Showing papers in "The Journal of Experimental Biology in 2004"

Oxidants, antioxidants and the ischemic brain

Abstract: Despite numerous defenses, the brain is vulnerable to oxidative stress resulting from ischemia/reperfusion. Excitotoxic stimulation of superoxide and nitric oxide production leads to formation of highly reactive products, including peroxynitrite and hydroxyl radical, which are capable of damaging lipids, proteins and DNA. Use of transgenic mutants and selective pharmacological antioxidants has greatly increased understanding of the complex interplay between substrate deprivation and ischemic outcome. Recent evidence that reactive oxygen/nitrogen species play a critical role in initiation of apoptosis, mitochondrial permeability transition and poly(ADP-ribose) polymerase activation provides additional mechanisms for oxidative damage and new targets for post-ischemic therapeutic intervention. Because oxidative stress involves multiple post-ischemic cascades leading to cell death, effective prevention/treatment of ischemic brain injury is likely to require intervention at multiple effect sites.

Unsteady forces and flows in low Reynolds number hovering flight:two-dimensional computations vs robotic wing experiments

Abstract: We compare computational, experimental and quasi-steady forces in a generic hovering wing undergoing sinusoidal motion along a horizontal stroke plane. In particular, we investigate unsteady effects and compare two-dimensional (2D) computations and three-dimensional (3D) experiments in several qualitatively different kinematic patterns. In all cases, the computed drag compares well with the experiments. The computed lift agrees in the cases in which the sinusoidal changes in angle of attack are symmetrical or advanced with respect to stroke positions, but lags behind the measured 3D lift in the delayed case. In the range of amplitudes studied here, 3-5 chords, the force coefficients have a weak dependence on stroke amplitude. As expected, the forces are sensitive to the phase between stroke angle and angle of attack, a result that can be explained by the orientation of the wing at reversal. This dependence on amplitude and phase suggests a simple maneuver strategy that could be used by a flapping wing device. In all cases the unsteady forces quickly reach an almost periodic state with continuous flapping. The fluid forces are dominated by the pressure contribution. The force component directly proportional to the linear acceleration is smaller by a factor proportional to the ratio of wing thickness and stroke amplitude; its net contribution is zero in hovering. The ratio of wing inertia and fluid force is proportional to the product of the ratio of wing and fluid density and the ratio of wing thickness and stroke amplitude; it is negligible in the robotic wing experiment, but need not be in insect flight. To identify unsteady effects associated with wing acceleration, and coupling between rotation and translation, as well as wake capture, we examine the difference between the unsteady forces and the estimates based on translational velocities, and compare them against the estimate of the coupling between rotation and translation, which have simple analytic forms for sinusoidal motions. The agreement and disagreement between the computed forces and experiments offer further insight into when the 3D effects are important. A main difference between a 3D revolving wing and a 2D translating wing is the absence of vortex shedding by a revolving wing over a distance much longer than the typical stroke length of insects. No doubt such a difference in shedding dynamics is responsible in part for the differences in steady state force coefficients measured in 2D and 3D. On the other hand, it is unclear whether such differences would have a significant effect on transient force coefficients before the onset of shedding. While the 2D steady state force coefficients underpredict 3D forces, the transient 2D forces measured prior to shedding are much closer to the 3D forces. In the cases studied here, the chord is moving between 3 to 5 chords, typical of hovering insect stroke length, and the flow does not appear to separate during each stroke in the cases of advanced and symmetrical rotation. In these cases, the wing reverses before the leading edge vortex would have time to separate even in 2D. This suggests that the time scale for flow separation in these strokes is dictated by the flapping frequency, which is dimensionally independent. In such cases, the 2D unsteady forces turn out to be good approximations of 3D experiments.

Interspecific and intraspecific views of color signals in the strawberry poison frog Dendrobates pumilio.

Abstract: Poison frogs in the anuran family Dendrobatidae use bright colors on their bodies to advertise toxicity. The species Dendrobates pumilio Schmidt 1858, the strawberry poison frog, shows extreme polymorphism in color and pattern in Panama. It is known that females of D. pumilio preferentially choose mates of their own color morph. Nevertheless, potential predators must clearly see and recognize all color morphs if the aposematic signaling system is to function effectively. We examined the ability of conspecifics and a model predator to discriminate a diverse selection of D. pumilio colors from each other and from background colors. Microspectrophotometry of isolated rod and cone photoreceptors of D. pumilio revealed the presence of a trichromatic photopic visual system. A typical tetrachromatic bird system was used for the model predator. Reflectance spectra of frog and background colors were obtained, and discrimination among spectra in natural illuminants was mathematically modeled. The results revealed that both D. pumilio and the model predator discriminate most colors quite well, both from each other and from typical backgrounds, with the predator generally performing somewhat better than the conspecifics. Each color morph displayed at least one color signal that is highly visible against backgrounds to both visual systems. Our results indicate that the colors displayed by the various color morphs of D. pumilio are effective signals both to conspecifics and to a model predator.

Force production and flow structure of the leading edge vortex on flapping wings at high and low Reynolds numbers.

Abstract: The elevated aerodynamic performance of insects has been attributed in part to the generation and maintenance of a stable region of vorticity known as the leading edge vortex (LEV). One explanation for the stability of the LEV is that spiraling axial flow within the vortex core drains energy into the tip vortex, forming a leading-edge spiral vortex analogous to the flow structure generated by delta wing aircraft. However, whereas spiral flow is a conspicuous feature of flapping wings at Reynolds numbers (Re) of 5000, similar experiments at Re=100 failed to identify a comparable structure. We used a dynamically scaled robot to investigate both the forces and the flows created by a wing undergoing identical motion at Re of ~120 and ~1400. In both cases, motion at constant angular velocity and fixed angle of attack generated a stable LEV with no evidence of shedding. At Re=1400, flow visualization indicated an intense narrow region of spanwise flow within the core of the LEV, a feature conspicuously absent at Re=120. The results suggest that the transport of vorticity from the leading edge to the wake that permits prolonged vortex attachment takes different forms at different Re.

