Journal of Experimental Biology最新文献

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.

In recent years, secondary bile acids (SBAs) have emerged as key signalling molecules influencing energy balance, feed intake and glucose and lipid homeostasis in mammals, yet their physiological roles in fish are still poorly understood. This study investigated the short-term effects - 6 h post-intragastric administration - of SBAs [500 µmol l-1 lithocholic acid (LCA), 1500 µmol l-1 deoxycholic acid (DCA) and their taurine conjugates: 1000 µmol l-1 T-LCA and 600 µmol l-1 T-DCA] on hepatic metabolism in rainbow trout. Specifically, we assessed mRNA abundance and activity of hepatic enzymes involved in glucose and lipid metabolism, and expression of metabolic regulators, circulating and hepatic metabolites, and hepatic genes related to BA transport, receptors and synthesis. Our results revealed that LCA potentially inhibits hepatic gluconeogenesis by reducing the enzymatic activity of glucose 6-phosphatase (G6pase), fructose 1,6-bisphosphatase (Fbpase) and phosphoenolpyruvate carboxykinase (Pepck), combined with prkaa1 (Ampk) upregulation and foxo1 downregulation. However, these molecular effects did not translate in this treatment into consistent changes in plasma or hepatic glucose levels. As for lipid metabolism, DCA increased the mRNA abundance of lipogenesis markers (acly, acc) and prkaa1. At the enzymatic level, DCA reduced Cpt-1 activity, while Acly activity showed contradictory responses. Despite these molecular changes, hepatic lipid content remained stable, hindering a clear interpretation of the putative lipogenic effects. Bile acid transport and synthesis showed tightly regulated, SBA-specific responses, with LCA specifically upregulating cyp8b1 and inhibiting fxr. Overall, these findings underscore the structural specificity and species dependence of SBA signalling in teleosts and highlight the importance of SBA identity and temporal dynamics in shaping metabolic regulation in fish.

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.

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.

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.

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.

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.

To counteract or to retreat presents a fundamental dilemma for biological organisms when facing adverse abiotic environmental conditions. In many cases, the predominant strategy animals adopt is to retreat. However, if counteraction is possible, and how the choice between counteraction and retreat is decided, are not clear. Here, we report that Drosophila larvae can actively counteract external mechanical pressure, inspired by Drosophila larval cleft-squeezing behaviour. We developed a behavioural paradigm to investigate the counteracting force of larvae in response to external pressures. Instead of retreating by crawling backward, a portion of Drosophila larvae could crawl forward and counteract against the external physical pressure. Under externally applied pressing forces of 25mN, 93.9% of forward peristaltic movements increased the counterforce, while 88.2% of backward peristaltic movements decreased it. The activeness in counteraction force was reflected by the longer inter-wave delay, more oscillation work and longer force wave period during consecutive forward peristaltic waves. As the external pressing force was increased from 25mN to 50mN, 75mN and 100mN, counteraction by forward peristalsis was less frequent, while retreat by backward peristalsis was more frequent when pressure is high. A reduction of the external pressure immediately following the counteracting forward peristalsis, which might serve as rewarding signal, could reinforce the counteraction and induce more ensuing forward peristalsis. The rewarding effect of reducing external pressure by forward crawling was much more than that by backward crawling. Our study sheds light on the intricate mechanisms underlying animal proactive responses to adverse abiotic environmental conditions.

Science is often claimed to be amid a reproducibility crisis, as evidenced by low replicability of many classic findings across multiple fields. Yet it is not clear how widespread this purported problem is. Physiological responses have potential for replicability issues because of laboratory-specific biases in animal maintenance as well as technically complex methodologies that are often undertaken using bespoke combinations of equipment. Here we take advantage of a cross-laboratory manipulative study on metabolic rate to assess the replicability of food restriction effects on metabolic scaling and level. Across seven skink species from the Egernia species complex and two universities, we found these responses to be extremely replicable. The slope of the interspecific metabolic scaling relationship was near one and animals reduced their mass-independent rates of energy use by an average of 32% in response to food restriction. This response was consistent across universities. Our study highlights that well designed and replicated studies with a large effect size can indeed be replicable and showcases the value of designing studies that allow tests of replicability to be incorporated explicitly. Such studies will be particularly valuable for treatment effects that generate a small effect size.