Journal of Experimental Biology最新文献

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.

When sexually mature, the marine annelid Platynereis dumerilii emerges at night from its tube and swims to the surface in search of a mate. Developing from the immature atoke to the mature epitoke, each of its four eyes doubles in diameter, but it is unclear what visual capacity these eyes have and which visual tasks they support. We assessed this question by comparing the anatomy and physiology of atoke and epitoke eyes. Platynereis dumerilii has four cephalic eyes in anterior and posterior pairs, which all have an adjustable pupil with similar dynamics. As the eyes grow, photoreceptors are added to the retina and the outer segments of the photoreceptors elongate 5-fold in the emergent epitoke. All eyes had a dynamic range of approximately 3 log units covering 0.01 to 10 W sr-1 m-2 and displayed clear photoinhibition at higher intensities. We detected no difference in photoreceptor physiology between posterior and anterior eyes. Their receptors had a spectral sensitivity matching a single opsin with a peak sensitivity around 490 nm being the visual pigment. The only difference we detected was in temporal resolution, where female epitoke vision was significantly faster [flicker fusion frequency (FFF)=9.5, 95% confidence interval (CI)=7.9-11.2] than that of both male epitokes (FFF=6.0, 95% CI=4.8-7.2) and atokes (FFF=7.3, 95% CI=6.2-8.5). Our results show that on developing to the epitoke, both sexes of P. dumerilii improve spatial resolution by enlarging their cup-eyes, while female epitokes also achieve higher temporal resolution. These changes could facilitate mate recognition of male epitokes by female epitokes.

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.

Crucian carp (Carassius carassius) is one of the most anoxia-tolerant vertebrates. While physiological underpinnings of its ability to withstand O2 deprivation are well studied, the ability to tolerate the return to normoxia is still enigmatic. Such reoxygenation is associated with detrimental oxidation damage in other organisms, where mitochondria play a central role in the damaging effects. This leads to the question whether mitochondrial adaptations play a central role in the anoxia and reoxygenation tolerance of crucian carp. We here addressed whether mitochondria from crucian carp circumvent the negative effects of anoxia-reoxygenation exposure, namely the generation of reactive oxygen species (ROS) and subsequent oxidative stress. Crucian carp brain and heart mitochondria generated up to 4-fold less hydrogen peroxide (H2O2; a major ROS) compared to the closely related, anoxia-intolerant, common carp (Cyprinus carpio). The lower H2O2 emission was partly explained by higher (∼15-30%) total oxidant scavenging capacity. Complex II-mediated flux was ∼40% reduced after anoxia-reoxygenation in crucian carp heart mitochondria. Mitochondrial H2O2 generation measured in vivo was unaffected by anoxia-reoxygenation exposure in heart, brain and gill, but reduced by ∼25% in liver. There were also tissue-specific increases in protein carbonylation (∼1.8-fold in brain and gills) and mitochondrial DNA (mtDNA) damage (∼1.5-fold in liver and heart), indicating that biphasic oxidative stress responses affect tissues differently. Our data show that crucian carp avoids excessive mitochondrial ROS generation upon exposure to anoxia-reoxygenation. The tissue-specific distribution of protein and mtDNA oxidation indicate that crucian carp balances body redox signalling to secure resilience during fluctuating O2 availability.

The energetic costs of carrying loads can significantly impact animal fitness but appear to vary dramatically among animals. For some, they equal the cost of carrying an equivalent amount of extra body mass, while others carry loads more economically. Locomotor systems can plastically respond to acute and chronic loading, but how such responses impact energetics of locomotion is unclear. We asked how loading affects the energetics of an immature hemimetabolous insect, the cockroach Blaberus discoidalis at rest and during locomotion at various speeds, and whether energetics change as animals adjust to chronic loading. Cockroaches carried loads economically as early as 2 hours after load addition, with no change in energetic costs during a 10-day period. We discuss the implications of these findings and potential mechanisms underlying economic load-carrying in arthropods.

The ability to generate propulsive force at different velocities is essential for animal locomotion but has often been depreciated. This study explored animals' locomotion under varying mechanical constraints by addressing whether force capacities measured during accelerations on level ground are representative of propulsion capacities exerted during steady velocity uphill running or running against a resistance. We hypothesised that locomotion against resistances induced by inertia, friction or gravity would lead to similar propulsive force capacities, step length, and step frequency. Nineteen human-participants performed 3 accelerated, 6 resisted, and 10 uphill sprints while their instantaneous velocity, step length, and step frequency were measured. The propulsive force capacities decreased linearly with velocity. This individual relationship was preserved among the disparate mechanical constraints, humans just shifting along this curve. Trivial (-2.0±21.7%, p=0.43) and small differences (-6.1±21.5%, p=0.24), and positive correlation (p<0.001) where indeed found between force capacities at similar velocities among uphill/accelerated (r=0.94) and resisted/accelerated (r=0.91) conditions, respectively. Spatio-temporal variables did not differ between conditions (<2%). Conducting similar analysis in a 12-animals dataset from the literature revealed that different experimental modalities are associated with similar propulsive force-velocity relationships within the same species. Extending the analogy between accelerated, uphill, and resisted running to the animal kingdom enabled comparisons between species based on propulsive force capacities and allometric scaling. Using humans as an experimental paradigm, we provided a framework for interpreting how environmental stressors affect movement strategies in many terrestrial species. In sports science, this study opens practical implications for the design of training and research protocols.