Journal of Experimental Biology最新文献

Terrestrial animals not only need to walk and run but also lie prone to rest and then stand up. Sit-to-stand (STS) and sit-to-walk (STW) transitions are vital behaviours little studied in species other than humans so far, but likely impose biomechanical constraints on limb design because they involve near-maximal excursions of limb joints that should require large length changes and force production from muscles. By integrating data from experiments into musculoskeletal simulations, we analysed joint motions, ground reaction forces, and muscle dynamics during STS and STW in a large terrestrial, bipedal and cursorial bird: the emu (Dromaius novaehollandiae; body mass ∼30 kg). Simulation results suggest that in both STS and STW, emus operate near the functional limits (∼50% of shortening/lengthening) of some of their hindlimb muscles, particularly in distal muscles with limited capacity for length change and leverage. Both movements involved high muscle activations (>50%) and force generation of the major joint extensor muscles early in the transition. STW required larger net joint moments and non-sagittal motions than STS, entailing greater demands for muscle capacity. Whilst our study involves multiple assumptions, our findings lay the groundwork for future studies to understand, for example, how tendon contributions may reduce excessive muscle demands, especially in the distal hindlimb. As the first investigation into how an avian species stands up, this study provides a foundational framework for future comparative studies investigating organismal morphofunctional specialisations and evolution, offering potential robotics and animal welfare applications.

Flying insects solve a daunting control problem of generating a patterned and precise motor program to stay airborne and generate agile maneuvers. In this motor program, each muscle encodes information about movement in precise spike timing down to the millisecond scale. Whereas individual muscles share information about movement, we do not know whether they have separable effects on an animal's motion, or whether muscles functionally interact such that the effects of any muscle's timing depend heavily on the state of the entire musculature. To answer these questions, we performed spike-resolution electromyography and electrical stimulation in the hawkmoth Manduca sexta during tethered flapping. We specifically explored how flight power muscles contribute to pitch control. Combining correlational study of visually induced turns with causal manipulation of spike timing, we discovered likely coordination patterns for pitch turns, and investigated whether these patterns can drive pitch control. We observed significant timing change of the main downstroke muscles, the dorsolongitudinal muscles (DLMs), associated with pitch turns. Causally inducing this timing change in the DLMs with electrical stimulation produced a consistent, mechanically relevant feature in pitch torque, establishing that power muscles in M. sexta have a control role in pitch. Because changes were evoked in only the DLMs, however, these pitch torque features left large unexplained variation. We found this unexplained variation indicates significant functional overlap in pitch control such that precise timing of one power muscle does not produce a precise turn, demonstrating the importance of coordination across the entire motor program for flight.

Bone loading is a crucial factor that constrains locomotor capacities of terrestrial tetrapods. To date, limb bone strains and stresses have been studied across various animals, with a primary emphasis on consistent bone loading in mammals of different sizes and variations in loading regimes across different clades and limb postures. However, the relationships between body size, limb posture and limb bone loading remain unclear in animals with non-parasagittally moving limbs, limiting our understanding of the evolution of limb functions in tetrapods. To address this, we investigated in vivo strains of the humerus and femur in juvenile to subadult American alligators as they walked with various limb postures. We found that principal strains on the ventromedial cortex of the femoral midshaft increased with larger sizes among the three individuals displaying similar limb postures. This indicates that larger individuals experience greater limb bone strains when maintaining similar limb postures to smaller individuals. Axial and shear strains in the humerus were generally reduced with a more erect limb posture, while trends in the femur varied among individuals. Given that larger alligators have been shown to adopt a more erect limb posture, the transition from sprawling to erect limb posture, particularly in the forelimb, might be linked to the evolution of larger body sizes in archosaurs, potentially as a means to mitigate limb bone loading. Moreover, both the humerus and femur experienced decreased shear loads compared with axial loads with a more erect limb posture, suggesting proportional changes in bone loading regimes throughout the evolution of limb posture.

The locomotor behavior of an animal strongly depends on the distribution of its body mass. Whenever changes occur in this distribution, the displacement of the body center of mass (CoM) may lead to a loss of balance. Ants are an interesting biological model with which to investigate how an animal copes with such changes because, when they transport food, their CoM may be displaced from its usual position. We studied the ant Formica rufa, whose diet consists mainly of liquid food, stored in the abdomen, but also includes prey transported in the mandibles. We investigated the kinematics of locomotion of the same individuals while walking unloaded and while transporting food internally or externally. We found that the kinematics of locomotion slightly differed in the two types of transport. Ants transporting food in their mandibles adopted a more erect posture and tended to be more often in static instability than ants transporting food internally. In addition, the amplitude of the vertical oscillations of their CoM was higher, which led to a jerky locomotion. However, owing to their erect position, the position of their overall CoM was actually not different from that of unloaded ants. Finally, the mechanical work achieved by ants to rise and accelerate their CoM was smaller in ants transporting food internally than in ants transporting food externally or in unloaded ants. This suggests that the morphology of F. rufa could make the transport of food in the gaster more mechanically efficient than the transport of food in the mandibles.

