Journal of Experimental Biology

Aerobic scope defines the energetic margin available for activity beyond maintenance and plays a central role in ecological performance. In many organisms, increasing body size or environmental stress can reduce this margin, a pattern often described as having "little left in the tank". However, species that rely on episodic but intense activity may require sufficient aerobic capacity from early life stages onward, particularly when individuals are relatively large at hatching or birth. Here, we examined the ontogenetic scaling of resting metabolic rate (RMR) and active metabolic rate (AMR) in the giant deep-sea scavenger Bathynomus doederleini across a broad size range (1.7-48.4 g) using intermittent-flow respirometry at 10 {degrees}C. RMR and AMR increased with body mass and exhibited nearly identical scaling exponents, resulting in a size-invariant factorial aerobic scope (median = 2.83). This pattern suggests that aerobic capacity is established early and maintained proportionally with maintenance costs, supporting locomotion and scavenging throughout ontogeny in an energy-limited environment.

Extreme climatic events impose considerable stress on organisms with consequences for key ecological interactions such as pollination. Because temperature directly affects metabolic processes, heat variations may also importantly influence the nutritional needs and feeding choices of animals. Here, we studied the effects of thermal stress on the nutritional choices and performances of bumblebees, using a 3D nutritional geometry design. At optimal temperature for colony development (30{degrees}C), bees successfully balanced carbohydrate, protein, and lipid collection, at levels beneficial for body weight and survival. Under cold stress (20{degrees}C), bees reduced their overall nutrient collection while selecting proportionally more carbohydrates, thereby prioritizing survival over weight gain. Under heat stress (35{degrees}C), nutrient balancing was disrupted and survival dropped. Notably however, across all temperatures, bees maintained stable lipid collection while flexibly adjusting the amount of carbohydrates and proteins, suggesting strong constraints on lipid regulation. Given the pivotal role of bees for pollination, identifying how their nutritional needs change in response to climatic conditions is of prior importance for food safety and the conservation of terrestrial ecosystems.

O_LIHigh northern latitudes experience extreme winters and pronounced environmental variation. Arctic animals possess remarkable and diverse physiological mechanisms to thrive under this variation, but such mechanisms are poorly studied, particularly in the aquatic realm. C_LIO_LIWe combined Arctic field and laboratory experiments to reveal how one of Earths most northerly distributed fish species, the Arctic char, seasonally adjusts its metabolism to conserve energy over winter while not feeding and to capitalize on more optimal growth conditions in summer. C_LIO_LILaboratory reared Arctic char were fed or food deprived at common summer (8{degrees}C) and winter (2{degrees}C) temperatures for >120 days. Oxygen consumption rates were assessed as a proxy for rate of aerobic metabolic energy expenditure. Cooling from 8 to 2{degrees}C reduced resting aerobic energy expenditure by 35%, while food deprivation independently drove a reduction of 46-50%. Combined, resting energy expenditure was 197% higher under simulated summer (fed at 8{degrees}C) than winter conditions (food deprived at 2{degrees}C). C_LIO_LIReductions in resting energy expenditure with food deprivation were driven, at least in part, by marked tissue-specific decreases in organ size and protein synthesis rates in tissues with central roles in growth and digestion. C_LIO_LIWild adult anadromous Arctic char exhibited, seasonal plasticity consistent with our laboratory experiments. Resting energy expenditure at 10{degrees}C was 27% higher after summer feeding than in the spring after winter fasting, while liver and digestive organ masses were also markedly reduced overwinter. C_LIO_LIIn contrast, peak aerobic metabolic performance and relative heart mass were largely maintained during food deprivation indicating a protection of systems that support aerobic metabolic capacity. C_LIO_LIDespite recruiting strategies for substantial energy savings, wild and laboratory reared Arctic char still largely depleted their on-board fat stores with food-deprivation, underscoring that these strategies are essential when food is limited. Given that the Arctic is among the most rapidly changing regions on Earth, temperatures, productivity, and the timing of key seasonal event are all shifting with implications for the efficacy of such strategies for high-latitude animals. C_LI

