Belgium

Understanding the mechanisms that mediate fish responses to the climate change stressors of high temperature and hypoxia is crucial for identifying environmental thresholds and implementing effective conservation and management strategies. Studies have examined the effects of hypoxia on fish upper thermal tolerance and cardiorespiratory physiology. In contrast, in this study, we fitted 10o C-acclimated Atlantic salmon (Salmo salar) with blood flow probes, placed them into respirometers, and measured their cardiorespiratory response to decreasing water oxygen levels (5% air sat. every 15 minutes) at 10o C and after temperature was first increased to 14 and 18o C overnight. No clear critical oxygen threshold (Pcrit ) was identified at 10o C, and the % air sat. at which the salmon went bradycardic was 42.4. Whereas values for Pcrit  and the oxygen level at which bradycardia were initiated in 14 and 18o C fish were 52.1 vs. 57.2 and 61.0 vs. 77.1, respectively. Fish at 10o C lost equilibrium (LOE) at 21.0 % air sat. vs. 27.5 at 14o C and 41.9 at 18o C. Interestingly, their LOE was inversely related to heart rate (fH , 29.1, 36.6 and 42.8 beats min-1  at 10, 14 and 18o C, respectively), and it was the inability of salmon at 18o C to increase stroke volume when fH  fell, and to increase blood oxygen extraction (MO2 /Q; which was much higher in normoxia at 18o C), that limited hypoxia tolerance. These data are consistent with recent studies which show that higher fHs  are detrimental to hypoxia tolerance, whereas the heart’s pumping capacity and increases in MO2 /Q are critical.

SEB Conference 2025

Constraints on Cardiac Pumping Capacity and Tissue Oxygen Extraction, Not Heart Rate, Limit Hypoxia Tolerance of Salmon at Warm Temperatures

cardiophysiology

atlantic salmon

warming

hypoxia

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SEB Conference 2024

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This research examined the cardiac thermal tolerance of Nile tilapia across different levels of biological organization to better understand the heart’s role in determining fish thermal tolerance.  First, we performed critical thermal minimum and maximum tests (at 2℃ h-1 ) on 25℃-acclimated adult tilapia (~ 350 g) fitted with Transonic®  flow probes [to measure cardiac output (Q) and heart rate (fH )] until the loss of equilibrium (LOE), which occured at ~9.5 and 40.5℃, respectfully. Given that these fish relied predominantly on fH  to modulate Q, and that LOE occurs due to the loss of homeostasis at the tissue/cellular level, we then measured cardiac electrocardiograms and electrical conduction in isolated hearts from fingerlings (<10 g) to acute changes in temperature (±0.5℃ min-1 ) until they experienced AV block. Cardiac failure in vitro occurred at ~ 14 and 38℃, respectively, suggesting that isolated hearts had a constrained thermal window (by ~22%). Futher, tilapia studied in vitro had: 1) higher values for both minimum and maximum fH  (by 61 and 17%, respectively); 2) a similar absolute scope for fH  (i.e., 115.5 beats min-1  in vitro vs. 110.7 beats min-1  in vivo); and 3) a temperature at maximum fH  that was 5℃ lower than in vivo. Collectively, these data suggest that while fH  (pacemaker function and electical conductance across the AV junction) largely determine the survival of tilapiain vivowhen exposed to acute changes in temperature, other important cardioprotective mechanisms (e.g., hormonal modulation and cholinergic tone) are crucial to preserving cardiac function.

Getting to the Heart of Things: Does Heart Rate Determine the Thermal Tolerance of Nile Tilapia (Oreochromis niloticus)?

In tiny biological systems, the storage and release of elastic energy during ultrafast movements is modulated by how structural materials deform in space and time. Trap-jaw ants deform their springy head capsules, a geometrically complex 3D structure, to power mandible strikes ranking among the fastest biological movements known. Visualizing deformation of these tiny, curved exoskeletons is challenging, requiring imaging tools to resolve micron-scale deformations across millimeter-scale structures (~2 mm, anterior–posterior) of strikes occurring in ~70 µs. To address this, we developed an ultra-high-speed Fourier light field microscope (FLFM) optimized for capturing real-time deformation of the trap-jaw ant head capsule with high spatial and temporal resolution. Our FLFM integrates an ultra-fast sensor (Photron E980S, achieves 1 MHz+ fps) with 3-6 array lenses to capture unique perspectives of the ant head capsule at 100,000 frames per second. White paint speckled on the ant heads provided optical features tracked using optical flow with sub-pixel precision in each perspective. A calibrated model of the optical system was then used to compute the 3D motion of the dots from the flow vectors. We resolved z-axis (in and out of the ant head capsule) recoil displacements averaging 33.3 ± 11.4 µm with a standard error of 2.5 μm— the first time such dynamic and distributed elastic recoil has been fully quantified in an ultrafast biological spring-latch system. This modular hardware and software approach can be adapted to other small-scale, high-speed systems, offering a new workflow for integrating high-speed imaging with 3D deformation analysis.

