Belgium

Artificial light at night (ALAN) is increasingly present in both terrestrial and aquatic systems and has been found to influence physiological and behavioural traits in wild animals in a range of habitats. In coral reef ecosystems, increasing human pressure often leads to more coastal infrastructure and boat traffic, resulting in an increase in ALAN exposure for reef organisms. Here, we aimed to investigate the effects of chronic ALAN exposure on social behaviour and risk-taking in a gregarious coral reef fish, Dascyllus trimaculatus. Wild fish were collected from sites containing both ALAN-exposed and control (ambient light levels) anemones around Moorea, French Polynesia. Fish underwent a three-chamber shoal choice test to assess diurnal sociability, followed by an emergence test to assess diurnal risk-taking behaviour. Activity levels were measured during both tests. No effect of ALAN exposure was found on daytime social behaviour or activity level. ALAN-exposed fish were, however, found to take less time to emerge from an anemone after a chase stimulus compared with control fish. The differences in risk-taking may be due to direct effects of ALAN exposure on risk-taking behaviour, or selective mortality of more risk-averse individuals, both potentially driven by increased nighttime activity levels during ALAN exposure. Increased nighttime activity may lead to increasing metabolic needs, driving increased risk-taking, or could lead to more risk-averse fish facing an increased risk of starvation or reduced growth. Our study adds to the existing literature and provides the first evidence that chronic ALAN exposure increases risk-taking behaviour in a marine fish.

SEB Conference 2025

Effects of artificial light-at-night on the diurnal risk-taking behaviour of a gregarious reef fish

reef fish

fish behaviour

artificial light-at-night

coral reef

pollution

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Deforestation has drastically reduced natural roost sites for European bats, with artificial roost boxes being a common conservation measure. However, concerns arise regarding the potential overheating of artificial roosts, particularly during summer heat waves. Female bats roosting in summer maternity colonies are especially vulnerable due to the hotter and more humid conditions compared to solitary males. This study investigated sex and seasonal differences in heat tolerance and evaporative cooling capacity in four species of vespertillinoid bats. Using indirect calorimetry and thermometry, we measured thermoregulation at air temperatures (Ta ) ranging from 28 to 48°C during spring (male bats only, females in reproductive phase) and summer (both males and females). Contrary to predictions, there were no sex differences in maximum Ta  tolerated or evaporative cooling efficiencies. While there were also no seasonal differences in maximum Ta  tolerated, male bats unexpectedly had lower maximum cooling efficiencies during summer compared to spring. Moreover, there were sex and seasonal differences in the patterns of increasing evaporative heat loss (EHL) with increasing Ta . Female bats started increasing EHL at higher Ta  than males during summer, and male bats increased EHL more gradually with rising Ta  in summer compared to spring. These differences in heat-dissipation strategies suggest potential adaptations for enhanced water conservation under hotter and more humid conditions, at both sex and seasonal levels. Using roost temperature and EHL data, we estimated daytime evaporative water costs of bats using artificial roosts, revealing that small bats are already at risk of lethal dehydration during present-day heat waves.

Seasonal and sex differences in the thermoregulatory responses of European vespertilionid bats at high air temperatures 

