Journal of Experimental Biology最新文献

Cetaceans spend considerable periods of time underwater, but much about the physiological response of these animals during a dive remains unknown. We present an approach that combines near-infrared spectroscopy (NIRS) with kinematic measurements to investigate bottlenose dolphin hemodynamics in managed settings during voluntary breathing at the surface, diving to a submerged target, and free swimming. For all conditions, oxygenated hemoglobin (HbO) initially increased following respiration as oxygen saturation increased and then decreased until the following breath. Deoxygenated hemoglobin (HbR) remained relatively steady during shorter respiration periods (near surface and swimming dives) but declined during the longer breath-holds and swimming dives. This was also seen in the calculated tissue saturation index (TSI), with up to an 8.9% decrease during extended breath-holds. The approach presented here provides new insights into the physiological responses of free-swimming animals and is an important step towards making these measurements from animals in the wild.

Despite decades of innovation, monitoring whales remains constrained by their brief surfacings, wide-ranging movements, and limitations of conventional survey methods. Unmanned aerial vehicles (UAVs) and thermal infrared (TIR) sensors offer non-invasive alternatives, yet most applications rely on short-lived direct detections. Here, we evaluate a novel approach using UAV-based TIR imaging to extract biological and behavioural information from thermal flukeprints, surface disturbances generated by whale tailbeats. Field surveys of free-ranging humpback whales (Megaptera novaeangliae) off Reunion Island demonstrated that flukeprint width robustly distinguished calves from adults. Flukeprint spacing provided swimming-speed estimates consistent with RGB-based measurements (mean error 0.42 m s⁻¹; median relative error 16%), while flukeprint-derived orientations aligned closely with visual headings (mean offset -3.1°). These results indicate thermal flukeprints capture age-class, movement, and directional information even when animals are partially visible or submerged. By extending observation beyond direct sightings, TIR-detected flukeprints offer a low-impact, complementary tool for cetacean monitoring.

The constrained lever model (CLM) predicts that the jaw adductor resultant muscle forces (RMF) must pass through a "triangle of support" (ToS) to prevent temporomandibular joint (TMJ) distraction during biting. The CLM defines distracting forces as perpendicular to the plane of the ToS, but the orientation of the ToS varies both within and between individuals based on bite point, gape, and differences in the height of the TMJ. We compare TMJ distractive forces estimated using a ToS plane versus a fixed, horizontal plane criterion across a range of gapes using muscle moments and forces for the three major jaw adductor muscles in 97 morphologically diverse primate species. At occlusion, 80% of the species experienced stabilizing compressive forces under a horizontal plane criterion, but only 44% of species had a RMF inside the ToS. This mismatch indicates that predictions of TMJ distraction and joint stability are highly dependent upon the comparison plane, which is challenging for comparisons between primates with varying TMJ heights, and consequently, ToS orientations. Joint stability increased with gape but varied little with taxonomy and across diet categories. These results provide strong evidence that the CLM is a poor predictor of the joint stability when the TMJs are elevated. These findings suggest future applications of the CLM should either focus on taxa with TMJs near the occlusal plane or calculate joint reaction forces directly to assess joint stability in mammals with elevated TMJs.

Mesoscale rough terrain constitutes the primary interactive environment for animal locomotion, yet how roughness variations at this scale influence animal movement remains poorly understood. This study investigates the locomotion of Camponotus japonicus on finely segmented, vertically undulating mesoscale rough terrain through integrated kinematic analysis and gait space clustering. We designed six terrains with different roughness levels, recorded ant locomotion using high-speed cameras, and then applied markerless pose estimation to extract time-series data of limb keypoints. Our results show that with increasing terrain roughness, ants exhibit reduced walking speed via shorter stride length and longer stride period. Footfall analysis reveals a pattern of lateral foot placement away from the body midline. Both phase analysis and gait space clustering indicate a gradual transition from the stereotyped tripod gait toward more variable tetrapod-like gaits. Speed-matched analysis indicates that, in addition to walking speed, terrain roughness also influences leg coordination. Together, these findings indicate that mesoscale rough terrain is associated with a reorganization of ants' spatiotemporal gait patterns. The discovery of these general, mesoscale environmental locomotive adjustment patterns provides crucial bio-inspired insights for multi-legged bionic robots to overcome locomotive adaptability bottlenecks in complex, unstructured environments.

