Journal of Experimental Biology最新文献

Animals in aquatic ecosystems impacted by global changes often face reduced availability of vital organic compounds, such as long-chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFA), which are essential for brain development and cognition. Cognitive skills are crucial for buffering the impacts of environmental stress on fitness, yet the link between the quality of diet and fitness-enhancing behaviours of individuals in food webs altered by global change remains unclear. We examined how dietary n-3 LC-PUFA affect brain development, social dominance and growth in territorial juvenile salmonids in a large-scale model of a natural pre-alpine stream. For this assessment, we used wild fish whose diet quality was estimated using stable isotope analysis, and hatchery-reared fish exposed to dietary treatments in a common-garden experiment. In both wild and common-garden experiment fish, diets low in n-3 LC-PUFA led to a decreased content of n-3 LC-PUFA in brain tissue but did not affect brain mass, morphology (i.e. mass of brain regions) or neuron numbers. Fish with lower brain n-3 LC-PUFA content exhibited reduced competitiveness in social interactions and suboptimal habitat use, resulting in slower somatic growth. Our findings indicate that the limited availability of n-3 LC-PUFA in aquatic food webs may impair the behavioural flexibility of top aquatic consumers, possibly with negative impacts on their capacity to maintain high fitness in ecosystems altered by environmental change.

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.

Oxygen acquisition and delivery to tissues is believed to be a key factor in heat tolerance, but testing this link has been challenging owing to methodological limitations to separate processes related to oxygen acquisition and oxygen delivery. In this study, we altered tissue oxygenation by manipulating light intensity using cnidarians that host endosymbiotic algae as model species. We first verified that light intensity determines net photosynthetic rates, showing that all species produced oxygen at the highest light intensity, and that chemically inhibiting photosynthesis successfully reduced oxygen production. We then tested the prediction that heat tolerance would be higher at higher light intensities and lower in specimens that no longer have internal oxygen production due to photosynthesis (chemical inhibition). Overall, photosynthetic specimens had a higher heat tolerance than inhibited specimens and increased light intensity improved heat tolerance for two of the three species we examined. Because inhibited specimens had lower heat tolerances, we conclude that oxygen dynamics are involved in shaping heat tolerance. Interestingly, light intensity also affected oxygen uptake and heat tolerance in some of the chemically inhibited specimens, indicating that either we did not achieve complete inhibition of photosynthesis or that light modulates aspects of cnidarian metabolism that are related to thermal tolerance, but which may extend beyond oxygen dynamics and the photosynthesis occurring in their algae.

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.

Sympatric ectotherms belonging to the same guild often exhibit differences in thermal ecophysiology as a result of their evolutionary history or current ecological interactions. This study investigated the thermal biology and hydroregulation of two sympatric lizard species, Liolaemus riojanus and L. cuyanus, in the challenging environment of the arid Monte Desert of Argentina. We examined field body temperatures (Tb), preferred temperatures (Tpref), thermoregulatory efficiency, critical thermal limits (CTmin, CTmax), panting temperature (Tpant) and total evaporative water loss (TEWL) under representative experimental temperatures. Despite similar field Tb and moderate thermoregulatory efficiency, significant interspecific differences emerged in laboratory traits. Liolaemus riojanus, the smaller species, exhibited a higher Tpref, a broader thermal tolerance (lower CTmin, higher CTmax), higher Tpant and lower TEWL compared with L. cuyanus. Furthermore, L. riojanus showed reduced EWL at high experimental temperatures (40°C), suggesting that species with higher thermal tolerance conserve water under warm conditions despite the higher surface area to volume ratio. Conversely, L. cuyanus displayed increased EWL with rising experimental temperatures, which is likely related to its relatively low CTmax and panting temperature, promoting water loss. These divergent physiological strategies likely contribute to thermal segregation in this harsh environment. Given the current trend towards aridification and climate warming, understanding the interplay between thermal and hydric traits is crucial for predicting the persistence of these lizards under changing environmental conditions and to guide management measures.