Journal of Experimental Biology最新文献

There has been much interest in understanding the mechanisms that determine the thermal tolerance of fishes. Given the importance of swimming for fish survival, it is critical to understand the mechanisms that determine why fish fatigue from exercise when temperatures increase to improve our ability to predict the impacts of climate change on fish populations. For the same reason, it is also necessary to understand the drivers of inter-individual and life stage variation in warming tolerance. Here, we used the CTswim methodology (i.e., exposing swimming fish to acute temperature increase) to examine how and why individuals and life stages differ in their warming tolerance. Specifically, we tested whether muscle lactate accumulation and enzyme activities indicative of aerobic and anaerobic capacity, predict inter-individual variation in CTswim at two life stages. We used Chinook salmon (Oncorhynchus tshawytscha) fry and parr acclimated to four temperatures for several weeks to further explore the effect of acclimation temperature on these mechanisms. Our findings indicate that the capacity to remain aerobic for as long as possible while swimming (and thus maintain low lactate) during acute warming is likely a factor determining fatigue in young fry, but that other factors may become more important as salmon age.

Understanding oxidative stress in ecological and evolutionary contexts requires reliable biomarker quantification across taxa, tissues, and experimental setups. However, storage conditions such as temperature and duration may bias these measurements. Here, we evaluated the stability of oxidative stress biomarkers, including three antioxidant enzymes (superoxide dismutase, glutathione reductase, glutathione peroxidase) and a lipid peroxidation marker (malondialdehyde) in amphibian, mammal, bird, and insect samples stored under various temperature conditions (-80 °C, -20 °C, 4 °C) from hours to eight months. Storage significantly affected biomarker values depending on the marker, tissue, and taxon. Notably, even long-term storage at -80 °C altered some markers. In insect samples, lipid peroxidation was also influenced by triglyceride levels, indicating a potential confounding factor. Our results highlight the need to consider storage effects in oxidative stress studies. We also provide practical recommendations, aiming to improve data reliability across field and laboratory eco-evolutionary studies, as well as biomedical contexts.

Muscle-tendon units (MTUs) tend to exploit their elastic elements to meet a range of energy-absorption and power input demands, but the extent of this may depend on how the muscle produces force. Muscle pre-activation is a habitual strategy observed in vivo during energy-absorbing demands, but it remains a question whether pre-activation alters the power input demands among elastic elements and muscle fascicles. To determine the effect of pre-activation on peak power input demands, we conducted in situ experiments using sonomicrometry and a linear actuator to simulate a pre-activation strategy in the lateral gastrocnemius MTU of wild turkeys (n=6). Onset timing of muscle activation was manipulated to start (1) simultaneously with or (2) before an active MTU stretch (i.e., no pre-activation versus with pre-activation). During MTU stretch, we quantified a peak power input decoupling ratio to determine the relative power input between muscle fascicles and elastic elements. We found that muscle pre-activation decreased the decoupling ratio (mean±s.d., 0.68±0.09 vs. 0.56±0.11; p=0.015; Cohen's d=1.49), signifying that muscle fascicles absorbed a greater percentage of total MTU peak power input. We also found that the MTU generated greater force with pre-activation by relying more on active fascicle lengthening during the late phase of MTU stretch, which allowed for greater peak power input capacity of the MTU. These findings highlight how a simple shift in muscle activation timing can prime the MTU to deal with greater peak power input during energy-absorbing activities.