Hypoxia–ischemia in the immature brain

Abstract: The immature brain has long been considered to be resistant to the damaging effects of hypoxia and hypoxia-ischemia (H/I). However, it is now appreciated that there are specific periods of increased vulnerability, which relate to the developmental stage at the time of the insult. Although much of our knowledge of the pathophysiology of cerebral H/I is based on extensive experimental studies in adult animal models, it is important to appreciate the major differences in the immature brain that impact on its response to, and recovery from, H/I. Normal maturation of the mammalian brain is characterized by periods of limitations in glucose transport capacity and increased use of alternative cerebral metabolic fuels such as lactate and ketone bodies, all of which are important during H/I and influence the development of energy failure. Cell death following H/I is mediated by glutamate excitotoxicity and oxidative stress, as well as other events that lead to delayed apoptotic death. The immature brain differs from the adult in its sensitivity to all of these processes. Finally, the ultimate outcome of H/I in the immature brain is determined by the impact on the ensuing cerebral maturation. A hypoxic-ischemic insult of insufficient severity to result in rapid cell death and infarction can lead to prolonged evolution of tissue damage.

Changes in gene expression associated with acclimation to constant temperatures and fluctuating daily temperatures in an annual killifish Austrofundulus limnaeus.

Abstract: SUMMARY Eurythermal ectotherms commonly thrive in environments that expose them to large variations in temperature on daily and seasonal bases. The roles played by alterations in gene expression in enabling eurytherms to adjust to these two temporally distinct patterns of thermal stress are poorly understood. We used cDNA microarray analysis to examine changes in gene expression in a eurythermal fish, Austrofundulus limnaeus , subjected to long-term acclimation to constant temperatures of 20, 26 and 37°C and to environmentally realistic daily fluctuations in temperature between 20°C and 37°C. Our data reveal major differences between the transcriptional responses in the liver made during acclimation to constant temperatures and in response to daily temperature fluctuations. Control of cell growth and proliferation appears to be an important part of the response to change in temperature, based on large-scale changes in mRNA transcript levels for several key regulators of these pathways. However, cell growth and proliferation appear to be regulated by different genes in constant versus fluctuating temperature regimes. The gene expression response of molecular chaperones is also different between constant and fluctuating temperatures. Small heat shock proteins appear to play an important role in response to fluctuating temperatures whereas larger molecular mass chaperones such as Hsp70 and Hsp90 respond more strongly to chronic high temperatures. A number of transcripts that encode for enzymes involved in the biosynthesis of nitrogen-containing organic osmolytes have gene expression patterns that indicate a possible role for these `chemical chaperones9 during acclimation to chronic high temperatures and daily temperature cycling. Genes important for the maintenance of membrane integrity are highly responsive to temperature change. Changes in fatty acid saturation may be important in long-term acclimation and in response to fluctuating temperatures; however cholesterol metabolism may be most critical for short-term acclimation to fluctuating temperatures. The variable effect of temperature on the expression of genes with daily rhythms of expression indicates that there is a complex interaction between the temperature cycle and daily rhythmicity in gene expression. A number of new hypotheses concerning temperature acclimation in fish have been generated as a result of this study. The most notable of these hypotheses is the possibility that the high mobility group b1 (HMGB1) protein, which plays key roles in the assembly of transcription initiation and enhanceosome complexes, may act as a compensatory modulator of transcription in response to temperature, and thus as a global gene expression temperature sensor. This study illustrates the utility of cDNA microarray approaches in both hypothesis-driven and `discovery-based9 investigations of environmental effects on organisms.

The hydrodynamics of eel swimming: I. Wake structure

Abstract: Eels undulate a larger portion of their bodies while swimming than many other fishes, but the hydrodynamic consequences of this swimming mode are poorly understood. In this study, we examine in detail the hydrodynamics of American eels (Anguilla rostrata) swimming steadily at 1.4 L s(-1) and compare them with previous results from other fishes. We performed high-resolution particle image velocimetry (PIV) to quantify the wake structure, measure the swimming efficiency, and force and power output. The wake consists of jets of fluid that point almost directly laterally, separated by an unstable shear layer that rolls up into two or more vortices over time. Previously, the wake of swimming eels was hypothesized to consist of unlinked vortex rings, resulting from a phase offset between vorticity distributed along the body and vorticity shed at the tail. Our high-resolution flow data suggest that the body anterior to the tail tip produces relatively low vorticity, and instead the wake structure results from the instability of the shear layers separating the lateral jets, reflecting pulses of high vorticity shed at the tail tip. We compare the wake structure to large-amplitude elongated body theory and to a previous computational fluid dynamic model and note several discrepancies between the models and the measured values. The wake of steadily swimming eels differs substantially in structure from the wake of previously studied carangiform fishes in that it lacks any significant downstream flow, previously interpreted as signifying thrust. We infer that the lack of downstream flow results from a spatial and temporal balance of momentum removal (drag) and thrust generated along the body, due to the relatively uniform shape of eels. Carangiform swimmers typically have a narrow caudal peduncle, which probably allows them to separate thrust from drag both spatially and temporally. Eels seem to lack this separation, which may explain why they produce a wake with little downstream momentum while carangiform swimmers produce a wake with a clear thrust signature.