Ultrafast fourier light-field microscopy reveals 3D recoil of tiny elastic structure

The ability to live in trees is a ubiquitous adaptation in mammals, but the specific mechanisms underlying the evolution of arboreal locomotion are variable among groups. For example, primates evolved in an arboreal context and acquired unique traits such as opposable first digits and nails instead of claws, which are still shared by the majority of extant species. However, the initial function of these specificities are still unclear. Studying the biomechanics of movements and forces exerted by the autopods during arboreal locomotion in primates and other arboreal mammals provides insight into the impact of the arboreal lifestyle on their morpho-functional adaptations. Here we developed an innovative force sensor technology that mimics the morpho-functional adaptation of distal pads of arboreal mammals. This patented technology measures the direction and intensity of contact forces, with a spatially resolved and dynamic resolution. Its design enables to make sensors of variable shapes and sizes and can be used in natural environments. We designed a version of this system in the shape of a branch to study the biomechanics of grasping during arboreal locomotion in various mammals in zoological parks. These data will notably allow to elucidate whether nails of primates allow them to apply more force compared to the claws of other mammals, by quantifying for the first time the variation of forces exerted by the different anatomical regions of the phalanges in those species. This technology and experimental methodology have multiple applications, ranging from biomechanics to haptics, health and robotics.

An innovative force sensor technology mimicking distal pads' functional morphology to study the evolution of locomotion in arboreal mammals

In this study, a micro force plate array is proposed that can simultaneously measure the triaxial ground reaction force of each leg of a small insect such as an ant. The distinct role of each leg is crucial to understanding the ant's locomotion mechanism. Based on the interaction of each leg with the ground, the mechanical work performed by each leg and the energy consumed during movement can be calculated to elucidate the locomotion pattern that allows ants to maintain high speed with minimal energy expenditure. Previously, the ground reaction force of a single leg has been measured by a small force plate. Similarly, multipoint measurement by a force plate array are needed to measure the ground reaction forces of all feet simultaneously. However, conventional strain gauge-type force plates require large strain bodies, and their mechanical structure makes the implementation of multipoint force plates difficult. In addition, a biaxial micro force plate array using MEMS (Micro Electro Mechanical System) technology for measuring the ground reaction forces of ants has recently been proposed. However, the fabrication process was complex, and it is difficult to array densely. In this study, a triaxial micro force plate array utilizing the sampling moiré method, a camera based displacement measurement technique, and a prism was fabricated and evaluated. Using the fabricated device, the ground reaction force of each leg of Camponotus japonicus was measured, confirming that the device is capable of measuring triaxial ground reaction forces simultaneously.

Simultaneous measurement of triaxial ground reaction forces on a walking ant's legs.

A bird’s beak has several functions, from feeding and drinking to singing, leading to a compromise in morphology. Adaptive evolution in relation to feeding ecology is an important driver in beak shape and size. To crack hard seeds, several species evolved a strong beak. Singing on the other hand is an important factor in sexual selection. Females usually prefer more complex songs and high trill rates, reached by fast beak movements. This leads to a trade-off between strong and fast beaks. The biomechanical principles underlying this force-velocity trade-off are, however, still unclear. In a first step to fill this knowledge gap, the anatomy of the jaw muscles was compared for a series of estrildid and fringillid finches varying in beak morphology and singing capacities. Using manual dissections, muscle fascicle lengths were measured and physiological cross-sectional area (PCSA) was calculated. Fascicle length and PCSA indicate the specialization of a muscle in either speed or force. As expected, the closing muscles are well developed in the strong biting species, but the imbalance with the opener muscles also increases. Conversely, for fast singers, a smaller imbalance between opening and closing is expected to facilitate singing. The weak correlations between metrics for singing performance and muscle architecture indicate that other factors are more important in determining song trill rates.

Need for speed: are jaw muscle fascicle length and PCSA different in species varying in singing capacities?

Seahorses and pipehorses exhibit prehensile capabilities, using their tails to grasp onto objects or anchor themselves. This adaptation is facilitated by unique musculoskeletal structures, including large gaps between bony plates,specialised joints, and a distinct hypaxial muscle architecture. The prehensile tail actuates through active and passive mechanisms, yet little is known about its detailed muscle organisation, muscle-skeletal attachments, and force transmission arrangement. 
This study investigates the musculoskeletal organisation of the seahorse tail using dissection, microscopic imaging, 3D reconstruction, and contrast-stained micro-computed tomography (µCT). We examine the organisation of hypaxial muscle fibres andunique organisation of parallel running tendon sheets in relation to the bony plates and vertebral column. The hypaxial muscle complex is enclosed in a thin connective tissue layer, forming a long "muscle sac"partially detached from the skeleton. Yet, its forces are transferred to the skeleton via parallel myosepta, extending diagonally over multiple segments, while the attachment architecture of the myosepta to the vertebrae and muscle sac remains unclear. 
By integrating µCT data with dissections, we visualise the muscle-tendon sheet sandwich structure, verify its attachments, and its role in controlled grasping. These findings enhance our understanding of force transmission in seahorse tails and provide insights for bioinspired robotics, particularly in semi-soft robotics and semi-flexible actuators.

