bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Gregarizing Factor Present In The Egg Pod Foam Of The Desert Locust Schistocerca Gregaria
Authors: Mccaffery Alan R. , Simpson Stephen J. , Islam M. Saiful , Roessingh Peter 
Published: April 2021

ABSTRACT
The behavioural phase state and coloration of hatchling Schistocerca gregaria were examined in a series of experiments to determine the means by which phase characteristics are passed between generations. Both crowding of solitary-reared females at the time of oviposition and high egg pod densities promoted behavioural gregarization, although the former appeared to be a rather more potent factor. In contrast, egg pod density alone appeared to promote the development of hatchlings with dark patterns characteristic of the gregarious phase. The phase characteristics of hatchlings were unaffected when sand previously used for oviposition was used to collect further egg pods. Early separation of presumptive gregarious eggs from egg pods laid by crowd-reared females led to solitarization of the hatchlings, indicating that a factor, either in or around the eggs, removed by early separation promoted gregarization. Both the eggs and foam plugs of egg pods from crowd-reared, gregarious females appeared to be a source of this gregarizing factor. In contrast, there was no evidence for a solitarization factor in egg pods from solitary-reared S. gregaria. Saline extracts of egg pod foam plugs produced an active factor which promoted gregarization both in eggs from solitary-reared females and in eggs from gregarious females which were separated and washed to removed the factor. Solitary eggs were influenced by the gregarizing factor in foam plug extracts for up to 1 day after oviposition. Saline extracts of foam plug retained their activity for up to 1 day. Initial studies on the properties of this factor were made. We conclude that the foam plugs of egg pods from crowd-reared, gregarious locusts contain a small (&lt;3 kDa), hydrophilic gregarizing factor which is produced at the time of oviposition and which predisposes hatchlings to attain characteristics of the gregarious phase.
A Protein Titration Hypothesis for the Temperature-Dependence of Tissue CO2 Content in Reptiles and Amphibians
Authors: Stinner J. N. , Hartzler L. K. , Grguric M. R. , Newlon D. L. 
Published: April 2021

ABSTRACT
Whole-body CO2 stores are known to increase with cooling in reptiles and amphibians (−Δ[CO2]/ΔT ). The aim of this study was to determine the mechanism(s) producing this inverse relationship. The Δ[CO2]/ΔT coefficients were determined for eight reptilian and one amphibian species and were found to differ by a factor of approximately 10, from −0.21 mmol kg−1 °C−1 in the Mediterranean spur-thighed tortoise Testudo graeca to −0.02 mmol kg−1 °C−1 in the bullfrog Rana catesbeiana. The Δ[CO2]/ΔT coefficients were correlated with values in the literature for in vivo plasma ΔpH/ΔT coefficients (Δ[CO2]/ΔT=−0.18–8.24ΔpH/ΔT; r2=0.87). Plasma electrolyte concentrations (Na+, K+, Ca2+, Mg2+, Cl−, inorganic phosphate, SO42−; and lactate), [protein], [CO2], PCO2 and pH were measured in chronically cannulated resting black racer snakes Coluber constrictor. When the temperature was reduced from 30 to 10 °C, pH increased slightly (by −0.0028 pH units °C−1), decreased by 7 mmHg, [CO2] increased by 3.2 mmol l−1 and [HPO42−+H2PO4−] increased by 0.7 mmol l−1. Concentrations of protein and of the remaining electrolytes were not significantly different (P&gt;0.05) at 30 and 10 °C. Net plasma protein charge, calculated from the principle of electroneutrality (the sum of the cations in mequiv = the sum of anions in mequiv), was −0.48 mequiv g−1 protein at 30 °C and −0.38 mequiv g−1 protein at 10 °C. This 21 % decrease was attributed to the increases in [CO2] (i.e. carbonic acid) and inorganic phosphate concentration. Between 30 and 10 °C, skeletal muscle pH and [CO2] in C. constrictor increased (by −0.009 units °C−1 and −0.125 mmol kg−1 °C−1, respectively), [Na+] and [Cl−] each decreased by approximately 12 mequiv l−1, and [K+] and the percentage of water did not change significantly. It is concluded that the increase in whole-body CO2 stores with cooling in reptiles and amphibians results from the passive effects of temperature changes upon the ionization constants of proteins and the active adjustment of (ventilatory regulation), so that −ΔpK is greater than −ΔpH. Active transmembrane ion-exchange processes do not appear to be involved.
Processing Of Defensive Pigment in Aplysia Californica: Acquisition, Modification And Mobilization Of The Red Algal Pigment R-Phycoerythrin By The Digestive Gland
Authors: Coelho L. , Prince J. , Nolen T. G. 
Published: April 2021

