been recognized to be a key link in the oxygen transport chain. In allometric variation it is heart rate and in adaptive variation it is essentially stroke volume, and hence heart size, that determines maximal cardiac output. Again, haematocrit is an important variable that allows the heart of athletic species to generate higher flux rates for oxygen. The pulmonary gas exchanger offers only a negligible resistance to oxygen flux to the periphery. However, in contrast to all other steps in the respiratory cascade, the lungs have only a minimal phenotypical plasticity and appear, therefore, to be built with considerable structural redundancy in all but the most athletic species. Because of the lack of malleability, the lungs may ultimately become limiting for when adaptive processes have maximized O2 flux through the malleable downstream elements of the respiratory system: the heart, microcirculation and muscle mitochondria.
Functional Adaptations of Oxygen-Transport Proteins
Authors: Terwilliger Nora B. 
Published: April 2021

ABSTRACT
Oxygen-transport proteins are multisubunit, circulating molecules that provide an efficient supply of oxygen to metabolically active metazoans. Hemoglobins, hemerythrins and hemocyanins have evolved in both structural and functional diversity and exhibit functional repertoires beyond that of simple, monomeric tissue myoglobins. Their phylogenetic distribution is intriguing, especially with respect to those organisms that express more than one type of oxygen-transport protein. An animal can modify the delivery of oxygen to its tissues by varying the rate of synthesis of these proteins or by selective expression of individual subunits and/or molecules.
Changes in levels of allosteric modifiers that affect the protein’s oxygenation properties will also modify oxygen delivery; some organisms have more ability than others to control concentrations of modulators. Hemoglobins have assumed functions in addition to oxygen transport, while hemocyanins have diversified through multiple gene duplications and functional specializations. Understanding the mechanisms of regulation of expression, synthesis and modulator levels is a key focus of current investigations.
Intracellular Oxygen Diffusion: the Roles of Myoglobin and Lipid at Cold Body Temperature
Authors: Sidell Bruce D. 
Published: April 2021

ABSTRACT
Cold temperature can constrain the rate of oxygen movement through muscle cells of ectothermic animals because the kinetic energy of the solvent–solute system decreases and the viscosity of the aqueous cytoplasm increases during cooling within the physiological range of body temperatures. These factors affect the movement of both dissolved oxygen and oxymyoglobin, the two predominant routes of intracellular oxygen diffusion in vertebrate oxidative muscles. In addition, reductions in temperature have been shown to increase the affinity of myoglobin for oxygen and to slow the rate of Mb O2-dissociation, compromising the ability of this oxygen-binding protein to facilitate intracellular oxygen diffusion. Experiments with both seasonally cold-bodied fishes and polar fish species suggest that several factors combine to overcome these limitations in delivery of oxygen from the blood to the mitochondria. First, reductions in body temperature induce increases in mitochondrial density of oxidative muscle cells, reducing the mean diffusional pathlength for oxygen between capillaries and mitochondria. Second, cold body temperature in both temperate-zone and polar fishes is frequently correlated with a high content of neutral lipid in oxidative muscles, providing an enhanced diffusional pathway for oxygen through the tissue. Third, recent data indicate that myoglobins from fish species bind and release oxygen more rapidly at cold temperature than do those from mammals. Data from both oxidative skeletal muscle and cardiac muscle of fishes suggest that these factors in various combinations contribute to enhance the aerobically supported mechanical performance of the tissues at cold cellular temperatures.
Oxygen Sensing, Hypoxia-Inducible Factor-1 and the Regulation of Mammalian Gene Expression
Authors: Ratcliffe Peter J. , O’rourke John F. , Maxwell Patrick H. , Pugh Christopher W. 
Published: April 2021

