Czechia

Most studies exploring ectotherms metabolic response to warming focus on respirometric approaches, thus only reflecting individual aerobic metabolism. Here, we measured the metabolic response and lactate body content of Gammarus pulex after a shift from low (12°C) to high (22°C) temperature by coupled oxygen consumption measurements (microrespirometry) and heat production (direct microcalorimetry). Following the shift to high temperature and after an initial increase, oxygen consumption gradually decreases, getting back to the value reported at low temperature. Such phenotypic plasticity may compensate for the temperature-induced increase of metabolic rate, commonly considered as an acclimation process in ectotherms. However, the simultaneous measurements of Gammarus pulex metabolic rate by direct microcalorimetry remained stable, highlighting an uncoupling between organism heat production, reflecting total metabolic rate, and oxygen consumption. This mismatch suggests an oxygen-disconnected metabolic process, concomitant with an increase in individual lactate body content at high temperature, suggesting a shift from aerobic to anaerobic metabolism. Seven days after the shift to high temperature, the estimated proportion of anaerobic metabolic rate represents up to 50% of total metabolism. Our results indicate that the decrease in aerobic metabolism does not reflect a decrease in total metabolic rate, assimilated to metabolic acclimation, but rather a shift to anaerobic processes to sustain the temperature-induced increased in organism energetic requirements.

SEB Conference Prague 2024

Metabolic acclimation: compensation or thermal stress?

global warming

ectotherms

acclimation

metabolism

technical paper

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SEB’s Annual Conference is celebrated for creating the perfect composition of research, new discoveries and collaborative connections. Be creative and innovative by exchanging ideas and knowledge with masters of biology from all over the world.

The Atlantic king scallop, Pecten maximus, as a subtidal species is more and more exposed to fluctuations in water temperature and pH variations due to the ongoing climate change. Its ability to swim makes scallops exceptional between bivalves and previous studies have shown that ocean warming (OW) and acidification (OA) can impact swimming performance of P. maximus. In particular, warming induced a decrease in the muscular index as well as a reduction in force and strength of the adductor muscle of P. maximus. However, the metabolic mechanisms behind these observed limitations in muscle performance are largely unexplored.
In this paper we present a semi-targeted metabolomic approach based on NMR spectroscopy for a retrospective study on frozen tissues of gill, mantle and adductor muscle of P. maximus, that were long-term acclimated under Ocean acidification, Ocean warming and the combination of both (OWA). 33 metabolites could be identified in all tissues, with organ depend differences in metabolite concentrations attributed to the specific functions of the individual organs. Metabolite changes to the different treatments showed that warming is the main driver for metabolic changes in gill and adductor muscle. 
In particular, energy-related metabolites, such as ATP and L-arginine, play an important role in the physiological response of scallops to OW and OWA.
With the help of a combined approach of pathway analysis and network exploration the warming induced changes in energy-related metabolites could be attributed to the observed limitations in swimming performance of P. maximus.

Metabolic profiling of muscle performance changes in the Atlantic king scallop, Pecten maximus, to ocean warming and acidification

The Northern shrimp (Pandalus borealis) is an ecologically and socio-economically important species in the North Atlantic, yet several of its different populations are collapsing due in part to global change drivers. Here, we aimed to elucidate the molecular mechanisms underlying shrimp responses to combined ocean warming (OW) and acidification (OA). Specifically, we profiled the phospholipidome of the abdominal muscle of female shrimp from four origins in the Northwest Atlantic, subjected to an orthogonal design of temperature (2, 6, or 10 °C) and pH (pH 7.75 or 7.40) scenarios. A suite of multivariate analyses revealed a complex interplay between shrimp origin and exposure to combined OW and OA, with OW primarily driving the phospholipidomic response, particularly at 10 °C. Warming to 10 °C altered phospholipids related to membrane thickness and lateral diffusion, and upregulated sphingomyelins. Notably, OA caused subtler effects, dependent on shrimp origin. Specimens from the Gulf of St. Lawrence showed an interactive effect of OW and OA, whilst those from the coasts of Newfoundland and Nova Scotia were not impacted by OA. Our finding has direct implications for prioritising conservation efforts on shrimp populations featuring a higher sensitivity to multiple stressors. Overall, our findings highlight the power of comparative omics to reveal different levels of intraspecific plasticity in the molecular response of marine organisms to future oceanic conditions. Our results will be refined by integrating multiomics and physiological traits within a multilayer framework to gain a comprehensive understanding of the response to global change drivers.

