bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physiological basis of temperature-dependent biogeography: trade-offs in muscle design and performance in polar ectotherms
Authors: Pörtner H. O. 
Published: April 2021

SUMMARYPolar, especially Antarctic, oceans host ectothermic fish and invertebrates characterized by low-to-moderate levels of motor activity; maximum performance is reduced compared with that in warmer habitats. The present review attempts to identify the trade-offs involved in adaptation to cold in the light of progress in the physiology of thermal tolerance. Recent evidence suggests that oxygen limitations and a decrease in aerobic scope are the first indications of tolerance limits at both low and high temperature extremes. The cold-induced reduction in aerobic capacity is compensated for at the cellular level by elevated mitochondrial densities, accompanied by molecular and membrane adjustments for the maintenance of muscle function. Particularly in the muscle of pelagic Antarctic fish, among notothenioids, the mitochondrial volume densities are among the highest known for vertebrates and are associated with cold compensation of aerobic metabolic pathways, a reduction in anaerobic scope, rapid recovery from exhaustive exercise and enhanced lipid stores as well as a preference for lipid catabolism characterized by high energy efficiency at high levels of ambient oxygen supply. Significant anaerobic capacity is still found at the very low end of the activity spectrum, e.g. among benthic eelpout (Zoarcideae).In contrast to the cold-adapted eurytherms of the Arctic, polar (especially Antarctic) stenotherms minimize standard metabolic rate and, as a precondition, the aerobic capacity per milligram of mitochondrial protein,thereby minimizing oxygen demand. Cost reductions are supported by the downregulation of the cost and flexibility of acid—base regulation. At maintained factorial scopes, the reduction in standard metabolic rate will cause net aerobic scope to be lower than in temperate species. Loss of contractile myofilaments and, thereby, force results from space constraints due to excessive mitochondrial proliferation. On a continuum between low and moderately high levels of muscular activity, polar fish have developed characteristics of aerobic metabolism equivalent to those of high-performance swimmers in warmer waters. However, they only reach low performance levels despite taking aerobic design to an extreme.
Fibre-type specific concentration of focal adhesion kinase at the sarcolemma: influence of fibre innervation and regeneration
Authors: Flück Martin , Ziemiecki Andrew , Billeter Rudolf , Müntener Markus 
Published: April 2021

SUMMARYIn skeletal muscles, focal adhesion complexes (FACs) form part of the costamere, a sarcolemmal protein complex that enables lateral transfer of forces and ensures the stability of the sarcolemma. The present investigation tested whether localisation of a major assembly factor of FACs, focal adhesion kinase (FAK), to the sarcolemma parallels the known modulation of FACs by fibre type (innervation pattern) and fibre regeneration. Immunohistochemical experiments indicated that FAK is preferentially associated with the sarcolemma in a high proportion (&gt;74 %) of the (slow-twitch) type I and(fast-twitch) type IIA fibres in normal rat soleus (N-SOL) muscle and of the type IIA fibres in extensor digitorum longus (N-EDL) muscle. In contrast, a low proportion (&lt;15 %) of fast-twitch type IIB and type I fibres in N-EDL showed sarcolemmal FAK immunoreactivity. Cross-reinnervation of slow-twitch rat SOL muscle with the fast EDL nerve induced slow-to-fast fibre transformation and led to a significant reduction in sarcolemmal FAK immunoreactivity in type I and type IIA fibres. Transplantation of the fast EDL into the slow SOL bed with regeneration and reinnervation of the muscle by the SOL nerve (T-EDL) caused a significant increase in sarcolemmal FAK immunoreactivity in new type I and hybrid I/II fibres and a corresponding reduction in sarcolemmal FAK immunoreactivity in `normal' IIA and IIB fibres. Conversely, sarcolemmal FAK immunoreactivity in small IIB fibres of T-EDL muscle was increased. Correspondingly, the transplanted and regenerated SOL(reinnervated by the fast EDL nerve) maintained the percentage of FAK-positive sarcolemma in the (regenerated) type I and IIA fibres. Thus, the expression and association of FAK with the sarcolemma are regulated (i) by factors that determine the fibre type and (ii) during fibre regeneration. Our data suggest that the integrity of sarcolemmal FACs is dependent on the fibre type and that FAC turnover is increased during regeneration of muscle fibres.
α1- and β-adrenoceptor stimulation differentially activate p38-MAPK and atrial natriuretic peptide production in the perfused amphibian heart
Authors: Aggeli Ioanna-Katerina S. , Gaitanaki Catherine , Lazou Antigone , Beis Isidoros 
Published: April 2021