Myoglobin: an essential hemoprotein in striated muscle

Abstract: Myoglobin is a cytoplasmic hemoprotein, expressed solely in cardiac myocytes and oxidative skeletal muscle fibers, that reversibly binds O2 by its heme residue, a porphyrin ring:iron ion complex. Since the initial discovery of its structure over 40 years ago, wide-ranging work by many investigators has added importantly to our understanding of its function and regulation. Functionally, myoglobin is well accepted as an O2-storage protein in muscle, capable of releasing O2 during periods of hypoxia or anoxia. Myoglobin is also thought to buffer intracellular O2 concentration when muscle activity increases and to facilitate intracellular O2 diffusion by providing a parallel path that augments simple diffusion of dissolved O2. The use of gene targeting and other molecular biological techniques has revealed important new insights into the developmental and environmental regulation of myoglobin and provided additional functions for this hemoprotein such as scavenging nitric oxide and reactive O2 species. These recent findings, coupled with additional emerging technologies and the discovery of other tissue globins, provide a framework for addressing new questions about myoglobin and readdressing old ones.

Acoustic communication in noise: regulation of call characteristics in a New World monkey.

Abstract: This study on common marmosets Callithrix jacchus is the first to examine noise-dependent mechanisms of vocal plasticity in a New World monkey. Since acoustic communication can be considerably impaired by environmental noise, some animals have evolved adaptations to counteract its masking effects. The studied marmosets increased the sound level of their spontaneous calls in response to increased levels of white noise broadcast to them. Possibly, such noise-dependent adjustment of vocal amplitude serves to maintain a specific signal-to-noise ratio that is favourable for signal production. Concurrently, the adjustment of vocal amplitude can maintain a given active space for communication. In contrast to some bird species, no noise-induced increase in the number of syllables per call series could be found, showing that an increased serial redundancy of vocal signals was not used to communicate under noisy conditions. Finally, we examined a possible noise-dependent prolongation of vocal signals. This approach was guided by the findings of perceptional studies, which suggest an increased detection probability of prolonged signals in noise by temporal summation. Marmosets indeed increased the duration of their call syllables along with increasing background noise levels. This is the first evidence of such mechanism of vocal plasticity in an animal communication system.

Are hsps suitable for indicating stressed states in fish

Abstract: In response to most stressors, fish will elicit a generalized physiological stress response, which involves the activation of the hypothalamic-pituitary-interrenal axis (HPI). As in other vertebrates, this generalized stress response comprises physiological responses that are common to a wide range of environmental, physical and biological stressors. Recently, several families of heat shock proteins (hsps) have been proposed as indicators of a generalized stress response at the cellular level. Recent findings that hsp levels, in various fish tissues, respond to a wide range of stressors have supported the use of these proteins as indicators of stressed states in fish. However, the cellular stress response can vary, for example, according to tissue, hsp family and type of stressor. This brief overview of these responses in fish asks the question of whether changes in levels and families of hsps can be used as a suitable indicator of stressed states in fish. By casting this question in the context of the well-established generalized physiological stress response in fish, we argue that the use of hsps as indicators of stressed states in fish in general is premature.

Noise-induced stress response and hearing loss in goldfish (Carassius auratus).

Abstract: Fishes are often exposed to environmental sounds such as those associated with shipping, seismic experiments, sonar and/or aquaculture pump systems. While efforts have been made to document the effects of such anthropogenic (human-generated) sounds on marine mammals, the effects of excess noise on fishes are poorly understood. We examined the short- and long-term effects of increased ambient sound on the stress and hearing of goldfish (Carassius auratus; a hearing specialist). We reared fish under either quiet (110-125 dB re 1 microPa) or noisy (white noise, 160-170 dB re 1 microPa) conditions and examined animals after specific durations of noise exposure. We assessed noise-induced alterations in physiological stress by measuring plasma cortisol and glucose levels and in hearing capabilities by using auditory brainstem responses. Noise exposure did not produce long-term physiological stress responses in goldfish, but a transient spike in plasma cortisol did occur within 10 min of the noise onset. Goldfish had significant threshold shifts in hearing after only 10 min of noise exposure, and these shifts increased linearly up to approximately 28 dB after 24 h of noise exposure. Further noise exposure did not increase threshold shifts, suggesting an asymptote of maximal hearing loss within 24 h. After 21 days of noise exposure, it took goldfish 14 days to fully recover to control hearing levels. This study shows that hearing-specialist fishes may be susceptible to noise-induced stress and hearing loss.

Dragonfly flight: free-flight and tethered flow visualizations reveal a diverse array of unsteady lift-generating mechanisms, controlled primarily via angle of attack.

