Journal of Experimental Biology最新文献

Marine heatwaves (MHW) have recently been proposed as more relevant in driving population changes than the continuous increase in average temperatures associated with climate change. The causal processes underpinning MHW effects in sharks are unclear but may be linked to changes in fitness caused by physiological trade-offs that influence the immune response. Considering the scarcity of data about the immune response of sharks under anomalous warming events, the present study analyzed several fitness indices and characterized the immune response (in the blood, epigonal organ, liver, spleen, and intestine) of temperate adult small-spotted catsharks (Scyliorhinus canicula) after a 30-day exposure to a Category II MHW. The results indicated that adult small-spotted catsharks have developed coping strategies for the MHW. Specifically, among the 35 parameters investigated, only the gonad-to-body ratio (GBR) and plasma glucose showed significant increases. In contrast, igm and tumor necrosis factor receptor (tnfr) gene expression in blood cells, tnfr in the epigonal organ, and the number of monocytes significantly decreased. Although a decline in immune function in small-spotted catsharks was revealed following the MHW exposure, energy mobilization restored homeostasis and indicated a shift in energy allocation towards reproduction. Group resilience may be due to the variable tolerance of individuals, the phenotypic plasticity of cellular immunity, thermal imprinting, and/or metabolic capacity of the individuals.

Oxygen availability is central to the energetic budget of aquatic animals and may vary naturally and/or in response to anthropogenic activities. Yet, we know little about how oxygen availability is linked to fundamental processes such as ion transport in aquatic insects. We hypothesized and observed that ion (22Na and 35SO4) uptake would be significantly decreased at O2 partial pressures below the mean Pcrit (5.4 kPa) where metabolic rates (MO2) are compromised, and ATP production is limited. However, we were surprised to observe marked reductions in ion uptake at oxygen partial pressures well above the Pcrit, where MO2 was stable. For example, SO4 uptake decreased by 51% at 11.7kPa, and 82% at the Pcrit (5.4kPa) while Na uptake decreased by 19% at 11.7kPa, and 60% at the Pcrit. Nymphs held for longer time periods at reduced PO2 exhibited stronger reductions in ion uptake rates. Fluids from whole body homogenates exhibited a 29% decrease in osmolality in the most hypoxic condition. The differential expression of atypical guanylyl cyclase (gcy-88e) in response to changing PO2 conditions provides evidence for its potential role as an oxygen sensor. Several ion transport genes (e.g., chloride channel and sodium-potassium ATPase) and hypoxia-associated genes (e.g., ldh and egl-9) were also impacted by decreased oxygen availability. Together, our work suggests that N. triangulifer can sense decreased oxygen availability and perhaps conserves energy accordingly, even when MO2 is not impacted.

The interaction of widespread stressors such as nitrate pollution and increasing temperatures associated with climate change are likely to affect aquatic ectotherms such as amphibians. The metamorphic and physiological traits of amphibian larvae during the critical onset of metamorphosis are particularly susceptible to these stressors. We used a crossed experimental design subjecting Rana temporaria larvae to four constant rearing temperatures (18, 22, 26, 28 °C) crossed with three environmentally relevant nitrate concentrations (0, 50, 100 mg×L-1) to investigate the interactive and individual effects of these stressors on metamorphic (i.e., growth and development) and physiological traits (i.e., metabolism and heat tolerance) at the onset of metamorphosis. Larvae exposed to elevated nitrate concentrations and thermal stress displayed increased metabolic rates but decreased developmental rate, highlighting interactive effects of these stressors. However, nitrate pollution alone had no effect on either metamorphic or physiological traits, suggesting that detoxification processes were sufficient to maintain homeostasis but not in combination with increased rearing temperatures. Furthermore, larvae exposed to nitrate displayed diminished abilities to exhibit temperature-induced plasticity in metamorphosis timing and heat tolerance, as well as reduced acclimation capacity in heat tolerance and an increased thermal sensitivity of metabolic rate to higher temperatures. These results highlight the importance of considering the exposure to multiple stressors when investigating how natural populations respond to global change.