Temperature is a key environmental constraint on insect population size and distribution, and a crucial factor limiting establishment and spread of invasive species. For most insects, cold exposure results in progressive loss of ion balance dependent on both exposure duration and intensity. This ionoregulatory collapse, characterized by extracellular hyperkalemia, causes cell death, tissue damage and eventually death. However, unlike these chill-susceptible species, recent work shows that truly cold hardy insects (e.g. freeze-avoidant mountain pine beetle larvae) only partially lose ion balance during severe cold exposure and maintain extracellular [K+ ] just below lethal cellular limits. Whether this is a common capacity amongst cold-hardy species is unknown, as are the mechanisms behind this phenomenon. Asian longhorn beetle larvae (Anoplophora glabripennis; ALB) are a destructive invasive forest pest that accumulates cryoprotectants and becomes partially freeze-tolerant in winter. We tested whether cryoprotectants can increase cold tolerance by acting as osmoprotectants that mitigate cold-induced ionoregulatory collapse. Specifically, we explored the ability of this species to maintain ion balance in the cold by measuring hemolymph ion concentrations (e.g. Na+ /K+ ) and cryoprotectants during a prolonged cold stress. ALB larvae lab-reared on artificial diet were sampled at multiple time points during cold exposure at temperatures approaching and beyond their freezing point to measure hemolymph osmolality and ion and cryoprotectant concentrations. Results from this study suggest that ALB have an ability to prevent ionoregulatory collapse in the cold, and by extension that such an ability may be a pre-requisite to evolving freeze tolerance or freeze avoidance in insects.

Keep an ion it! Prevention of cold-induced ionoregulatory collapse in the freeze-tolerant Asian longhorn beetle (Anoplophora glabripennis)

Most insects, including Drosophila melanogaster, suffer from a progressive loss of ion and water balance that causes cell, and ultimately organismal, death. This ionoregulatory collapse has been linked to temperature-induced reductions in membrane-bound transporter activity (e.g. Na+ /K+ -ATPase, H+ -ATPase) in the renal system. Cold acclimation can improve low temperature tolerance and is associated with an increase in water and ion transport rates in the Malpighian tubules (analogous to kidneys) of cold acclimated flies, but a paradoxical reduction in the activity of ATPases in the same tissues. This raises questions about whether the current models of ion transport apply to cold-acclimated insects, or if modulation by other mechanisms, such as membrane structural reorganization allow for improved renal function in the cold. Here, we report the results of transcriptomic sequencing of the anterior Malpighian tubules of warm and cold-acclimated flies before, during, and after a cold stress. We used these results to construct gene networks, using a weighted gene correlation network analysis method. These results link networks of genes to specific traits and suggest that physiological state of tubules before a cold stress is more important to preventing downstream injury than a short-term response to chilling. They further suggest that cold acclimation elicits a tissue repair response in tubules during recovery, as opposed to an immune response seen in warm acclimated flies. Together, these findings allow us to generate hypotheses on how cold acclimation allows insects to adjust their cold tolerance.

Networking in the cold: connecting renal transcriptional plasticity to chill injury prevention through gene network analysis.

This study aims to create an autorotating winged aerial vehicle inspired by the samara fruit of the Dipterocarpaceae family. The samara fruit of Dipterocarpaceae can fly through autorotation after detaching from a branch. Its design may be optimized to carry more nutrients and achieve longer flight durations. Therefore, in this study, we attempted to optimize the wing shape for maximum thrust and flight duration using QMIL, a propeller design software developed by Dr. Mark Drela, and compared it with the actual wing shape of the samara fruit. A genetic algorithm was employed as the optimization method. PyAutoGUI in Python was used for the automated execution of the genetic algorithm and QMIL. The lift coefficients at 0%, 50%, and 100% positions from the wing root were used as optimization parameters. As a result, we confirmed that the propeller shape maximizing thrust and flight duration closely resembled the wing shape of the Dipterocarpaceae samara fruit. According to this result, we plan to develop an autorotating winged aerial vehicle based on the calculated optimal design.

Optimal Wing Design for Autorotating Aerial Vehicle Inspired by Samara Fruit of Dipterocarpaceae Family

The wing tips of birds are formed by a series of primary feathers. When birds such as raptors are gliding, their primary feathers spread vertically and horizontally, and form slotted wing tips. Although the wing tip slots have been proposed to improve aerodynamic performance, the effects of the three-dimensional angles of the feathers and the advantages of wing tip slots remain unclear due to the high degrees of freedom feather positioning at the wing tip. In this study, we modeled the bird wings as a set of rectangular wings, following previous experimental studies, and evaluated their aerodynamic performance by two- and three-dimensional numerical simulation and optimization. We compared the performance of the slotted wings with those without slots and found that the slotted wings weaken wing tip vortices, enhancing the lift-to-drag ratio. Gapped wingtips can generate aerodynamic forces near the wingtips, which are ineffective for aerodynamic force generation due to wingtip vortices in normal wings. Combined with their lightweight nature, these features have the potential to improve maneuverability. These results offer insight into the evolution of avian wing morphology and inform the design of flying robots.

