bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metabolic responses of shorebird chicks to cold stress: hysteresis of cooling and warming phases
Authors: Ricklefs Robert E. , Williams Joseph B. 
Published: July 2003

SUMMARYWe developed a protocol for determining the maximum rate of oxygen consumption of shorebird chicks (Scolopacidae and Charadriidae) in response to cold challenge. We first subjected the chicks to gradually decreasing temperatures until their metabolism peaked and began to decrease. We ended the cooling phase of a trial when a chick's body temperature Tb had declined typically to 32–34°C. After this point, we gradually increased the temperature in the metabolism chamber until normal Tb values and thermoneutral resting metabolism were restored. We refer to this cycle as the down–up (DU) protocol. We estimated instantaneous oxygen consumption(V̇O2) using the equation of Bartholomew et al.(1981). V̇O2 and Tb were monitored continuously during the trials.Here, we illustrate typical temperature and metabolism dynamics of the DU protocol by describing several trials in detail, and we discuss the implications of these results for the control of metabolism and regulation of Tb. Chicks subjected to the DU protocol exhibited three distinct phases of metabolic response to ambient temperature(Ta). In Phase I, V̇O2 increase was directly related to the gradient between Tb and Ta, consistent with a Newtonian response to cooling. During Phase II, chicks sustained a maximum level of V̇O2 that decreased as Tb dropped, exhibiting a Q10 of approximately 2. Based on the slope of the relationship between V̇O2 and Tb during Phase II, we were able to estimate maximum V̇O2 at a standardized high Tb. Phase II continued until chick Tb began to rise as a result of the gradually increasing Ta. During Phase III, the Tb-adjusted rate of oxygen consumption decreased from the maximum level at low Tb to the resting level at high Tb in the thermoneutral zone. Further trials with faster and slower rates of chamber cooling showed that V̇O2 during Phase I varied in proportion to the difference between Tb and Ta (ΔT), whereas during Phase III it responded to Tb.Even though chicks may be capable of generating enough heat to regulate Tb during the early part of Phase I of the DU protocol,the constantly decreasing Ta created a time lag between Ta and the chick's metabolic response, leading to body cooling. The hysteresis observed between Phase I and Phase III suggests that chicks rewarm passively while being brooded following the decrease in Tb experienced during active foraging. The results of the DU protocol suggest that Tb should be measured continuously during measurements of maximum oxygen consumption, and that peak values should be adjusted by Tb to make them comparable with other studies.
Oxidative stress stimulates multiple MAPK signalling pathways and phosphorylation of the small HSP27 in the perfused amphibian heart
Authors: Gaitanaki Catherine , Konstantina Stathopoulou , Chrysa Stavridou , Beis Isidoros 
Published: July 2003

SUMMARYWe investigated the activation of three subfamilies of MAPKs (ERK, JNKs and p38-MAPK) by oxidative stress in the isolated perfused amphibian heart. Activation of p43-ERK by 100 μmol l-1 H2O2was maximally observed within 5 min, remained elevated for 30 min and was comparable with the effect of 1 μmol l-1 PMA. p43-ERK activation by H2O2 was inhibited by PD98059 but not by SB203580. The p46 and p52 species of JNKs were maximally activated by 2.5- and 2.1-fold,respectively, by 100 μmol l-1 H2O2 within 2 min. JNK activation was still detectable after 15 min, reaching control values at 30 min of treatment. p38-MAPK was maximally activated by 9.75-fold by 100 μmol l-1 H2O2 after 2 min and this activation progressively declined thereafter, reaching control values within 45 min of treatment. The observed dose-dependent profile of p38-MAPK activation by H2O2 revealed that 30 μmol l-1 H2O2 induced maximal phosphorylation,whereas 100–300 μmol l-1 H2O2induced considerable activation of the kinase. Our studies also showed that the phosphorylation of MAPKAPK2 by H2O2 followed a parallel time-dependent pattern and that SB203580 abolished this phosphorylation. Furthermore, our experiments clearly showed that 30 μmol l-1 H2O2 induced a strong, specific phosphorylation of HSP27. Our immunohistochemical studies showed that immune complexes of phosphorylated forms of both p38-MAPK and HSP27 were strongly enhanced by 30 μmol l-1 H2O2 in the perinuclear region as well as dispersedly in the cytoplasm of ventricular cells and that SB203580 abolished this phosphorylation. These data indicate that oxidative stress is a powerful activator of all three MAPK subfamilies in the amphibian heart. Stimulation of p38-MAPK and the consequent phosphorylation of HSP27 may be important in cardioprotection under such conditions.
Biophysical properties of the pelt of a diurnal marsupial, the numbat(Myrmecobius fasciatus), and its role in thermoregulation
Authors: Cooper C. E. , Walsberg G. E. , Withers P. C. 
Published: July 2003