Molecular Responses of the Northern shrimp facing combined Ocean Warming and Acidification across the Northwest Atlantic Reveal Intraspecific Plasticity

In ectothermic species, changes in environmental conditions can be reflected in mitochondria, which are known for their high level of sensitivity and plasticity. These can result in either a functional change within the mitochondrion itself, a variation in total density within a tissue, or even a combination of the two. Therefore, experimental data must be presented with an adequate measure of mitochondrial density to be interpretable and scientifically backed. One of the most effective ways to quantify mitochondrial density (MD) is through transmission electron microscopy (TEM). However, proxies of mitochondrial density are often used in lieu. Commonly, quantifications of mitochondrial protein content, enzyme activity, and mitochondrial DNA copy numbers are employed as estimates of MD. The most frequently used estimates include measurements of citrate synthase (CS), complex I, and complex IV activity, but results vary greatly between studies. Indeed, mitochondrial plasticity, especially in ectotherms, may partly explain these discrepancies. This ongoing project therefore embodies a comprehensive approach evaluating if the use of mitochondrial density markers can be generalized in ectothermic animals. We show that despite cold-acclimated Drosophila (D. melanogaster) having higher complexe IV activity, and a tendency for increased CS activity, these commonly employed mitochondrial density markers were poor predictors of differences in various measurements of MD (i.e. number of mitochondria, fractional area, and surface density) evaluated by TEM. Conversely, neither differences were observed between enzymatic activities nor MD measurements between differentially acclimated beetles (Leptinotarsa decemlineata). The analysis of further density markers is ongoing.

Testing traditions: Validating mitochondrial density markers in ectothermic species

In recent years, an important decline of honey bee populations is observed, in part due to environmental variations caused by climate change. Particularly, increased temperatures during winter and spring bring forth new challenges, as the transition from winter to summer is crucial for the colony's survival. We have recently demonstrated that honey bee mitochondria undergo drastic changes between the winter and summer seasons, which is attributed to their different roles within the hive. Specifically, winter bees have lower CI-linked respiration but increased mtG3PDH- and CII-linked respiration. However we do not know whether and how this affects ATP and reactive oxygen species (ROS) production. Further, the regulation mechanisms behind this drastic change in phenotype is unknown. In this study, we investigated the seasonal differences in mitochondrial oxygen consumption, ATP production, and site-specific ROS production in honey bees (Apis mellifera). We also evaluated supercomplex assembly to determine if this could explain the changes observed in the mitochondrial parameters measured. Our results demonstrate that even though CI-linked respiration is diminished in winter bees, ATP production by CI is increased, suggesting that CI is more efficient in winter. Differences were also detected in terms of ROS production, with summer bees producing less ROS than all other season. In terms of supercomplex assembly, we are currently performing the analyses, which has never been done in honey bees, and will be included in this talk. We hypothesize that supercomplex assembly could shed light on the results described above, explaining the contrasting mitochondrial phenotypes observed between seasons.

Seasonal effect on metabolism and mitochondrial supercomplex assembly in honey bees (Apis mellifera)

There is global scientific and commercial interest in understanding the impacts of climate warming and heatwaves on the resilience of fish populations. While heat is thought to act at a fundamental level on biological reaction rates, protein structure and cell membrane fluidity, much has been made of the role of oxygen in governing these processes. The “gill-oxygen limitation” (GOL) hypothesis proposes that the growth of fish gills does not keep pace with the increase in metabolic requirements of the body as fish grow, resulting in a progressive mismatch between oxygen supply and demand that is exacerbated at high temperatures. We have empirically tested this hypothesis in thermally acclimated fish in recent years and found no supportive evidence; gills have the plasticity to grow proportionally with metabolism to ensure that oxygen supply and demand are matched as fish grow, even at elevated temperatures. We have, however, found some evidence for oxygen supply limitations across the gills during acute thermal exposures, exacerbated as fish increase in size. This talk will discuss the current state of knowledge on these topics with an aim to shed light on the mechanisms compromising fish resilience to acute heatwaves and chronic warming.

