Belgium

Animals exhibit escape behaviours as a defence against predators. In this study, we investigated the escape behaviour of mosquitoes when threatened by hosts such as humans and other animals. While previous studies have examined escape behaviours in various animals, most have focused on two-dimensional stimulus-response relationship, overlooking the complexity of three-dimensional behaviours. To address this gap, we developed a mosquito-swatting robot and an experimental arena where both the direction of the stimulus and the mosquitoes’ initial position can be controlled in three-dimensional space. Using this setup, we observed the mosquitoes’ three-dimensional and anisotropic escape strategies. Our results confirmed that the swatting robot effectively induces the mosquito escape behaviour. Detailed observations of their escape manoeuvres revealed the critical role of leg thrust in take off and a mechanism that compensates for their inherent low manoeuvrability. Additionally, we found that the relative direction of the gravity strongly influences the time taken for mosquitoes to escape. In the case where mosquitoes collided with the robot piston during escape, acceleration was 3-4 times higher than normal, suggesting passive escape mechanism by collision. Our methodology provides new insights into mosquito escape behaviour and may contribute to novel physical control strategies for mosquito management.

SEB Conference 2025

Three-dimensional and anisotropic escape strategies of mosquito revealed by swatting robot

escape beheviour

mosquito

biomechanics

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SEB Conference 2024

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Female mosquitoes detect host odours using olfactory receptors on the flagellum of their antennae. However, it is unclear how well antenna morphology is adapted to capture odour molecules. In this study, we measured Culex pipiens antenna geometry using microscope images and performed computational fluid dynamic analyses on an idealised three-dimensional model. The flow around the antennae was used to simulate the particle motion of odour molecules, and thereby test the effect of fibrillae length on odour molecule capture rate. Results suggest that the fibrillae hinder the movement of odour molecules toward the olfactory receptors on the flagellum and increase the aerodynamic drag on the antenna. The increase of drag increases the cost of flight but may enhance sensitivity to sounds, which is important for mosquito reproduction. This finding indicates a potential trade-off between olfactory and auditory functions in mosquito antennae.

The effect of mosquito antennal morphology on odour molecule capture.

This study focuses on the wing coloration of long-distance flying seabirds, many of which exhibit a characteristic black-and-white wing pattern, with a notable tendency for black wingtips. Since black surfaces absorb more solar radiation than white surfaces, they tend to heat up, thereby warming the surrounding air. This temperature difference can affect the airflow around the wing and its wake, potentially altering aerodynamic characteristics. In this study, a 3D-printed experimental model based on a NACA airfoil was developed, incorporating an internal heater to investigate the effects of wing surface temperature variation on the surrounding airflow. Wind tunnel experiments and oil flow visualization tests were conducted to analyze how surface heating affects boundary layer properties and flow separation. The experimental setup featured a film heater embedded inside the wing, enabling continuous heating to better simulate the flight conditions of birds. The results showed that the lift-to-drag ratio improved within a specific range of angles of attack. This suggests that surface heating altered boundary layer characteristics and helped suppress flow separation. These findings indicate that optimizing wing coloration and surface heating could contribute to improving the flight efficiency of long-distance flying seabirds, and thus applicable to the development of high efficiency aircraft wings.

Effects of Wing Coloration on Flight Performance of Long-Distance Flying Seabirds

A novel biomimetic approach to understanding the aerodynamic and stabilizing functions of the barn owl’s tail is presented. A full‐size, 3D‐printed replica of a barn owl configured in a natural gliding posture with an actuated, movable tail was designed and manufactured for controlled wind tunnel experiments. Aerodynamic forces—including lift, drag, and pitching moments—were systematically measured over a range of angles of attack and tail pitches, with the results calibrated against established literature. Analysis revealed that although the tail contributes only marginally to overall aerodynamic efficiency, it plays a critical role in generating stabilizing pitching moments, particularly under small perturbations. Wind tunnel tests further assessed the tail’s effectiveness in supplying stabilizing moments, showing that for minor disturbances, tail actuation maintains pitch stability at a low energetic cost. To further elucidate the barn owl’s dynamic behavior in pitch, a simplified differential equations model was developed to simulate its response to gust-induced and other disturbances; the effects of disturbance frequency were also evaluated. Owing to the bird’s low moment of inertia, even minimal tail actuation produced significant stabilizing effects without compromising efficiency. Thus, the study indicates that pairing a low‐moment‐of‐inertia airframe (like the birds' body) with an active stability augmentation system may reduce or eliminate the need for a large horizontal stabilizer, thereby enhancing both aerodynamic agility and structural efficiency. These findings provide novel insights into the aerodynamic control strategies of gliding birds and offer promising design principles for the development of bio-inspired aerial vehicles.

Quantification of the dynamic response (pitch) of a replica barn owl (Tyto Alba) under atmospheric disturbance with an actively controlled tail.