Animals need to precisely perceive and integrate the environmental cues to orient and select the appropriate motor responses required for navigating. This is the case, for instance, of the optokinetic reflex (OKR) and the optomotor response (OMR) in Drosophila melanogaster, where optic flow stimulation modulates the head or the body and legs motor activity respectively. Despite large bodies of literature on both the OKR and the OMR, there is still a limited understanding, in flies, of the impact on these responses of concomitant, and potentially conflicting, sensory inputs. To investigate this aspect, we used fruit flies walking on a sphere, presented with optic flow stimulation leading to the OMR together with the simultaneous exposure to olfactory stimulation, either using established repellent or masking compounds. We analysed the effect of different substances, and of their concentration, on the dynamics of the flies response to moving gratings, evaluating the fly walking path as well as average speed and duration. This analysis revealed several alterations between the compounds tested, in agreement with reported data on the simpler OKR. In conclusion, we show that concomitant exposure to repellents and maskers may consistently affect fundamental processes (the OKR and OMR) available to insects for informing themselves while navigating through the environment.

Although predation is a major driver of group living across taxa and the antipredator benefits of grouping are well established, the energetic costs experienced by groups under predation remain largely unexplored. In the current study, we use wild, white mullet (Mugil curema, Valenciennes 1836), to provide the first real-time quantification of the energetic cost of escape in schooling fish using intermittent, closed-loop respirometry. We found that small groups exposed to predators showed a 53.8% increase in their organismal metabolic rate (MO2) as compared to groups without predator exposure. When we evaluated antipredator behaviors such as escape response, group cohesion, and displacement of the group centroid, we found a positive correlation to energetic costs. We then investigated whether escape responses are socially modulated by comparing the energetic costs of escape across solitary individuals, solitary individuals with visual access to a group, and groups. We found that escape frequency and energetic costs to predation were comparable across social contexts, indicating that escape may be an intrinsic survival response independent of cues from group members. Furthermore, we found that fish exposed to predators showed markedly reduced feeding, suggesting that predation constrains energy acquisition in addition to imposing direct energetic costs. Our results provide the first direct quantification of the energetic costs of escape in a schooling fish, offering new insights into the physiological trade-offs underlying collective antipredator defenses.

Winter survival in dormant animals depends on conserving finite energy reserves, yet winter temperatures fluctuate around shifting means. In ectotherms, metabolic rate increases exponentially with temperature, so thermal variability is expected to accelerate energy loss, with important consequences for overwinter survival and population persistence under climate change. However, it remains unclear whether dormant ectotherms can compensate physiologically for thermal variability. We overwintered Bombus impatiens queens under constant (2, 3, 4{degrees}C) or variable (2 {+/-} 6{degrees}C or 4 {+/-} 6{degrees}C) regimes for six weeks, then measured metabolic rates across a range of temperatures. The temperature dependence of metabolic rate shifted in response to thermal experience, but the direction of compensation depended on mean temperature: variability centered on 2{degrees}C elevated metabolic rate and increased thermal sensitivity relative to all other conditions, whereas variability centered on 4{degrees}C reduced metabolic rate and dampened thermal sensitivity relative to constant 4{degrees}C. We used these metabolic responses to simulate rates of lipid depletion and found that survival trajectories echoed physiological shifts: experiencing variability around 2{degrees}C would reduce subsequent survival time, whereas experiencing variability around 4{degrees}C would preserve subsequent survival even under variable future conditions. Thus, identical thermal variance produced opposite energetic outcomes depending on the mean temperature around which fluctuations occurred. Integrating both temperature means and variability is, therefore, essential for predicting overwintering survival in a changing world.