SUMMARYWe investigated the activation of p38-MAPK by various adrenergic agents in the perfused Rana ridibunda heart. Phenylephrine (50 μmol l-1) rapidly induced the differential activation of all three mitogen-activated protein kinase (MAPK) subfamilies (ERK, JNKs and p38-MAPK)in this experimental system. Focusing on p38-MAPK response to phenylephrine,we found that the kinase phosphorylation reached maximal values at 30 s,declining thereafter to basal values at 15 min. p38-MAPK activation by phenylephrine was verified as exclusively α1-AR-mediated. Furthermore, SB203580 (1 μmol l-1) abolished the kinase phosphorylation by phenylephrine. Isoproterenol (50 μmol l-1)was also shown to activate p38-MAPK in a time- and temperature-dependent manner. A marked, sustained p38-MAPK activation profile was observed at 25°C, while at 18°C the kinase response to isoproterenol was modest. Isoproterenol effect on p38-MAPK stimulation was β-AR-mediated. Immunohistochemical studies revealed the enhanced presence of phosphorylated p38-MAPK and atrial natriuretic peptide (ANP) in both phenylephrine- and isoproterenol-stimulated hearts, a reaction completely blocked by the respective specific antagonists, or the specific p38-MAPK inhibitor SB203580. These findings indicate a functional correlation between p38-MAPK activation and ANP accumulation in the perfused amphibian heart.
Jumping in a winged stick insect
Authors: Burrows Malcolm , Morris Oliver 
Published: April 2021

SUMMARYThe Thailand winged stick insect (Sipyloidea sp.) flees rapidly from a disturbance by jumping forwards when stimulated on the abdomen and backwards when stimulated on the head. The mechanisms underlying these fast movements were analysed by measuring movements of the body and legs from images captured at 250 Hz.A forward jump of both adults and nymphs involves movements of the abdomen and the middle and hind pairs of legs. The abdomen is raised and swung forwards by flexion at the joint with the metathorax and at the joint between the meso- and metathorax. At the same time, the tibiae of the hind and middle legs are extended and their femora depressed. The femoro-tibial joints of the legs are not fully flexed before a jump, and no structures in these joints appear to store muscular energy. The whole jumping sequence takes approximately 100 ms and results in take-off angles of 10-35° at velocities of 0.6-0.8 m s-1 and with an acceleration of 10 m s-2. The abdominal angular velocity was 2000° s-1and the tip of the abdomen moved at linear velocities of some 1 m s-1, while the maximum rate of tibial extension was 4000°s-1.Rapid backward movements result either in the collapse of the body onto the ground, with a displacement away from the stimulus of approximately half a body length, or in the propulsion of the insect off its perch. Neither movement involves curling of the abdomen.From a horizontal posture, the forward jumps result in a displacement of a few body lengths. More lift can be generated in adults by elevating the hind wings as the abdomen is swung forwards and depressing them as the legs lose contact with the ground. In this way, jumps can lead directly to flapping flight. Take-off into flight can, however, be achieved without the abdominal movements seen during jumping.From a vertical posture, a forward jump propels the insect upwards and backwards before it falls to the ground horizontally displaced from its perch. Backward movements result in the insect falling with little horizontal displacement from its perch.
Fuel use and metabolic response to endurance exercise: a wind tunnel study of a long-distance migrant shorebird
Authors: Jenni-Eiermann Susanne , Jenni Lukas , Kvist Anders , Lindström Åke , Piersma Theunis , Visser G. Henk 
Published: April 2021