The accelerometer, an onboard sensor, enables remote monitoring of animal posture and movement, allowing researchers to deduce behaviors. Despite the automated analysis capabilities provided by deep learning, data scarcity remains a challenge in ecology. We explored transfer learning to classify behaviors from acceleration data of critically endangered hawksbill sea turtles (Eretmochelys imbricata). Transfer learning reuses a model trained on one task from a large dataset to solve a related task. We applied this method using a model trained on green turtles (Chelonia mydas) and adapted it to identify hawksbill behaviors such as swimming, resting and feeding. We also compared this with a model trained on human activity data. The results showed an 8% and 4% F1-score improvement with transfer learning from green turtle and human datasets, respectively. Transfer learning allows researchers to adapt existing models to their study species, leveraging deep learning and expanding the use of accelerometers for wildlife monitoring.

It is thought that the magnitude of center of mass (COM) oscillations can affect stability and locomotor costs in arboreal animals. Previous studies have suggested that minimizing collisional losses and maximizing pendular energy exchange are effective mechanisms to reduce muscular input and energy expenditure during terrestrial locomotion. However, few studies have explored whether these mechanisms are used in an arboreal context, where stability and efficiency often act as trade-offs. This study explores three-dimensional COM mechanics in an arboreal primate - the squirrel monkey (Saimiri sciureus) - moving quadrupedally at various speeds on instrumented arboreal and terrestrial supports. Using kinetic data, values of energy recovery, COM mechanical work and power, potential and kinetic energy congruity, and collision angle and fraction were calculated for each stride. Saimiri sciureus differed from many other mammals by having lower energy recovery. Although few differences were observed in COM mechanics between substrates at low or moderate speeds, as speed increased, COM work was done at a much greater range of rates on the pole. Collision angles were higher, whereas collision fractions and energy recovery values were lower on the pole, indicating less moderation of collisional losses during arboreal versus terrestrial locomotion. These data support the idea that the energetic demands of arboreal and terrestrial locomotion differ, suggesting that arboreal primates likely employ different locomotor strategies compared with their terrestrial counterparts - an important factor in the evolution of arboreal locomotion.

The ability for snakes to ingest large prey (macrostomy) is a widespread, derived trait that involves distending the skin during ingestion and metabolic upregulation during digestion. The material behavior of the skin must accommodate significant stretch associated with a large prey bolus, but data remain sparse for how the material properties of snake skin vary: longitudinally within an individual, after ingesting large prey and among species. To test whether these three factors affected the mechanical properties of snake skin, we quantified uniaxial stresses and strains in circumferential loops of skin from the neck, mid-body and tail of fasted and recently fed Boa constrictor. We also tested skin from several pre-cloacal longitudinal positions in fasted snakes that included two non-macrostomates (Afrotyphlops lineolatus, Anilius scytale) and a highly specialized macrostomate species that eats only bird eggs (Dasypeltis gansi). For B. constrictor, the anterior-most skin failed at higher strains for fed (mean±s.e.m. 2.17±0.10) compared with unfed individuals (1.80±0.04), and maximal stiffness (Young's modulus) had a significant increase posteriorly. The values of Young's modulus for the anterior-most skin of D. gansi (0.050±0.014 MPa) were by far the lowest observed both within that species and among all species. The material properties of skin of the two non-macrostomate species had little longitudinal variation. Hence, the extent of longitudinal variation in skin properties is both species dependent and affected by feeding. The more distensible skin in macrostomates relative to the non-macrostomate species tested suggests that more compliant anterior skin is a derived trait that facilitates macrostomy.

Subterranean mammals representing a single subspecies occurring along an aridity gradient provide an appropriate model for investigating adaptive variation in thermal physiology with varying levels of precipitation and air temperature. This study examined the thermal physiological adaptations of common mole-rats (Cryptomys hottentotus hottentotus) across five populations along an aridity gradient, challenging the expectation that increased aridity would lead to reduced metabolic rate, lower body temperatures and broader thermoneutral zones. No significant, consistent differences in metabolic rate, body temperature or thermal conductance were observed between populations, suggesting uniform thermoregulatory mechanisms across habitats. Instead, behavioural strategies such as huddling and torpor may play a more prominent role than physiological adaptations in managing temperature regulation and water balance. The study also observed osmoregulatory differences, with populations employing distinct behavioural cooling strategies in response to water availability. These results underscore the need for further research into the responses of subterranean species to climate change, particularly in understanding how increasing global temperatures and aridification might influence species distribution if they lack the physiological capacity to adapt to future climatic conditions.

Drosophila female germline development and maintenance require both local stem cell niche signaling and systemic regulation. Here, we show the indispensable function of the Drosophila melanogaster olfactory circuit in normal oogenesis and fecundity. Lack of olfactory inputs during development causes a reduction in germline stem cells. Although germline stem cells proliferate normally, the germline cysts undergo caspase-mediated apoptosis, leading to decreased follicle production and egg-laying in flies with defective olfaction. Strikingly, activation of olfactory circuits is sufficient to boost egg production, demonstrating that chemosensory-activated brain-derived inputs promote gamete development. Given the energy demands of oogenesis and its direct consequence on fitness, we propose that olfactory-stimulated systemic regulation evolved tightly with downstream diet-responsive pathways to control germline physiology in response to nutritional status. Additionally, these findings raise the possibility that sensory-mediated stem cell maintenance is a generalizable mechanism spanning a myriad of neuronal circuits, systems and species.