Birds are capable of performing elaborate flight maneuvers in variable environmental conditions. While flight is an adaptable and skilled motor behavior, we know surprisingly little about how birds master this ability. Across species, skilled motor behaviors show practice-related changes or improvements in performance and understanding which features of a motor behavior change with learning can lend insight into the constraints, flexibility, and optimization of motor behavior. Here, we combined high-speed video recordings and pose-tracking software to analyze the kinematics of thousands of flights in zebra finches over multiple days of flight training and over different distances. Small birds, such as the zebra finch, use an intermittent flap-bounding flight style that alternates between flapping phases and flexed-wing bounding phases. We found that birds increase their flight speed and the time spent bounding and reduce variability in the bound position over ten days of flight performance. These motor changes to flight show savings, as performance is maintained even after two months without flight experience. Moreover, these same parameters are adjusted when birds fly longer distances, indicating that they may be key to flight flexibility. We built kinematic models to determine what features birds might be optimizing toward with learning and found that the data was best fit by a model simultaneously optimizing for minimum energy and flight duration. Taken together, our data highlight that flap-bounding flight shows hallmarks of skilled motor learning and lend new insight into the function of bounds.

Understanding the nutritional preferences of honey bees (Apis mellifera) is essential for comprehending their behavioral ecology and the division of labor within a colony. While gustatory sensitivity to sucrose is well-documented in workers, a significant research gap exists regarding the sensory responses of queens and their reactions to caste-specific nutrition such as royal jelly. This study utilized the proboscis extension response (PER) assay to compare the food preferences of three distinct bee categories: foragers, 1-day-old workers, and queens. Subjects were presented repeatedly, in a pseudorandom order, with water, sucrose, royal jelly, and a sucrose-royal jelly mixture as gustatory stimuli. Foragers exhibited a high responsiveness to sucrose and showed uniformly low responsiveness to other stimuli. Although 1-day-old workers showed high responsiveness to sucrose, unlike foragers, they also responded to the sucrose-royal jelly mixture. Queens displayed a unique response profile, with near-ceiling responsiveness to both royal jelly and the mixture, followed by response to sucrose solution without habituation. Additionally, responsiveness to the sucrose was higher in foragers than in 1-day-old workers. These findings suggest that the honey bee gustatory and sensory system is tuned to the specific nutritional requirements of caste and age.

O_LIEctotherms in thermally variable environments mediate energy expenditure through both physiological and behavioural responses. However, many studies focus on constant temperature acclimation, and few consider behaviour and physiology in unison. It is unclear how acclimation to thermal variability affects locomotory choices, activity timing, and performance across daily thermal cycles. C_LIO_LIWe investigated the effects of thermal variability in the temperate dung beetle Onthophagus taurus. Following acclimation to a low amplitude (22{degrees}C {+/-} 2{degrees}C) or a high amplitude (22{degrees}C {+/-} 10{degrees}C) temperature regime, we measured behaviour and metabolic rate across temperatures. We hypothesised that O. taurus adjusts its locomotive strategy and search window when kept in high amplitude fluctuating temperatures to reduce energy loss associated with high temperature exposure. C_LIO_LIWe found that differences in energy expenditure were determined by propensity for flight which differed between acclimation treatments, particularly at intermediate temperatures. We also found that, following acclimation to a high amplitude of thermal variability, O. taurus exhibited a greater intensity of activity over a narrower window of time, and O. taurus acclimated to a low amplitude of thermal variability showed nocturnal activity. C_LIO_LIWe then used the data to model activity through the growing season over five years. Biophysical models were built using NicheMapR Microclimate and Ectotherm functions to test the length of potential searching time across seasons, the temperatures individuals are exposed, and locomotive strategy. Model outputs showed that acclimation to higher amplitudes of thermal variability increased accumulated degree-hours of activity relative to the low variability acclimation group. Individuals acclimated to higher amplitudes of thermal variability showed greater accumulated degree-hours in spring and fall, but exhibited shorter periods of activity during summer, with the model predicting increased opportunities for flight. Comparatively, O. taurus from the low variability acclimation treatment showed increased night activity in summer but did not fly. C_LI

We present here a normal table for post-embryonic development in the California newt (Taricha torosa), part of a genus of newts frequently studied for their toxicity and role within a predator-prey relationship. We generated the table by observing larvae collected as eggs in the wild and hatched and reared in the lab through metamorphosis. Building upon an established table consisting of 40 embryonic stages of development, our table consists of 13 stages based on discrete anatomical changes, primarily in limb development, and concludes at Stages 12-13 when the larvae undergo metamorphosis. We also describe more gradual phenotypic changes and their correlation to discrete stages in the developmental timeline. Finally, we illustrate the variability of the timing for reaching these stages in a controlled lab environment, demonstrating that time from hatching is not a reliable metric for standardizing results for diverse studies involving developing larvae. This staging table and accompanying observations will facilitate cross-study integration of research with larval T. torosa.