Passive forces generated by the jaw adductor muscles and their connective tissues are thought to play a protective role in the feeding system by limiting gape to avoid hyperextension and minimize distractive forces at the temporomandibular joint. However, passive muscle forces have only been measured in individual jaw adductors of two non-primate mammals, and it is unknown how these forces translate to bite force at the occlusal surface and affect gape behaviors. We measured in vivo passive bite forces in eight adult Macaca mulatta at anterior (I1) and posterior (M1) bite points across linear gapes ranging from 15-50 mm. Active bite force data were collected at the anterior bite point from two of these macaques (one male; one female) using a custom-built bite force transducer across linear gapes ranging from 10-60 mm. We demonstrate that M. mulatta passive bite forces increase with gape and vary by bite point with forces larger at M1 compared to I1 for both linear and angular gapes. Our experimental data and Hill-type muscle models of both active and passive forces suggest that passive bite forces are absolutely and relatively small at the occlusal surface in macaques and play a minimal role in constraining gape. These are the first empirical data on bite force passive tension in primates, and the first data to suggest that the macaque jaw adductor muscles exhibit unusually high compliance potentially relating to selection for large gape behaviors.

Aerobic capacities in arachnids are closely linked with considerable structural variation in their respiratory systems. However, all scorpions are non-tracheated and possess four pairs of book lungs, yet they vary greatly in their locomotor activity patterns. Many non-burrowing species express short bursts of activity whereas other species dig deep burrows within hours, suggesting more aerobically-fueled exercise. We hypothesized that locomotion in surface-dwellers is more dependent on anaerobic ATP synthesis, and that this would be reflected in their exercise performance and functional adaptation to potential disturbance to resting-state homeostasis. We used an experimental design consisting of two surface-dwelling Buthidae species (Hottentotta judaicus and Leiurus hebraeus), a burrowing buthid (Buthus israelis) and two burrowing Scorpionidae (Scorpio fuscus and S. palmatus). Maximum running speeds were higher for buthids, which were also more prone to fatigue than scorpionids. Higher respiratory exchange ratios recorded for buthids during activity and subsequent recovery indicated higher reliance on anaerobically-fueled locomotion compared with scorpionids. Our data show that quicker removal of excess CO2 resulting from anaerobic exercise and hemolymph buffering in buthids is associated with significantly higher carbonic anhydrase activity in their hemolymph, compared with that of scorpionids. Efficient CO2 emission may also contribute to the lower respiratory water losses of buthids, and thus assist in facing both biotic and abiotic challenges of surface existence, from which the scorpionid burrows provide refuge.

Honeybee venom (apitoxin) is a potent mixture of biologically active peptides and enzymes, primarily evolved as a defence against insect predators - including other bees. Recent evidence suggests that honeybees also employ components of apitoxin for both external and internal defence against parasites and microbial infections. Consequently, they are predicted to exhibit a remarkable resistance to their own venom, which they frequently encounter within colonies. To investigate this phenomenon, we examined the physiological responses of honeybee workers and drones to envenomation. Individuals were injected with a crude venom dose equivalent to 7.1 µg of melittin (≈ LD₂₀). Venom exposure significantly affected multiple physiological parameters, including the levels and gene expression of adipokinetic hormone and vitellogenin, antioxidative markers, lipofuscin accumulation, and haemolymph arginine kinase concentration. Ultrastructural analyses further revealed profound alterations in thoracic muscle, including mitochondrial and myofibrillar degradation. Notably, workers and drones exhibited distinct physiological responses to venom. Our results indicate that honeybees mount a complex, multi-level defence to their own toxin, highlighting their potential as a unique model for studying endogenous anti-toxin mechanisms. Insights from this system may inspire future biomedical and biotechnological applications.