Aerodynamic effects of slotted wing tips in avian flight - a numerical study

A particularly concerning group of environmental contaminants are endocrine-disrupting chemicals (EDCs) that can interfere with the endocrine system by mimicking or blocking endogenous hormones. Disruption of hypothalamus-pituitary-axes (HP-axes) can lead to serious health problems, e.g., thyroid malfunctioning (HPT-axis), interference with reproduction (HPG-axis), impaired stress response (HPI-axis), as well as (neuro)behavioural changes. As a rule, organisms are continuously exposed to multiple EDCs simultaneously, since EDCs deriving from cosmetics, packaging, pesticides, food, and other everyday products, end up in the environment. This urges the need to assess the physiological impact of EDC mixtures and to understand the mechanisms and targets affected. The zebrafish (Danio rerio) is a particularly suitable preclinical model to assess these toxicological effects for several reasons. Firstly, their rapid development can be easily non-invasively monitored due to its transparent body. Secondly, the zebrafish is a vertebrate species with a surprisingly high degree of homology to humans with respect to organ systems, physiology, genomics, and behaviour. Indeed, the model can be used to understand molecular mechanisms and targets given its fully annotated genome, ease of genomic manipulation, as well as a wide array of already available transgenic reporter lines of hypothalamus-pituitary-axes biomarkers, and well-characterised behavioural assays. Together, these provide valuable insights into molecular mechanisms and natural behaviour, survival, and reproductive success, all of which are highly relevant for understanding the impact of EDCs. In this study, we assess the impact of various EDC mixtures on the HP-axes of zebrafish from a molecular, physiological, and behavioural point of view.

Zebrafish (Danio rerio): a quick and versatile preclinical model to screen effects of endocrine-disrupting chemicals (EDCs). 

The effects of an acute exposure at sublethal concentrations to trifluoroacetic acid (TFA), a pollutant belonging to the PFAS family, were analysed using Carcinus aestuarii collected from Mediterranean lagoons presenting different levels of pollution. The goal was to evaluate crab response to pollution and potential differences based on the site of origin. Analyses of C. maenas did not show significant differences in morphometric parameters in the hepatopancreas (B-cell vacuolization rate, vacuole surface, epithelium thickness), neither between populations nor according to pollution levels. In contrast, analyses of C. aestuarii populations exposed to TFA revealed a dose-dependent effect to pollution, leading to increased mortality, altered hemolymph osmolarity, and significant histopathological changes such as gill lamellae dilations and necrotic lesions. This study highlights the negative impact of TFA on Carcinus aestuarii and underscores the necessity to implement strict environmental regulations related to PFAS to protect marine coastal biodiversity.

The effects of a PFAS (trifluoroacetic acid, TFA) on the physiology of Mediterranean green crabs, Carcinus aestuarii.