Potential for gill-oxygen limitation in acute but not chronic thermal tolerance

The severity and frequency of marine heatwaves (MHWs) have increased dramatically across the globe, particularly in the last decade. In ectotherms like fishes, temperature directly influences oxygen transport, leading to changes in oxygen consumption (i.e., metabolic rates). The effects of temperature on metabolism have consequences for organismal function, including swimming performance. Performance is expected to decline as metabolic demands accumulate at temperatures beyond a fish’s optimum, though declines may be mitigated through various means, including plastic responses. Rapid changes in temperature, exemplified through MHWs, may outpace an individual’s acclimation capacity, leaving them more vulnerable to detrimental thermal effects.
We investigated how heatwave exposure (i.e., +2°C and +4°C above normal summer temperature) over a five-day period affects the metabolic rate and swimming performance of a common nearshore marine fish species, the shiner perch (Cymatogaster aggregata), on San Juan Island, Washington. Using a swim tunnel respirometer, we measured standard and maximum metabolic rate (SMR and MMR, respectively), as well as critical swimming speed (Ucrit) and optimal swimming speed (Uopt). SMR was highest with moderate heatwave exposure (+2°C), while MMR was highly variable within treatments and increased slightly at the highest treatment temperature (+4°C). Ucrit did not vary across temperatures, but Uopt did decline with increasing temperatures. These findings provide insight into how this species may respond to future projected marine heatwaves, and also highlight the need for further studies focusing on metabolic performance across a range of relevant temperatures and acclimation periods.


Effects of heatwave exposure on the metabolism and swimming performance of a nearshore marine fish, Cymatogaster aggregata

Lab-reared organisms allow researchers to understand aspects of our natural environment under controlled conditions contributing knowledge to policy development, risk assessment, and environmental systems. However, it is important to consider whether lab-reared organisms are actually representative models for their wild counterparts. To address this, our study compared the toxicity of ultraviolet filters (UVFs) between lab-reared and wild-caught Daphnia pulex to understand the effect of life-history on environmental exposures. 48-hour exposures of daphnids to avobenzone, oxybenzone, or octocrylene found minimal differences in both lethal and sublethal acute toxicity; however, several large deviations in chronic toxicity were observed over 21 day exposures. Wild daphnids exposed to 100 μg/L of octocrylene exhibited a 53% reduction in total reproduction compared to lab daphnids, as well as a 16% smaller core body size. In addition, differences in mortality were apparent between each population, as lab Daphnia experienced 30% higher mortality to 100 µg/L oxybenzone, while wild Daphnia experienced 30% higher mortality to 100 µg/L octocrylene. Overall, these results highlight a clear difference between the tolerance of lab-reared and wild organisms to UVFs, and that these differences are chemical specific. These results highlight the need for more environmentally relevant test methods for the use of model organisms across a multitude of fields, including physiology and toxicology. While the practicality and accessibility of lab-reared model organisms is an important tool, it is worth considering the use of their wild counterparts to provide a more accurate picture of these organismal functions in nature.

They're Sisters Not Twins: Understanding the differences in lab-reared & wild caught Daphnia pulex responses to ultraviolet filter exposure.