ABSTRACT
The marine snail Aplysia californica obtains its purple defensive ink exclusively from the accessory photosynthetic pigment r-phycoerythrin, which is found in the red seaweeds of its diet. The rhodoplast digestive cell, one of three types of cell lining the tubules of the digestive gland, appears to be the site of catabolism of red algal chloroplasts (rhodoplasts) since thylakoid membranes, including phycobilisome-sized membrane-associated particles, were found within the large digestive vacuoles of this cell. Immunogold localization showed that there was a statistically significant occurrence of the red algal phycobilisome pigment r-phycoerythrin within these rhodoplast digestive vacuoles, but not in other compartments of this cell type (endoplasmic reticulum, mitochondria, nucleus) or in other tissues (abdominal ganglion).
Immunogold analysis also suggested that the rhodoplast vacuole is the site for additional modification of r-phycoerythrin, which makes it non-antigenic: the chromophore is either cleaved from its biliprotein or the biliprotein is otherwise modified. The hemolymph had spectrographic absorption maxima typical of the protein-free chromophore (phycoerythrobilin) and/or r-phycoerythrin, but only when the animal had been feeding on red algae. Rhodoplast digestive cells and their vacuoles were not induced by the type of food in the diet: snails fed green seaweed and animals fed lettuce had characteristic rhodoplast cells but without the large membranous inclusions (rhodoplasts) or phycobilisome-like granules found in animals fed red seaweed.
Two additional cell types lining the tubules of the digestive gland were characterized ultrastructurally: (1) a club-shaped digestive cell filled with electron-dense material, and (2) a triangular ‘secretory’ cell devoid of storage material and calcium carbonate.
The following model is consistent with our observations: red algal rhodoplasts are freed from algal cells in the foregut and then engulfed by rhodoplast digestive cells in the tubules of the digestive diverticula, where they are digested in membrane-bound vacuoles; r-phycoerythrin is released from phycobilisomes on the rhodoplast thylakoids and chemically modified before leaving the digestive vacuole and accumulating in the hemolymph; the pigment then circulates throughout the body and is concentrated in specialized cells and vesicles of the ink gland, where it is stored until secreted in response to certain predators.
Ontogeny Of Hemocyanin Function In The Dungeness Crab Cancer Magister: Hemolymph Modulation Of Hemocyanin Oxygen-Binding
Authors: Brown A. Christine , Terwilliger Nora B. 
Published: April 2021

ABSTRACT
The in vivo oxygen-binding characteristics of Cancer magister whole hemolymph were compared across developmental stages with those of purified hemocyanin. When the 25S hemocyanins from first-instar juvenile and adult C. magister were dialyzed against first-instar juvenile saline, the P50 values at pH 7.8 differed by 54 %: 2.16 kPa for the adult and 4.68 kPa for the first-instar juvenile. Since both purified proteins were examined under identical conditions, this represents an intrinsic stage-specific difference in hemocyanin O2-affinity. When the two types of hemocyanin were dialyzed against their respective stage-specific salines, the oxygen affinities differed by only 28 %: 3.39 kPa for the adult and still 4.68 kPa for the first-instar juvenile. Thus, the intrinsic difference in hemocyanin O2-affinity was reduced by the stage-specific differences in hemolymph ion concentrations. Even more significant is the fact that the whole-hemolymph P50 values of the juvenile and adult were indistinguishable at in vivo pH and divalent cation levels specific for each stage. Thus, despite significant differences in the intrinsic oxygen affinity of the purified 25S hemocyanin during development, the whole-hemolymph oxygen-binding properties are conserved. In the juvenile crab, it appears that the low-affinity hemocyanin serves to modulate the effects of a weak renal regulation of [Mg2+]. As ion regulation is enhanced during development and divalent cation levels decrease, the crab synthesizes higher-affinity hemocyanin.
Intratesticular Distribution Of Cyritestin, A Protein Involved In Gamete Interaction
Authors: Forsbach Alexandra , Heinlein Uwe A. O. 
Published: April 2021

