Journal of Comparative Physiology A

The electrophysiological process of auditory transduction in insects remains largely conjecture due to the unknown role of ion channels localised to the cilia, but experimental evidence supports either NompC or Nan-Iav as the auditory mechanotransduction ion channel. Here, we knocked down two key genes that code for the two candidate sound-activated ion channels using dsRNA-mediated RNA interference. We measured sound-evoked activity of the auditory nerve and intracellular electrical currents from the ciliated ending of individual auditory receptors. We found that the sound-evoked nerve activity was reduced in nompC, nan and ift88 knockdown. Using whole-cell patch clamp recordings we found that nompC and nan knockdown resulted in reduced sound-evoked transduction current. Stochastic depolarisations hypothesised to be mediated from one of the candidate mechanotransduction ion channels, either NompC or Nan-Iav, where not affected by knockdown of either channel. The discrete depolarisations are therefore mediated through another unidentified ion channel. We test the hypothesis that discrete depolarisations are graded action potentials that travel toward the soma through noise analysis of the transduction current and analysis of discrete depolarisations to voltage-steps. As a positive control we also knocked down ift88, a protein essential for transporting proteins, including ion channels, along the cilium and found both the transduction current and the discrete depolarisations decreased. Key pointsO_LIInjection of dsRNA decreased RNA of nompC and nan C_LIO_LISound-evoked nerve activity is reduced for RNAi-mediated knockdown of nompC and nan C_LIO_LINompC and Nan both contribute to the transduction current C_LIO_LIThe stochastic discrete depolarisations are not due to NompC or Nan-Iav ion channel but to a third unidentified ion channel. C_LIO_LINoise analysis of the transduction current and the discrete depolarisations suggests they are graded action potentials that travel in the direction of the soma. C_LIO_LIKnockdown of ift88 reduced both the transduction current and discrete depolarisations. C_LI Significance StatementInsects are important to understand, economically, agriculturally and medically. However, we still do not understand fundamental aspects of how insects detect their own body movements, vibrations and sound. These senses are detected by insect chordotonal organs, specialised miniaturised mechanoreceptors that convert movements into electrical signals through specialised ion channels. Previous experimental work has advocated either NompC or Nan-Iav as the mechanosensitive ion channel. Here, for the first time, we reduced the expression of both nompC and nan and measured the sound-evoked transduction current directly from neurons in a specialised auditory chordotonal organ. In contradiction to previous studies, we show that both ion channels contribute to the transduction current and find that electrical signals termed "discrete depolarisations" travel toward the soma.

Absorption of CO2 by global oceans is decreasing pH resulting in ocean acidification (OA). Impacts on shellfish have been documented in ecologically and commercially important species. We examined the influence of diet and OA between two populations of red abalone (Haliotis rufescens) a species of aquaculture importance and declining wild populations. Populations experience different exposure histories: strong upwelling (Van Damme, California [VD]) historically exposed to low-pH conditions and weak-intermittent upwelling (Santa Barbara, California [SB]). Abalone were cultured under control-pH or OA-conditions and fed crustose coralline algae (CCA) or diatoms used in aquaculture. We tested treatment effects of population, settlement diet, and OA-exposure on survival as influenced by larval-energy stores. Survival in both populations was enhanced by CCA when cultured under both treatment conditions; however, by later stages, this effect remained only for SB. SB had reduced post-settlement survival when cultured under OA-conditions, whereas post-settlement survival of VD was not. Diet affected the relationship between larval-energy and post-settlement survival; a positive relationship when fed diatoms and a negative relationship with CCA. The relationship between larval energy and post-settlement survival was stronger in VD. CCA enhanced juvenile growth in SB cultured abalone at both three-months and one-year post-settlement. Settlement diets can reduce the impacts of OA on early-life stages of abalone, but population differences driven by underlying energetics affect the consistency of this outcome. These findings illuminate the impacts from OA, suggesting populations may be at risk, and inform strategies for developing and sustaining shellfish aquaculture in the face of changing ocean conditions.