It is thought that the magnitude of center of mass (COM) oscillations can affect stability and locomotor costs in arboreal animals. Previous studies have suggested that minimizing collisional losses and maximizing pendular energy exchange are effective mechanisms to reduce muscular input and energy expenditure during terrestrial locomotion. However, few studies have explored whether these mechanisms are used in an arboreal context, where stability and efficiency often act as tradeoffs. This study explores three-dimensional center of mass mechanics in an arboreal primate-the squirrel monkey (Saimiri sciureus)-moving quadrupedally at various speeds on instrumented arboreal and terrestrial supports. Using kinetic data, values of energy recovery, center of mass mechanical work and power, potential and kinetic energy congruity, and collision angle and fraction were calculated for each stride. Saimiri differed from many other mammals by having lower energy recovery. Although few differences were observed in center of mass mechanics between substrates at low or moderate speeds, as speed increased, center of mass work was done at a much greater range of rates on the pole. Collision angles were higher, while collision fractions and energy recovery values were lower on the pole, indicating less moderation of collisional losses during arboreal versus terrestrial locomotion. These data support the idea that the energetic demands of arboreal and terrestrial locomotion differ, suggesting that arboreal primates likely employ different locomotor strategies compared to their terrestrial counterparts-an important factor in the evolution of arboreal locomotion.

Subterranean mammals representing a single subspecies occurring along an aridity gradient provide an appropriate model for investigating adaptive variation in thermal physiology with varying levels of precipitation and air temperature (Tair). This study examined the thermal physiological adaptations of common mole-rats (Cryptomys hottentotus hottentotus) across five populations along an aridity gradient, challenging the expectation that increased aridity would lead to reduced metabolic rate (MR), lower body temperatures (Tb), and broader thermoneutral zones (TNZ). No significant, consistent differences in MR, Tb, or thermal conductance were observed between populations, suggesting uniform thermoregulatory mechanisms across habitats. Instead, behavioral strategies such as huddling and torpor may play a more prominent role than physiological adaptations in managing temperature regulation and water balance. The study also observed osmoregulatory differences, with populations employing distinct behavioral cooling strategies in response to water availability. These results underscore the need for further research into the responses of subterranean species to climate change, particularly in understanding how increasing global temperatures and aridification might influence species distribution if they lack the physiological capacity to adapt to future climatic conditions.

While birds' impressive singing abilities are made possible by the syrinx, the upper vocal system (i.e., trachea, larynx, and beak) could also play a role in sound filtration. Yet, we still lack a clear understanding of the range of elongation this system can undertake, especially along the trachea. Here, we used biplanar cineradiography and X-ray Reconstruction of Moving Morphology (XROMM) to record 15 species of cadaveric birds from 9 different orders while an operator moved the bird's cadaveric heads in different directions. In all studied species, we found elongation of the trachea to be correlated with neck extension, and significantly greater (ranging from 18% to 48% for the whole motion; and from 1.4% to 15.7% for the singing positions) than previously reported on a live singing bird (3%). This elongation or compression was not always homogeneous along its entire length. Some specimens showed increased lengthening in the rostral part and others in both the rostral and caudal parts of the vocal tract. The diversity of elongation patterns shows that trachea elongation is more complex than previously thought. Since tracheal lengthening affects sound frequencies, our results contribute to our understanding of the mechanisms involved in complex communication signals, one of the amazing traits we share with birds.

Multiple species of frogs in the Ranidae family have been observed to 'skitter' across the water surface, but little is understood about the biomechanical or physical mechanisms that underlie this behavior. All documented descriptions are anecdotal, asserting simply that the frogs can cross the water surface without sinking. To study this form of interfacial locomotion, we recorded high speed video of the northern cricket frog Acris crepitans and quantified its kinematics. We also compared its semi-aquatic behavior with the frogs' terrestrial locomotion. Contrary to expectations based on anecdotal knowledge, we found that cricket frogs do not maintain an above-surface position throughout the locomotor cycle. Instead, the frogs are completely submerged during both the launching and landing phase of a jump cycle, similar to porpoising in other animals. It is possible that leg-retraction time constrains these frogs from performing true surface-only locomotion.