Abstract: SUMMARY Here we show, by qualitative free- and tethered-flight flow visualization, that dragonflies fly by using unsteady aerodynamic mechanisms to generate high-lift, leading-edge vortices. In normal free flight, dragonflies use counterstroking kinematics, with a leading-edge vortex (LEV) on the forewing downstroke, attached flow on the forewing upstroke, and attached flow on the hindwing throughout. Accelerating dragonflies switch to in-phase wing-beats with highly separated downstroke flows, with a single LEV attached across both the fore- and hindwings. We use smoke visualizations to distinguish between the three simplest local analytical solutions of the Navier–Stokes equations yielding flow separation resulting in a LEV. The LEV is an open U-shaped separation, continuous across the thorax, running parallel to the wing leading edge and inflecting at the tips to form wingtip vortices. Air spirals in to a free-slip critical point over the centreline as the LEV grows. Spanwise flow is not a dominant feature of the flow field – spanwise flows sometimes run from wingtip to centreline, or vice versa – depending on the degree of sideslip. LEV formation always coincides with rapid increases in angle of attack, and the smoke visualizations clearly show the formation of LEVs whenever a rapid increase in angle of attack occurs. There is no discrete starting vortex. Instead, a shear layer forms behind the trailing edge whenever the wing is at a non-zero angle of attack, and rolls up, under Kelvin–Helmholtz instability, into a series of transverse vortices with circulation of opposite sign to the circulation around the wing and LEV. The flow fields produced by dragonflies differ qualitatively from those published for mechanical models of dragonflies, fruitflies and hawkmoths, which preclude natural wing interactions. However, controlled parametric experiments show that, provided the Strouhal number is appropriate and the natural interaction between left and right wings can occur, even a simple plunging plate can reproduce the detailed features of the flow seen in dragonflies. In our models, and in dragonflies, it appears that stability of the LEV is achieved by a general mechanism whereby flapping kinematics are configured so that a LEV would be expected to form naturally over the wing and remain attached for the duration of the stroke. However, the actual formation and shedding of the LEV is controlled by wing angle of attack, which dragonflies can vary through both extremes, from zero up to a range that leads to immediate flow separation at any time during a wing stroke.

Erythropoietin and the hypoxic brain.

Abstract: Normal tissue function in mammals depends on adequate supply of oxygen through blood vessels. A discrepancy between oxygen supply and consumption (hypoxia) induces a variety of specific adaptation mechanisms at the cellular, local and systemic level. These mechanisms are in part governed by the activation of hypoxia-inducible transcription factors (HIF-1, HIF-2), which in turn modulate expression of hypoxically regulated genes such as those encoding vascular endothelial growth factor (VEGF) and erythropoietin (EPO). EPO is a glycoprotein that is produced mainly by interstitial fibroblasts in the kidneys of the adult and in hepatocytes in the foetus. Released into the circulation, EPO makes its way to the bone marrow, where it regulates red cell production by preventing apoptosis of erythroid progenitor cells. Recently, EPO has emerged as a multifunctional growth factor that plays a significant role in the nervous system. Both EPO and its receptor are expressed throughout the brain in glial cells, neurones and endothelial cells. Hypoxia and ischaemia have been recognised as important driving forces of EPO expression in the brain. EPO has potent neuroprotective properties in vivo and in vitro and appears to act in a dual way by directly protecting neurones from ischaemic damage and by stimulating endothelial cells and thus supporting the angiogenic effect of VEGF in the nervous system. Thus, hypoxia-induced gene products such as VEGF and EPO might be part of a self-regulated physiological protection mechanism to prevent neuronal injury, especially under conditions of chronically reduced blood flow (chronic ischaemia). In this review, I will briefly summarize the recent findings on the molecular mechanisms of hypoxia-regulated EPO expression in general and give an overview of its expression in the central nervous system, its action as a growth factor with non-haematopoietic functions and its potential clinical relevance in various brain pathologies.

Hypoxic survival strategies in two fishes: extreme anoxia tolerance in the North European crucian carp and natural hypoxic preconditioning in a coral-reef shark

Abstract: Especially in aquatic habitats, hypoxia can be an important evolutionary driving force resulting in both convergent and divergent physiological strategies for hypoxic survival. Examining adaptations to anoxic/hypoxic survival in hypoxia-tolerant animals may offer fresh ideas for the treatment of hypoxia-related diseases. Here, we summarise our present knowledge of two fishes that have evolved to survive hypoxia under very different circumstances. The crucian carp (Carassius carassius) is of particular interest because of its extreme anoxia tolerance. During the long North European winter, it survives for months in completely oxygen-deprived freshwater habitats. The crucian carp also tolerates a few days of anoxia at room temperature and, unlike anoxia-tolerant freshwater turtles, it is still physically active in anoxia. Moreover, the crucian carp does not appear to reduce neuronal ion permeability during anoxia and may primarily rely on more subtle neuromodulatory mechanisms for anoxic metabolic depression. The epaulette shark (Hemiscyllium ocellatum) is a tropical marine vertebrate. It lives on shallow reef platforms that repeatedly become cut off from the ocean during periods of low tides. During nocturnal low tides, the water [O(2)] can fall by 80% due to respiration of the coral and associated organisms. Since the tides become lower and lower over a period of a few days, the hypoxic exposure during subsequent low tides will become progressively longer and more severe. Thus, this shark is under a natural hypoxic preconditioning regimen. Interestingly, hypoxic preconditioning lowers its metabolic rate and its critical P(O(2)). Moreover, repeated anoxia appears to stimulate metabolic depression in an adenosine-dependent way.

Role of trehalose phosphate synthase and trehalose during hypoxia: from flies to mammals.

Abstract: SUMMARY Trehalose is a nonreducing disaccharide in which the two glucose units are linked in an α,α-1,1-glycosidic linkage. The best known and most widely distributed pathway of trehalose synthesis involves the transfer of glucose from UDP-glucose to glucose 6-phosphate to form trehalose-6-phosphate and UDP via the trehalose-6-phosphate synthase (TPS1). Trehalose-6-phosphate phosphatase (TPS2) then converts trehalose-6-phosphate to free trehalose. This sugar is present in a wide variety of organisms, including bacteria, yeast, fungi, insects, invertebrates and plants, and because of its particular physical features, trehalose is able to protect the integrity of cells against a variety of environmental stresses such as desiccation, dehydration, heat, cold and oxidation. Our current studies described here indicate that trehalose protects Drosophila and mammalian cells from hypoxic and anoxic injury. The mechanism of this protection is probably related to a decrease in protein denaturation through protein–trehalose interactions.