Many social insects, such as ants, change their behavior stereotypically from nursing to foraging as they age, a concept known as temporal polyethism. Biogenic amines are associated with these specific behaviors, but much about them remains poorly understood in these animals. Many aminergic systems lack anatomical characterization, and little is known about the expression of genes required for the aforementioned behavioral phenotypes. Here, we studied Pogonomyrmex barbatus brains and identified the neurons that produce two relevant amines, dopamine and octopamine, by detecting their synthesis enzymes, tyrosine hydroxylase and tyramine beta-hydroxylase, and their transcripts. We also compared the expression of both genes in young nurses and mature foragers by measuring the fluorescence intensity. Dopaminergic and octopaminergic neurons are predominantly located in the protocerebrum and in the subesophageal zone. Neurons that produce dopamine are also present in the optic lobes, whereas octopamine-producing ones show clusters in the antennal lobes. Both genes are downregulated as the organism ages. A reduction in the expression of these genes might be correlated with the mature workers increased propensity to perform extranidal tasks, such as foraging.

In vertebrates, top-down visual attention is a cognitive process where internal goals modulate the tuning of peripheral sensory systems. This leads to increased perceived contrast to both goal-relevant objects and areas of the visual field that are attended. Such a system would also be beneficial to bees, enabling them to detect and recognise the most profitable flowers in their environment. We tested whether bumblebees possess a top-down attentional system resembling that seen in vertebrates. We trained two groups of bees to collect rewards under high contrast targets. To potentially induce a difference in attention while searching for the targets, one group received a higher concentration of sucrose rewards compared to the other. During tests, the targets were presented with a series of lower contrasts to measure the contrast sensitivity curves of the bees induced by the different learnt reward levels. We predicted a stronger effect of any attention-like process on contrast sensitivity in the high reward group. We also repeated this experiment with the neonicotinoid pesticide imidacloprid dissolved in the sucrose rewards to test whether this affects bee attention. Across all test contrasts, higher rewards significantly increased bee accuracy when locating targets, lowered contrast thresholds and reduced the latency to make first choices. Imidacloprid reduced bee accuracy but did not influence first choice latency. These results suggest that learnt floral rewards can influence bee behavioural contrast sensitivity in a manner resembling vertebrate top-down attention and that imidacloprid may modulate this through effects on their nervous system.

Nitrogenous waste excretion is essential for all developmental stages of fish. Embryonic fish excrete urea, transitioning to cutaneous and later branchial ammonia excretion. In zebrafish, ammonia excretion involves rhesus glycoproteins Rhbg and Rhcgb in keratinocytes and ionocytes, but the developmental moment they appear in the gill remains unclear. Potential redundancy between Rhbg and Rhcgb in ammonia excretion is also not fully investigated, nor is the difference in response to low pH. We hypothesized that rhesus glycoproteins are partially redundant, and that they differ in their response to low pH as ammonia excretion enables ionocytes to exchange Na+ and H+ (Rh-NHE-metabolon). We predicted that a loss of rhbg or rhcgb induces compensatory responses. We characterized the transition from urea to branchial ammonia excretion from 0 to 8 days-post fertilization (dpf) and the response to pH 5.0 on the expression and localization of rhesus glycoproteins in control zebrafish and rhbg or rhcgb-crispants. Effects of high external ammonia (HEA, 500 M NH4Cl) and 10 mM HEPES-buffering were further characterized in rhcgb-crispants. Rhag and Rhbg appeared in the gill at 5 dpf, while Rhcgb appeared at 6 dpf. A loss of rhbg or rhcgb did not impact baseline N-excretion, illustrating that zebrafish can maintain ammonia excretion without the full complement of rhesus glycoproteins. We observed no compensatory increase in rhesus glycoproteins, but expression of the transporter hippocampus-abundant transcript 1b increased. HEA-exposed rhcgb-crispants switched to urea as primary nitrogen waste. Together, these findings underline the plasticity of the larval in dealing with nitrogenous waste.

