Journal of Experimental Biology最新文献

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.

Visual perturbations may lead to an illusory self-motion and affect balance control. We studied effects of different visual perturbations in 16 healthy young participants walking on a treadmill, by assessing foot placement and center of mass (CoM) states. Three different visual perturbations were applied: fixating on a stationary target while the background moved to the right (MB), tracking the target moving rightward over a stationary background with head rotation (MT-HR), and tracking the moving target with eye movement only (MT-EM). Deviations of foot placement, CoM and trunk orientation due to the visual perturbation were assessed. Linear models were fit to the kinematic data to predict foot placement from CoM state at mid-swing. Over the whole trial, MT-HR and MT-EM caused an increase in step width variability, CoM position variability and RMS of foot placement errors simultaneously. During visual perturbation epochs specifically, in MB, a left deviation of foot and CoM trajectories was observed from the start of the background movement. In MT-HR and MT-EM, a right deviation of foot and CoM trajectories was observed only after the target had stopped moving. Contrary to our expectations, foot placement errors did not coincide with subsequent CoM deviations in the opposite direction. An obvious change in frontal plane trunk orientation was found only in MT-HR. While all visual perturbations affected control of the CoM trajectory in the frontal plane, these effects appeared caused by effects on control of heading as well. Head rotation appears to additionally disturb balance through a coupling with trunk orientation.

High temperature events are becoming more severe with climate change, altering species interactions and ecological networks. Symbionts can influence the thermal tolerance of their hosts, yet the mechanisms underlying these effects are poorly understood. We tested the impact of a high temperature event on the molecular interactions among a caterpillar host, Manduca sexta, its parasitoid wasp, Cotesia congregata, and the wasp's symbiotic virus. As in many host-parasitoid systems, high temperatures are lethal to developing parasitoids, but not hosts. Typically the parasitoid's viral symbiont immunosuppresses M. sexta. Here we show that elevated temperatures led to an impairment of this immunosuppression, persisting for days after the event ended. Viral gene expression in the host was altered by heat, with distinct expression patterns tied to the virus's genomic architecture. Specifically, viral transcription varied according to the gene's position on viral circular genomic segments: genes located on circles known to integrate into host DNA exhibited increased or unchanged expression following high temperature exposure, while genes on non-integrating circles showed marked reductions in expression. These results demonstrate that high temperatures can disrupt parasitic immunosuppression, which could help explain the lower thermal tolerance of parasitoids relative to hosts. The genomic structure of the viral symbiont may be associated with these effects, but additional research is needed to evaluate this hypothesis. Our findings highlight the importance of complex interactions between environmental temperature, microbial symbionts, and host immunity in the ecological responses of host-parasitoid systems to high temperature events.

Insects move their antennae to actively sense their environment. Regarding olfaction, it is not clear how these movements might be optimized for sampling the odor environment. Honey bees have movable rod-like antennae the last of segment of which contains several thousand pore plate sensillae that contain dendrites of olfactory sensory neurons. Walking honey bees typically move antennae in an almost constant manner. These movements can be impacted by odor valence, either innate or learned, suggesting that these movements are under sensory control. However, it is unclear if these movements are under active control or are simply fixed responses to stimulation. Here we evaluated antennal movements of stationary bees when placed in odor plumes with different structures. Antennae took up on average two different positions both in the absence and presence of odor in the plume. One corresponded to upwind and toward the odor source. The other position was across the plume. Bees rapidly switched between positions both in the presence and absence of odor. The frequency of forward and lateral positioning depended on the presence/absence of odor and on the structure of the plume, which suggests that movement is involved in sensing of odor filaments. We conclude that these movements represent active sensing, analogous to sniffing in mammals. Future investigations need to focus on the connection between antennal movements and physiological sensing as well as on analyses of odor-driven antennal movements in freely moving bees. Our results also suggest that active sensing may differ across insects with different antennal morphologies.

Many fishes exploit the terrestrial environment. Some of these amphibious species use it as an ecological release, others for feeding, while others use land to escape aquatic stressors. Another hypothesis is that amphibious fishes leave water to thermoregulate, but there is little corroborating data. One of the most intriguing fish that emerges onto land is the mangrove rivulus (Kryptolebias marmoratus), which can survive on land for up to 75 days. The mangrove rivulus emerges to escape from warm water and initially benefits from enhanced evaporative cooling on land. However, emergence imposes an immediate hypoxemia due to reduced gas exchange over the gills and an accumulation of CO2 that impairs Haemoglobin-O2 binding. In other ectothermic species, hypoxia is known to decrease thermal preference. Before physiological acclimation restores respiratory function, it is therefore plausible that fish that have emerged onto land will seek cooler temperatures beyond what is achieved by simple evaporative cooling. To test this idea, two strains of laboratory-raised mangrove rivulus were placed in a thermal gradient that provided the option of land and water to determine how their preferred temperature was informed by choice of the surrounding environment. We hypothesized that selecting land would be associated with anapyrexia, or a purposeful selection of lower temperatures. In trials where thermal gradients were provided in aquatic, terrestrial, or combined settings, mangrove rivulus selected cooler temperatures only when on land. These findings support the premise that terrestrial emergence serves an active thermoregulatory strategy.

The optokinetic response (OKR), a reflex enabling stable visual processing by minimizing retinal slip, has been well characterized in teleosts over the last decades. While previous work on teleost OKR mostly focused on its horizontal component, mammals are known to perform vertical and torsional OKR in addition to horizontal OKR. In this study, we characterize the vertical optokinetic response (vOKR) in larval zebrafish and compare it to the horizontal OKR (hOKR) and the vertical vestibulo-ocular reflex (vVOR). Our simultaneous camera-based tracking of vertical and horizontal eye positions reveals a distinct vOKR in larval zebrafish, but with a much smaller dynamic range compared to the hOKR and without any quick phases (resetting saccades). When presented with constant roll-rotating visual stimuli, zebrafish exhibit a brief initial vertical eye rotation in the direction of the stimulus, followed by a period without further slow phase response and interspersed with only spontaneous saccades. This behavior contrasts sharply with the periodical occurrence of resetting saccades (quick phases) during hOKR. The initial vertical response is tuned to similar spatial frequencies and angular velocities as the hOKR. We furthermore show that the vVOR has a much larger vertical dynamic range than the vOKR, demonstrating that the neuronal circuitry itself - and not the oculomotor plant - is the limiting factor. While it is unclear whether the observed differences in vertical versus horizontal optokinetic control have an adaptive value for zebrafish, the identified differences are drastic and informative for further studies on visuomotor circuits in teleosts.