Suction-feeding is a common method for capturing prey by aquatic organisms. This method allows for the adaption of predators by enabling them to consume a wide range of prey. Suction- feeding is a complex fish-fluid interaction governed by various hydrodynamic forces: inertia, unsteady, viscous and pressure gradients that are described by the coupling between the flow physics equations (Navier-Stokes) and the dynamic behavior of the fish (motion and forces). This study focuses on estimating the pressure within the flow field surrounding the mouth of a bluegill sunfish (Lepomis macrochirus) during suction-feeding utilizing Particle Image Velocimetry (PIV). We used high-speed imaging for measurements of the fish buccal kinematics (period and amplitude). The pressure field is estimated from the velocity fields measured by PIV via the Poisson equation. The boundary conditions for the pressure field are determined from the integral momentum equation, separately, for each phase of the suction-feeding cycle. The spatial pressure distribution varied significantly as a function of phase. We explore the suction-feeding process by quantifying the pressure field that drives the flow towards the buccal cavity, where the location of a low-pressure zone varies throughout the feeding cycle.

Pressure field surrounding bluegill sunfish (Lepomis macrochirus) during suction-feeding

Functional trade-offs impose important constraints on the biomechanics of musculo-skeletal systems. In songbirds, for example, a force-velocity trade-off has been described in singing, showing that hard-biting birds sing at lower syllable rates. However, we do not yet know whether and how this also affects their feeding kinematics. Many songbirds are granivorous, i.e., rely on seeds as their major food source. Thus, we analysed seed processing in two granivorous species, canaries (bite force ≈3 N) and Java finches (bite force ≈10 N), using X-ray Reconstruction of Moving Morphology (XROMM). We show that canaries move their beaks at a ≈23% higher angular velocity and at a ≈31% higher frequency compared to Java finches. Furthermore, canaries use a wider range of motion in both the upper and lower beak during seed processing. Last, we show that these differences in beak biomechanics are also associated with differences in seed processing strategies in the tested species: Java finches crack the seeds more easily than canaries, but they often crush the inner kernel and consequently drop parts of it. Canaries, however, are able to remove the shell without crushing the seed and swallow the kernel in whole. This suggests that a force-accuracy trade-off might be at play in the beak's fine motor control. Our results indicate that a combination of trade-offs (force-velocity, force-frequency, and force-accuracy) has an impact on the feeding biomechanics of granivorous songbirds and hence may play an important role in the adaptation to specific seed types.

Biting fast or biting hard? Comparative XROMM analysis reveals functional trade-offs in beak movements of feeding songbirds.

Formins are an evolutionarily old family of cytoskeletal regulators whose roles include microfilament capping, actin nucleation, and modulation of microtubule dynamics. Plant class I formins typically exhibit a unique domain organization, with most of them being transmembrane proteins with possible cell wall-binding motifs exposed to the extracytoplasmic space. Although such transmembrane formins are traditionally considered mainly as plasmalemma-localized proteins, they could also, at least temporarily, reside in endomembranes. Some of them decorate the plasmodesmata. We are currently developing techniques to use a photoswitchable fluorochrome for examining the effects of formin mutations on intercellular transport. Moreover, the main housekeeping Arabisopsis thaliana class I formin, AtFH1, relocates between the plasmalemma and several endomembrane compartments during cell division and differentiation in root tissues, with transient tonoplast localization at the transition/elongation zone border. However, it is unclear whether the tonoplast-localized AtFH1 performs any biologically relevant function or whether is merely briefly occurs at the tonoplast en route towards vacuolar degradation. We shall present observations suggesting that both possibilities are mutually compatible: while mutational loss of AtFH1 affects tonoplast organization, the formin also enters the vacuole lumen. Another Class I formin, AtFH5, also enters the vacuole via an autophagic pathway under certain conditions and contributes to specific stress resistance. We propose a model where class I formins may serve as “active cargoes” of membrane trafficking, i.e. membrane-embedded proteins that modulate the fate of membrane compartments they reside on.
This work has been supported by the Czech Science Foundation grant 22-33471S.


Metabolic acclimation: compensation or thermal stress?

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Metabolic acclimation: compensation or thermal stress?

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Metabolic profiling of muscle performance changes in the Atlantic king scallop, Pecten maximus, to ocean warming and acidification

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