Flower-visiting insect populations are declining since the 1990s, especially because of the decrease of floral resources in agricultural settings. Mass flowering crops can help increase resource availability, and plant breeding can be directed towards selecting varieties attracting more flower-visiting insects. This requires the implementation of an automated high-throughput phenotyping tool for assessing the attractiveness of plant genotypes to flower-visiting insects. In this study, (i) we present a procedure to take standardized images of sunflower heads with camera traps continuously at day and night in the field; (ii) we trained two versions of a deep learning model, named PolliCrop, to automatically detect and identify three classes of the main insects visiting sunflower on these images (non-Bombus bees, bumble bees, lepidopterans); (iii) we assessed and validated the ability of PolliCrop to correctly predict the true visitation frequencies of the insect classes on three sunflower genotypes; (iv) we presented two statistical approaches to compare the insect visitation frequencies between plant genotypes, one including weather variables, and the other one without. One PolliCrop version yielded satisfying performance to correctly detect the three insect classes. In particular, it correctly predicted the insect visitation frequencies on two sunflower genotypes in a range of {+/-}10%. The other PolliCrop version can be useful in certain contexts of images and objectives. PolliCrop can be extended in the future to other crop species by training PolliCrop on new images captured in these crops. The field experimental design to set up for comparing the attractiveness between genotypes is also discussed.

Animals rely on a wide range of environmental signals, including celestial and terrestrial cues for navigation. While celestial cues, such as the sun, play a major role in maintaining a constant heading during long-distance migration and dispersal, terrestrial cues provide an animal with a short-range navigation system, ideal to pinpoint highly specific locations. In Monarch butterflies, the simulation of a terrestrial landmark, i.e. a vertical stripe, induces an attraction behavior (all animals head toward the stimulus) while a small green light spot, simulating the sun, elicits menotactic orientation (animals adopt individual-specific headings relative to the stimulus). However, the mechanisms underlying how the animal distinguishes between a stimulus as a terrestrial landmark versus a celestial cue remains unclear. To explore this, we tested non-migratory Monarch butterflies (Danaus plexippus) in a flight simulator. The inner surface of simulator was equipped with an area of LEDs, allowing to present different visual stimuli to the butterflies during tethered flight. By systematically manipulating the stimulus width, height, brightness, and elevation we found that Monarch butterflies exhibited attraction behavior to high contrast areas, like stripe edges. Menotactic behavior was not achieved by solely decreasing the stimulus to a small light spot but also required for the stimulus to be presented at higher elevation to be interpreted as a sun stimulus. These findings suggest that multiple parameters, inherently set by the butterflys navigation system, are critical to interpret a visual stimulus as celestial cue or terrestrial landmark, producing dynamic switches between different orientation strategies during navigation.

Many insects enter diapause, a programmed state of developmental arrest that enables survival under adverse environmental conditions. In Drosophila melanogaster Meigen, 1830, diapause is characterized by reproductive arrest and reduced intestinal growth, accompanied by suppressed intestinal stem cell (ISC) activity. Juvenile Hormone (JH) promotes ISC proliferation under favorable conditions, but its capacity to modulate stem cell dynamics during cold-induced diapause remains unclear. Here, we investigated whether JH signaling can reactivate midgut remodeling in adult females maintained at 11. At this temperature, flies exhibited pronounced gut atrophy and elevated Phospho-histone H3 (PH3+) cell abundance, consistent with temperature-dependent G2/M phase arrest JH treatment significantly increased the proportion of Delta-positive progenitor cells in the anterior (R2) and posterior (R5) midgut regions at both 11 and 25, demonstrating that JH acts as a conserved mitogen for the ISC pool irrespective of thermal environment. A trend toward reduced PH3+ accumulation in the posterior midgut following JH treatment (p = 0.061) suggests possible facilitation of mitotic exit, though this effect did not reach statistical significance. Despite cellular-level changes, JH treatment did not restore overall gut size, indicating that the 72-84 hour exposure window was insufficient for subsequent tissue hypertrophy. Additionally, we identified a recurrent cold-induced pathology of gut distension, provisionally termed Lumen Obstruction Syndrome (LOS), which was independent of JH signaling. These findings reveal an uncoupling of JH-driven stem cell expansion from gross organ growth under diapause conditions, highlighting the selective sensitivity of the ISC compartment to endocrine signaling during environmental stress.