SUMMARYThis study examines fuel use and metabolism in a group of long-distance migrating birds, red knots Calidris canutus (Scolopacidae), flying under controlled conditions in a wind tunnel for up to 10 h. Data are compared with values for resting birds fasting for the same time. Plasma levels of free fatty acids, glycerol and uric acid were elevated during flight, irrespective of flight duration (1-10 h). Triglyceride levels, the estimated concentration of very-low-density lipoproteins (VLDLs) and β-hydroxybutyrate levels were lower during flight, while glucose levels did not change. In flying birds, plasma levels of uric acid and lipid catabolites were positively correlated with the residual variation in body mass loss, and lipid catabolites with energy expenditure (as measured using the doubly labelled water method), after removing the effect of initial body mass. The plasma metabolite levels indicate: (i) that the rates of catabolism of lipids from adipose tissue and of protein are higher during flight; (ii) that low ketone body concentrations probably facilitate fatty acid release from adipose tissue; (iii) that low triglyceride and VLDL levels do not indicate the use of an additional pathway of fatty acid delivery, as found in small birds; and(iv) that the relationships between energy expenditure, body mass loss and metabolic pattern suggest that a higher individual energy expenditure entails a higher rate of catabolism of both lipids and protein and not a shift in fuel substrate.
Wingbeat frequency of barn swallows and house martins: a comparison between free flight and wind tunnel experiments
Authors: Liechti Felix , Bruderer Lukas 
Published: April 2021

SUMMARYThe flight paths and wingbeat patterns of 39 barn swallows (Hirundo rustica) and 26 house martins (Delichon urbica) were recorded by tracking radar during the spring migration. Depending mostly on flight angle,hirundines performed anything from continuous flapping flight during climbing to single pulse-like wing beats during descent. Unlike most other passerines,hirundines rarely showed regular flapping and rest phases, allowing them to be distinguished from other bird migrants by radar echo signatures. Effective wingbeat frequency (Feff) was calculated as the mean number of wing beats per second, including non-flapping phases. Under comparable flight conditions, Feff was higher in house martins than in barn swallows. Within species, Feff values were higher during climbing and slow flying than during descent. Of the variance in Feff, 71 % could be explained by climb rate,air speed and species; similar results were obtained in the wind tunnel. Under comparable flight conditions, barn swallows and house martins in free flight had significantly lower values of Feff than individuals in wind tunnel experiments (by 40 % and 32 %, respectively). This difference may at least partly be due to the shorter wings of the juveniles tested in the wind tunnel during autumn. However, it seems unlikely that this can account for all of the large difference. It is suggested that wind tunnel experiments might overestimate birds' flight costs compared with free flight.
The heart rate/oxygen consumption relationship during cold exposure of the king penguin: a comparison with that during exercise
Authors: Froget G. , Handrich Y. , Maho Y. Le , Rouanet J.-L. , Woakes A. J. , Butler P. J. 
Published: April 2021

SUMMARYThis study investigated whether exposure to low ambient temperature could be used as an alternative to exercise for calibrating heart rate (fH)against rate of oxygen consumption(V̇O2) for subsequent use of fH to estimate V̇O2 in free-ranging animals. Using the relationship between the oxygen pulse (OP, the amount of oxygen used per heart beat) and an index of body condition (or nutritional index, NI), a relationship between fH and V̇O2 was established for resting king penguins exposed to a variety of environmental temperatures. Although there was a small but significant increase in the OP above and below the lower critical temperature (-4.9°C), there was no difference in the relationship obtained between the OP and body condition (NI)obtained above or below the lower critical temperature. These results were then compared with those obtained in a previous study in which the relationship between fH and V̇O2 had been established for king penguins during steady-state exercise. The relationship between OP and NI in the present study was not significantly different from the relationship between resting OP and NI in the previous study. However, the relationship was different from that between active OP and NI. We conclude that, at least for king penguins, although thermoregulation does not affect the relationship between resting OP and NI, temperature cannot be used as an alternative to exercise for calibrating fH against V̇O2 for subsequent use of fH to estimate V̇O2 in free-ranging animals.
Smelling home: a good solution for burrow-finding in nocturnal petrels?
Authors: Bonadonna Francesco , Bretagnolle Vincent 
Published: April 2021

