Belgium

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 (&lt;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.

SEB Conference 2025

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

central venous pressure

tilapia

cardiac

electrophysiology

heart rate

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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.

technical paper

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Quantifying energy intake in free-ranging fish is crucial for understanding the mechanisms that drive foraging, growth, and reproduction. However, because direct observations of feeding are difficult in highly mobile species living in the open ocean, estimating their energy intake in the wild is extremely challenging. In homeotherms, digestion-induced heat production leads to an increase in body temperature, which is known as the Heat Increment of Feeding (HIF). In tunas, which are regionally endothermic, HIF has been observed using internal temperature sensors in electronic tags. Previous studies demonstrated that energy intake can be estimated based on HIF in species such as Pacific bluefin (Thunnus orientalis) and skipjack tuna (Katsuwonus pelamis). However, no studies have explored the applicability of this method in yellowfin tuna (T. albacares). This study aimed to quantify the relationship between food consumption and HIF in yellowfin tuna. We conducted feeding experiments in an offshore sea cage in Japan in February and November 2024 using a total of 40 archival tagged fish. We found that the extent of HIF of yellowfin tuna significantly increased with the amount of food provided. Using a mixed-effects model with accounting for individual variation, we established the equation to estimate energy intake based on HIF. We applied this method to archival tagging data from yellowfin tuna collected in the Eastern Pacific Ocean to demonstrate its application for estimating energy intake in the wild.

Inferring energy intake of yellowfin tuna (Thunnus albacares) based on the heat increment of feeding

Understanding the upper thermal tolerance thresholds of animals is an important component in predicting their responses to anthropogenic climate change. Methodology for testing this in fish is well established, with the temperature at which loss of equilibrium (LOE) occurs defined as the critical thermal maximum (CTmax). The effect of rapidly increasing temperature on heart rate has been investigated in Mytilus mussels, with Arrhenius break point temperature and flatline temperature identified as key indicators of thermal tolerance. While valuable, these are extreme end point measurements that do not allow assessment of the behavioural mechanisms mussels use to cope with increased thermal stress. Currently, there are no widely used behavioural indicators of thermal tolerance limits in mussels. Here, we investigated the effects of rapidly warming temperature on valve gape behaviour and heart rate in two lineages of Mytilus currently inhabiting the Australian coastline: native M. planulatus and hybrids of M. planulatus with invasive M. galloprovincialis. By concurrently measuring heart rate and valve behaviour under rapid warming, we assess if these parameters are important behavioural mechanisms for bivalves under thermal stress and if variation exists between mussel lineages. Our results provide insight into how Australian Mytilus populations will be affected by climate change in an ocean warming hotspot.

Thermal tolerance of native and hybrid Australian mussels: implications under a warming climate

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.

Soft robots are made from flexible, deformable materials that allow for gentle and adaptive interactions with their environment. They are often inspired by biological organisms to overcome specific challenges that conventional, rigid robots face. One of these challenges is operating in environments that are inaccessible or unsuitable for electronically controlled robots. However, most soft robots can still only walk in a straight line, without any mechanism to steer them. We present an approach inspired by Bos bison to steer a soft quadruped robot. By analysing a large video dataset of free-ranging American bison, we found that they bend their spines laterally while walking in curves and applied these findings to our recently developed quadruped soft walker with parasagittal gait. We manoeuvred the walker around various obstacles and tested it for speed, load bearing capacity, and stability. Our results show how lateral bending can be used to steer quadruped robots. Although the robot can already carry more than 300 g, our analysis also suggests additional factors that contribute to steering in heavy animals, which we plan to implement. We expect our work to be a starting point for more sophisticated steering mechanisms for electronics-free, pneumatic soft robots.

