Belgium

The radial lattice spacing (LS) of actin and myosin filaments is a fundamental determinant of muscle force generation, yet its regulation remains an open question. While the assumption of volume constancy provides a phenomenological plausibility check, it lacks a mechanistic basis for LS changes during fiber contraction. We introduce a novel model demonstrating that electrostatic repulsion between charged filaments, governed by Debye-Hückel theory, dictates LS adaptations. Under the simple assumption of energy conservation, the model predicts LS variations across sarcomere lengths with remarkable accuracy, aligning closely with experimental data and outperforming traditional volume-based models.By explaining macroscopic muscle behavior with molecular interactions, the model offers deeper insight into the physics of muscle function. The refined understanding of LS dynamics enhances predictive capabilities in musculoskeletal modeling, with implications for physiology, biomechanics, and robotics. Adaptability to different muscle types further broadens its relevance, offering potential applications in understanding pathological conditions affecting sarcomere structure or the development of targeted drugs.Providing a first-principles explanation for LS regulation, this work challenges conventional assumptions and establishes a new foundation for multi-scale muscle research, from molecular mechanisms to whole-body movement.

SEB Conference 2025

Filaments repel while muscles propel: A bio-physical explanation of lattice spacing

muscle model

electrostatics

biomechanics

technical paper

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As global warming progresses, organismal pace-of-life (POL) traits evolve in response to shifting climates. A new hypothesis states that, apart from the food digestive metabolism, the mitochondrial phenotype (efficiency and density) contributes to POL-variations across thermal regimes. We investigated the thermal evolution and plasticity of the POL and its underlying mechanisms by making use of the southward range expansion of the damselfly Ischnura elegans, from France into warmer regions of Spain. Alongside the ancestral French region, we studied two Spanish regions: a ‘new edge’ region founded 10 years ago (Salamanca) and an ‘old edge’ region founded 70 years ago (Murcia-Alicante). In a common garden experiment, larvae and adults from all regions were exposed to French and Spanish summer temperatures. Our results confirmed that the old edge region evolved a faster POL than the ancestral region when exposed to Spanish temperatures. As hypothesized, the old edge individuals had higher mitochondrial and digestive efficiencies supporting their evolved fast POL. Additionally, the larvae and adults showed higher mitochondrial densities, further sustaining this pace. In contrast, the new edge region showed unexpectedly maladaptive traits, exhibiting a slower POL than the ancestral region when exposed to Spanish temperatures. These individuals increased their food intake, likely prioritizing energy allocation toward repair mechanisms to cope with thermal stress. Our findings suggest that the traditional POL framework, which links food intake to fast POL traits, may require refinement as we show for the first time that the mitochondrial phenotype is a driver of the POL during thermal evolution.

Energized and efficient: digestive efficiency and mitochondrial phenotype underlie the rapid evolution of a faster pace-of-life in a range-expanding species

Environmental temperature affects organisms’ physiology, behaviour and reproduction with costs for fitness and survival. Under climate change, extreme weather events are predicted to increase in frequency and intensity, yet it is not well known how organisms adjust to these rapid variations. Short-term fluctuating temperatures can alter an endotherms’ thermoregulatory capacity, which can be influenced by energy metabolism. On the organismal level, metabolic rate can vary with rapid temperature variations, especially outside the thermoneutral zone, and at the cellular level, mitochondrial function adjusts to meet energy demands. We investigated if repeated exposure to short-term thermal fluctuations can hinder or alleviate metabolic costs of responding to cold temperatures. To achieve this, wild great tits (Parus major) were caught in late autumn and separated into three groups: control, heatwave, and cold spell. First, all birds were kept in a controlled ambient temperature (16°C). Birds in the heatwave and cold spell groups were then subjected to three short-term temperature fluctuations (for 48 hours, 7 days apart), with temperature increasing or decreasing by 10°C from the ambient temperature. Overnight whole-body metabolic rate (basal metabolic rate and metabolic rate below thermoneutrality) and mitochondrial function were assessed at the beginning and end of the experiment. Additionally, after the first wave, daytime metabolic rate was measured below thermoneutrality to study immediate changes. The results of this study could provide insights into how animals can cope with increased climate instability, by investigating the responses to temperature fluctuations and capacity for metabolic plasticity, at both the whole-body and cellular level.