SUMMARYNumbats are unusual marsupials in being exclusively diurnal and termitivorous. They have a sparse (1921 hairs cm-2) and shallow(1.19 mm) pelt compared with other marsupials. Coat reflectivity is low (19%)for numbats compared with nocturnal marsupials, but absorptivity is similar to that of diurnal North American ground squirrels (72%), indicating that the coat of the numbat may be adapted for acquisition of solar heat. Numbat coat thermal resistance decreases significantly with wind speed from 45.9 s m-1 (at 0.5 m s-1) to 29.8 s m-1 (at 3 m s-1). Erecting the fur significantly increases pelt depth (6.5 mm)and coat resistance (79.2–64.2 s m-1) at wind speeds between 0.5 m s-1 and 3 m s-1. Numbat coat resistance is much lower than that of other marsupials, and wind speed has a greater influence on coat resistance for numbats than for other mammals, reflecting the low pelt density and thickness.Solar heat gain by numbats through the pelt to the level of the skin(60–63%) is similar to the highest value measured for any mammal. However the numbat's high solar heat gain is not associated with the same degree of reduction in coat resistance as seen for other mammals, suggesting that its pelt has structural and spectral characteristics that enhance both solar heat acquisition and endogenous heat conservation. Maximum solar heat gain is estimated to be 0.5–3.6 times resting metabolic heat production for the numbat at ambient temperatures of 15–32.5°C, so radiative heat gain is probably an important aspect of thermoregulation for wild numbats.
Acutely elevated vasopressin increases circulating concentrations of cortisol and aldosterone in fasting northern elephant seal (Mirounga angustirostris) pups
Authors: Ortiz Rudy M. , Wade Charles E. , Ortiz C. Leo , Talamantes Frank 
Published: July 2003

SUMMARYThe physiological actions of vasopressin (VP) in marine mammals are not well defined. To help elucidate its hormonal and renal effects in this group of mammals, northern elephant seal (Mirounga angustirostris) pups(N=7; 99±4 kg) were first infused with 0.9% saline (control;220 ml), followed 24 h later with VP (as a 20 ng kg-1 bolus, then 2 ng kg-1 min-1 for approximately 35 min in 225±16 ml saline). During both control and VP periods, blood samples were collected prior to infusion, and 15, 30, 60, 120 min and 24 h after infusion to examine the hormonal responses of the pups to VP. Renal responses were quantified from 24 h urine samples obtained prior to infusion (control) and 24 h post-infusion. Compared to the control period, infusion of VP increased plasma concentrations of cortisol over a 120 min period and aldosterone over 30 min,while plasma renin activity (PRA) was decreased for a 120 min period. The plasma urea:creatinine ratio was elevated following infusion of VP. Urine output and osmotic clearance were increased by 69±18% (mean ± s.e.m.) and 36±10%, respectively, but free water clearance and glomerular filtration rate were not significantly altered 24 h post-infusion of VP. Solute (osmolality, Na+, K+ and Cl-) excretion and fractional excretion of electrolytes were also increased when compared to control values. The increase in cortisol concentration suggests that VP may possess corticotropin releasing hormone-like activity in elephant seals. If osmotic diuresis and natriuresis are typical consequences of elevated [VP] in fasting pups, then not increasing VP normally during the fast may serve as a protective mechanism to avoid the potential loss of Na+ induced by elevated [VP]. Therefore, under natural fasting conditions, pups may be highly sensitive to small changes in[VP], resulting in the maintenance of water and electrolyte balance.
Ontogeny of baroreflex control in the American alligatorAlligator mississippiensis
Authors: Crossley Dane A. , Hicks James W. , Altimiras Jordi 
Published: July 2003