Semi-aquatic mammals have evolved adaptations for aquatic locomotion, an activity which differs greatly from terrestrial locomotion due to the denser and more viscous medium. Furthermore, semi-aquatic species cannot fully specialise since they need to balance their adaptations to fit their needs in both environments. Mustelids provide a valuable model for studying the evolution of such adaptations, as the group encompasses a wide range of aquatic specializations. Previous studies on their skeletal limb anatomy suggest a correlation between increased robustness and the higher biomechanical demands of swimming. To meet the elevated force requirements of swimming, we hypothesize that skeletal changes are accompanied by modifications in muscle architecture, specifically an increase in force-generating potential in distal limb muscles. To investigate this, we conducted manual dissections to measure muscle mass, fascicle length, pennation angle and to calculate the physiological cross-sectional area (PCSA). PCSA and fascicle length serve as indicators of specialization for either high force generation or increased contraction speed, providing a quantitative insight into muscle  performance potential. The next phase is to link these anatomical adaptations to specific functional demands of aquatic (and terrestrial) locomotion. Future steps involve gathering kinematic data of terrestrial and aquatic locomotion in live animals and modelling these locomotor patterns. By integrating anatomical and functional data across a gradient of aquatic specialization in mustelids (fully terrestrial ferrets < infrequently aquatic minks < habitually aquatic otters), this study aims to enhance our understanding of the evolution of aquatic locomotion in mustelids and, more broadly, in mammals.

Comparative muscle architecture in (semi-aquatic) mustelids and subsequent steps to identify musculoskeletal adaptations for aquatic locomotion

Birds rely on their beak as a versatile, multi-functional tool during various behaviours. Depending on a bird’s ecology, a beak may be specialised for producing high bite forces (e.g., to break down hard food items) or fast oscillation rates (e.g., to produce elaborate birdsong). Previous studies indicated that high bite force and fast beak movements oppose one-another, suggesting a force-velocity trade-off. However, the underlying mechanisms contributing to this trade-off in songbirds have not been studied in detail. We hypothesise that the contractile properties of the avian jaw muscles, specifically their normalised rates of force rise during contraction and force decay during relaxation, are a limiting factor for maximal beak oscillation rates. To test our hypothesis, we measured the tetanic, isometric half-contraction and half-relaxation times of beak opener and beak closer muscles in a weak biting (canary) and a hard biting (Java sparrow) songbird in vitro. We observed that, in the harder biting species, both muscle types are slower in contraction and relaxation. Furthermore, within both species, beak closer muscles were slower in contraction and relaxation compared to beak opener muscles. We conclude that muscles which are adapted to high force production need more time to contract and relax compared to muscles producing low maximal forces. These findings suggest that the contractile properties of avian jaw musculature may contribute to the observed force-velocity trade-off in songbird beak movements. Our results further suggest that the muscles involved in forceful biting may contain a greater proportion of slow, fatigue-resistant fibres.

Contractile properties of jaw muscles contribute to force-velocity trade-off in beak movements of songbirds

Mammals with a cursorial lifestyle exhibit elongated distal limb bones and generally more hinge-like joints in the limbs. Elongated limbs and other cursorial traits have been shown to reduce locomotion costs, but the role of hinge-like joints has not been examined independently. Hinge-like joints stabilize the limb against sideways excursion and restrict movement to a single (parasagittal) plane. Thus, it has been suggested that this enhances locomotor efficiency, due to a reduction of required muscular joint control. However, this assumption has not been explicitly tested in relation to hinge-like joints, independent of other cursorial adaptations.
Here, we first aim to assess the hinge-like nature of elbows in mammals of various locomotor types. We will quantify the restriction to a single axis of rotation in the humero-radial joint of cursorial species by measuring and comparing the osteological range of pronation and supination. Next, we evaluate locomotor efficiency during steady-state locomotion by comparing in vivo ground reaction forces (GRF) in the same species. We expect cursorial species to exhibit relatively lower medio-lateral forces. This will indicate how efficiently GRF are channeled unidirectionally in the fore-aft direction during steady-state locomotion. Additionally, to determine whether increased hinge-like morphology corresponds to more unidirectional stresses on elbow bones, we will analyze anisotropy in the trabecular structure of the humerus, ulna, and radius. We expect cursorial species to exhibit lower anisotropy. This study contributes to the understanding of the interface of form and function in mammalian cursorial locomotion.

Do hinge-like joints really aid in more efficient locomotion?
Ground reaction forces and bone microstructure in cursorial mammals

Small birds use a distinct pattern of intermittent flight known as ‘flap-bounding’, distinguished by alternating phases of rapid flapping and tucked-wing ballistic movement. Previous theoretical and experimental studies suggest that this behaviour reduces energetic costs or regulates horizontal velocity during long flights. However, we observed zebra finches using flap-bounding even during short perch-to-perch flights. Furthermore, individuals converged on a consistent flight path with training, initiating the bound at a specific point in their trajectory. To investigate what objectives are driving this learned behaviour, we developed an analytical model of flap-bounding and applied a gradient-free optimisation method to test multiple hypothesized objectives: minimising energy, minimising flight time, minimising or maximising bounding duration, minimising bounding velocity, and minimising landing deceleration. By comparing the optimised trajectories to experimental data, our results suggest that the learned trajectory is not dictated by a single objective but instead represents a compromise among competing performance goals. While future work will refine the analytical model with more complexity, these findings demonstrate that during short flights, zebra finches choose trajectories that balance multiple, potentially contradictory, goals.