AThe impact of short-term temperature fluctuations on whole-body metabolism and mitochondrial function

Climate change-induced heat waves significantly threaten biodiversity by disrupting critical behaviours, such as parental care, essential for offspring development and survival. While parental care can buffer offspring against environmental stressors, its components may respond differently to heat stress. In this study, we investigated how elevated temperatures affect parental care and its buffering role in reproductive performance in the burying beetle Nicrophorus nepalensis across critical life stages. Using experimental warming, we tested the effects of mild (20°C) and severe (22°C) heat stress, compared to ambient temperatures (18°C), on pre-hatching care (carcass preparation) and post-hatching care (offspring provisioning). Severe heat stress completely inhibited egg hatching, whereas mild heat stress reduced brood size and offspring weight. Reciprocal experiments, where carcasses prepared under ambient and heat-stressed conditions were exchanged between breeding females, revealed that heatwaves affecting only one care period did not significantly alter reproduction. However, when both pre- and post-hatching periods were exposed to heat stress, reproductive success declined sharply. Females breeding under heat stress exhibited higher energy expenditure, shown by greater body mass loss during provisioning. Notably, heat stress had long-lasting effects on offspring through carcass preparation, resulting in smaller adult sizes and higher mortality rates. These findings demonstrate that different parental care components respond variably to heat stress, with cascading effects on offspring development. This study highlights the importance of assessing parental care behaviours and their interactions across life stages to better understand species' vulnerability to rising temperatures.

Heat stress shapes parental care and reproductive success in burying beetles across critical life stages

Understanding how heat stress affects performance and reproductive fitness is essential for predicting the fate of species and populations. Our aim was to test phenotypic and reproductive responses to a heat wave in zebrafish (Danio rerio), and the potential role of DNA methylation in mediating these responses. We exposed wild-type and DNA methyltransferase 3a (DNMT3a) knock-out fish to a control temperature (25°C) and a +5°C heatwave for 28 days. Zebrafish acclimated to compensate swimming performance for warming. After re-acclimation at 25°C, the swimming performance of the heatwave-treated fish returned to pre-warming levels, indicating that thermal acclimation in adults is reversible. DNMT3a knock-out altered responses to heating, identifying DNA methylation as a mechanism underlying acclimation. Heatwave and genotype interacted to reduce the number of fertilised eggs produced (at one-tailed significance). Heating reduced offspring survival in wild-type fish, and survival was further reduced in DNMT3A knock-out fish. Our data show that despite acclimation compensating for heating, there was a reduction in reproductive success. Warming and disruption of DNA methylation by anthropogenic factors therefore can reduce fitness and potentially impact population size.

A heat wave induces compensatory acclimation of performance but reduces reproductive fitness

The characteristic buzz of bees, produced by their indirect (thoracic) flight muscles, has been extensively studied in the context of flight. In particular, many studies have investigated how the wingbeat frequency is influenced by abiotic factors such as air density, temperature, and humidity but is primarily constrained by biomechanical factors such as resonance of the thorax and the need to generate lift. However, these same muscles also produce vibrations in non-flight contexts, including communication, defence, and buzz-pollination. During these behaviours, the wings are decoupled from the system, providing a more direct route to assessing the determinants of muscle contraction frequency. Interestingly, mass-dependence is absent in non-flight buzzing, suggesting that other factors dominate when the wings are removed from the system. Here, we summarise multiple experiments on wild and lab-reared bumblebees to explore these factors. In particular, we demonstrate the role of thorax temperature in determining muscle biomechanics, and show that exposure to heavy metals, which interfere with calcium signalling, can reduce contraction frequency. We highlight that studying non-flight vibrations in bees provides valuable insights into asynchronous muscle function, offering a rich avenue for future research.

What determines the pitch of a bee's buzz?

Freshwater ecosystems face growing threats from chemical pollution and climate warming. However, their combined effects on freshwater invertebrates remain poorly understood, particularly the mechanisms linking (sub)individual responses to broader ecological impacts.
To fill this gap, we assessed the effects of environmentally realistic concentrations of pharmaceutical contaminants (PhACs) and warming on freshwater invertebrates in outdoor mesocosms. We explored the physiological responses of Asellus aquaticus (Isopoda) and Cloeon dipterum (Ephemeroptera) in winter and summer, revealing seasonal differences in sensitivity: in winter, PhACs reduced energy availability and increased oxidative damage, while in summer, they boosted energy levels but reduced the population size. These physiological and population-level changes translated into ecosystem-level effects, including reduced leaf litter decomposition and altered insect emergence.
Building on these findings, we investigated the effects of a PhAC-and-pesticide mixture and warming to examine how sublethal effects of environmentally realistic pollutant mixtures cascade to population and ecosystem levels. Preliminary insights suggest that interactions between chemical stressors and warming drive unexpected shifts in zooplankton population size and structure, reinforcing the need to move beyond mortality-based assessments toward more ecologically relevant endpoints.
Our results highlight the vulnerability of aquatic invertebrates to warming in combination with low levels of pollution, demonstrating cascading impacts from individuals to ecosystems. These findings emphasize the need for integrative approaches to assess and mitigate the ecological consequences of emerging contaminants in a changing climate.