Animals tend to approach and consume food that is palatable, energetically advantageous, or nutritious. Although appetitive taste behavior is hardwired, it can be modulated by experience. Previously, we were able to suppress it by pairing appetitive tastants with aversive stimuli, such as bitter quinine. Here, we present a taste memory assay where a taste stimulus is paired with rewarding sugar intake. We tested an array of neutral or appetitive substances (conditioned stimulus, CS) and rewarding reinforcements (unconditioned stimulus, US), and determined optimal conditions for a robust and reliable Reward Taste Conditioning (RTC) assay. We ultimately used a moderate concentration of fructose as CS paired with a sweeter sucrose as US, allowing us to characterize the properties of the reinforcement and the resulting memory. We found that tight forward pairing of CS and US is necessary for memory formation, and repeated unpaired presentation of the CS extinguishes the memory. Without further interference, the memory is sustained for at least 60 minutes after training. We determined that genes involved in short-term memory and intact mushroom bodies are required for RTC. This assay is a fast and robust way to investigate the involvement of genes specific to reward taste learning, and to determine neuronal sub-types and the circuits involved in appetitive taste memory. Considering that the reward and aversive taste assays are designed to be very similar, it will allow for comparison between memories with opposite valence and further our understanding of the detailed neuronal architecture underlying acquired taste memories.

Flying animals use a combination of sensory modalities to maintain stable flight in the face of external and internal perturbations. Although insects rely extensively on vision for this task, members of the order Diptera possess specialized mechanosensory organs called halteres, which contain hundreds of strain-sensing campaniform sensilla that encode forces on the base of the structures as they oscillate during flight. Although the importance of halteres for flight stabilization is supported by past experiments involving surgical ablation or artificial manipulation, the requirement of the campaniform sensilla themselves has yet to be directly demonstrated. We investigated the role of haltere campaniform sensilla in the fruit fly, Drosophila melanogaster, by using a collection of Gal4 driver lines which are expressed in different populations of campaniform neurons while recording the equilibrium responses of tethered flies subjected to rotation about their yaw axis. We show that the magnitude of the wing and head motor responses of flies decrease linearly with increasing number of campaniform sensilla genetically silenced or ablated, providing direct evidence for the involvement of these mechanosensory structures in the detection of angular velocity during flight.

Atmospheric oxygen, which is essential for energy metabolism, can directly influence an animal's heat tolerance by affecting oxygen transport processes, especially in those living in oxygen-poor environments such as plant tissues, underground or aquatic environments. Yet, oxygen availability and heat tolerance are rarely studied together, limiting our ability to predict their combined effects on insect performance. This study examines the larval tolerance of a large xylophagous cerambycid beetle Cacosceles newmannii to combined hypoxic and thermal stress using performance assays (duration of righting response) coupled with metabolomic and transcriptomic analyses. Metabolomic profiling showed that most metabolites were downregulated in the body but upregulated in the haemolymph as stress increased. Transcriptomic profiles clustered primarily by temperature (25 °C vs 35 °C), independent of oxygen level. Cacosceles newmannii appeared capable of modulating its performance to reduce the energy costs and physiological damage induced by hypoxia. This suggested a high baseline hypoxia tolerance rather than a rapid plastic (induced) physiological hypoxia response, probably due to the species' endophytic lifestyle. Conversely, thermal stress led to a predictable increase in metabolic activity but did not markedly affect performance, triggering adjustments to maintain cellular functions while limiting the impact of stresses expected under conditions of high temperature, such as desiccation. In short, our study highlights the distinct metabolic pathways mobilised to cope with hypoxic versus thermal stress, emphasizing the importance of integrated approaches in understanding insect responses to environmental challenges. These findings have significant implications for understanding the species' ecology, with applications for pest management and sustainable agriculture in the context of climate change.