Journal of Experimental Biology最新文献

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.

Nutritional composition has the potential to play a critical role in immune function and pathogen susceptibility. While food restriction generally suppresses immunity, the effects of macronutrient balance on host defense remain unclear. Here, we investigated how dietary protein-to-carbohydrate (p:c) ratios influence immune function and survival in the desert locust (Schistocerca gregaria) following exposure to the entomopathogenic fungus Metarhizium robertsii. Locusts were maintained on diets with varying p:c ratios, and their survival, pathogen load, growth rate, food consumption and immune responses were assessed. Locusts consuming a protein-biased diet exhibited heightened phenoloxidase but suffered higher mortality and greater fungal sporulation post-infection. These results show that increased immune investment does not necessarily translate to improved survival. Importantly, our findings have direct implications for locust biocontrol strategies using Metarhizium fungi. Given the slow mode of action of fungal pathogens, increasing plant protein content via nitrogen fertilization could accelerate host mortality while enhancing fungal sporulation and facilitating pathogen transmission within locust populations. This study underscores the role of macronutrient balance in shaping host-pathogen interactions and offers a novel approach to improving the efficacy of fungal biopesticides.

Climate change and extreme climatic events pose significant challenges to biodiversity. Studying species' physiological tolerances is required to predict their vulnerability and response to these threats, particularly at the margins of their distribution, where they are frequently at their environmental limits. While temperature constraints have attracted considerable interest, the combined effects of rising temperatures and aridification remain underrepresented in climate impact assessments, despite their synergistic role in intensifying physiological stress. Herein, we compared two parapatric vipers, Vipera aspis and Vipera latastei, which exhibit contrasting climatic niches and hybridise in their contact zone in northern Spain. Vipera aspis inhabits cooler, wetter environments, while V. latastei is adapted to warmer, drier habitats. First, we used open-flow respirometry to measure standard metabolic rate (SMR) and total evaporative water loss (TEWL) in pregnant females at three temperatures (15, 25 and 33°C). Vipera aspis exhibited higher SMR and TEWL than V. latastei and their hybrids, particularly at its preferred body temperature (33°C), reflecting its distinct temperate-adapted physiology. Second, we simulated a realistic drought (14 days) on neonates born from these females, manipulating both free-standing water and air water vapour deficit. In the drought-simulated treatment, mass loss and postnatal growth inhibition were most pronounced in V. aspis, while the hybrids exhibited on average an intermediate response between those of the two species. The warm- and dry-adapted V. latastei, therefore, exhibits greater drought tolerance under climate change scenarios, potentially providing a physiological advantage in the future dynamics of contact zones.

Climate change, including seawater warming and salinity fluctuations, is increasingly affecting marine ecosystems worldwide. The blue mussel, Mytilus edulis, widely distributed along the temperate coasts of the Northern Hemisphere, thrives in environments characterized by temperature fluctuations and salinity gradients. In particular, populations in the Baltic and North Seas are exposed to significant variation in these factors, which can affect the reproductive capacity of blue mussels, essential for sustainability of their populations. This study assessed the effects of varying temperature and salinity on the reproductive performance of blue mussels from the Baltic and North Seas, focusing on sperm motility, ATP content and fertilization success. Additionally, sperm mitochondrial function in Baltic Sea mussels was examined under different temperature and osmolarity conditions. The results showed that mussels from both populations tolerated seawater warming, but were sensitive to cold and low salinity, with sperm motility and fertilization success significantly impaired under these conditions. The salinity window for sperm motility and fertilization was population specific: optimal ranges were a salinity of 13-17 for Baltic Sea mussels and 21-35 for North Sea mussels. Notably, North Sea mussels were unable to reproduce at salinity 9, whereas Baltic Sea mussels were severely impaired at salinity 5. High temperature (25°C) reduced mitochondrial respiratory efficiency and increased reactive oxygen species (ROS) production, while osmolarity did not appear to be a key factor. These findings highlight population-specific reproductive traits in M. edulis and link sperm performance to mitochondrial function, providing new insights into benthic adaptation to changing coastal environments.