Belgium

Muscle inertia should affect the mechanical output of muscle, with its effects being greatest at larger sizes, and greater accelerations. Muscle inertia is known to affect the mechanical output of isolated muscle preparations; however, its influence during natural, whole-body movement remains unclear. In this study, forces were compared between a traditional one-dimensional massless muscle model , and a muscle model in which muscle mass was distributed along its length. Kinematic and electromyographic data were collected from twenty participants performing walking, running, hopping and sit-to-stand tasks, and muscle was geometrically scaled using factors of 0.1, 1 and 10. The results showed that muscles modelled at a scale factor of 10 exhibited significantly higher root-mean-squared errors (RMSE) in normalised time-varying forces, reaching up to 7.23% of maximum force for the vastus lateralis during running compared to a maximum RMSE of 0.31% for scales 0.1 and 1. Furthermore, tasks involving higher muscle accelerations, such as running and hopping, resulted in greater mass effects than lower-cadence activities. These mass effects were smaller than those we have previously predicted from 3D muscle models. These findings underscore the importance of accounting for muscle mass in larger muscles during rapid movements, and the need to account for complete 3D muscle deformations and dynamics when understanding muscle force and function.

SEB Conference 2025

Muscle Mass affects the scaling of Force Predictions from 1D Hill-Type Models During Human Movement

muscle mechanics

inertia

muscle mass

skeletal muscle

technical paper

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Muscle fibre type distribution may be influenced by clinical state and differs between individuals. For example, chronic heart failure patients experience a shift from fast to show fibres, while sprinters have a larger fraction of fast fibres than non-sprinters. However, in vivo changes in fibre type distribution are accompanied by alterations in other muscle properties, most notably size and strength, making it difficult to isolate their effects on movement. This challenge can be overcome using predictive simulations, which synthesize motion and control based on a performance criterion. This study investigated the impact of fibre type distribution on gait biomechanics using predictive simulations.
We simulated walking (1.33 m/s) using the predictive simulation framework, PredSim. Ninety-two muscles were each represented by a Hill-type muscle model with two motor units containing all its slow and fast fibres, respectively. The baseline model used experimentally derived physiological cross-sectional area fractions for slow and fast fibres. These proportions were then varied from 6% to 96% slow fibres to assess their effects on walking biomechanics.
Metabolic cost of transport gradually decreased (~26% in total) as the fractions of slow fibres increased from 6% to 96%. Spatiotemporal characteristics, joint angles, joint torques, and muscle coordination were similar in most conditions, excepting at the highest slow fibre fractions (>86% slow). While the latter effects were modest during walking, we hypothesize that fibre type composition may have greater impacts on more demanding tasks, such as running. Overall, these findings suggest that muscle fibre type composition meaningfully affects gait biomechanics.

Muscle fibre type distribution influences walking biomechanics: A predictive simulation study

The effects of climate change are expected to vary across aquatic habitats and geographic areas, so understanding how coldwater fish respond to warming below the species level will be essential for effective conservation and management. Brook trout, thermal generalists among salmonids, exhibit substantial phenotypic plasticity, giving rise to diverse ecotypes and life histories across their wide range, yet this diversity has not been captured in previous work on thermal performance. We investigated how brook trout from 14 populations with distinct ancestries, rearing environments, and life histories responded to thermal stress to elucidate the factors driving intraspecific variation in thermal performance. To do so, we quantified the metabolic plasticity of over 250 brook trout ranging from 46–448 mm (fork length) by briefly acclimating fish to either 15°C or 20°C in a laboratory setting. Standard and maximum metabolic rates were assessed both at their acclimated temperature and, without further acclimation, at the alternate temperature to evaluate aerobic scope under optimal and thermally challenging conditions. The differences detected in our study highlight the importance of examining thermal tolerance below the species level, as phenotypic plasticity, ontogeny, and heritable traits interact to shape resilience and the potential for adaptation in the face of environmental change.

Metabolic response to thermal change in fourteen populations of brook trout (Salvelinus fontinalis)

Genetic studies on the Arctic key fish species Polar cod, Boreogadus saida, from the Svalbard archipelago have been limited by relatively sparse sampling, primarily focusing on open-water areas with few or no fjord locations included. These studies have not yet provided conclusive evidence of genetic differentiation between Svalbard and other populations. This study therefore sought to ascertain whether a more extensive sampling program, encompassing 10 fjord stations along the north and west coast of Svalbard, could reveal functional differences on the transcriptomic level and indicate potential local adaptations, thereby providing insights into the presence of differentiated ecotypes. Thus, we conducted a RNASeq experiment along an environmental cline. The sampled stations varied from open water locations with well mixed water columns to closed, silled fjords with a strong thermocline, huge temperature differences across the water column (e.g., Billefjorden ΔT = 7 °C), and oxygen depletion in the deep-water layer (O2  < 70 % air saturation). The analysis revealed significant transcriptomic variation in response to the environmental gradient. The gene expression was primarily influenced by oceanic conditions (Atlantic or Arctic), local abiotic factors, and food availability, with primary production playing a key role in the different gene expression patterns observed between the clusters. These findings suggest local adaptation and the existence of four potential Polar cod ecotypes along the north-west coast of Svalbard and that a more detailed population-genomic analysis is essential to further explore the population structure of Polar cod in the high Arctic archipelago.