Amphibians are a classical object for physiological studies, and they are of great value for developmental studies owing to their transition from an aquatic larval form to an adult form with a terrestrial lifestyle. Axolotls (Ambystoma mexicanum) are of special interest for such studies because of their neoteny and facultative pedomorphosis, as in these animals, metamorphosis can be induced and fully controlled in laboratory conditions. It has been suggested that their metamorphosis, associated with gross anatomical changes in the heart, also involves physiological and electrical remodeling of the myocardium. We used whole-cell patch clamp to investigate possible changes caused by metamorphosis in electrical activity and major ionic currents in cardiomyocytes isolated from paedomorphic and metamorphic axolotls. T4-induced metamorphosis caused shortening of atrial and ventricular action potentials (APs), with no changes in resting membrane potential or maximum velocity of AP upstroke, favoring higher heart rate possible in metamorphic animals. Potential-dependent potassium currents in axolotl myocardium were represented by delayed rectifier currents IKr and IKs, and upregulation of IKs caused by metamorphosis probably underlies AP shortening. Metamorphosis was associated with downregulation of inward rectifier current IK1, probably serving to increase the excitability of myocardium in metamorphic animals. Metamorphosis also led to a slight increase in fast sodium current INa with no changes in its steady-state kinetics and to a significant upregulation of ICa in both atrial and ventricular cells, indicating stronger Ca2+ influx for higher cardiac contractility in metamorphic salamanders. Taken together, these changes serve to increase cardiac reserve in metamorphic animals.

The dive response involves three main components - breath holding, reduced heart rate and increased peripheral vasoconstriction - and is ubiquitous during forced dives in air-breathing vertebrates; however, numerous studies in free-diving animals have shown that the heart rate response to diving varies considerably in a manner that suggests cognitive control. Furthermore, studies on free-diving animals and controlled experiments in trained animals both indicate that the dive response can be conditioned, such that the reduction in heart rate begins before submergence and the extent of the reduction is set early in the dive. In addition, numerous species also experience an increase in heart rate and blood flow during ascent at the end of a dive, a phenomenon commonly called 'ascent tachycardia'. Collectively, these data suggest that although the dive response is under autonomic control, many species can vary its magnitude depending on the length and type of the planned dive - an indication of a role for cognition in the overall physiological responses associated with diving. Here, we provide examples of the conditioned cardiac responses - including anticipatory changes in heart rate - in several diving species and propose potential underlying mechanisms. We also discuss how the anticipatory cardiovascular responses not only improve diving capacity, but also prevent diving-related problems, such as decompression sickness or barotrauma, through a mechanism described by the selective gas exchange hypothesis.

Development of the heart is a very intricate and multiplex process as it involves not only the three spatial dimensions but also the fourth or time dimension. Over time, the heart of an embryo needs to adapt its function to serve the increasing complexity of differentiation and growth towards adulthood. It becomes even more perplexing by expanding time into millions of years, allocating related species in the tree of life. As the evolution of soft tissues can hardly be studied, we have to rely on comparative embryology, supported heavily by genetic and molecular approaches. These techniques provide insight into relationships, not only between species, but also between cell populations, signaling mechanisms, molecular interactions and physical factors such as hemodynamics. Heart development depends on differentiation of a mesodermal cell population that - in more derived taxa - continues in segmentation of the first and second heart field. These fields deliver not only the cardiomyocytes, forming the three-dimensionally looping cardiac tube as a basis for the chambered heart, but also the enveloping epicardium. The synchronized beating of the heart is then organized by the conduction system. In this Review, the epicardium is introduced as an important player in cardiac differentiation, including the conduction system.