ABSTRACT
A great many aspects of the anatomy and physiology of large animals are constrained by the need to match oxygen supply to cellular metabolism and appear likely to involve the regulation of gene expression by oxygen. Some insight into possible underlying mechanisms has been provided by studies of erythropoietin, a haemopoietic growth factor which stimulates red cell production in response to hypoxia. Studies of hypoxia-inducible cis-acting sequences from the erythropoietin gene have led to the recognition of a widespread transcriptional response to hypoxia based on the activation of a DNA-binding complex termed hypoxia-inducible factor-1 (HIF-1). Perturbation of the transcriptional response by particular transition metal ions, iron chelators and certain redox-active agents have suggested a specific oxygen sensing mechanism, perhaps involving a haem protein in a flavoprotein/cytochrome system. In addition to erythropoietin, HIF-1-responsive genes include examples with functions in cellular energy metabolism, iron metabolism, catecholamine metabolism, vasomotor control and angiogenesis, suggesting an important role in the coordination of oxygen supply and cellular metabolism. In support of this, we have demonstrated an important role for HIF-1 in tumour angiogenesis. HIF-1 itself consists of a heterodimer of two basic-helix–loop–helix proteins of the PAS family, termed HIF-1α and HIF-1β, although other closely related members of this family may also contribute to the response to hypoxia. We have fused domains of HIF-1 genes to heterologous transcription factors to assay for regulatory function. These experiments have defined several domains in HIF-1α which can independently confer the hypoxia-inducible property, and they suggest a mechanism of HIF-1 activation in which post-translational activation/derepression of HIF-1α is amplified by changes in HIF-1α abundance most probably arising from suppression of proteolytic breakdown. Pursuit of the mechanism(s) underlying these processes should ultimately lead to better definition of the oxygen-sensing process.
Multilayer Reflectors in Animals Using Green and Gold Beetles as Contrasting Examples
Authors: Parker Andrew R. , Mckenzie David R. , Large Maryanne C. J. 
Published: April 2021

ABSTRACT
The light reflectors in the beetles Calloodes grayanus and Anoplognathus parvulus are examined. Contrasting multilayer reflectors are revealed. Calloodes grayanus appears a weak green colour, matching its background leaves, while A. parvulus is strongly metallic-gold coloured. The former reflection is diffuse, as the result of a structure causing scattering that overlies the multilayer reflector, whereas the latter reflection is strongly directional. The green colour of C. grayanus is achieved by a multilayer reflector with a fixed spatial periodicity, here termed ‘regular’, which is far removed from the quarterwave, or physically ‘ideal’, condition. The gold colour of A. parvulus is achieved by a type of reflector which involves systematically changing optical thicknesses of the component layers with depth in the structure. A layer of melanin underlies the reflector of C. grayanus to absorb the transmitted portion of light and prevent its back-reflectance, which would otherwise alter the green colour. The resultant structural reflectance from C. grayanus effectively matches green pigments, which are rare in beetles.
Visual Pigments, Oil Droplets and Cone Photoreceptor Distribution in the European Starling (Sturnus Vulgaris)
Authors: Hart N. S. , Partridge J. C. , Cuthill I. C. 
Published: April 2021

ABSTRACT
Microspectrophotometric measurements of retinal photoreceptors from the European starling (Sturnus vulgaris) revealed four classes of single cone, containing visual pigments with wavelengths of maximum absorbance (λmax) at 563, 504, 449 and close to 362 nm. The two longer-wave-sensitive single cones contained brightly coloured oil droplets which cut off light below 572 and 514 nm, respectively. The 449 nm λmax pigment was associated with a ‘colourless’ oil droplet with peak measured absorptance below 400 nm. The ultraviolet-sensitive visual pigment was paired with a transparent oil droplet which showed no significant absorption above 350 nm. A single class of double cone was identified, both members of which contained the longwave-sensitive (λmax 563 nm) visual pigment. The principal member of the double cone contained an oil droplet with a topographically variable cut-off wavelength below 471 nm; the oil droplet found in the accessory member was only measured in the ventral retina and displayed three distinct peaks of absorption at approximately 430, 450 and 480 nm. Rod photoreceptors had a λmax at 503 nm. A new polynomial for fitting visual pigment templates to ultraviolet-sensitive visual pigment data is given. Topographic density measurements of the different cone classes were made using Nitroblue-tetrazolium chloride to label selectively bleached photoreceptors. The two classes of shortwave-sensitive single cone were more abundant in the dorsal retina, and longwave-sensitive single cones were notably less abundant in the dorso-temporal region of the retina, which subserves binocular vision.
Prey capture in the weakly electric fish Apteronotus albifrons: sensory acquisition strategies and electrosensory consequences
Authors: Nelson Mark E. , Maciver Malcolm A. 
Published: April 2021