Morphology predicts suction feeding performance in centrarchid fishes.

Abstract: Suction feeding fish differ in their capacity to generate subambient pressure while feeding, and these differences appear to relate to morphological variation. We developed a morphological model of force transmission in the fish head and parameterized it with measurements from individual fish. The model was applied to 45 individuals from five species of centrarchid fishes: Lepomis macrochirus, Lepomis punctatus, Lepomis microlophus, Micropterus salmoides and Pomoxis nigromaculatus. Measurements of epaxial cross-sectional area, epaxial moment arm, buccal area and buccal area moment arm were combined to estimate pressure generation capacity for individual fish. This estimation was correlated with pressure measured in fish feeding on elusive prey to test the model’s ability to predict pressure generation from morphology. The model explained differences in pressure generation found among individuals (P<0.001, r 2 =0.71) and produced a realistic estimate of normalized muscle stress during suction feeding (68.5±6.7·kPa). Fish with smaller mouths, larger epaxial cross-sectional area and longer epaxial moments, such as L. macrochirus (bluegill sunfish), generated lower pressures than fish with larger mouths, smaller cross-sectional area and shorter moments, such as M. salmoides (largemouth bass). These results reveal a direct trade-off between morphological requirements of feeding on larger prey (larger mouth size relative to body depth) and the ability to generate subambient pressure while suction feeding on elusive prey. Summary

Swimming of larval zebrafish: ontogeny of body waves and implications for locomotory development

Abstract: SUMMARY Fish larvae, like most adult fish, undulate their bodies to propel themselves. A detailed kinematic study of the larval body wave is a prerequisite to formulate a set of functional requirements that the locomotor system must fulfil to generate the observed swimming kinematics. Lateral displacement and curvature profiles were obtained for zebrafish ( Danio rerio ) larvae at 2–21 days post-fertilisation for three swimming behaviours (cyclic swimming, slow starts and fast startle responses) using high-speed video. During cyclic swimming, fish larvae maintain tail beat frequencies of up to 100 Hz. The corresponding longitudinal strains, estimated from the peak curvatures of the midline, reach up to 0.19 in superficial tissue. The strain rate can reach 120 s –1 . The wave of curvature travels along the body at a near-constant rate. Posterior to the stiff head, body-lengthspecific curvature is high and rises gently along the entire trunk to a maximum value of 6. Burst-and-coast swimming generates similar peak curvatures to cyclic swimming, but curvature rises more steeply from head to tail. Fish larvae exhibit phase shifts of 57–63° between the wave of lateral displacement and the wave of curvature, resulting in a 1:1.2 ratio of body wave length to curvature wave length. During C-starts, muscle strain can reach 0.19 and superficial longitudinal strain rates approach 30 s –1 . Fish larvae do not initiate their escape response with a standing wave of curvature, although their C-starts approach a standing wave as the larvae grow older. The performance demands derived from swimming kinematics suggest that larval axial muscles have very short contraction cycles (10 ms), experience considerable strains (up to 0.2) and strain rates (up to 30 s –1 in white muscle fibres) yet are able to power swimming for several seconds.

The cost of foraging by a marine predator, the Weddell seal Leptonychotes weddellii: pricing by the stroke

Abstract: Foraging by mammals is a complex suite of behaviors that can entail high energetic costs associated with supporting basal metabolism, locomotion and the digestion of prey. To determine the contribution of these various costs in a free-ranging marine mammal, we measured the post-dive oxygen consumption of adult Weddell seals ( N =9) performing foraging and non-foraging dives from an isolated ice hole in McMurdo Sound, Antarctica. Dives were classified according to behavior as monitored by an attached video-data logging system (recording activity, time, depth, velocity and stroking). We found that recovery oxygen consumption showed a biphasic relationship with dive duration that corresponded to the onset of plasma lactate accumulation at approximately 23 min. Locomotor costs for diving Weddell seals increased linearly with the number of strokes taken according to the relationship: locomotor cost =– 3.78+0.04 × stroke number ( r 2=0.74, N =90 dives), where locomotor cost is in ml O2 kg–1. Foraging dives in which seals ingested Pleuragramma antarcticum resulted in a 44.7% increase in recovery oxygen consumption compared to non-foraging dives, which we attributed to the digestion and warming of prey. The results show that the energy expended in digestion for a free-ranging marine mammal are additive to locomotor and basal costs. By accounting for each of these costs and monitoring stroking mechanics, it is possible to estimate the aerobic cost of diving in free-ranging seals where cryptic behavior and remote locations prevent direct energetic measurements.

On the nature of pre-freeze mortality in insects: water balance, ion homeostasis and energy charge in the adults of Pyrrhocoris apterus

Abstract: SUMMARY Three acclimation groups [i.e. non-diapause (LD), diapause (SD) and diapause, cold-acclimated (SDA)] of the adult bugs Pyrrhocoris apterus differed markedly in their levels of chill tolerance. Survival time at a sub-zero, but non-freezing, temperature of –5°C (Lt50) extended from 7.6 days, through 35.6 days, to >60 days in the LD, SD and SDA insects, respectively. The time necessary for recovery after chill-coma increased linearly with the increasing time of exposure to –5°C, and the steepness of the slope of linear regression decreased in the order LD>SD>SDA. The capacity to prevent/counteract leakage of Na+ down the electrochemical gradient (from haemolymph to tissues) during the exposure to –5°C increased in the order LD

Cellular oxygen sensing need in CNS function: physiological and pathological implications