ABSTRACT
Cyritestin, a member of the ADAM family of proteins, has been shown to be involved in the interaction between sperm and egg during fertilization. The protein is a transmembrane protein associated with the sperm acrosome. In the present study, electron microscopy was used to trace the distribution of the cyritestin molecule in intratesticular germ cells, particularly in haploid round spermatids where the acrosomal structure is differentiating. Our results indicate that cyritestin is transported to the forming acrosomal vesicle through the Golgi apparatus to become part of the acrosomal membrane. Differential staining with antibodies recognizing either the metalloprotease-like domain or the cytoplasmic domain of cyritestin indicates that processing of the molecule leading to the loss of the pro- and metalloproteinase-like domains begins during germ cell stage 6 and is completed before stage 15.
Predicting Force Generation by Lamprey Muscle During Applied Sinusoidal Movement Using A Simple Dynamic Model
Authors: Williams Thelma L. , Bowtell Graham , Curtin N. A. 
Published: April 2021

ABSTRACT
Experiments were performed on single-myotome preparations of lamprey muscle, to discover whether force developed by intermittent tetanic stimulation during imposed sinusoidal movement could be predicted by data collected from isometric and constant-velocity experiments. We developed a simple dynamic model consisting of a set of simultaneous ordinary differential equations with unknown parameters. Appropriate values of the parameters were found by fitting numerical solutions of the differential equations to data from the isometric and constant-velocity experiments. Predictions were made of the time course of force developed during imposed sinusoidal movement in which the phase between muscle shortening and tetanic stimulation was varied to cover the whole phase spectrum. The match between the predicted and recorded time courses was very good for all phases, and particularly for those phases that are seen during swimming in the intact animal.
Salt and Water Relations, and Nitrogen Excretion, in the Amphibious African Freshwater Crab Potamonautes Warreni in Water and in Air
Authors: Morris S. , Aardt W. J. Van 
Published: April 2021

ABSTRACT
Mechanisms of salt and water conservation, and nitrogen excretion, were investigated in the freshwater amphibious crab Potamonautes warreni from the High Veld of South Africa. Adaptations to fresh water were assessed as pre-adaptations to air-breathing, and nitrogen excretion was examined as a potential constraint to terrestrial excursions. P. warreni was able to regulate water and salt loss in water up to 40 % sea water, but not in 80 % sea water. The water permeability of P. warreni was low and, since 97 % of the haemolymph filtrate was reabsorbed in the antennal organ, urinary water loss was minimal (0.7 μl g−1 h−1). The minimum equilibrium [Na] of P. warreni was low (0.116 mmol l−1), as were the rates of both Na loss (0.22 μmol g−1 h−1) and Ca loss (0.29 μmol g−1 h−1). The low loss rates were due to urinary salt conservation of approximately 90 % or better and to low permeability , and were compensated for by a high-affinity uptake mechanism (Jmax=0.76 μmol g−1 h−1 and Km=0.18 mmol l−1). Acclimating P. warreni to low Na concentrations increased maximum net Na uptake rate to 1.77 μmol g−1 h−1.
Nitrogen excretion in P. warreni was almost 100 % ammoniotelic, and there was no accumulation of haemolymph or urinary ammonia or urea when in air. P. warreni was unable to excrete ammonia to air, but in water the rate of excretion was nearly 70 μmol kg−1 h−1. Crabs in amphibious conditions showed pulses of elevated NH3 excretion (350 μmol kg−1 h−1) when subsequently submerged, while for crabs breathing air for 3 days this pulse reached 4.9 mmol kg−1 h−1. Air-breathing P. warreni with artificially irrigated branchial chambers excreted double the amount of NH3via the gills compared with crabs from amphibious conditions.
Water and salt conservation form useful pre-adaptations to terrestrial forays. While the relatively low water loss extends the duration of emersion, P. warreni is required to return briefly to water to excrete stored nitrogenous waste. The nature of the store remains to be determined.
Environmental Effects on Undulatory Locomotion in the American Eel Anguilla Rostrata: Kinematics in Water and on Land
Authors: Gillis Gary B. 
Published: April 2021