Muscle mass significantly influences skeletal muscle behaviour, potentially explaining why traditional massless Hill-type models struggle to predict the forces generated by larger muscles during dynamic, submaximal contractions. However, the applicability of mass-enhanced Hill-type models in human locomotion remains unexplored. Here, we compared the predicted force from a 1D mass-enhanced Hill-type muscle model with a traditional 1D massless Hill-type muscle model across a range of experimentally measured human movements. Kinematic and electromyographic data were collected from twenty participants performing locomotor tasks and supplemented with existing cycling data. Muscle size was geometrically scaled by factors from 0.1 to 10, which causes lengths to be scaled proportionally, cross-sectional area and peak isometric force F0 with the square, and mass with the cube of the factor. Muscle tissue mass (inertia) and cadence increased the differences between mass-enhanced and massless predictions of force and power. At high cadence and the largest scale, the normalized root mean square difference between force traces reached 7% of F0, (averaged across muscles). However, differences between models were minimal (<1%) at human-sized scale 1. Real muscle additionally deforms in 3D, we still do not know the extent to which this extra dimensionality affects muscle forces for these human movements.

Aerodynamic performance in airplanes and flying animals can be controlled by changes in wing shape and size, but during flapping flight another key component is wing motion. Observations of free-flying animals reveal natural wing motions, but testing causal mechanisms requires controlled manipulation of flapping kinematics. In flapping wings, aerodynamic interactions between the two wings are expected to depend on wingbeat phase, wing proximity, and wing attitude. How these interactions influence force production remains unclear. Here we used a robotic flapping wing and quantitative flow measurements to test the effect of wing interactions between wings flapped above or below the body in combination with pitch timing during upstroke-downstroke transitions. We show that both force magnitude and direction depend strongly on these parameters. High wing position combined with early pitching enhanced vertical force, whereas low position and late pitching increased thrust. Maximum aerodynamic efficiency was achieved flapping around the horizontal plane and pitching late. Transition phases strongly affected thrust generation and produced substantial body pitch torques. These findings demonstrate that small kinematic adjustments can markedly alter aerodynamic performance and be used for tailless flight control. This offers mechanistic explanations for observed animal wing motions and novel strategies for controlling flapping drones.

Capturing and handling wild animals is essential for ecological and evolutionary research, yet their effects on physiology, behaviour, and reproductive success remain poorly understood. We investigated short- and longer-term consequences of a capture-handling-restraint protocol in wild great tits (Parus major) over three breeding seasons. To assess short-term responses, we measured circulating corticosterone, a metabolic hormone that responds to unpredictable challenges, and automatically recorded provisioning behaviour. We also explored whether environmental and individual traits were related to provisioning latency (i.e., time to resume provisioning after capture). To evaluate longer-term effects, we monitored provisioning in the days following capture and related it to reproductive success (fledgling number and body condition). We predicted that longer handling would increase stress-induced corticosterone and provisioning latency, that these variables would be positively correlated, and that higher corticosterone and longer latencies would be associated with lower reproductive success. After capture, great tits showed elevated corticosterone and delayed provisioning. Contrary to our predictions, handling duration was negatively associated with stress-induced corticosterone in males (but not females) and did not affect provisioning latency. Provisioning latency was unrelated to corticosterone, environmental, or individual variables. Following capture, parents resumed provisioning, and short-term responses had little influence on reproductive success. We show that parental behaviour and physiology are affected by capture restraint protocols on the short term, but offspring condition and survival are not. However, these results should be interpreted cautiously, as our study lacks an uncaptured control group. Our findings highlight that evaluating welfare impacts requires rigorous study design incorporating both immediate and longer-term behavioural and fitness effects.