Extraocular motoneurons are the final neuronal relay implicated in gaze motor control and are known to be subdivided in functional subgroups, differently implicated in ocular motion dynamics. However, the maturation of these functional populations of extraocular motoneurons, in relation with the development of gaze-stabilizing reflexes remains largely unexplored. In amphibian tadpoles, the angular vestibulo-ocular reflex (VOR) appears later than other visuo-vestibular ocular reflexes and matures until the metamorphosis climax. Two types of Abducens motoneurons have been described to participate to the angular VOR in larval frog: spontaneous motor units, exhibiting a robust resting activity and silent motor units recruited only during head motion. The aim of this study was to investigate the maturation of these two types of Abducens motor units in relation with the development of the angular VOR by evaluating their discharge dynamic in response to head rotation in semi-intact preparations of larval Xenopus laevis. During larval life, the discharge modulation during sinusoidal head rotations increases significantly for silent units only, demonstrating a better sensitivity of this Abducens motoneuron sub-population to horizontal semicircular canal activation. In addition, this functional maturation was accompanied by an increase of the myelination in the lateral rectus motor nerve, promoting a faster conductivity in late larval stages than in early one. These findings showed that the development of the angular VOR is supported by a selective maturation of extraocular motoneurons subpopulations, specifically implicated in the improvement of the ocular kinematic during the reflex.

The shift to terrestrial environments in ancestrally aquatic animals is often associated with key physiological and physical changes, including shifts in respiratory physiology and in some cases, even the evolution of completely novel respiratory structures. Examining how respiration operates across a gradient of submersion states in ancestrally aquatic terrestrial animals may shed light on how complex biological traits shift under different selective regimes. In this work, we begin exploring respiration in terrestrially-adapted land crabs that still use their gills to respire while underwater. We tested the relationship between aquatic respiratory rates, body size, and sex in red devil vampire crabs (Geosesarma hagen) at two ecologically-relevant temperatures. We found small females respire more than small males at 28{degrees}C, while large females respire more than large males at 21{degrees}C. Additionally, body size is a significant factor affecting respiratory rates of both sexes at 21{degrees}C and warmer temperatures significantly increase respiration in small crabs of both sexes. Interactions between these factors also led to emerging trends that can be explained by both physiological rules, such as reproductive investment and surface-to-volume ratios and heat transfer. We also report a temperature coefficient (Q10) of 1.52 for this species, showing an expected 52% change in respiratory and metabolic rate for every 10{degrees}C increase. This work also demonstrates the importance of understanding how and to what extent biological variables like sex and body size interact with abiotic environmental factors when measuring physiological traits in ectothermic invertebrate animals.

Honey bees can swim on the water surface toward dark regions, a behavior known as scototaxis that may facilitate escape from water. Although this behavior has been reported in both honey bees and solitary bees, variation among honey bee species remains poorly understood. We compared scototaxis during swimming in four honey bee species representing two nesting types: open-nesting (Apis florea and A. dorsata) and cavity-nesting (A. cerana and A. mellifera). Individual bees were released into a water-filled arena containing a dark sector, and their landing angles were recorded. All species exhibited significant orientation toward the dark sector. However, open-nesting species showed significantly stronger orientation than cavity-nesting species. No significant differences were detected between replicate colonies within species or between species within the same nesting type, whereas differences between nesting types were highly significant. Hierarchical clustering based on orientation strength placed Osmia, a solitary cavity-nesting bee from our previous study, in the same behavioral cluster as the two open-nesting Apis species rather than the cavity-nesting honey bees. We also measured swimming duration, distance, and velocity, but found no consistent differences between nesting types. These results demonstrate substantial interspecific variation in swimming scototaxis. The behavioral clustering is consistent with the hypothesis that strong scototaxis represents an ancestral trait that has been reduced in the derived A. cerana/A. mellifera lineage.