Abstract: Structural and functional integrity of brain function profoundly depends on a regular oxygen and glucose supply. Any disturbance of this supply becomes life threatening and may result in severe loss of brain function. In particular, reductions in oxygen availability (hypoxia) caused by systemic or local blood circulation irregularities cannot be tolerated for longer periods due to an insufficient energy supply to the brain by anaerobic glycolysis. Hypoxia has been implicated in central nervous system pathology in a number of disorders including stroke, head trauma, neoplasia and neurodegenerative disease. Complex cellular oxygen sensing systems have evolved for tight regulation of oxygen homeostasis in the brain. In response to variations in oxygen partial pressure (P(O(2))) these induce adaptive mechanisms to avoid or at least minimize brain damage. A significant advance in our understanding of the hypoxia response stems from the discovery of the hypoxia inducible factors (HIF), which act as key regulators of hypoxia-induced gene expression. Depending on the duration and severity of the oxygen deprivation, cellular oxygen-sensor responses activate a variety of short- and long-term energy saving and cellular protection mechanisms. Hypoxic adaptation encompasses an immediate depolarization block by changing potassium, sodium and chloride ion fluxes across the cellular membrane, a general inhibition of protein synthesis, and HIF-mediated upregulation of gene expression of enzymes or growth factors inducing angiogenesis, anaerobic glycolysis, cell survival or neural stem cell growth. However, sustained and prolonged activation of the HIF pathway may lead to a transition from neuroprotective to cell death responses. This is reflected by the dual features of the HIF system that include both anti- and proapoptotic components. These various responses might be based on a range of oxygen-sensing signal cascades, including an isoform of the neutrophil NADPH oxidase, different electron carrier units of the mitochondrial chain such as a specialized mitochondrial, low P(O(2)) affinity cytochrome c oxidase (aa(3)) and a subfamily of 2-oxoglutarate dependent dioxygenases termed HIF prolyl-hydroxylase (PHD) and HIF asparaginyl hydroxylase, known as factor-inhibiting HIF (FIH-1). Thus specific oxygen-sensing cascades, by means of their different oxygen sensitivities, cell-specific and subcellular localization, may help to tailor various adaptive responses according to differences in tissue oxygen availability.

The tube cement of Phragmatopoma californica: a solid foam

Abstract: Phragmatopoma californica is a marine polychaete that builds protective tubes by joining bits of shell and sand grains with a secreted proteinaceous cement. The cement forms a solid foam (closed cells) via covalent crosslinking, as revealed by electron and laser scanning confocal microscopy. The cement contains extractable calcium and magnesium, and non-extractable phosphorus. Amino acid analysis demonstrated that the phosphorus is in the form of phosphoserine and that >90% of serine in the cement (i.e. 28 mol% of residues) is phosphorylated. In addition to previously identified basic proteins, the cement contains a highly acidic polyphosphoserine protein as a major component. We propose a model for the structure and bonding mechanism of the cement that has the following major features: (1) within the secretory pathway of cement gland cells, the electrostatic association of the oppositely charged proteins and divalent cations (Ca2+ and Mg2+) condense the cement proteins into dehydrated secretory granules; (2) the condensation of the cement leads to the separation of the solution into two aqueous phases (complex coacervation) that creates the closed cell foam structure of the cement; (3) rehydration of the condensed cement granules after deposition onto tube particles contributes to the displacement of water from the mineral substrate to facilitate underwater adhesion; and (4) after secretion, covalent cross-linking through oxidative coupling of DOPA gradually solidifies the continuous phase of the cement to set the porous structure.

Swimming gaits, passive drag and buoyancy of diving sperm whales Physeter macrocephalus.

Abstract: SUMMARY Drag and buoyancy are two primary external forces acting on diving marine mammals. The strength of these forces modulates the energetic cost of movement and may influence swimming style (gait). Here we use a high-resolution digital tag to record depth, 3-D orientation, and sounds heard and produced by 23 deep-diving sperm whales in the Ligurian Sea and Gulf of Mexico. Periods of active thrusting versus gliding were identified through analysis of oscillations measured by a 3-axis accelerometer. Accelerations during 382 ascent glides of five whales (which made two or more steep ascents and for which we obtained a measurement of length) were strongly affected by depth and speed at Reynold9s numbers of 1.4–2.8×107. The accelerations fit a model of drag, air buoyancy and tissue buoyancy forces with an r2 of 99.1–99.8% for each whale. The model provided estimates (mean ± s.d.) of the drag coefficient (0.00306±0.00015), air carried from the surface (26.4±3.9 l kg-3 mass), and tissue density (1030±0.8 kg m-3) of these five animals. The model predicts strong positive buoyancy forces in the top 100 m of the water column, decreasing to near neutral buoyancy at 250–850 m. Mean descent speeds (1.45±0.19 m s-1) were slower than ascent speeds (1.63±0.22 m s-1), even though sperm whales stroked steadily (glides 5.3±6.3%) throughout descents and employed predominantly stroke-and-glide swimming (glides 37.7±16.4%) during ascents. Whales glided more during portions of dives when buoyancy aided their movement, and whales that glided more during ascent glided less during descent (and vice versa), supporting the hypothesis that buoyancy influences behavioural swimming decisions. One whale rested at∼ 10 m depth for more than 10 min without fluking, regulating its buoyancy by releasing air bubbles.