Foraging bee decision-making research has focused on choice determinants, and the variability and underlying causes of pre-choice latency remain understudied. Here, individual bumblebees (Bombus impatiens) were trained to associate one colored stimulus with a medium-value reward and another with a novel, higher-value reward. The experimental design consists of seven blocks, each containing four consecutive single-stimulus presentations followed by a forced binary choice. The latency to choose a stimulus and the type of choice during dual-choice trials were analysed. In dual-choice trials, bees in the yellow-high reward group showed a slower increase in high-reward selection than those in the blue-high group, suggesting persistent innate color bias. Response latencies for the low-reward stimulus systematically increased across blocks, indicating progressive devaluation. Early learning phases showed a temporary increase in response latency, extending previous findings on experience-dependent adjustments in acceptance thresholds. Latency in single-stimulus trials correlated with binary choice results, though choice proved a stronger indicator of preference than latency. Certain options elicited faster responses when presented with an alternative than when presented alone. Together, these findings support a deliberative model of bumblebee decision-making, in which pre-choice latency is modulated by innate preferences, associative learning, and immediate context.

Understanding how fish navigate complex natural environments requires bridging fine-scale biomechanics with ecological behavior. We investigated the volitional movement and energetics of wild red drum (Sciaenops ocellatus) across laboratory, mesocosm, and field settings. Using flow-respirometry, we quantified metabolic costs and swimming kinematics under ecologically relevant flow conditions shaped by bluff bodies mimicking mangrove roots and oyster mounds. Fish swimming in turbulent wakes exhibited reduced oxygen consumption and altered tailbeat dynamics, especially at high flow speeds. In a large outdoor mesocosm, dual accelerometers revealed a rich behavioral repertoire, including maneuvering and rest, which is not easily observable in confined lab settings. Spectral analysis and clustering identified eight distinct locomotory states, highlighting the limitations of summed acceleration metrics. Field telemetry tracked wild red drum across a 54 km estuarine corridor for a three-year period through an array of 36 acoustic receivers, revealing movement patterns shaped by tidal flow and physical habitats. Hydrodynamic modeling revealed that while laboratory trials demonstrated substantial energetic savings at high flows (approaching 100 cm/s), wild fish were detected predominantly in low-velocity microhabitats (<30 cm/s) near structurally complex features. This mismatch suggests that habitat selection is an adaptive strategy driven by ecological factors such as foraging opportunities, predation refuge, and site fidelity, rather than hydrodynamic efficiency alone. Our multi-scalar approach demonstrates that while flow-structure interactions can reduce locomotor costs for fish, habitat use in the wild reflects broader ecological constraints, offering a framework for integrating biomechanics, physiology, and ecology in conservation-relevant contexts.

Tropical pollinators forage in environments where floral resources vary in space and time, requiring flexible strategies to optimise foraging efficiency. One such strategy, floral constancy - the temporary restriction to a single flower type - strongly influences foraging success and plant-pollinator interactions. We aimed to: (1) quantify spontaneous colour preferences and constancy in the Asian giant honeybee Apis dorsata, (2) test whether reward concentration modulates these preferences, (3) evaluate how quickly learned associations override spontaneous biases, (4) determine whether bees can use multiple colour associations simultaneously, and (5) assess whether local floral spectral patterns correlate with bee preferences. Bees trained to a neutral UV-grey stimulus showed a strong spontaneous preference and high constancy to blue, revealing a robust short-wavelength bias. Crucially, the strength of this spontaneous bias depended on reward concentration; Low-reward conditions elicited strong blue constancy, whereas high-reward conditions weakened it, demonstrating that reward expectation shapes spontaneous colour choices. This bias was flexible. When bees learned that yellow was rewarding they switched their preferences. Bees sequentially trained to both colours visited blue and yellow, showing no overall bias, or effect of the last-trained colour, indicating that recent experiences disrupt colour-specific constancy and generate largely random foraging choices. Bees were capable of learning and retaining two colours simultaneously, effectively suppressing the influence of spontaneous preferences. Finally, analysis of the communitys floral spectral distribution revealed a strong dominance of short-wavelength flowers, suggesting that long-term selection by the local floral environment may underlie the spontaneous blue preference observed in A. dorsata.