Making it turn: Applying bison kinematics to soft robots

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 

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

Breeding for resilience to climate change requires considering adaptive traits such as stomatal conductance and growth responses to environmental conditions, but these traits are difficult to select for. 50 years of maize breeding increased yield two-fold in dry fields, but affected neither stomatal conductance nor growth sensitivity to drought, in opposition to plant architecture that was improved with generations of selection. Stomatal conductance measured indoor was nevertheless positively related to grain yield, but in fields with favourable conditions only.  Plant architecture had a positive effect in all conditions. Hence, selection for yield probably favoured traits that positively affect yield regardless of environmental conditions, such as plant architecture, but not traits with unstable effect on yield. New methods of selection are therefore required to improve these traits. Robotized indoor phenotyping allows measuring them at high throughput for speed breeding, but is often considered as non-relevant for field conditions. We show that adaptive traits can be inferred in different fields, based on genotypic values obtained indoor and on environmental conditions in each considered field. The modelling of environmental effects allowed translation from indoor to fields, but also from one field to another field. Indeed, values of considered traits matched between indoor and field conditions. Genomic prediction resulted in adequate ranking of genotypes for the tested traits, although with lesser precision for elite varieties presenting reduced phenotypic variability. Hence, it distinguished genotypes with high or low values for adaptive traits, conferring either spender or conservative strategies for water use under future climates.

Can phenomics allow novel breeding approaches for traits involved in tolerance to climate change ?

Photosynthesis phenotyping under future field conditions: the role of CO₂ and light competition.

The ability of plant organs to sense their local curvature and driving the progressive establishment of organ straightening is known as proprioception. This is a key mechanism in achieving correct shape and regulating the growth dynamics in combination with gravisensing and light perception. In this study, we aim to explore molecular players driving proprioception inArabidopsis. Previous experiment using myosin-XI mutants suggested a role of actin in this process. The proprioceptive insensitivity in this mutant could be either due to the disruption of their cargo function or due to the modification of tension in actin cables. To explore the role of actin filaments we analyzed actin network with confocal microscopy. In wild type, during the gravitropic-upward-curving-phase, these long actin bundles deviate from their straight-alignment and become wavy. During the de-curving-phase, these actin bundles regain their straight configuration. Then we produced RNAi-villin plants where actin configuration was specifically altered in fibre cells in stem. Using computational phenotypic tool, these lines appeared to be insensitive to proprioception confirming the importance of actin filament in controlling plant posture. We are exploring the actin configuration in both mutants and how it could modify the growth pattern and auxin action during plant movements.

Exploring the Dynamics of Actin Networks and Auxin signalling in proprioception process in Arabidopsis

As climate change intensifies throughout the 21st  century, droughts are expected to become more frequent and severe, posing a major threat to agricultural productivity and global food security. Innovative strategies are needed to improve water management and promote plant growth under stress conditions.This study investigates bacterial encapsulation as a novel approach to enhance plant resilience. Specifically, it evaluates the efficacy of encapsulating plant growth promoting rhizobacteria (PGPR) in an alginate-starch matrix and its effect on maize (Zea mays) under water stress. The capsules were characterised in terms of size, morphology, structural integrity and resistance to assess their ability to protect the bacteria and provide controlled release.The effectiveness of encapsulation in mitigating water stress was assessed using physiological and biochemical parameters. The results indicate that encapsulation preserved bacterial viability under drought conditions and facilitated their gradual release into the environment. Maize plants exposed to encapsulated PGPR showed increased root and shoot biomass under water deficit.In shoots, encapsulated bacteria increased metabolic activity (ETS), antioxidant response (catalase activity) and photosynthetic pigment concentration. In roots, osmolyte accumulation (sugars and proline), metabolic activity (ETS) and antioxidant response (catalase) increased. These changes contributed to improved plant adaptation to drought by promoting

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Inferring energy intake of yellowfin tuna (Thunnus albacares) based on the heat increment of feeding

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What Role Does Central Venous Pressure Play in Supporting Cardiac Function in Nile Tilapia (Oreochromis niloticus) Exposed to Environmental Challenges?