Aquatic vertebrates are increasingly used in neuroscience research, yet underwater visual stimulation remains a challenge. Commonly used monochromatic stimuli have been shown to be inadequate to activate many visual neurons properly, and underwater refraction artifacts are prone to ruin stimulus designs. Here, we present MARINER - a visual stimulator, which remedies these issues and integrates concurrent behavioral and neurophysiological two-photon calcium imaging recordings. MARINERs full-field visual stimulation combined with receptive field mapping reveals that the visual field of larval zebrafish is larger than previously thought, extending almost down below the fish, and is spatially biased to better utilize motion content in naturalistic visual scenes. Using chromatic motion nulling, we further show that behavioral responses and task-associated sensory neurons are colorblind for "red" and "green" during the larvas optokinetic response. The MARINER stimulator facilitates naturalistic stimulation and faithful presentation of colored visual underwater stimuli for small aquatic species.

Most organisms have evolved mechanisms to reduce the negative effects of toxins in their diet. Some animals that are toxin specialists, such as dendrobatid poison frogs, have amino acid substitutions in proteins targeted by the toxins that prevent or limit the toxins ability to bind and exert its bioactive effects. The Phantasmal poison frog, Epipedobates tricolor, has amino acid substitutions in its neuronal nicotinic acetylcholine receptors that were previously shown to provide resistance to the highly potent neurotoxin epibatidine in vitro. However, it is unclear whether E. tricolor resists the physiological effects of epibatidine in vivo. To investigate this, we examined the effects of epibatidine exposure on the locomotion and behavior of E. tricolor. We performed whole-animal performance assays and behavioral evaluations at multiple time points following the administration of high yet biologically relevant levels of epibatidine. These assays were followed by alkaloid quantification to track chemical concentrations in the skin. Epipedobates tricolor exhibited similar locomotor performance and behavior at both epibatidine doses compared to controls and regardless of the quantity of alkaloid accumulated into the skin. However, we observed an impact of low-percentage ethanol solutions on behavior when compared to water controls, as well as general impacts of handling stress (regardless of the administered solution type), which should be considered in future experimental designs. Overall, we demonstrate that E. tricolor likely avoids a physiological fitness trade-off between toxin ingestion and the defensive benefits of epibatidine sequestration. Our study suggests that the ability to ingest toxins involves multi-faceted resistance mechanisms. Highlights- Whole-animal performance assay shows no impact of epibatidine on frog behavior - Epipedobates tricolor is 20-5000 times more resistant to epibatidine than mice - Assays demonstrate that frogs are sensitive to 6% ethanol and handling stress

Mass coral bleaching events driven by marine heatwaves are increasing in frequency and severity, yet the long-term recovery trajectories of surviving corals remain poorly understood. Here, leveraging a cohort of individual coral colonies with a decade of tracked environmental and bleaching history, we captured structural shifts in the coral thermal performance landscape. Specifically, we quantified thermal performance curves (TPCs) for photosynthesis and calcification in bleaching-resistant and bleaching-susceptible colonies of two ecologically dominant reef-building corals (Montipora capitata and Porites compressa) at four and six years following the 2019 marine heatwave in K[a]neohe Bay, Hawaii (2023 and 2025, respectively). Coral thermal performance shifted substantially between 2023 and 2025, and these shifts differed between species, bleaching phenotypes, and traits. In P. compressa, photosynthetic thermal optimum (Topt) shifted downward over time by 1.6{degrees}C across both phenotypes, suggesting recalibration toward prevailing conditions at the potential cost of future heat tolerance. In M. capitata, photosynthetic performance was lower in bleaching-susceptible corals in 2023 but converged by 2025, suggesting susceptible colonies recovered. In contrast, Topt of photosynthesis remained persistently higher in bleaching-resistant colonies, likely reflecting established symbiont communities. Critically, photosynthesis and calcification did not recover in parallel. Calcification TPCs for both phenotypes of M. capitata were stable across both timepoints, whereas calcification TPCs in P. compressa continued to change through 2025. These findings demonstrate that coral thermal performance is not static following heatwaves but continues to be reshaped over multi-year recovery periods, and that species-specific traits and strategies can fundamentally constrain the pace and coupling of physiological recovery. Furthermore, elevated thermal tolerance acquired through a heatwave can erode during prolonged periods of ambient temperatures. As recurrent bleaching events shorten recovery windows, understanding these dynamic physiological trajectories are essential for understanding and forecasting reef futures.

