Journal of Experimental Biology最新文献

The vertebrate stomach is responsible for the secretion of hydrochloric acid (HCl) and is the first site of protein digestion in the gut. The secretion of HCl occurs through the gastric proton pump, a hydrogen-potassium ATPase (HKA) composed of α and β subunits encoded by the ATP4A and ATP4B genes, respectively. In the past, the evidence for the role of the gastric acid secretion in nutrient digestion and absorption, growth, and postprandial energy metabolism has been gathered using indirect methods such as diet modulation experiments, or the use of proton-pump inhibitors. These methods may introduce confounding factors and lead to erroneous conclusions. With the aim of directly observing the role of the gastric proton pump, we have generated a knockout (KO) model using targeted gene editing. Using atp4a-null Astyanax mexicanus, we examined the growth rate, nitrogen and energy metabolism, and nutrient assimilation in the presence and absence of gastric acidification. Our results show no effect of KO on growth or appetite, but a significant reduction in post-prandial nitrogen excretion and oxygen consumption (specific dynamic action). Furthermore, atp4a-/- animals had significantly less body magnesium, calcium, phosphorus and protein, while having more lipid in their carcasses. Importantly, administration of proton-pump inhibitors suppressed growth in both experimental groups indicating possible off-target effects of these drugs. This study is the first to directly examine the impact of gastric acidification on body composition, growth and metabolism and offers new and targeted evidence on the importance of stomach acidification for gut and digestion homeostasis.

Zn accumulates in the jaws of green worms, Nereis aibuhitensis, a phylum of annelid worms, to enhance the mechanical properties of the jaws for predation and migration. In this study, we precisely mapped the localization of zinc and identified the matrix proteins responsible for its binding in the jaws. X-ray diffraction (XRD) analysis revealed no distinct crystalline peaks in powdered jaw samples, indicating that zinc exists predominantly in a non-crystalline form. X-ray absorption fine structure (XAFS) spectra further demonstrated that zinc coordinates with organic molecules containing imidazole groups, implicating histidine (His) residues in zinc binding. Elemental analyses by Inductively coupled plasma mass spectrometry (ICP-MS) and particle-induced X-ray emission (PIXE) showed zinc concentrated on the inner side of the jaw tip, while halogens were mainly localized on the outer surfaces of the jaw. A comparison of protein extracts from the zinc-rich jaw tip and the zinc-poor bottom showed a specific protein band at the tip region, identified as a His-rich protein (Nai11527). These findings reveal a previously uncharacterized mechanism whereby histidine-rich proteins bind zinc to reinforce jaw structure. This study advances our understanding of biomineralization and offers a promising blueprint for the design of novel bio-inspired materials with enhanced mechanical properties.

Diving performance by marine mammals is associated with marked changes in tissue oxygen (O2) and carbon dioxide (CO2) levels. Yet, the primary metric for diving recovery in most studies has focused exclusively on restoring tissue O2, despite the importance of CO2 offloading as a major determinant for diving homeostasis. To assess the combined role of respiratory and blood gases, we compared post-exercise O2 and CO2 recovery rates in bottlenose dolphins (Tursiops truncatus, n=2) and beluga whales (Delphinapterus leucas, n=4). System-wide recovery mechanisms were also examined, including blood pH, breathing patterns, and peripheral vasodilation. Following maximal swim repetitions, respiratory O2 and CO2 levels returned to resting levels within 8.5 min for belugas (VO2: 8.4±0.8 min; VCO2: 8.5±0.9 min; mean±s.d.) and 3.5 min for dolphins (VO2: 3.4±0.8 min; VCO2: 3.4±0.7 min). Blood O2 and CO2 recovery durations also varied by species. Belugas required 12-15 min to reach resting levels, whereas dolphins' blood O2 remained within resting levels and CO2 recovered in ∼4-7 min. Blood pH, driven by changes in pCO2, returned to resting levels between 12-15 min for belugas, but remained elevated throughout the recorded recovery period for dolphins. Blood lactate also remained near double the resting values for both species. Overall, we found that CO2's compounding effects with blood lactate appear to play a dominant role in odontocete dive recovery, which will dictate the duration of full physiological recovery by wild odontocetes following escape responses from anthropogenic disturbances.

The brain is energetically expensive. Energy availability may, therefore, determine whether costly cognitive processes such as long-term memory can be expressed. However, there is a limited understanding of the metabolic costs associated with long-term memory formation. Here, we explored the potential induced costs of long-term memory formation using honeybees (Apis mellifera) as a model species. We monitored the sucrose intake of bees over the 20-hour period following a classical spaced olfactory conditioning protocol that induced long-term memory formation, relative to a control group that experienced the same reward schedule but no odour pairing. Bees in the experimental treatment drank significantly more sucrose than controls. We then tested whether the increased energy demands of long-term memory formation showed parallel increases in metabolic rate, by measuring carbon dioxide production in groups of bees at four timepoints following conditioning (1-hour, 4-hours, 24-hours and 72-hours). We found no change in metabolic rate between learning and control groups across all time points, suggesting that long-term memory formation does not impact metabolic rate to an extent that is detectable by our group metabolic rate protocol. While our findings point to dietary costs associated with long-term memory formation, any metabolic consequences may operate at a resolution below that detectable in group-level analyses and may be more effectively examined using individual or cellular-level energy flux approaches.