The finch formula: decoding flap-bounding tactics during flight training 

Holometabolous insects often undergo a metabolic shift as adults due to feeding cessation. In the seed beetle Acanthoscelides obtectus, which enters a post-larval starvation phase, metabolic strategies are key to survival and longevity. This study contrasts two experimental evolution lines with divergent life histories: a short-lived, early-reproducing line (E, ~7 days) and a long-lived, late-reproducing line (L, ~15 days).
Targeted metabolomics revealed significant differences in amino acid metabolism between the two A. obtectus lines. Notably, amino acid concentrations were consistently lower in the long-lived L line than in the E line across all ages, with this distinction evident as early as day 1. This suggests a sustained, higher rate of amino acid catabolism in L beetles, potentially providing an alternative energy source to compensate for reduced complex I activity and the absence of fatty acid oxidation. Furthermore, tricarboxylic acid (TCA) cycle intermediates indicated line-specific mitochondrial adaptations. Higher succinate-to-fumarate ratio observed at day 1 in L beetles suggests increased complex II activity, which could offset the lowered complex I activity. These metabolomic findings strongly corroborate previous respirometry data, supporting metabolic rewiring in L beetles that favours alternative electron entry points into the mitochondrial electron transport system.
Our results highlight that metabolic plasticity, driven by enhanced amino acid catabolism and altered TCA cycle flux, is critical for extending survival in the L line. These adaptations provide insights into bioenergetic mechanisms governing lifespan in insects and highlight how mitochondrial remodelling contributes to the evolution of different ageing patterns.

Amino acid catabolism and mitochondrial shifts support increased longevity in the seed beetle Acanthoscelides obtectus

Parasites can impair host performance through various physiological processes, including alterations to host metabolism. Since mitochondria are responsible for cellular energy production, it is likely that disruptions in host cellular metabolism contribute to changes in metabolism at the organismal level. However, some studies investigating parasite-induced alteration in cellular metabolism have been limited by the presence of parasites in the target tissues. Before analyzing these key tissues, it is critical to confirm that the measured enzyme activities reflect those of the hosts rather than the parasites themselves. Here, we tested a parasite extraction protocol to evaluate the extent to which parasite contamination impacts estimates of cellular enzyme activities in hepatic tissues of wild pumpkinseed sunfish (Lepomis gibbosus) infected with bass tapeworm (Proteocephalus ambloplitis). We tested four treatments: uninfected livers, cleaned infected livers, infected livers (repopulated) and parasites alone. We then compared the activity of key metabolic enzymes among groups. PCR tests were used to assess parasitic contamination after applying the parasite extraction protocol on hepatic tissue. Enzyme activities of cleaned livers and contaminated livers were similar even if PCR tests revealed contamination. The intensity of cestode infection also did not influence enzyme activity, which suggests that parasite presence in the livers does not impact the accuracy of the enzyme activity estimates made. Through this protocol, we show that parasite contamination has no effect on metabolism measurements showing that the study of parasitized organs is possible. We also recommend the use of this protocol to avoid any biases in highly infected individuals.

Mitochondrial enzyme activity in fish livers is not impacted by parasite presence

Pollutants drive adaptive metabolic and evolutionary responses. However, this pollution-driven rapid evolution in invertebrates, particularly its effects on metabolism and mitochondrial oxidative phosphorylation (OXPHOS), remains overlooked. Using the European green crab Carcinus maenas, we investigated: (i) whether historic exposure to cadmium induces adaptive metabolic and mitochondrial responses; and (ii) if pre-exposure to cadmium confers protection from another source of pollution, copper. Crabs were captured from the wild from one site exposed to cadmium pollution but naïve to copper and a second reference site which had no cadmium or copper. After four months of depuration, animals were exposed to either 8.2 nM cadmium, or 20 nM copper-hydrate, or clean seawater. Mitochondrial respiration in heart homogenates was measured using high performance respirometry (Oroboros). Reactive oxygen species production (ROS) and antioxidant content was measured in hemolymph spectrofluorometrically (C-H2 DFFDA) and electrochemically (BRS system), respectively. While all crabs showed similar mitochondrial routine respiration values, the historically polluted crabs had higher OXPHOS respiration, higher electron transport system capacity, and enhanced capacity of complex II (CII), accompanied by increased ROS formation and higher antioxidant defences. Exposure to cadmium or copper did not affect any of the parameters considered in historically polluted crabs. In contrast, reference animals responded with a decreased complex I (CI) and increased CII contribution. This may reduce CI-associated ROS formation while enabling detoxification and (or) other defence mechanisms. Our findings suggest that long-term metal exposure induces mitochondrial adaptations that enhance resilience to pollution, potentially facilitating the invasion success of C. maenas in contaminated environments.

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