SUMMARY
Many burrowing petrels are able to return to their nests in complete darkness. The well-developed anatomy of their olfactory system and the attraction that food-related odour cues have for some petrel species suggest that olfaction may be used to recognize the burrow. In contrast,surface-nesting petrels may rely on visual cues to recognise their nest. We performed experiments on nine species of petrel (with different nesting habits) rendered anosmic either by plugging the nostrils or by injecting zinc sulphate onto the nasal epithelium. Compared with shamtreated control birds,we found that anosmia impaired nest recognition only in species that nest in burrows and that return home in darkness. Therefore, petrels showing nocturnal activity on land may rely on their sense of smell to find their burrows, while petrels showing diurnal activity or surface nesters may disregard olfactory cues in favour of visual guidance.
Behavioral evidence for post-pause reduced responsiveness in the electrosensory system ofGymnotus carapo
Authors: Schuster Stefan 
Published: April 2021

SUMMARYGymnotiform weakly electric fish find their way in the dark using a continuously operating active sensory system. An electric organ generates a continuous train of discharges (electric organ discharges, EODs), and tuberous high-frequency electroreceptors monitor the pattern of transcutaneous current flow associated with each EOD. Here, I report that a prior interruption to the continuous train of EODs dramatically affects a response shown by many pulse-type gymnotids. In this so-called novelty response, fish normally raise their electrosensory sampling rate in response to novel sensory stimuli. The gymnotid Gymnotus carapo was induced to pause its EODs briefly, and the novelty response to sensory stimuli given post-pause was analyzed. Mechanosensory stimuli given as early as 20 EODs after a pause elicited clear novelty responses, but strong high-frequency electrical stimuli were ineffective at this time. Moreover, high-frequency electrical stimuli remained less efficient in eliciting normal-sized responses until approximately 2000 EODs, or 40s, after a pause. The post-pause inefficiency of high-frequency stimuli was not due to an inappropriate choice of intensity or their temporal patterning and did not result from the stimulation that caused the pausing. Low-frequency stimuli that also recruited ampullary electroreceptors were more efficient than high-frequency stimuli in eliciting post-pause responses. These findings show that continuous activity is required either to maintain sensitivity to high-frequency electrical stimuli or to ensure that such stimuli are able to modulate efficiently the pacemaker that sets the discharge frequency.
Social regulation of gonadotropin-releasing hormone
Authors: White Stephanie A. , Nguyen Tuan , Fernald Russell D. 
Published: April 2021

SUMMARY
Behavioral interactions among social animals can regulate both reproductive behavior and fertility. A prime example of socially regulated reproduction occurs in the cichlid fish Haplochromis burtoni, in which interactions between males dynamically regulate gonadal function throughout life. This plasticity is mediated by the brain, where neurons that contain the key reproductive regulatory peptide gonadotropin-releasing hormone (GnRH)change size reversibly depending on male social status. To understand how behavior controls the brain, we manipulated the social system of these fish,quantified their behavior and then assessed neural and physiological changes in the reproductive and stress axes. GnRH gene expression was assessed using molecular probes specific for the three GnRH forms in the brain of H. burtoni. We found that perception of social opportunity to increase status by a male leads to heightened aggressiveness, to increased expression of only one of the three GnRH forms and to increases in size of GnRH-containing neurons and of the gonads. The biological changes characteristic of social ascent happen faster than changes following social descent. Interestingly, behavioral changes show the reverse pattern:aggressive behaviors emerge more slowly in ascending animals than they disappear in descending animals. Although the gonads and GnRH neurons undergo similar changes in female H. burtoni, regulation occurs viaendogenous rather than exogenous social signals. Our data show that recognition of social signals by males alters stress levels, which may contribute to the alteration in GnRH gene expression in particular neurons essential for the animal to perform in its new social status.
Cellular distribution of a high-affinity glutamate transporter in the nervous system of the cabbage looperTrichoplusia ni
Authors: Gardiner Richard B. , Ullensvang Kyrre , Danbolt Niels C. , Caveney Stanley , Donly B. Cameron 
Published: April 2021