Heart rate (HR) and its variability (HRV), mediated by the autonomic nervous system are key indicators of diving physiology and behavioral state, in vertebrates. However, these indicators remain understudied in cetaceans due to the technical challenges of recording electrocardiograms (ECGs) underwater. To overcome these challenges, we developed a waterproof device based on an all-in-one suction-cup that integrate an ECG-accelerometer logger with bipolar electrodes. Using this device, we obtained high-resolution ECG signals in bottlenose dolphins (Tursiops truncatus, n=8), belugas (Delphinapterus leucas, n=2), and orcas (Orcinus orca, n=1) during breathing and apnea. This approach allowed us to highlight species-specific features of the ECG waveform, consistent with a biphasic T wave in the three species of cetaceans and a bifid P wave unique to belugas, which were independent from the respiration state. Resting surface HRs were 70 {+/-} 4 bpm in dolphins, 51 {+/-} 1 bpm in belugas, and 50 {+/-} 2 bpm in the orca and exhibited pronounced oscillation related to the mechanism of respiratory sinus arrhythmia. As expected, short apneas ([~] 1 min) induced bradycardia in all three species (53 {+/-} 5, 33 {+/-} 3, and 37 {+/-} 2 bpm, respectively). In dolphins this bradycardia was coupled with a significant decrease of the coefficient of variability of RR intervals, one of the indices of HRV. Moreover, we were surprised to observe HR oscillations throughout apnea, suggesting a persistent fluctuation of autonomic modulation. Thus, to better understand autonomic modulation in cetaceans we employed food (fishes, squids, gelatin, etc.) as a strong rewarding stimulus. For that we compared HR and HRV during 2-min of food deprivation versus continuous feeding periods. In dolphins, food deprivation produced no significant change in HR or HRV from resting surface values, whereas continuous feeding decreased HR of about 20 % and increased HRV metrics (StDRR, CVRR, RMSSD). Belugas showed similar responses, with a HR decline of about 40 % and an increase HRV indices. These findings established baseline HR and HRV parameters during breathing or apnea for three cetacean species and demonstrate that autonomic responses to appetitive stimuli can be non-invasively quantified, validating a novel tool to investigate cetacean cardiovascular physiology and environmental perception.

The measurement of light received at the cornea of the eye is a paramount consideration for the understanding of the relation between environmental illumination and the non-image-forming effects of light. The field of view (FOV) at the cornea is less than a full hemisphere, because it is partially occluded by human facial morphology. The International Commission on Illumination (CIE) has defined a standard model of human FOV. A suitably designed physical occluder attached to the sensor (of a light meter) has been proposed as a means of incorporating the effect of human FOV when taking measurements. Similarly, when using simulation to predict light received at the cornea, a geometrical description of the occluder at the eye point(s) can be added to the 3D model of the scene. The first occluder model proposed to represent CIE human FOV was enumerated in terms of: the CIE definition; the radius of the occluder; and, the radius of the light sensor disc. We present a simpler model based only on the CIE definition and the occluder radius. Both models were tested using a virtual goniophotometer. Various sensor response functions describing the spatial sensitivity across the sensor disc, including several we characterized through laboratory measurements, were included in the test. For all functions considered, the performance of the simpler occluder model was equivalent to or better than the model first proposed.

The tick Ixodes ricinus is the main vector of human and animal pathogens in Europe. Despite its importance in epidemiology and medicine, our understanding of physiological mechanisms controlling blood feeding, osmoregulation, or development are still limited. Here, we identify novel neuropeptide invertebrate parathyroid hormone-like peptide (iPTH) and its two receptors - PTHR1 and PTHR2 in I. ricinus. Functional aequorin-based assay confirmed specific activation of both receptors by iPTH. Using RT-qPCR we detected the PTHR1 transcript in the synganglion, while increased expression levels of PTHR2 were found in the salivary glands, hindgut and female gonads. RNA-mediated knockdown of iPTH receptors in nymphs resulted in delayed blood feeding, and a high incidence of defects in adult ecdysis. Consistent with observed phenotypes, iPTH is expressed in multiple neurons of the synganglion which project arborizing axons to the salivary glands, rectal sack and skeletal muscles. iPTH was colocalized with orcokinin-immunoreactivity (OK-IR) in all neurons that innervate these peripheral tissues. iPTH is further colocalized with tachykinin (TK) in Pd1DL1 neurons, suggesting coordinated action with other neuropeptides. Our findings indicate that iPTH signaling is required for normal feeding, development and successful ecdysis.