Animals must continually balance foraging with the risk of predation. In complex natural environments, this means quickly distinguishing between threats and harmless situations. We investigated how site-associated coral reef fishes decide to escape in response to visual cues mimicking predator attacks, using controlled underwater presentations of looming stimuli at varying speeds. We measured escape responses across species and social contexts, comparing them to predator attack speeds observed in the same habitat. Escape responses were highly sensitive to the speed of the looming stimulus, with no responses occurring at low speeds. The speeds triggering escape matched those of predator attacks, whereas cruising swim speeds never triggered a response. Species employed distinct antipredator strategies: Brown Chromis foraged away from shelter with high responsiveness, whereas Bicolor Damselfish remained shelter-dependent with lower escape propensities. Contrary to expectations, the social factors did not affect responses in this study. These findings demonstrate that reef fish are highly sensitive to the approach speed of objects, with species-specific strategies further shaping behaviors. By combining realistic visual threats with natural predator attack data, this study offers insight into how animals make escape decisions in complex, real-world environments.

Ctenophores are one of our most distant animal relatives and highly abundant and widespread marine predators, yet much of their biology remains undiscov-ered. Their bodies are dominated by a gelatinous, largely extracellular mesoglea of unknown composition. Ctenophores lack homologs for fibrous collagens that form the typical metazoan extracellular matrix (ECM), so the composition of their extracellular material is unknown. Using spectroscopic analyses of Mnemiopsis lei-dyi and Pleurobrachia pileus mesoglea, we found abundant mucus-related proteins and sulfated polysaccharides. The mucins and glycans appear unlinked, unlike the typical heavily glycosylated mucins. Our results suggest that ctenophores have a mucus-like mesoglea, a marked contrast from standard collagenous ECMs and mucus. This study indicates that ctenophores are even more different from other animals than previously appreciated, and expands our understanding of soft body composition and biophysics in animals.

Floral displays attract pollinators through a finely tuned interplay of colour, pattern, shape, and scent. Yet, the question remains: how do bees respond when these traits are stripped to their simplest form, with only visual cues at play? In this field study, we examined the foraging behaviour of Apis mellifera on artificial flowers differing solely in background colour (white or yellow) and UV patterning, while shape and scent were held constant. Across three summer days, standardized stimuli were placed within a natural meadow, and bee-flower interactions were recorded and analyzed by Bayesian hierarchical models. The results reveal a clear preference for yellow over white backgrounds and prolonged visitation in the presence of ring-shaped UV patterns, whereas full UV coverage acted as a deterrent. These effects, though moderate, were consistently modulated by abiotic covariates, particularly radiation, temperature, and time of day. Negligible inter-individual variation and a substantial share of residual variance further underline the context-dependent complexity of foraging. In sum, our findings demonstrate that visual floral traits, while influential, are interpreted through the dual lens of environmental contingency and the bees inherent cognitive machinery.

Iron is an essential nutrient for all types of organisms, including insects and the microbes that infect them. We predicted that insects fed an iron-supplemented diet would accumulate more iron in their hemolymph, and, because infectious microbes acquire iron from their hosts, that this extra iron would increase the severity of bacterial infections. To test this hypothesis, we studied the effects of dietary iron supplementation on infection outcomes in Manduca sexta (tobacco hornworm). Larvae were fed an artificial diet, with or without antibiotics, or the same diets supplemented with 10 mM iron. Control and iron-treated larvae were inoculated with non-pathogenic Escherichia coli or the entomopathogenic Enterococcus faecalis, and bacterial load and larval survival were measured. We found that dietary iron supplementation increased the iron content of hemolymph by approximately 20 fold; however, contrary to our prediction, this increase in iron did not result in an increase in the bacterial load of either E. coli or E. faecalis. The effect of iron supplementation on survival was more complicated. As expected, for larvae inoculated with nonpathogenic E. coli, iron supplementation had no effect. For larvae inoculated with E. faecalis, the effect of iron supplementation depended on whether antibiotics were present in the diet. Without antibiotics, iron supplementation prolonged larval survival; with antibiotics, iron supplementation decreased larval survival. The results of this study do not support the hypothesis that dietary iron supplementation increases infection severity in M. sexta. Instead, the results support the viewpoint that the relationship between dietary iron and infection outcome is complex.