Journal of Comparative Physiology A

Cilia are the major effectors in Ctenophores, but very little is known about their transmitter control and integration. Here, we present a simple protocol to monitor and quantify cilia activity in semi-intact preparations and provide evidence for polysynaptic control of cilia coordination in ctenophores. Next, we screen the effects of several classical bilaterian neurotransmitters (acetylcholine, dopamine, L-DOPA, serotonin, octopamine, histamine, gamma-aminobutyric acid (GABA), L-aspartate, L-glutamate, glycine), neuropeptides (FMRFamide), and nitric oxide (NO) on cilia beating in Pleurobrachia bachei and Bolinopsis infundibulum. Only NO inhibited cilia beating, whereas other tested transmitters were ineffective. These findings further suggest that ctenophore-specific neuropeptides could be major candidate signaling molecules controlling cilia activity in representatives of this early-branching metazoan lineage.

The vertebrate retina uses neurotransmitters to regulate its various functions and adjust vision according to the day/night cycle. Dopamine is probably one of the most important of these neurotransmitters. It is released by dopaminergic amacrine cells in the retina and exerts its regulatory effects, in part, through the cAMP pathway. It has been demonstrated that dopamine affects the phototransduction cascade in isolated amphibian rods. Furthermore, elevated intracellular levels of cAMP increase the light sensitivity of vertebrate rods and modulate the response of vertebrate cones. These effects can be triggered by dopamine receptors and adjust vision to daily light variations. Therefore, the evolution of dopamine loops in the retina is of interest, and the lamprey, being the most primitive vertebrate, could be valuable in this regard. In the present study, we examined whether the photoresponse properties of long (cone-like) and short (rod-like) photoreceptors in the river lamprey could be regulated by dopamine or cAMP level modulation. Using suction pipette recording, we demonstrated that dopamine slightly increased short photoreceptors sensitivity and it slowed the rising and falling phases of photoresponses in long photoreceptors and increased the integration time, with no effect on the sensitivity to brief flashes. The second part of our study -- an immunohistochemical analysis of the lamprey retina -- revealed that both D1 and D2 dopamine receptors are expressed in both types of lamprey photoreceptors. Our results suggest that the regulation of photoreceptor functions by the neurotransmitter dopamine originated in the early stages of vertebrate evolution, specifically during the Cambrian period. SummaryThe lamprey, a primitive vertebrate, is a valuable object for studying the evolution of dopamine loops in the vertebrate retina. This study shows that photoresponse properties of lamprey photoreceptors are regulated by dopamine in a different way compared to gnathostomes.

Echinophthiriidae is a family of aquatic lice parasitizing aquatic carnivorans, each member distinguished by their uniquely modified, curved setae. Echinophthirius horridus is known to parasitize a wide range of phocid (earless) seals as opposed to exhibiting the more species-specific parasitism of other echinophthiriid lice. In this study, we use a combination of bright field microscopy, confocal laser scanning microscopy (CLSM), and line drawings to provide a detailed description of the general body setae of E. horridus and discuss its possible significance as an adaptation to a marine lifestyle.

The crustacean Talitrus saltator is known to use many celestial cues during its orientation along the sea-land axis of sandy shores. In this paper, we investigated the existence of the eye regionalization by morphological, electrophysiological and behavioural experiments. Each ommatidium possesses five radially arranged retinular cells producing a square fused rhabdom by R1-R4 cells; the smaller R5 exist between R1 and R4. The size of R5 rhabdomere is largest in dorsal part and becomes gradually smaller in median and ventral part of the eye. Spectral-sensitivity measurements were recorded from either dorsal or ventral parts of the compound eye to clarify the chromatic difference. Results show that the dorsal part is green and UV-blue dichromatic, whereas the ventral part is UV (390 nm) with a substantial population of 450 nm receptors with the responses in the longer wavelength region. To evaluate the orienting behaviour of individuals, their eyes were black painted either in the dorsal or ventral part, under natural sky or a blue filter with or without the vision of the sun. Results show that animals painted on the dorsal part of their eyes tested under the screened sun were more dispersed and in certain cases their directions deflected than other groups of individuals. Furthermore, sandhoppers subjected to the obscuring of this area met in any case high difficulties in their directional choices. Therefore, our present work indicates the existence of a regionalization of the compound eye of T. saltator. Summary statementThis work provides evidences of the morphological and electrophysiological regionalization of the compound eye and the visual capabilities for behaviour involved in the recognition of the celestial compass orienting factors in crustaceans.