Sublethal Yet Significant: How Pollutants and Warming Impact Freshwater Invertebrates and Ecosystem Functioning

Foundation models have revolutionized artificial intelligence by providing versatile, pre-trained architectures that can be adapted to various downstream tasks. In the realm of plant biodiversity, Pl@ntNeth as emerged as a large-scale, AI-driven plant identification system. In this presentation, we investigate the potential of using Pl@ntnet as base for various computer vision tasks beyond species identification, combining it with generalist foundation models positionned upstream or downstream in the pipeline to enable zero-shot possiblity. We test our method on publicly available datasets and which allow comparison with existing supervised and other zero-shot methods.

Pl@ntNet as a foundation model

Photosynthesis is the workhorse for growth of all crops and is one of the key targets for improving agricultural productivity. Its efficiency differs both between and within species, with responses intensively measured under varying CO2  concentrations and light intensities (represented by A-Ci  and A-Q curves). While many published kinetic models of photosynthesis were used to simulate photosynthetic response and to propose different hypotheses, their kinetic parameters were collected from literature or estimated in different species. Yet, the differences in kinetic parameters of enzymes involved in photosynthesis between different genotypes are not fully explored. Moreover, photosynthetic traits are the integrated outcome of genetic factors, environmental conditions, and their complex interactions that renders their accurate prediction from genetic markers challenging. To address these problems, we parameterized a kinetic model for C4  photosynthesis allowing accurate simulation of A-Ci  or A-Q curves measured for 68 inbred lines from a maize population grown in two seasons. The genotype-specific kinetic parameters were then used to train a machine learning model capable of predicting parameter values for genotypes with only genomic data available. The predicted parameters were used to simulate photosynthesis for unseen genotypes and seasons by integrating environmental conditions. The photosynthetic rates simulated at saturating light using our approach, KineticGP, outperformed the predictions of baseline genomic models for unseen genotypes across seasons.

KineticGP, a computational framework for genomic prediction of leaf photosynthesis traits

Anthropogenic CO2  emissions are leading to rising global temperatures and increasingly extreme weather events. High vapour pressure deficit (VPD), which often occurs during heatwaves, reduces stomatal opening, which could negate crop photosynthetic gains associated with higher atmospheric CO2  concentrations. Studying the interactive effects of increased CO2  and VPD using free-air concentration enrichment (FACE) under field conditions is challenging due to technical difficulties associated with regulating temperature and moisture content. To bypass this limitation, we conducted high-VPD (3.14 kPa) heatwave experiments on spring wheat (Triticum Aestivum) at high temperatures (37 °C) and low relative air humidity (50%) in climate-controlled growth chambers set to ambient (450 ppm) or elevated (720 ppm) CO2  concentration.
We find that elevated CO2  concentration combined with high-VPD treatment leads to higher saturating light photosynthesis and maximum rate of rubisco carboxylation (Vcmax ), but this is also associated with much greater evaporative demand than might be expected. Transpiration and thermal profiling within chambers revealed high CO2  grown plants often had higher levels of water-flux and cooler leaves than ambient CO2  equivalent plants, and overall this resulted in higher plant water usage. Light-shift assays showed that photosynthetic performance was tightly linked with stomatal performance during heatwaves at either CO2  concentration, with stomatal conductance only reducing by 37-38% during complete darkness for both CO2  treatments, which could have considerable implications for future water-use efficiency. Together, our results highlight that high CO2  and rising VPD together could aid photosynthetic performance, but this will be at the expense of higher water usage.

Saving FACE: Utilising growth chambers to study rising CO2 concentration and VPD impacts on wheat photosynthesis and water usage

Research on the photosynthetic response to environmental factors is mostly centred on light energy capture and carbon assimilation. Our understanding of how environmental factors impact photosynthate consumption (sink activity), and how these changes in sink activity affect the photosynthetic response is more limited. At the leaf level, consumption of photosynthates and sink limitations are usually quantified in terms of triose phosphate utilization (TPU). A big limitation to understanding the role of sink limitations on the photosynthetic response to environmental factors is the time-consuming steady state measurements needed to quantify TPU. Here, I present multi-species evidence supporting the Dynamic Assimilation Technique (DAT) as reliable and accurate non-steady state approach to the quantification of TPU and other biochemical limitations. I will further discuss the potential of using DATs approaches to estimate TPU proxies under 60 seconds using abrupt changes in CO2  concentrations. Field research suggested that the seasonal dynamics of carbon assimilation extend beyond concurrent environmental factors,  and sink activities strongly interacted with plant development to  ultimately limits photosynthesis. As we integrate multiple environmental factors in control environment experiments, plants’ internal carbon balance remains challenging to control and a potential source of variation. Experimental manipulation of sink strength in control environments suggested cross-level response in plant development, carbon partitioning and carbon assimilation. Results call for further consideration of carbon balance and sink limitations in photosynthetic research, and the development of rapid methods for leaf-level sink activity quantification.

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Energized and efficient: digestive efficiency and mitochondrial phenotype underlie the rapid evolution of a faster pace-of-life in a range-expanding species

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PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES

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