Seascape transcriptomics in Polar cod: profiling along an environmental cline

Understanding thermal physiology is critical for predicting population shifts due to climate change. During heatwaves, fish are particularly vulnerable due to increased energy demands and reduced oxygen levels in warmer waters. Current perceptions of heatwave risks often focus on short-term mortalities, neglecting fitness effects associated with sub-lethal physiological constraints.
In Atlantic salmon (Salmo salar), age at maturity, a key life-history trait, is genetically linked to aerobic scope — an essential metabolic attribute for energy allocation. Energy allocation is highly responsive to environmental temperatures, but how do different life history genotypes respond to heatwave temperatures?
First, we present a thermal performance curve for aerobic scope for juvenile salmon after acclimation. We also examine physiological differences between two vgll3 genotypes, which are linked to early or late maturation in adult salmon. We measured specific dynamic action, the metabolic cost of digestion and food assimilation, and aerobic scope of salmon juveniles at 15 and 20 °C to observe how fish manage energy expenditure as temperatures rise.
This study has significant implications for understanding the fitness of Atlantic Salmon and linking the effects of heatwaves to their life history and physiological fitness. Variation in how different genotypes respond to non-optimal temperatures allows for more accurate predictions of how populations may change in terms of genotypic structure and behaviour. This research is crucial for understanding evolutionary responses to climate change and for developing conservation strategies, both globally and within Finnish waters.

Is thermal performance during heatwaves predicted by life history genotypes in salmon?

Early life environmental conditions are key fitness determinants that can modulate the expression of morphological, behavioral, and life-history traits. The impact of early life conditions is hypothesized to be reflected at the cellular level in the length of telomeres, the protective DNA structures at the ends of chromosomes. In many animal species, telomeres shorten with age and are related to individual life expectancy. Previous studies have also showed that telomere length is partly heritable, and that this trait is also potentially influenced by parental effects and environmental conditions. The aim of this project is to assess the genetic and environmental (e.g., temperature, brood size, and breeding habitat) determinants of telomere length in Tree Swallow (Tachycineta bicolor) nestlings. Our preliminary results suggest the presence of a genetic and/or a maternal effect influencing early-life telomere length. We also found significant differences in telomere length of nestlings among broods from different females , highlighting the need for further investigation into the determinants of this variability. This project will contribute to a better understanding of aging dynamics and life-history strategies across contrasting environmental conditions.

Determinants of early-life telomeres length in Tree swallows

Climate warming is directly affecting aquatic ectotherms. In addition, aquatic animals are constantly threatened by potential infections from various pathogens. Heatwaves and warming of habitats have been associated with increases in disease outbreaks and mortality in several ectotherms, suggesting the immune system can be an important component determining climate impacts. Fish rely heavily on the innate immune system with its generalist leukocytes in fighting pathogens, cell signalling, repairing wounds and regenerating tissue. The aim was therefore to investigate how temperature affects the immune response and regeneration. We did this byin vivoimaging of transgenic zebrafish (Danio rerio) larvae, with fluorescent neutrophils and macrophages, that were incubated at either 20°C, 28°C, 31°C, 33°C or 35°C. We performed tail amputations and observed the immune cell recruitment for 12 hours and tail regeneration over three days, while maintaining the thermal treatments. Both immune cell recruitment and regeneration were strongly affected by temperature. Recruitment of neutrophils was faster and higher in recruited cell numbers with increasing temperature. Macrophages, however, showed impaired recruitment at the highest temperature. Tissue regeneration displayed a typical thermal performance curve, where 20°C showed the slowest regeneration, increasing regeneration with temperature up to 35°C, over where it declined. These results suggest that fishes might be more vulnerable to infections at warm temperatures, and it is possible that the climate change driven disease outbreaks we observe in natural populations can be partly explained by a decreased function of the innate immune response.

The effect of temperature on the immune response in zebrafish by in vivo imaging

Environmental stressors such as chemical and light pollution can have detrimental effects on the fitness of animals. One proposed link between these stressors and survival are telomeres, which play an important role in genome protection, ageing and somatic maintenance and are known to be shortened due to harsh environmental conditions. Amphibians are especially susceptible to environmental stressors because of their permeable skin and complex life cycle, characterized by metamorphosis from larvae to adults, making them an ideal model species to investigate possible effects of anthropogenic disturbance on telomere length. Therefore, we test the effects of chemical and light pollution on the telomere dynamics of the European green toad (Bufotes viridis) from larval stage until adulthood, in controlled lab experiments as well as in field studies in and around Vienna. We are developing a real-time quantitative polymerase chain reaction (qPCR) assay to analyze the relative telomere length (RTL) from DNA swabs from the larval, juvenile and adult stages. This longitudinal approach to understanding telomere dynamics of amphibians is the first one of this kind and the results will broaden our understanding about how anthropogenic disturbance acts on wildlife on a molecular basis and will therefore help to further improve animal conservation.