Skeletogenesis is a tightly regulated process that is highly sensitive to abiotic factors and environmental change. Any skeletal abnormalities arising in early life can have lifelong consequences. Freshwater fish must cope with increased temperatures and declining pH, as well as with pollutants released into the environment by human activities. Our study aims to determine whether warming modulates the impacts of low pH and the environmental pollutant cadmium on zebrafish skeletal development. Zebrafish larvae were exposed to warming (31.5°C), acidification (pH 4.5) and cadmium (nominal concentration of 0.3 µM) in E3 medium from 0 till 7 days post fertilization. Whole-body calcium content and mineralisation of craniofacial structures were reduced by low pH, cadmium, and a combination of both. Warming accelerates all physiological processes, including calcification, and was shown to partly mitigate the disruption of mineralization induced by acidification. This attenuating effect of warming was found even after accounting for the thermal effects on development by comparing fish at the same developmental stage. In contrast, cadmium-induced disruption was not attenuated by warming. By comparing the larval locomotor behaviour, it was shown that cadmium and acidification affect swimming behaviour dependent on environmental temperature, and mainly during the night. However, the combined effects of low pH and cadmium on swimming distance were not modulated by warming. In summary, we found that multiple stressors influence each other, and impact calcium metabolism, bone development and swimming behaviour of zebrafish larvae. We found evidence for a mitigation of stressor effects in a warming context.

Swimming respirometry was performed on juvenile (age 0+) Atlantic bluefin tuna, mean (± SD, n=6) mass 565±90g, to measure elements of respiratory metabolism and exercise performance. At 19°C, the mean standard metabolic rate (106±48 mgO2·h-1) maximum metabolic rate (555±51 mgO2·h-1) and absolute aerobic scope (449±83 mgO2·h-1) were lower than mass-corrected rates of adult Pacific bluefin, but considerably higher than other active sympatric Mediterranean fishes at similar mass and temperature. The tuna ceased swimming at a speed of 2.0±0.2 bodylengths·s-1 (BL·s-1). Video analysis revealed that the juvenile tuna cruised spontaneously at 3.1±0.6 BL·s-1 (n=8) in their rearing tank, significantly faster than achieved in the tunnel. Extrapolation of respirometry data to 3 BL·s-1 estimated a routine metabolic rate for swimming of over 650 mgO2·h-1. The results indicate that juvenile Atlantic bluefin tuna are high performance animals with elevated metabolic costs for their lifestyle of ceaseless swimming.

The majority of fish swim by aerobic muscular force, and so there has been considerable interest in the metabolic basis for swimming. Most of this work has measured whole-body oxygen consumption as a metabolic proxy, without any quantification of the actual energy that is produced at the cellular level. In this study, we explored links between organism level metabolic rate [both standard (SMR) and maximal (MMR)], mitochondrial function [the rates of oxygen consumption associated with oxidative phosphorylation (OXPHOS) and offsetting proton leak (i.e. OXPHOS coupling efficiency; OxCE)] and swim performance (Ucrit) using the European minnow (Phoxinus phoxinus). We also measured the relative proportion of aerobic (slow-twitch) and anaerobic (fast-twitch) muscle fibres within the muscle tissue. Lastly, we measured mitochondrial reactive oxygen species (ROS) production rates and the telomere lengths of the minnows (because rates of telomere shortening are known to be influenced by ROS). We found that the critical swimming speed of a fish was unrelated to measures of mitochondrial efficiency (OxCE) or MMR, or to the proportion of aerobic fibres within the muscle mass. However, Ucrit was positively related to individual SMR and OXPHOS capacity, indicating that better swimmers are supported by a higher baseline metabolism and a greater cellular capacity for producing ATP. There was also a significant link between OxCE and rates of mitochondrial ROS production, but this was unrelated to telomere length. This study exemplifies how cellular energy production can influence overall performance.

Cetaceans are often assumed to employ very high oxygen extractions of ∼40-60% and high tidal volumes (60-80% of vital capacity) to decrease surface time and increase foraging time at depth. However, such oxygen extractions and tidal volumes are greatly at odds with gas exchange in terrestrial mammals, and may, if incorrect, lead to severe overestimations of field metabolic rate (FMR) in wild animals when modeling oxygen uptake from respiration rates. Here, we tested the hypothesis that bottlenose dolphins have such high average oxygen extractions and tidal volumes. By measuring oxygen extractions and tidal volumes of >2000 breaths before and after a 2 min apnea bout in three trained bottlenose dolphins, we show that average pre-apnea resting oxygen extractions are between 17% and 25%, less than half of what has historically been reported for cetaceans. Following apnea, initial oxygen extractions are high (∼60%) but drop below pre-apnea levels in 11-20 breaths. Tidal volumes in this experimental setting were between 21% and 37% of vital capacity, consistent with recent findings for marine mammals, but less than half the 60-80% often assumed for cetaceans in FMR modeling. We therefore reject the hypothesis that bottlenose dolphins on average employ high oxygen extractions and high tidal volumes at rest and following short apneas. Consequently, using fixed high values for tidal volumes and oxygen extractions when modeling FMR from breathing rates in wild cetaceans may possibly lead to overestimations of their energy expenditure, food requirements and ecological roles.