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, whether counteraction is possible and how the choice between counteraction and retreat is decided are not clear. Here, we report that Drosophila melanogaster larvae can actively counter 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 pressure. Instead of retreating by crawling backward, some D. melanogaster larvae could crawl forward and act against the external physical pressure. Under externally applied forces of 25 mN, 93.9% of forward peristaltic movements increased the counteracting force, while 88.2% of backward peristaltic movements decreased it. The active nature of the counteracting force was reflected by a longer inter-wave delay, more oscillation work and a longer force wave period during consecutive forward peristaltic waves. As the external force was increased from 25 mN to 50, 75 and 100 mN, counteraction by forward peristalsis became less frequent, while retreat by backward peristalsis was more frequent. A reduction of the external pressure immediately following the counteracting forward peristalsis, which might serve as rewarding signal, reinforced the counteraction and induced more forward peristalsis. The rewarding effect of reducing external pressure by forward crawling was much greater than that produced by backward crawling. Our study sheds light on the intricate mechanisms underlying animal proactive responses to adverse abiotic environmental conditions.

Nutrients, including vital organic compounds, vary in availability across ecosystems, with the potential to act as a strong source of selection for traits that increase nutrient acquisition and biosynthesis. Compared with freshwater ecosystems, marine ecosystems are much richer in the omega-3 long-chain polyunsaturated fatty acid docosahexaenoic acid (DHA) and thus marine animals establishing new freshwater populations are faced with the challenge of acquiring DHA. However, the relative roles of DHA synthesis capacity and diet in the freshwater establishment process remain unresolved. We used common garden experiments to explore phenotypic responses to dietary nutrient content in threespine sticklebacks (Gasterosteus aculeatus) that varied in their genetic capacity for DHA synthesis. We found that diet as well as presumed metabolic adaptation to freshwater nutritional environments (population identity) had strong effects on stickleback phenotype and performance. Sticklebacks enriched with marine-derived fatty acids including DHA grew more and were in better condition compared with controls. Those fed diets with more DHA also accumulated more DHA in muscle tissue. Freshwater sticklebacks accumulated more DHA compared with those from a marine population. However, populations with greater fads2 copy number did not consistently have higher performance or DHA accumulation. Together, these results suggest that DHA availability during development can strongly influence phenotype and performance, with the potential to act as a source of selection. Our findings also suggest that mechanisms beyond the accumulation of fads2 copies, such as plasticity in expression or variation in other DHA synthesis pathway genes, could be important adaptations to the nutritional constraints of freshwater.

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.

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 the 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 took 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.

Metabolic rate represents fundamental processes in ecology and evolution; it determines the rate at which organisms oxidize substrates to energy for growth, reproduction and survival. Metabolic limits, minimum energy use for self-maintenance and maximum expansion of aerobic performance define individuals' energy allocation capabilities. We studied the co-expression between metabolic limits in a species representing an ancient marsupial lineage and hypothetical plesiomorphic mammalian physiology. We partitioned covariation between basal (BMR) and maximum (V̇O2,max) metabolic rates to between- and within-individual components. Contrary to predictions of the aerobic model for endothermy evolution, we found a near-zero BMR-V̇O2,max correlation on the between-individual level, suggesting null genetic co-variance, or its cancellation by an among-individual maintenance-to-capacity trade-off. Instead, a substantial within-individual BMR-V̇O2,max correlation revealed plastic co-expression of the traits in the wild animals responding to environmental variation. Within-individual V̇O2,max-lean mass correlation reinforces the importance of this bioenergetic plasticity mechanism. We conclude that endothermic strategies can be sustained not only by fixed genetic coupling, but also by flexible, condition-dependent trait integration, hypothetically reflecting a physiological plastic property of the early stages of therian evolution.

Metabolic features of the deep-water coral Madrepora oculata were investigated for specimens originating from approximately 800 m depth in the Bay of Biscay (Northeast Atlantic). Incubations of live specimens were carried out as a function of temperature (7°C, 10°C and 13°C), and for the first time as a function of hydrostatic pressure (atmospheric and natural pressures). An influence of temperature was observed, with an approximately 40% reduction of oxygen consumption at a temperature cooler than in situ, but no obvious increase in a warmer experimental environment. CO2 production increased upon warming from 7°C to 13°C. Hydrostatic pressure had a significant influence on ammonium excretion (and on O:N ratio), suggesting a stress response following exposure to atmospheric pressure. It is the first time that such a response to pressure variation has been observed, calling for increased attention towards pressure effects on live deep-water corals. According to the expected shoaling of the aragonite saturation horizon, studies of deeper-living samples, situated at the lower boundary of their natural depth distribution, appear necessary to better understand the impact of ocean acidification on reef-building scleractinian corals. The present work shows that some biological features are pressure-sensitive, and suggests that investigations on such corals should be undertaken at in situ pressure.