Telomere dynamics of the European green toad (Bufotes viridis) in the context of urbanization and pollution

Martin Becker and Stanislav Gorb
Department of Functional Morphology and Biomechanics, Zoological Institute, Kiel University, Am Botanischen Garten 1–9, D-24118, Kiel, Germany.
e-mail: mbecker@zoologie.uni-kiel.de
 
Abstract
The process of pollen release, transfer and capture is the most critical step in reproduction of higher plants and requires several steps of detachment and reattachment of pollen grains to different surfaces. As a response to their specific biotic or abiotic factors, pollen grains have developed strong variability of size, shape and surface microstructure, which affects their adhesion properties in a specific manner and contributes to the pollination syndrome of a plant. However, despite decades of research and a great public awareness, the adhesion forces have rarely been measured directly.
In the present study, we used a mass centrifugation setup with glass as a standard substrate, to characterize time dependent adhesion properties of pollen grains from four anemophilous species and compared them to the results of previous studies. Our results show strong differences in adhesion between species studied in fresh and aged state, which can be related to their respective pollination ecology. We discuss the species-specific adhesive properties of pollen grains in order to collect a broad set of quantitative data about adhesion properties of pollen grains and to understand their role in the process of pollination. The methodological aspects of the study are also discussed and centrifugation method is suggested as a standard approach for this kind of experiments.
 
Key words: adhesion, centrifugation, pollination, anemophily, plant, biomechanics

Time-dependent attachment properties of pollen grains in anemophilous plants tested by the mass centrifugation method

Autophagy is the evolutionarily well-conserved process during which cell components are degraded and recycled. One of the crucial, but poorly understood steps of autophagy is autophagic body degradation in vacuole. To this day, no enzyme involved in this autophagy stage in plants has been identified. However, vacuolar processing enzymes (VPE) constitute great candidates as they are key vacuolar enzymes that activate other hydrolases. Our team is addressing this hypothesis by conducting studies on isolated embryonic axes of white lupin (Lupinus albus L.) and Andean lupin (Lupinus mutabilis Sweet) cultured in vitro under various carbon (sugar) and nitrogen (asparagine) conditions. Sugar starvation induces autophagy, whereas asparagine (Asn) slows down autophagic body breakdown. So far, we detected a significantly higher VPE activity in sugar-starved axes (-S) than in sucrose-fed axes (+S), which was lowered in -S axes fed with asparagine (-S+Asn) and treated with autophagy inhibitors that interrupt this process at different stages. Ultrastructure observations, using a VPE inhibitor, showed an accumulation of autophagic bodies in the vacuoles of the -S axes. We performed the RNA-seq analysis and identified five transcripts of genes encoding VPE in each lupin species, within which four were most similar to the γVPE and one to the βVPE isoform of Arabidopsis thaliana. The RT-qPCR analysis revealed that only two γVPE-like genes showed higher levels of transcripts in the -S axes than in the +S axes. This may indicate that only given VPE participate in autophagic body degradation during sugar starvation-induced autophagy in lupin embryonic axes.

Study on the role of vacuolar processing enzymes (VPE) in autophagic body degradation during carbon starvation-induced autophagy

A non-destructive multi-omic approach was adopted to integrate phenome (imaging phenotyping and physiological gas exchange) and volatilome analyses (detection of Volatile Organic Compounds, VOCs) to investigate plant-plant communication in tomato (Solanum lycopersicum). A wild-type (WT) and a mutant (MT) for a gene putatively encoding for an odor receptor were analyzed. WT and MT plants (receivers) were closed in containers, together with WT plants previously subjected to water stress (emitters). The VOCs released by the emitters are supposed to function as chemical signals, enhancing defensive mechanisms (priming) of neighboring plants against future stressors. After 24 hours, a subset of WT and MT receivers was subjected to water stress to evaluate the priming effect. The preliminary analysis of phenomic data reveals differences between stressed and non-stressed plants, hindering the detection of the priming response. The Principal Component Analysis of volatilome data confirms this separation and further distinguishes between WT and MT plants. Statistical and supervised machine learning methodologies can significantly enhance the analysis of complex datasets. To this end, we are implementing models capable of identifying common latent components across -omic analyses, rigorously selecting the most informative features, improving both the interpretability and robustness of the analysis. This approach has proven particularly effective for datasets with limited sample sizes and is expected to enable the identification of potential critical biomarkers and distinctive response patterns. The innovative integration of multi-omics and artificial intelligence techniques opens new avenues for studying plant communication while advancing both fundamental knowledge and applied research strategies.

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