The queen bee is the central individual responsible for colony establishment, growth, and survival. Reliable confirmation of successful mating, continued queen presence, and normal reproductive performance is essential for effective colony management. We present a queen bee detection system based on an array of Hall-effect sensors and a miniature magnetic tag attached to the queen. The system is designed for continuous operation and real-time monitoring. A prototype was developed, constructed, and evaluated under both laboratory and field conditions. Field experiments conducted in an apiary demonstrated that the system can reliably detect queen bee passages through the hive entrance, enabling the identification of activities associated with mating flights. The results confirm the feasibility of Hall-effect sensing for automated, non-invasive queen bee monitoring and establish magnetic sensing as a promising new measurement modality for precision apiculture.

Environmental warming is generally expected to increase metabolic demand in ectotherms. However, facultatively endothermic insects such as bumblebees regulate body temperature and may reduce thermogenic investment under warm conditions, potentially altering physiological performance and responses to climate change. We combined flow-through respirometry and infrared thermography to test how elevated ambient temperature (25 vs 35{degrees}C) affects feeding energetics and postprandial metabolism in the bumblebee Bombus terrestris. Bees maintained substantially lower thoracic temperature excess at 35{degrees}C than at 25{degrees}C, both before and during feeding. Feeding metabolic rate was also lower at 35{degrees}C and was strongly positively associated with thoracic temperature excess, indicating that feeding energetics were primarily explained by thermoregulatory state rather than ambient temperature alone. Elevated temperature reduced both the probability and energetic magnitude of specific dynamic action (SDA), including total SDA expenditure, early postprandial metabolism, and peak metabolic amplitude. In contrast, SDA duration and time to peak response showed little temperature dependence. Our results demonstrate that warming can suppress energetic expenditure in facultatively endothermic pollinators by limiting thermogenic investment and postprandial metabolic responses, potentially constraining the energetic flexibility underpinning foraging performance under climate warming.

Temperatures in aquatic ecosystems have been affected by anthropogenic activities such as agricultural and industrial water use, and climate change caused by greenhouse gas emissions. Changes in water temperature directly affect the cellular and organismal physiology of fishes because most fishes are ectotherms. These effects can take different forms, such as increased cellular stress and reactive oxygen species (ROS) production. However, the type and magnitude of response depend on the duration and the frequency of the exposure to elevated water temperature. In this study, we investigated the long-term effects of exposure to daily thermal fluctuations occurring during early-life stages of zebrafish, Danio rerio, on gene expression and CTmax in later developmental stages. To do so, wild-type zebrafish were exposed daily to a + 5{degrees}C fluctuation in temperature from ambient (28 {degrees}C) to 33 {degrees}C over the first 30 days post fertilization (dpf), before being held until 90 dpf at ambient temperature. The fish that experienced daily thermal fluctuation were compared to a control group that was kept at 28 {degrees}C throughout the experiment and sampled at the same timepoints. Samples were collected at 18 (larval), 30, 60 (juvenile), and 90 (adult) dpf to study the expression of heat shock proteins and oxidative stress genes. The thermotolerance of fish was tested using CTmax trials at 60 and 90 dpf. Daily thermal fluctuation over the first 30 dpf led to a significant increase in the expression of hsp47, gstp1a, sod1, and sod2 genes at 60 dpf, and hsp47, hsp90aa1, hsp90ab1, cat, glulb, gstp1a, sod1, and sod2 genes at 90 dpf. The only significant increase detected during the larval stage was glulb at 18 dpf. Fish that experienced thermal fluctuation also had a higher CTmax at 60 dpf, but this increased thermotolerance significantly decreased from 60 to 90 dpf, where it was not different between treatments. Overall, our study demonstrates that early-life thermal stress increased cellular stress responses and thermotolerance in zebrafish into later ontological stages.