Cardiac plasticity in fishes: environmental influences and intraspecific differences

Abstract: Fish cardiac physiology and anatomy show a multiplicity of intraspecific modifications when exposed to prolonged changes in environmentally relevant parameters such as temperature, hypoxia and food availability, and when meeting the increased demands associated with training/increased activity and sexual maturation. Further, there is evidence that rearing fish under intensive aquaculture conditions significantly alters some, but not all, aspects of cardiac anatomy and physiology. This review focuses on the responses of cardiac physiology and anatomy to these challenges, highlighting where applicable, the importance of hyperplastic (i.e. the production of new cells) vs hypertrophic (the enlargement of existing cells) growth to the adaptive response of the heart. In addition, we summarize recent studies that have explored the relationship between the myocardial protection afforded by preconditioning and myocardial hypoxia tolerance. This latter research clearly demonstrates the capacity of the fish heart to adjust to short-term perturbations, and shows that it can be difficult to predict how short-term and long-term alterations in cardiac physiology will interact.

Insect oviposition induces volatile emission in herbaceous plants that attracts egg parasitoids

Abstract: The egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) responded to synomones emitted by leguminous plants induced by feeding and oviposition activity of the bug Nezara viridula (L.) (Heteroptera: Pentatomidae). This was shown by laboratory bioassays using a Y-tube olfactometer. Broad bean leaves ( Vicia faba L.) damaged by feeding activity of N. viridula and on which host egg mass had been laid produced synomones that attracted T. basalis. By contrast, undamaged leaves or feeding-damaged leaves without eggs did not attract wasp females. French bean plants ( Phaseolus vulgaris L.) also emitted attractive synomones when they were damaged by host feeding and carrying egg masses. Thus, release of feeding- and oviposition-induced synomones does not seem to be plant-specific. Synomone production was shown to be a systemically induced plant physiological response to feeding damage and oviposition. Also, parts of the plant that were left undamaged and did not carry host eggs emitted attractive synomones when other parts of the plant were damaged by feeding and carrying eggs. Furthermore, wasps were not attracted by N. viridula egg masses offered alone or combined with damaged broad bean leaves. Thus, the attractiveness of feeding-damaged leaves carrying eggs is due to induction by feeding and oviposition rather than due to a combined effect of attractive volatiles released from eggs and damaged leaves. The production of synomones was influenced by the age of the host egg mass, because feeding-damaged leaves bearing egg masses attracted the parasitoid until the eggs were ∼72-96 h old but not once the larvae had hatched from the eggs (∼120 h old). These results show that annual plants are able to produce synomones as a consequence of feeding and egg mass oviposition by a sucking insect.

A computational study of the aerodynamic forces and power requirements of dragonfly (Aeschna juncea) hovering.

Abstract: Aerodynamic force generation and mechanical power requirements of a dragonfly (Aeschna juncea) in hovering flight are studied. The method of numerically solving the Navier-Stokes equations in moving overset grids is used. When the midstroke angles of attack in the downstroke and the upstroke are set to 52 degrees and 8 degrees, respectively (these values are close to those observed), the mean vertical force equals the insect weight, and the mean thrust is approximately zero. There are two large vertical force peaks in one flapping cycle. One is in the first half of the cycle, which is mainly due to the hindwings in their downstroke; the other is in the second half of the cycle, which is mainly due to the forewings in their downstroke. Hovering with a large stroke plane angle (52 degrees ), the dragonfly uses drag as a major source for its weight-supporting force (approximately 65% of the total vertical force is contributed by the drag and 35% by the lift of the wings). The vertical force coefficient of a wing is twice as large as the quasi-steady value. The interaction between the fore- and hindwings is not very strong and is detrimental to the vertical force generation. Compared with the case of a single wing in the same motion, the interaction effect reduces the vertical forces on the fore- and hindwings by 14% and 16%, respectively, of that of the corresponding single wing. The large vertical force is due to the unsteady flow effects. The mechanism of the unsteady force is that in each downstroke of the hindwing or the forewing, a new vortex ring containing downward momentum is generated, giving an upward force. The body-mass-specific power is 37 W kg(-1), which is mainly contributed by the aerodynamic power.

Assessing a relationship between bone microstructure and growth rate: a fluorescent labelling study in the king penguin chick (Aptenodytes patagonicus).

Abstract: SUMMARY Microstructure–function relationships remain poorly understood in primary bone tissues. The relationship between bone growth rate and bone tissue type, although documented in some species by previous works, remains somewhat unclear and controversial. We assessed this relationship in a species with extreme adaptations, the king penguin ( Aptenodytes patagonicus ). These birds have a peculiar growth, interrupted 3 months after hatching by the austral winter. Before this interruption, chicks undergo extremely rapid statural and ponderal growth. We recorded experimentally (by means of fluorescent labelling) the growth rate of bone tissue in four long bones (humerus, radius, femur and tibiotarsus) of four king penguin chicks during their fastest phase of growth (3–5 weeks after hatching) and identified the associated bone tissue types (`laminar9, `longitudinal9, `reticular9 or `radial9 fibro-lamellar bone tissue). We found the highest bone tissue growth rate known to date, up to 171 μm day –1 (mean 55 μm day –1 ). There was a highly significant relationship between bone tissue type and growth rate ( P –6 ). Highest rates were obtained with the radial microarchitecture of fibro-lamellar bone, where cavities in the woven network are aligned radially. This result supports the heuristic value of a relationship between growth rate and bone primary microstructure. However, we also found that growth rates of bone tissue types vary according to the long bone considered ( P –5 ) (e.g. growth rates were 38% lower in the radius than in the other long bones), a result that puts some restriction on the applicability of absolute growth rate values (e.g. to fossil species). The biomechanical disadvantages of accelerated bone growth are discussed in relation to the locomotor behaviour of the chicks during their first month of life.

Unsteady aerodynamic forces of a flapping wing.