ABSTRACT
Historically, the study of swimming eels (genus Anguilla) has been integral to our understanding of the mechanics and muscle activity patterns used by fish to propel themselves in the aquatic environment. However, no quantitative kinematic analysis has been reported for these animals. Additionally, eels are known to make transient terrestrial excursions, and in the past it has been presumed (but never tested) that the patterns of undulatory movement used terrestrially are similar to those used during swimming. In this study, high-speed video was used to characterize the kinematic patterns of undulatory locomotion in water and on land in the American eel Anguilla rostrata. During swimming, eels show a nonlinear increase in the amplitude of lateral undulations along their bodies, reaching an average maximum of 0.08L, where L is total length, at the tip of the tail. However, in contrast to previous observations, the most anterior regions of their bodies do not undergo significant undulation. In addition, a temporal lag (typically 10–15% of an undulatory cycle) exists between maximal flexion and displacement at any given longitudinal position. Swimming speed does not have a consistent effect on this lag or on the stride length (distance moved per tailbeat) of the animal. Speed does have subtle (although statistically insignificant) effects on the patterns of undulatory amplitude and intervertebral flexion along the body. On land, eels also use lateral undulations to propel themselves; however, their entire bodies are typically bent into waves, and the undulatory amplitude at all body positions is significantly greater than during swimming at equivalent speeds. The temporal lag between flexion and displacement seen during swimming is not present during terrestrial locomotion. While eels cannot move forwards as quickly on land as they do in water, they do increase locomotor speed with increasing tailbeat frequency. The clear kinematic distinctions present between aquatic and terrestrial locomotor sequences suggest that eels might be using different axial muscle activity patterns to locomote in the different environments.
Flight Thermogenesis and Energy Conservation in Hovering Hummingbirds
Authors: Chai Peng , Chang Andrew C. , Dudley Robert 
Published: April 2021

ABSTRACT
As the smallest homeotherms, hummingbirds suffer from low thermal inertia and high heat loss. Flapping flight is energetically expensive, and convective cooling due to wing and air movements could further exacerbate energy drain. Energy conservation during flight is thus profoundly important for hummingbirds. The present study demonstrates that heat produced by flight activity can contribute to thermoregulatory requirements in hovering hummingbirds. The rate of oxygen consumption, as an indicator of metabolic cost, was measured during hover-feeding and compared with that during perch-feeding. In hover-feeding, oxygen consumption increased only moderately between 35 and 5°C in contrast to the sharp increase during perch-feeding over the same temperature range. This result suggests that heat produced by contraction of the flight muscles substituted for regulatory thermogenesis to accommodate for heat loss during exposure to low temperature. With declining air temperatures, the mechanical power requirements of hovering decreased slightly, but metabolic costs increased moderately. As a result, the mechanical efficiency of the muscle in converting metabolic power to mechanical power was reduced. Changes in wingbeat kinematics also accompanied the reduction in muscle efficiency. Wingbeat frequency increased but stroke amplitude decreased when hovering in the cold, suggesting thermoregulatory roles for the flight muscles. Hovering hummingbirds modulated their wingbeat frequency within a narrow range, reflecting the physical constraints of tuning to a natural resonant frequency with an elastic restoring force. We hypothesize that, by forcing the resonant system of the wings and thorax to oscillate at different frequencies, muscle contraction in the cold generates more heat at the expense of mechanical efficiency. This mechanism of modulating the efficiency of muscle contraction and heat production allows flying hummingbirds to achieve energy conservation at low air temperatures.
Mitochondrial Oxygen Affinity, Respiratory Flux Control And Excess Capacity Of Cytochrome c Oxidase
Authors: Gnaiger Erich , Lassnig Barbara , Kuznetsov Andrey , Rieger Gunde , Margreiter Raimund 
Published: April 2021

