Journal of Experimental Biology最新文献

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.

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.

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.

Photosynthetic sacoglossan sea slugs sequester the chloroplasts of the algae they feed upon and keep these organelles functional in the cells of their ramified digestive system. Whether the stolen chloroplasts - kleptoplasts - influence animal behavioural responses towards light is uncertain. To address this matter, we: (1) determined the light preferences of the photosynthetic sea slug Elysia crispata when offered different light spectra (450, 517, 520-650 and 665 nm) and intensities (60, 180, 425 and 1400 µmol photons m-2 s-1); and (2) established whether the light intensity preferences of E. crispata were different when fed algae acclimated to low (40 µmol photons m-2 s-1) and high irradiance (425 µmol photons m-2 s-1). Sea slugs were collected from a coral reef in the Gulf of Mexico and transported to the laboratory to perform controlled experiments. During trials, sea slugs exhibited marked exploratory behaviour. However, results show that E. crispata avoids red light (665 nm) and prefers low irradiance (60 µmol photons m-2 s-1), showing that both light spectrum and intensity are relevant to their behaviour. Furthermore, sea slugs increased their selection for high irradiance after being fed algae acclimated to high light. These results support our hypothesis that the acclimation state of the acquired kleptoplasts affects sea slug behaviour towards light. Light perception and photobehaviour in photosynthetic sea slugs seem to depend not only on animal photoreceptors, but also on a communication network between the endosymbiotic chloroplasts and the animal host.

Hopkins Marine Station, Stanford University's marine science center, exemplifies five attributes that could be said to characterize field stations in general: history, location, isolation, focus and fragility. Founded in 1892, the Marine Station has a long history of notable research on subjects ranging from the biochemistry of photosynthesis to developmental biology, intertidal ecology and comparative physiology. Five Nobel laureates have been influenced by classes they attended at Hopkins, and the nearly 700 undergraduate research projects conducted at the Marine Station have sparked seminal studies on subjects as disparate as marine pollution and climate change. Current research spans topics from environmental DNA to the conservation of fisheries and the biomechanics of foraging whales. The Marine Station's scientific and educational goals are facilitated by its location on the edge of Monterey Bay and its isolation from the university's main campus, which combine to encourage a sense of intellectual community and a productive focus on the marine environment and its inhabitants. However, Hopkins' location and isolation do pose their own risks. As with most field stations, isolation from the main campus has at times made the Marine Station vulnerable to closure when money was tight, and owing to its proximity to the shore, sea-level rise poses an existential threat. In these times of rapid environmental and societal change, it is important to recognize both the value and the fragility of field institutions such as Hopkins Marine Station.

A major problem in current biomechanical literature is the extent to which in silico data can be validated by in vivo data across taxonomic scales. Despite frequent incongruence between in silico and in vivo data gained from precisely the same individual, biologists and palaeontologists continue to publish in silico data of single bones intended to represent entire species. Here, we aim to bridge this gap by investigating whether jaw morphology alone can be used to validate biomechanical models on the intraspecific level in a phenotypically diverse lizard, Podarcis pityusensis. We tested this by investigating how effectively in vivo bite force measurements from eight populations of this species are predicted by biomechanical models. We used alcohol-preserved specimens from each location to generate population-average and male-average morphologies of mandibles and dentaries, from which we calculated mechanical advantage as well as strength estimates from finite element analysis. Overall, we found a general lack of population-level correlation between in vivo and in silico data; however, strength estimates from finite element analysis did follow the same bite∼size relationship as in vivo bite, suggesting that biomechanical analysis of even a single bone can produce useful bite force estimates. We encourage researchers to create in silico models with maximally complex shape data and caution that intraspecific variation is a crucial aspect of in vivo and in silico biomechanics.