Functional Morphology of Seahorse Tail Prehension: Scaffolded from Microscopical and µCT Analysis 

Evidence is becoming overwhelming that human activities are driving environmental alterations from multiple perspectives, including chemical, ecological, and physical changes. These environmental alterations can have profound impacts on animals, particularly from a physiological standpoint. However, the cognitive system of animals is highly susceptible to both external environmental influences and internal physiological states, suggesting that cognition could also be significantly affected by these alterations. Here, I present a recent set of studies on freshwater teleost fish, the most endangered group of vertebrates, exploring whether and how anthropogenic stressors affect cognition. Various chemical alterations in aquatic environments induce neurotoxicity, directly impairing cognitive function. Microplastics, although indirectly, also impair cognitive functioning. Physical disturbances, such as light pollution, influence cognitive phenotypes, especially during early development. Lastly, ecological changes, such as the introduction of non-native species, affect cognitive variability through hybridization. All these findings converge on the same conclusion: although more challenging to observe, most anthropogenic stressors significantly impair cognition in fish. These cognitive disruptions should be recognized as major contributors to fitness reduction in altered environments, as cognition governs most adaptive behavioral responses. Considering cognition in future studies will likely reveal that the impact of human activities on animals is greater than previously believed.

Fish minds in troubled waters

Low oxygen concentration in the water, known as hypoxia, occurs naturally but is expected to become more frequent and severe due to current global changes and anthropogenic pressures. Organisms can adjust to a change in their environment via plasticity, but the timing of this plasticity has been overlooked, especially in ecophysiology aspects such as cognition. Cognition, referring to the ability of animals to make decisions, is essential for successful foraging, anti-predatory responses, and many other key functions linked directly to survival. Hypoxia, for instance, may modify different aspect of cognition, like the problem-solving and/or learning/memorizing cognition, what is then crucial to study in the current context of global changes. To address this question, we exposed three groups of three-spined stickleback Gasterosteus aculeatus to different hypoxia regimes: a control group that has always been in normoxia (>90% of O2  throughout the day), a group that has always been exposed to fluctuating hypoxia (>90% of O2  during the day and 30% of O2  during the night to mimic more natural conditions), and a group that has been in normoxia until 4 months-old, and then exposed to fluctuating hypoxia. Their problem-solving and learning/memorizing cognition were assessed using a decision-making and a detour test with an increase of complexity, leading to a reward. Assessing the impact of hypoxia at different developmental stages on cognition provides important insights on the capacity of fish to deal with their changing environments, primordial for predicting the global response of an organism to environmental changes.

Does timing matter? The impact of hypoxia at different developmental stages on fish cognition

p53 is a tumour suppressor conserved from sea anemones, worms, insects to vertebrates, but is not conserved in plants. Upon limited DNA-damage, p53 induces cell cycle arrest activating the DNA repair machinery. Under excessive DNA-damage p53 induces cell death. Mutations inTP53occur in more than 50% of human cancers, indicating its importance in cancer suppression. 
Traditional p53 research involves the use of patient biopsies, (transgenic) animal models, cancer cell cultures, or tedious and expensive cell transfection experiments. While these methods collectively boosted our understanding of how p53 operates and led to identification of effective cancer treatment therapies, each approach has its own practical and ethical considerations that often limit p53 research to specialists’ groups in high-income countries.  
We have developed an alternative to animal-experimentation for the study of p53 using Arabidopsis expressing p53 under a conditional expression promoter.  
In this talk I will introduce our results demonstrating that p53 expression in plants is suitable for investigating central mechanisms of p53 regulation and function. We believe that implementing plants for p53 research will reduce animal experimentation, bureaucratic burden, experimental costs while broadening its study to under-represented countries. Importantly, this has the potential to identify novel aspects of p53 function with applications in cancer prevention and treatment.

Designing plant systems for a more efficient and sustainable investigation of p53 activity

Opportunities for increased rate of progress in the use of phenotyping have greatly been enhanced by improvements in machine-learning (ML) models for both image analytics and for time-series type analyses. These two classes of ML problems have great utility in plant phenotyping where solutions have been constrained by difficulties in generating sufficient training data. In image analytics, training data is expensive as annotation of images is labour-intensive. For this class of ML problems, transfer learning and domain adaptation concepts permit synthetic images to be converted to ‘real’ images at low cost, with these images being used to enhance the ML algorithms to identify plant parts and organs. Synthetic data from bio-physical models also has a role in ML. In our work, we use bio-physical models to train ML algorithms to invert satellite reflectance data and estimate crop traits such as crop leaf area index and biomass over time more efficiently than do benchmark naïve inversions based on brute-force parameterisation. In designing further improvements to ML models, we also apply techniques referred to as ‘physics-informed machine learning’ (PIML) which aim to further constrain the ML inversion models to behave within known biological relationships.

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Getting to the Heart of Things: Does Heart Rate Determine the Thermal Tolerance of Nile Tilapia (Oreochromis niloticus)?

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