ABSTRACT
Sensory systems are faced with the task of extracting behaviorally relevant information from complex sensory environments. In general, sensory acquisition involves two aspects: the control of peripheral sensory surfaces to improve signal reception and the subsequent neural filtering of incoming sensory signals to extract and enhance signals of interest. The electrosensory system of weakly electric fish provides a good model system for studying both these aspects of sensory acquisition. On the basis of infrared video recordings of black ghost knifefish (Apteronotus albifrons) feeding on small prey (Daphnia magna) in the dark, we reconstruct three-dimensional movement trajectories of the fish and prey. We combine the reconstructed trajectory information with models of peripheral electric image formation and primary electrosensory afferent response dynamics to estimate the spatiotemporal patterns of transdermal potential change and afferent activation that occur during prey-capture behavior. We characterize the behavioral strategies used by the fish, with emphasis on the functional importance of the dorsal edge in prey capture behavior, and we analyze the electrosensory consequences. In particular, we find that the high-pass filter characteristics of P-type afferent response dynamics can serve as a predictive filter for estimating the future position of the prey as the electrosensory image moves across the receptor array.
Design features for electric communication
Authors: Hopkins Carl D. 
Published: April 2021

ABSTRACT
How do the communication discharges produced by electric fish evolve to accommodate the unique design features for the modality? Two design features are considered: first, the limited range of signaling imposed on the electric modality by the physics of signal transmission from dipole sources; and second, the absence of signal echoes and reverberations for electric discharges, which are non-propagating electrostatic fields.
Electrostatic theory predicts that electric dicharges from fish will have a short range because of the inverse cube law of geometric spreading around an electrostatic dipole. From this, one predicts that the costs of signaling will be high when fish attempt to signal over a large distance. Electric fish may economize in signal production whenever possible. For example, some gymnotiform fish appear to be impedance-matched to the resistivity of the water; others modulate the amplitude of their discharge seasonally and diurnally.
The fact that electric signals do not propagate, but exist as electrostatic fields, means that, unlike sound signals, electric organ discharges produce no echoes or reverberations. Because temporal information is preserved during signal transmission, receivers may pay close attention to the temporal details of electric signals. As a consequence, electric organs have evolved with mechanisms for controlling the fine structure of electric discharge waveforms.
Neural architecture of the electrosensory lateral line lobe: adaptations for coincidence detection, a sensory searchlight and frequency-dependent adaptive filtering
Authors: Berman Neil J. , Maler Leonard 
Published: April 2021

ABSTRACT
The electrosensory lateral line lobe (ELL) of weakly electric fish is the only nucleus that receives direct input from peripheral electroreceptor afferents. This review summarises the neurotransmitters, receptors and second messengers identified in the intrinsic circuitry of the ELL and the extrinsic descending direct and indirect feedback pathways, as revealed by recent in vitro and in vivo studies. Several hypotheses of circuitry function are examined on this basis and on the basis of recent functional evidence: (1) fast primary afferent excitatory postsynaptic potentials (EPSPs) and fast granule cell 2 GABAA inhibitory postsynaptic potentials (IPSPs) suggest the involvement of basilar pyramidal cells in coincidence detection; (2) voltage-dependent EPSPs and IPSPs, dendritic spike bursts and frequency-dependent synaptic facilitation support a sensory searchlight role for the direct feedback pathway; and (3) the contributions of distal and proximal inhibition, anti-Hebbian plasticity and beam versus isolated fiber activity patterns are discussed with reference to an adaptive spatio-temporal filtering role for the indirect descending pathway.
Encoding and processing of sensory information in neuronal spike trains
Authors: Gabbiani F. , Metzner W. 
Published: April 2021