Abstract: The unsteady aerodynamic forces of a model fruit fly wing in flapping motion were investigated by numerically solving the Navier-Stokes equations. The flapping motion consisted of translation and rotation [the translation velocity (u(t)) varied according to the simple harmonic function (SHF), and the rotation was confined to a short period around stroke reversal]. First, it was shown that for a wing of given geometry with u(t) varying as the SHF, the aerodynamic force coefficients depended only on five non-dimensional parameters, i.e. Reynolds number (Re), stroke amplitude (Phi), mid-stroke angle of attack (alpha(m)), non-dimensional duration of wing rotation (Delta tau(r)) and rotation timing [the mean translation velocity at radius of the second moment of wing area (U), the mean chord length (c) and c/U were used as reference velocity, length and time, respectively]. Next, the force coefficients were investigated for a case in which typical values of these parameters were used (Re=200; Phi=150 degrees; alpha(m)=40 degrees; Delta tau(r) was 20% of wingbeat period; rotation was symmetrical). Finally, the effects of varying these parameters on the force coefficients were investigated. In the Re range considered (20-1800), when Re was above approximately 100, the lift ((L)) and drag ((D)) coefficients were large and varied only slightly with Re (in agreement with results previously published for revolving wings); the large force coefficients were mainly due to the delayed stall mechanism. However, when Re was below approximately 100, (L) decreased and (D) increased greatly. At such low Re, similar to the case of higher Re, the leading edge vortex existed and attached to the wing in the translatory phase of a half-stroke; but it was very weak and its vorticity rather diffused, resulting in the small (L) and large (D). Comparison of the calculated results with available hovering flight data in eight species (Re ranging from 13 to 1500) showed that when Re was above approximately 100, lift equal to insect weight could be produced but when Re was lower than approximately 100, additional high-lift mechanisms were needed. In the range of Re above approximately 100, Phi from 90 degrees to 180 degrees and Delta tau(r) from 17% to 32% of the stroke period (symmetrical rotation), the force coefficients varied only slightly with Re, Phi and Delta tau(r). This meant that the forces were approximately proportional to the square of Phi n (n is the wingbeat frequency); thus, changing Phi and/or n could effectively control the magnitude of the total aerodynamic force. The time course of (L) (or (D)) in a half-stroke for u(t) varying according to the SHF resembled a half sine-wave. It was considerably different from that published previously for u(t), varying according to a trapezoidal function (TF) with large accelerations at stroke reversal, which was characterized by large peaks at the beginning and near the end of the half-stroke. However, the mean force coefficients and the mechanical power were not so different between these two cases (e.g. the mean force coefficients for u(t) varying as the TF were approximately 10% smaller than those for u(t) varying as the SHF except when wing rotation is delayed).

Structural and functional adaptation to hypoxia in the rat brain.

Abstract: Chronic exposure to a hypoxic environment leads to structural and functional adaptations in the rat brain. One significant adaptation is a decrease in intercapillary distances through a near doubling of the capillary density, which begins after about 1 week of hypoxic exposure and is completed by 3 weeks. Hypoxic angiogenesis is controlled by activation of downstream genes by Hypoxia Inducible Factor-1 and Angiopoietin-2. The processes that increase capillary density are reversible upon restoration of the ambient oxygen concentration. Capillary regression, which also occurs over a 3-week period, is accomplished through activation of apoptosis. The implication from these observations is that the brain naturally functions in a low, but controlled, oxygen environment. Acute imbalances in oxygen delivery and metabolic demand are addressed through changes in blood flow; persistent imbalances activate mechanisms that adjust capillary density. The mechanisms that control these processes decline with age.

Chaperones, protein aggregation, and brain protection from hypoxic/ischemic injury.

Abstract: Chaperones, especially the stress inducible Hsp70, have been studied for their potential to protect the brain from ischemic injury. While they protect from both global and focal ischemia in vivo and cell culture models of ischemia/reperfusion injury in vitro, the mechanism of protection is not well understood. Protein aggregation is part of the etiology of chronic neurodegenerative diseases such as Huntington's and Alzheimer's, and recent data demonstrate protein aggregates in animal models of stroke. We now demonstrate that overexpression of Hsp70 in hippocampal CA1 neurons reduces evidence of protein aggregation under conditions where neuronal survival is increased. We have also demonstrated protection by the cochaperone Hdj-2 in vitro and demonstrated that this is associated with reduced protein aggregation identified by ubiquitin immunostaining. Hdj-2 can prevent protein aggregate formation by itself, but can only facilitate protein folding in conjunction with Hsp70. Pharmacological induction of Hsp70 was found to reduce both apoptotic and necrotic astrocyte death induced by glucose deprivation or oxygen glucose deprivation. Protection from ischemia and ischemia-like injury by chaperones thus involves at least anti-apoptotic, anti-necrotic and anti-protein aggregation mechanisms.

Ammonia excretion in aquatic and terrestrial crabs

Abstract: The excretory transport of toxic ammonia across epithelia is not fully understood. This review presents data combined with models of ammonia excretion derived from studies on decapod crabs, with a view to providing new impetus to investigation of this essential issue. The majority of crabs preserve ammonotely regardless of their habitat, which varies from extreme hypersaline to freshwater aquatic environments, and ranges from transient air exposure to obligate air breathing. Important components in the excretory process are the Na+/K+(NH4+)-ATPase and other membrane-bound transport proteins identified in many species, an exocytotic ammonia excretion mechanism thought to function in gills of aquatic crabs such as Carcinus maenas, and gaseous ammonia release found in terrestrial crabs, such as Geograpsus grayi and Ocypode quadrata. In addition, this review presents evidence for a crustacean Rhesus-like protein that shows high homology to the human Rhesus-like ammonia transporter both in its amino acid sequence and in its predicted secondary structure.