ABSTRACT
The oxygen affinity of the enzyme system involved in mitochondrial respiration indicates, in relation to intracellular oxygen levels and interpreted with the aid of flux control analysis, a significant role of oxygen supply in limiting maximum exercise. This implies that the flux control coefficient of mitochondria is not excessively high, based on a capacity of mitochondrial oxygen consumption that is slightly higher than the capacity for oxygen supply through the respiratory cascade. Close matching of the capacities and distribution of flux control is consistent with the concept of symmorphosis. Within the respiratory chain, however, the large excess capacity of cytochrome c oxidase, COX, appears to be inconsistent with the economic design of the respiratory cascade. To address this apparent discrepancy, we used three model systems: cultured endothelial cells and mitochondria isolated from heart and liver. Intracellular oxygen gradients increase with oxygen flux, explaining part of the observed decrease in oxygen affinity with increasing metabolic rate in cells. In addition, mitochondrial oxygen affinities decrease from the resting to the active state. The oxygen affinity in the active ADP-stimulated state is higher in mitochondria from heart than in those from liver, in direct relationship to the higher excess capacity of COX in heart. This yields, in turn, a lower turnover rate of COX even at maximum flux through the respiratory chain, which is necessary to prevent a large decrease in oxygen affinity in the active state. Up-regulation of oxygen affinity provides a functional explanation of the excess capacity of COX. The concept of symmorphosis, a matching of capacities in the respiratory cascade, is therefore complemented by ‘synkinetic’ considerations on optimum enzyme ratios in the respiratory chain. Accordingly, enzymatic capacities are matched in terms of optimum ratios, rather than equal levels, to meet the specific kinetic and thermodynamic demands set by the low-oxygen environment in the cell.
Structure/Function Of Oxygen-Regulated Isoforms In Cytochrome c Oxidase
Authors: Burke Patricia V. , Poyton Robert O. 
Published: April 2021

ABSTRACT
Eukaryotic cytochrome c oxidases are complex oligomeric membrane proteins composed of subunit polypeptides encoded by both nuclear and mitochondrial genomes. While the mitochondrially encoded subunits are encoded by unique genes, some of the nuclear-encoded subunits are encoded by multigene families. The isoforms produced by these multigene families are tissue-specific and/or developmentally regulated in mammals and environmentally regulated in lower eukaryotes. Isoforms for one of the subunits, V, in the yeast Saccharomyces cerevisiae and one of the subunits, VII, in the slime mold Dictyostelium discoideum are regulated differentially by oxygen concentration. Extensive studies with the yeast subunit V isoforms have revealed that the genes for these proteins are switched on or off at very low oxygen concentrations (0.5–1 μmol l−1 O2) and that they affect the catalytic properties of holocytochrome c oxidase differentially. By altering an internal step in electron transfer between heme a and the binuclear reaction center (composed of heme a3 and CuB), the ‘hypoxic’ isoform, Vb, enhances the catalytic constant three-to fourfold relative to the ‘aerobic’ isoform, Va. Modeling studies suggest that this occurs by an interaction between transmembrane helix VII of subunit I and the transmembrane helix in subunit V. The inverse regulation of these two isoforms allows cells to assemble different types of holoenzyme isoenzymes in response to oxygen concentration. Oxygen also regulates the level of transcription of the genes for the other nuclear-coded subunits of yeast cytochrome c oxidase and affects the level of two of the mitochondrially encoded subunits (I and II) post-transcriptionally. Thus, the level of cytochrome c oxidase activity that is produced at different oxygen tensions in yeast is determined in part by the number of holoenzyme molecules that are assembled and in part by the oxygen-regulated isoforms of subunit V. The possibility that this type of control exists in other organisms is considered.
Oxygen Sensing and the Transcriptional Regulation of Oxygen-Responsive Genes in Yeast
Authors: Kwast Kurt E. , Burke Patricia V. , Poyton Robert O. 
Published: April 2021

ABSTRACT
The budding yeast Saccharomyces cerevisiae is a facultative aerobe that responds to changes in oxygen availability (and carbon source) by initiating a biochemically complex program that ensures that energy demands are met under two different physiological states: aerobic growth, supported by oxidative and fermentative pathways, and anaerobic growth, supported solely by fermentative processes. This program includes the differential expression of a large number of genes, many of which are involved in the direct utilization of oxygen. Research over the past decade has defined many of the cis-sites and trans-acting factors that control the transcription of these oxygen-responsive genes. However, the manner in which oxygen is sensed and the subsequent steps involved in the transduction of this signal have not been precisely determined. Heme is known to play a pivotal role in the expression of these genes, acting as a positive modulator for the transcription of the aerobic genes and as a negative modulator for the transcription of the hypoxic genes. Consequently, cellular concentrations of heme, whose biosynthesis is oxygen-dependent, are thought to provide a gauge of oxygen availability and dictate which set of genes will be transcribed. But the precise role of heme in oxygen sensing and the transcriptional regulation of oxygen-responsive genes is presently unclear. Here, we provide an overview of the transcriptional regulation of oxygen-responsive genes, address the functional roles that heme and hemoproteins may play in this regulation, and discuss possible mechanisms of oxygen sensing in this simple eukaryotic organism.