ABSTRACT
Recently, a statistical signal-processing technique has allowed the information carried by single spike trains of sensory neurons on time-varying stimuli to be characterized quantitatively in a variety of preparations. In weakly electric fish, its application to first-order sensory neurons encoding electric field amplitude (P-receptor afferents) showed that they convey accurate information on temporal modulations in a behaviorally relevant frequency range (&lt;80 Hz). At the next stage of the electrosensory pathway (the electrosensory lateral line lobe, ELL), the information sampled by first-order neurons is used to extract upstrokes and downstrokes in the amplitude modulation waveform. By using signal-detection techniques, we determined that these temporal features are explicitly represented by short spike bursts of second-order neurons (ELL pyramidal cells). Our results suggest that the biophysical mechanism underlying this computation is of dendritic origin. We also investigated the accuracy with which upstrokes and downstrokes are encoded across two of the three somatotopic body maps of the ELL (centromedial and lateral). Pyramidal cells of the centromedial map, in particular I-cells, encode up- and downstrokes more reliably than those of the lateral map. This result correlates well with the significance of these temporal features for a particular behavior (the jamming avoidance response) as assessed by lesion experiments of the centromedial map.
Molecular Biology of the Apteronotus NMDA Receptor NR1 Subunit
Authors: Dunn Robert J. , Bottai Daniele , Maler Leonard 
Published: April 2021

ABSTRACT
The complete sequences and expression patterns of the NR1 (aptNR1) subunit of the N-methyl-D-aspartate (NMDA) receptor and its alternative splice isoforms have been determined for the weakly electric fish Apteronotus leptorhynchus. The deduced amino acid sequence of aptNR1 is approximately 88 % identical to the NR1 sequences of other vertebrate. Two of the three alternative splice cassettes previously described for mammalian NR1s, N1 and C1, are present in aptNR1, but the third cassette, C2, is not found. In addition, two teleost-specific splice cassettes occur on the N-terminal side of the C1 sequence. The cellular patterns of aptNR1 expression, including the patterns of N1 and C1 splicing, have been mapped using the in situ hybridization technique. High levels of aptNR1 mRNA were detected throughout the central nervous system including most neurons of the electrosensory system, with the highest levels in electrosensory lateral line lobe pyramidal cells. Expression of the N1 splice isoform was higher in more caudal regions of the brain, and expression of the C1 splice isoform was higher in more rostral regions. The N1 splice isoform was present in almost all NR1-positive cells, in contrast to the C1 splice isoform which was restricted to a subset of NR1-positive cells. These results demonstrate that the NR1 subunit of the NMDA receptor is evolutionarily conserved across species and that regulation of alternative RNA splicing modulates the properties of NR1 in different neurons of the central nervous system of A. leptorhynchus.
Synaptic plasticity in the mormyrid electrosensory lobe
Authors: Bell Curtis C. , Han Victor Z. , Sugawara Yoshiko , Grant Kirsty 
Published: April 2021

ABSTRACT
The mormyrid electrosensory lateral line lobe (ELL) is one of several different sensory structures in fish that behave as adaptive sensory processors. These structures generate negative images of predictable features in the sensory inflow which are added to the actual inflow to minimize the effects of predictable sensory features. The negative images are generated through a process of association between centrally originating predictive signals and sensory inputs from the periphery. In vitro studies in the mormyrid ELL show that pairing of parallel fiber input with Na+ spikes in postsynaptic cells results in synaptic depression at the parallel fiber synapses. The synaptic plasticity observed at the cellular level and the associative process of generating negative images of predicted sensory input at the systems level share a number of properties. Both are rapidly established, anti-Hebbian, reversible, input-specific and tightly restricted in time. These common properties argue strongly that associative depression at the parallel fiber synapse contributes to the adaptive generation of negative images in the mormyrid ELL.