SUMMARYGlutamate functions as a neurotransmitter in the central nervous system(CNS) and neuromuscular junctions in insects. High-affinity glutamate transporters are responsible for keeping the resting levels of excitatory amino acids below the synaptic activation threshold by removing them from the extracellular fluid, thereby preventing them from reaching toxic levels. Peptides representing the N- and C-terminal regions of a glutamate transporter cloned from the cabbage looper caterpillar (Trichoplusia ni) were synthesized and used to generate polyclonal antibodies. The antibodies produced immunohistochemical staining in both muscular and nervous system T. ni tissues. Neuromuscular junctions in the skeletal muscles produced the most intense labelling, but no visceral muscle or sensory nerves were labelled. In the CNS, the neuropile of the ganglia, but not the connectives, gave a diffuse staining. Electron microscopical examination of ganglia and neuromuscular junctions showed that the plasma membrane of glial cells, but not that of neurons was labelled, in agreement with the notion that most of the glutamate uptake sites in this insect are in glial cells.
Cutaneous blood flow in the pigeonColumba livia: its possible relevance to cutaneous water evaporation
Authors: Ophir E. , Arieli Y. , Marder J. , Horowitz M. 
Published: April 2021

SUMMARYThe heat-acclimated rock pigeon is thought to use cutaneous water evaporation (CWE) as the `preferred' route for heat dissipation, and this mechanism is controlled by adrenergic signaling. In the present study, we tested the hypothesis that adjustments in skin blood flow are a crucial component of this adaptation. Skin blood flow was measured by laser Doppler flowmetry and by ultrasonic flowmetry in heat-acclimated (HAc) and non-acclimated (NAc) pigeons. Skin blood flow, CWE and rectal and skin temperatures were measured under heat exposure(Ta=50°C) or following propranolol (1.3 mg kg-1) or clonidine (80 μg kg-1) administration. Using laser Doppler flowmetry, we found a significant increase (1.3-fold) in skin blood flow in the dorsal skin of HAc pigeons following propanolol administration. In contrast, a significant decrease (0.7-fold) was observed in NAc birds. Injection of clonidine resulted in a significant decrease in skin blood flow in both HAc and NAc pigeons (0.4- and 0.5-fold, respectively). Heat exposure increased blood perfusion in both groups (2.5- and 1.8-fold,respectively). Using ultrasonic flowmetry, we showed that both propanolol and clonidine increase the arterial blood flow (Qa) in HAc pigeons, while venous blood flow (Qv) decreases. In contrast, no significant changes were found in NAc pigeons. As shown by the effect of clonidine, augmentation of skin blood flow is not a prerequisite for CWE, but normally coincides with a greater difference in arterial—venous pressure. Possible regulatory mechanisms are discussed.
How fins affect the economy and efficiency of human swimming
Authors: Zamparo P. , Pendergast D. R. , Termin B. , Minetti A. E. 
Published: April 2021

SUMMARYThe aim of the present study was to quantify the improvements in the economy and efficiency of surface swimming brought about by the use of fins over a range of speeds (v) that could be sustained aerobically. At comparable speeds, the energy cost (C) when swimming with fins was about 40 %lower than when swimming without them; when compared at the same metabolic power, the decrease in C allowed an increase in v of about 0.2 ms-1. Fins only slightly decrease the amplitude of the kick (by about 10 %) but cause a large reduction (about 40 %) in the kick frequency. The decrease in kick frequency leads to a parallel decrease of the internal work rate (Ẇint, about 75 %at comparable speeds) and of the power wasted to impart kinetic energy to the water (Ẇk, about 40 %). These two components of total power expenditure were calculated from video analysis (Ẇint) and from measurements of Froude efficiency(Ẇk). Froude efficiency(ηF) was calculated by computing the speed of the bending waves moving along the body in a caudal direction (as proposed for the undulating movements of slender fish); ηF was found to be 0.70 when swimming with fins and 0.61 when swimming without them. No difference in the power to overcome frictional forces(Ẇd) was observed between the two conditions at comparable speeds. Mechanical efficiency[Ẇtot/(Cv), where Ẇtot=Ẇk+Ẇint+Ẇd]was found to be about 10 % larger when swimming with fins, i.e. 0.13±0.02 with and 0.11±0.02 without fins (average for all subjects at comparable speeds).