SUMMARYBaroreflex regulation appears in different species at different points in embryonic development. This study was designed to understand the development of the baroreflex in embryos of the American alligator at four different points of embryonic development (60%, 70%, 80% and 90% of a total incubation period of 72 days) and in 1-week-old hatchlings. Data from a separate study on 1-year-old alligators were included for comparison. The gain of the cardiac limb of the baroreflex was calculated from heart rate changes triggered by pharmacological manipulation of arterial pressure with sodium nitroprusside and phenylephrine. The results demonstrated that a vagally mediated hypertensive baroreflex was present during the final 30% of alligator development. A hypotensive baroreflex was not present in embryos but appeared in hatchlings, mediated by a combined effect of vagal and sympathetic efferents. Absolute baroreflex gain was maximal at 80% of incubation (41.22 beats kPa–1 min–1) and dropped thereafter,reaching a minimum in 1-year-old alligators (9.69 beats kPa–1min–1). When the baroreflex gain was normalized to resting arterial pressure and heart rate, the maximum gain was observed in 1-year-old alligators (normalized index of 2.12 versus 0.75 in hatchlings and 0.69 as the highest gain in embryos). In conclusion, baroreflex regulation appeared during embryonic development with a substantial gain. These findings indicate that embryonic development is a period of preparation for cardiovascular regulatory mechanisms that will be necessary in adult life and that the baroreflex control mechanism is required for cardiovascular control during ontogeny.
Rapid mechano-sensory pathways code leg impact and elicit very rapid reflexes in insects
Authors: Höltje Markus , Hustert Reinhold 
Published: July 2003

SUMMARYThe temporal sequence of mechanoreceptor input arriving at the motoneuron level in the central nervous system (CNS) after distal mechanical contact was studied for the locust middle leg. Different types of afferent information from potential contact areas after selective stimulation showed propagation times of no less than 8 ms from mechanosensory hairs, campaniform sensilla(CS) and spurs of the distal leg segments. Impact of the same mechanical stimuli, even if very delicate, elicits strain that is transferred in less than 1 ms via the cuticle and stimulates proximal CS on the trochanter and femur. These propagate the afferents that code distal leg contact in about 1 ms to the CNS, where they connect mono- and polysynaptically to motoneurons of the depressor trochanteris system. The elicited excitatory postsynaptic potentials (EPSPs) contribute to rapid efferent commands, since single EPSPs already rise near firing threshold of the motoneurons. The short delays in this mechano-neuronal-muscular pathway from the tip of a leg to the neuromuscular synapses (5–7 ms) can very rapidly raise muscle tension in the trochanteral depressors at new leg contacts during locust landing and locomotion. At substrate contact, proximal leg CS contribute to very rapid motor responses supporting the body.
Polymorphism of red receptors: sensitivity spectra of proximal photoreceptors in the small white butterflyPieris rapae crucivora
Authors: Qiu Xudong , Arikawa Kentaro 
Published: July 2003

SUMMARYThe compound eye of the small white butterfly Pieris rapae crucivora contains three anatomically distinct types of ommatidia. They differ in pigmentation around the rhabdom, colour of tapetal reflection and violet light-induced autofluorescence, indicating physiological differences between them. We recently reported that the ommatidia are in fact spectrally heterogeneous: in the distal part of the tiered retina they contain different sets of the spectral receptors R1–4. This study examines whether the ommatidia in the proximal retinal tier also show the spectral heterogeneity for the receptors R5–8. We recorded the sensitivity spectra of the proximal photoreceptors, and subsequently injected the dye Alexafluor 568 into proximal photoreceptors, to localize the cell and identify the ommatidial type to which it belonged. We analysed 13 successfully labeled proximal photoreceptors, and found that the sensitivity spectrum of the proximal photoreceptors in types I and III ommatidia peaks at 620 nm, whereas that of type II ommatidia peaks at 640 nm. The difference in the sensitivity spectra can be explained by the anatomical characteristics of each ommatidial type. This is the first demonstration of red receptor polymorphism in insects. The polymorphic red receptor system most probably enhances contrast sensitivity and/or color discrimination in the long wavelength spectral region.
Swimming performance studies on the eastern Pacific bonitoSarda chiliensis, a close relative of the tunas (family Scombridae) Swimming performance studies on the eastern Pacific bonitoSarda chiliensis, a close relative of the tunas (family Scombridae) II. Kinematics
Authors: Dowis Hawkins J. , Sepulveda Chugey A. , Graham Jeffrey B. , Dickson Kathryn A. 
Published: July 2003