Environmental factors such as temperature and oxygen are well-established modulators of animal physiology, but the influence of social context remains under-integrated into comparative and environmental physiology. Although numerous studies across behavioural, ecological and biomedical fields show that social interactions alter metabolic, hormonal, immune and stress-related traits, these insights are not routinely incorporated into physiological study design or interpretation. Social effects arise through mechanisms such as isolation, dominance hierarchies, altered energy use and social buffering, and can amplify or dampen responses to abiotic stressors. Because metabolic and hormonal pathways regulate multiple physiological systems, socially induced shifts can cascade to affect cardiovascular, immune, neural, digestive, osmoregulatory and reproductive function over both acute and evolutionary time scales. Thus, overlooking social context places researchers at risk of taking two critical missteps in comparative and environmental physiology: (1) measuring animals under socially unrealistic or uncontrolled conditions, which can yield unrepresentative physiological estimates; and (2) extrapolating these findings to natural populations where trait expression is influenced by social dynamics that are absent from the experimental context. Together, these issues might bias estimates of physiological trait values, plasticity and heritability, and limit the ecological relevance and predictive power of physiological research. Here, we outline general strategies to incorporate social context into experimental design, including the use of emerging tools that allow physiological measurements in naturalistic social settings. Integration of social context, alongside abiotic drivers, will improve our capacity to predict organismal responses to environmental change through comparative physiological research.

When larvae of Manduca sexta pass a critical weight, they initiate an endocrine cascade that leads to molting and metamorphosis. The critical weight coincides with a leveling off of the metabolic rate, and we hypothesize that it is the size at which the metabolic needs of a growing body reach the maximum capacity of the tracheal system to deliver oxygen. We examined two simple predictions about the role of oxygen supply in the regulation of growth: first, that restricting access to oxygen by blocking spiracles should affect growth and metabolism, and second, that placing larvae in a hypoxic atmosphere shortly before they reached the critical weight should prematurely trigger cessation of growth and metamorphosis. When sets of spiracles were blocked, growth rate was reduced, as was the metabolic rate and the body size at metamorphosis. The effect of blocking the posterior-most spiracles was greater than that of blocking the anterior-most ones, suggesting the presence of a required abdominal factor. Contrary to expectations, placing larvae in hypoxia a day before they reached the critical weight delayed the molt significantly, suggesting that hypoxia is not a trigger for the initiation of metamorphosis. Nevertheless, an increase in lactate levels in the second half of the final instar, and the leveling off of metabolic rate, indicate that a metabolic shift occurs at the critical weight. Ecdysone secretion in starved and hypoxic larvae was delayed by about 2 days relative to feeding controls, which explains the delayed timing of the metamorphic molt.

Flying animals face extreme energetic demands, relying mainly on carbohydrates and lipids, with occasional contributions from proteins and amino acids. In nectar-feeding species such as butterflies and hummingbirds, sugars are the primary fuel, yet the extent to which nectar-derived amino acids support flight versus other functions remains unclear. Using 13C-labelled nectar, we tracked the metabolic fate of sugars and amino acids during flight in Pieris rapae butterflies. We found that proline and glycine, two abundant nectar amino acids, were oxidized alongside sugars. We also compared females subjected to low- versus high-intensity flight. High flight intensity females incorporated less glycine into tissues, implying greater diversion toward energy use during flight. In contrast, they deposited more threonine - an essential amino acid - into their abdomens, prioritizing reproduction and storage. These findings reveal the role of nectar-derived nutrients in supporting locomotion and reproduction, while showing how nectar use can modulate trade-offs between flight and fecundity.