The ongoing rise in the global aging population, coupled with the excessive use of various resources, has significantly exacerbated environmental challenges, with the increased detection of pollutants in surface waters. This situation poses serious risks to aquatic ecosystems and human health. While various analytical techniques are employed in water monitoring to identify contaminants, the analytical methods employed are often inadequate for providing early predictions or to fully capture underlying mechanisms for the observed effects in the ecosystem. This limitation highlights the need for more comprehensive approaches to pollution assessment. Consequently, there is a growing support form effect-based methods that assess the responses of key species, such as daphnids, to pollutants. Daphnids are critical freshwater organisms that serve as valuable indicators of ecosystem health. In the context of New Approach Methodologies, they provide significant advantages due to their alignment with the principles of the 3Rs (Reduce, Refine, Replace) and their similar toxicity responses to more complex organisms, enhancing the application from phylotoxicological studies. Our research focuses on the impact of a range of commonly encountered pollutants, including pharmaceuticals, heavy metals, and industrial chemicals, on daphnid physiology. By integrating phenotypic endpoints, such as growth and reproduction, with metabolic fingerprints, we aim to provide deeper mechanistic insights into the actions of these pollutants. Ultimately, identifying metabolic disruptions can yield more sensitive assessment metrics, allowing us to capture the mechanisms of action more accurately. This enables timely predictions of pollution hotspots, facilitating proactive management strategies to mitigate environmental damage before it becomes irreversible.

A systems approach to understand and predict pollution 

The settleable part of atmospheric matter (SePM) produced by iron ore processing can cross-contaminate the aquatic environment. SePM is a complex mixture of particles, including metals and metallic nanoparticles, capable of causing critical sublethal damage to aquatic biota. Accordingly, this investigation analyzed the potential damage of multiple SePM levels (SL - 0.0, 0.095, 0.171, 0.309, 0.556, and 1.0 g·L-1 , 96 hours) to the early development of fish using a highly representative toxicological model, the zebrafish, Danio rerio. Although mortality was not affected, SePM impacted multiple levels of biological organization. SePM anticipated hatching to 24h (SL 0.309, 0.556, and 1.0); caused morphological alterations (especially tail bending – SL 0.095 and pericardial edema – SL 0.171); and changed heart rate (6 % decrease – SL 0.171, and 8.75% increase – SL 0.309 and 0.556). Moreover, SePM contamination caused a general reduction of the ability to buffer reactive oxidative species (SL 0.095, 0.171, 0.556, and 1.0), LPO levels were similar in all SL. LDH was reduced (SL 0.095, 0.171, 0.556, and 1.0), while AChE activity and locomotor behavior were unaffected. These early impacts may directly affect fish development and the survival of natural fish populations. This was the first investigation to examine SePM effects on early fish development and underscored the need for a comprehensive assessment of the SePM problem, especially addressing long-term development under SePM contamination and potential transgenerational effects.

Atmospheric particulate matter affects the early development parameters of fish

Excretion of nitrogenous waste is essential for all animals, and the type of waste is largely determined by water availability. Adult teleostean fish excrete ammonia primarily via their gills, which adds to water pollution in intensive aquaculture, and can impact fish health. Larval fish initially produce urea and shift to ammonia excretion after hatching, first via the skin, then via the gills. 
We studied the transition from cutaneous to branchial ammonia excretion. We investigated the expression and localization of ammonia transporters (rhesus glycoproteins) in zebrafish up to 8 days post-fertilization (dpf) and coupled these data to measurements of nitrogenous waste excretion and expression of marker genes for osmoregulation and urea production. We discovered a differential change in rhesus glycoprotein localization: Rhag and Rhbg translocate to gill filaments before 5 dpf, while Rhcgb translocates to the gills between 5 and 6 dpf and is localized in ionocytes. These findings indicate two pathways of ammonia excretion that transition independently, which is corroborated by correlating gene expression and developmental stage: post-hatch larvae up to 6 dpf show increased rhag, rhbg and rhcga expression, while 7-8 dpf zebrafish show increased expression of rhcgb and osmoregulatory marker Na+ /H+ -exchanger 3b. Expression of the uncharacterized rhcgl1 gene increased in a similar pattern, hinting towards involvement of additional rhesus glycoproteins in ammonia excretion. Our research suggests two distinct ammonia excretion pathways in zebrafish, and their relative contributions to ammonia excretion, as well as effects of environmental factors (e.g., pH and environmental ammonia) are subject of our future studies.

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Seasonal and sex differences in the thermoregulatory responses of European vespertilionid bats at high air temperatures

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