SUMMARYThe swimming kinematics of the eastern Pacific bonito Sarda chiliensis at a range of sustained speeds were analyzed to test the hypothesis that the bonito's swimming mode differs from the thunniform locomotor mode of tunas. Eight bonito (fork length FL 47.5±2.1 cm, mass 1.25±0.15 kg) (mean ± s.d.) swam at speeds of 50–130 cm s-1 at 18±2°C in the same temperature-controlled water tunnel that was used in previous studies of tunas. Kinematics variables, quantified from 60 Hz video recordings and analyzed using a computerized, two-dimensional motion analysis system, were compared with published data for similar sized tunas at comparable speeds. Bonito tailbeat frequency, tailbeat amplitude and stride length all increased significantly with speed. Neither yaw (6.0±0.6%FL) nor propulsive wavelength (120±65% fish total length) varied with speed,and there were no mass or body-length effects on the kinematics variables for the size range of bonitos used. Relative to similar sized yellowfin(Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas at similar speeds, the bonito has a lower tailbeat frequency, a higher yaw and a greater stride length. The lateral displacement and bending angle of each intervertebral joint during a complete tailbeat cycle were determined for the bonito at a swimming speed of 90 cm s-1. The pattern of mean maximum lateral displacement (zmax) and mean maximum bending angle (βmax) along the body in the bonito differed from that of both chub mackerel Scomber japonicus and kawakawa tuna Euthynnus affinis; zmax was highest in the bonito. This study verifies that S. chiliensis is a carangiform swimmer and supports the hypothesis that the thunniform locomotor mode is a derived tuna characteristic associated with changes in this group's myotomal architecture. The finding that yaw and zmax were greater in the bonito than in both mackerels and tunas suggests that swimming kinematics in the bonito is not intermediate between that of tunas and mackerels, as would be predicted on the basis of morphological characteristics.
Swimming performance studies on the eastern Pacific bonitoSarda chiliensis, a close relative of the tunas (family Scombridae) I. Energetics
Authors: Sepulveda C. A. , Dickson K. A. , Graham J. B. 
Published: July 2003

SUMMARYA large swim tunnel respirometer was used to quantify the swimming energetics of the eastern Pacific bonito Sarda chiliensis (tribe Sardini) (45–50 cm fork length, FL) at speeds between 50 and 120 cm s-1 and at 18±2°C. The bonito rate of oxygen uptake(V̇O2)–speed function is U-shaped with a minimum V̇O2 at 60 cm s-1, an exponential increase in V̇O2 with increased speed, and an elevated increase in V̇O2 at 50 cm s-1 where bonito swimming is unstable. The onset of unstable swimming occurs at speeds predicted by calculation of the minimum speed for bonito hydrostatic equilibrium (1.2 FL s-1). The optimum swimming speed (Uopt) for the bonito at 18±2°C is approximately 70 cm s-1 (1.4 FL s-1) and the gross cost of transport at Uopt is 0.27 J N-1m-1. The mean standard metabolic rate (SMR), determined by extrapolating swimming V̇O2 to zero speed, is 107±22 mg O2 kg-1 h-1. Plasma lactate determinations at different phases of the experiment showed that capture and handling increased anaerobic metabolism, but plasma lactate concentration returned to pre-experiment levels over the course of the swimming tests. When adjustments are made for differences in temperature,bonito net swimming costs are similar to those of similar-sized yellowfin tuna Thunnus albacares (tribe Thunnini), but the bonito has a significantly lower SMR. Because bonitos are the sister group to tunas, this finding suggests that the elevated SMR of the tunas is an autapomorphic trait of the Thunnini.
Evolved patterns and rates of water loss and ion regulation in laboratory-selected populations ofDrosophila melanogaster
Authors: Folk Donna G. , Bradley Timothy J. 
Published: July 2003

SUMMARYWe have investigated water loss from, and ion regulation within, the hemolymph and tissues of five replicate populations of Drosophila melanogaster that have undergone laboratory selection for enhanced desiccation resistance (i.e. the D populations). We compared the patterns and rates of water loss and the ion content of the D populations prior to and during desiccation with those of five replicate control (C) populations. The net rate of water loss in the C flies was ∼3-fold greater than that of the D flies during the initial hours of desiccation. After 8 h, both C and D flies had considerable reductions in water loss rate. During 24 h of desiccation,the tissue water content of the D flies was conserved, while the C flies were faced with significant loss of tissue water during the initial 8 h of desiccation. We propose that the increased hemolymph volume of the D flies plays a role in buffering water loss from the tissues. One consequence of this large hemolymph pool is that the hydrated D flies contained approximately seven times more sodium within the hemolymph than did the hydrated C flies. Despite a continual loss of hemolymph volume in the D flies during lengthy periods of desiccation, the sodium content of the hemolymph was significantly reduced only during a single event. We provide evidence that the regulation of extracellular sodium, as well as chloride, occurred via excretory processes during desiccation. In addition, whole-body potassium was not significantly decreased in the D flies during desiccation but was reduced(i.e. excreted) in the C flies; hence, we suggest that the potassium content paralleled tissue water level.
Regulation of urine reprocessing in the maintenance of sodium and water balance in the terrestrial Christmas Island red crabGecarcoidea natalisinvestigated under field conditions
Authors: Morris Stephen , Ahern Mark D. 
Published: July 2003

SUMMARYLand crabs produce isosmotic urine but reduce salt loss by reabsorbing salt via the gills to produce a dilute excretory fluid (P). This branchial salt reclamation is regulated in response to changes in dietary salt availability. The regulation of branchial Na reabsorption and osmotic status was investigated in the terrestrial crab Gecarcoidea natalis on Christmas Island. Confinement within field enclosures had no general effect on salt and water balance compared with crabs free in the rainforest but there were seasonal effects. Extracellular fluid volume was 27.9% body mass during the wet season but only 22.7% in the dry season. Urine production was 53 ml kg-1 day-1 in the dry season but 111 ml kg-1day-1 in the wet season, while water flux rates were 140 ml kg-1 day-1 and 280 ml kg-1 day-1,respectively. Serotonin but not dopamine increased urine production by at least 16% but only during the dry season when rates were seasonally lowered. Crabs acclimated to drinking 50% seawater increased haemolymph osmotic pressure and downregulated branchial reabsorption of salt. Net Na flux(Jnet) and unidirectional Na influx(Jin) were investigated in branchial perfusion experiments. In red crabs acclimated to drinking freshwater, Jin, Jnet and the activity of the Na+/K+-ATPase were increased by serotonin, indicating that the increase of sodium absorption was due to a stimulation of the ATPase. Red crabs drinking 50% seawater reduced Jnet primarily due to increased passive loss (Jout), since both Jin and Na+/K+-ATPase were unchanged. Serotonin and dopamine abolished the increased diffusive loss and re-established Jnet with no change in Jin. G. natalis exhibits different regulatory systems. Branchial salt uptake can be adjusted via the leak component when adequate salt is available but also by stimulated active uptake under diluting conditions. The gills are important sites of ion pumping in euryhaline aquatic crabs, and the upregulation of Jnet in red crabs is reminiscent of that in marine crabs. Serotonergic stimulation of branchial uptake, independent of cAMP, and hormonally modulated ion leakage are presently unique to terrestrial species.
Geographic variation in energy storage and physiological responses to freezing in the gray treefrogsHyla versicolorandH. chrysoscelis
Authors: Irwin Jason T. , Lee Jr Richard E. 
Published: July 2003

SUMMARYThe physiological responses supporting freeze tolerance in anurans are well known, but the evolution of this trait remains little studied. This is the first common-garden study of geographic variation in cryoprotective responses to freezing and the degree of freeze tolerance. We studied the gray treefrogs(Hyla versicolor and H. chrysoscelis) from sympatric sites in Minnesota, Indiana and Missouri. Patterns in the literature suggest that northern frogs produce more cryoprotectants upon freezing, but we found no geographic variation in cryoprotective responses or degree of freeze tolerance. The concentration of glucose produced upon freezing was higher than previously reported for this species (liver: 475 μmol g–1dry mass). Unfrozen frogs had high levels of glycerol (liver: approx. 150μmol g–1 dry mass), and did not produce more upon freezing. Liver glycogen content (concentration multiplied by liver mass) was highest in frogs from Minnesota and Missouri, and was stored in preference to lipids in Minnesota frogs, possibly to provide energy for the longer northern winters. Minnesota frogs accumulated more ice (53.4±1.8%) after freezing to–2.5°C than Indiana frogs (45.5±3.3%). The two species differed in body size but not in any of the physiological parameters measured. We conclude that these populations show no adaptive variation in freeze tolerance and that comparing published studies may be misleading because of different acclimation and feeding regimes.