Flight control requires active sensory feedback, and insects have many sensors that help them estimate their current locomotor state, including campaniform sensilla, which are mechanoreceptors that sense strain resulting from deformation of the cuticle. Campaniform sensilla on the wing detect bending and torsional forces encountered during flight, providing input to the flight feedback control system. During flight, wings experience complex spatio-temporal strain patterns. Because campaniform sensilla detect only local strain, their placement on the wing is presumably critical for determining the overall representation of wing deformation; however, how these sensilla are distributed across wings is largely unknown. Here, we test the hypothesis that campaniform sensilla are found in stereotyped locations across individuals of Manduca sexta, a hawkmoth. We found that although campaniform sensilla are consistently found on the same veins or in the same regions of the wings, their total number and distribution can vary extensively. This suggests that there is some robustness to variation in sensory feedback in the insect flight control system. The regions where campaniform sensilla are consistently found provide clues to their functional roles, although some patterns might be reflective of developmental processes. Collectively, our results on intraspecific variation in campaniform sensilla placement on insect wings will help reshape our thinking on the utility of mechanosensory feedback for insect flight control and guide further experimental and comparative studies.

OverviewThis dataset originates from a preliminary respirometry study on carabid beetles from the Elbe Estuary (Northern Germany), encompassing species from freshwater and saltmarsh habitats along a salinity gradient. The study was designed to establish and validate a workflow for measuring oxygen consumption, including chamber setup, sensor recording, drift correction, and calculation of absolute and mass-specific metabolic rates. Oxygen consumption was measured for five species (Carabus auratus, Carabus granulatus, Limodromus assimilis, Poecilus versicolor and Pterostichus niger) using sealed glass vials connected to an optical oxygen system. The dataset provides individual-level measurements and serves primarily as a methodological reference for future respirometry studies on ground-dwelling arthropods. The O2 consumption rates of carabid beetles showed interspecific differences and followed metabolic scaling theory, revealing an inverse relationship between body mass and mass-specific metabolic rates across species (Figure 3). O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=127 SRC="FIGDIR/small/720111v1_fig3.gif" ALT="Figure 3"> View larger version (17K): org.highwire.dtl.DTLVardef@f41f27org.highwire.dtl.DTLVardef@12939eeorg.highwire.dtl.DTLVardef@19a4630org.highwire.dtl.DTLVardef@17611ba_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 3:C_FLOATNO Oxygen consumption rates of Carabid species per (a) animal in [ml O2 h-1] and as (b) mass-specific consumption rate [ml O2 h-1 g-1]. Points represent mean oxygen consumption per individual (C. auratus: n = 2; L. assimilis: n = 6; P. versicolor: n = 7; P. niger: n = 6). C_FIG

Sensory perception is the ability through which an organism is able to process sensory stimuli from the environment. This stimulus is transmitted from the peripheral sensory organs to the central nervous system, where it is interpreted. Drosophila melanogaster larvae possess peripheral sense organs on their head, thoracic, and abdominal segments. These are specialized to receive diverse environmental information, such as olfactory, gustatory, temperature or mechanosensory signals. In this work, we complete the description of the morphology of external larval sensilla and provide a comprehensive map of the ultrastructure of the different types of sensilla that comprise them. This was achieved by 3D electron microscopic analysis of partial and whole body volumes, which contain high-resolution and complete three-dimensional data of the anatomy of the sensilla and adjacent ganglia. Our analysis revealed three main types of sensilla on thoracic and abdominal segments: the papilla sensillum, the hair sensillum and the knob sensillum. They occur solitary or organized in compound sensilla such as the thoracic keilins organ or the terminal sensory cones. We present a spatial map defining these sensilla by their position on thoracic and abdominal segments. Further, we identify and name the sensilla at the larval head and the last fused abdominal segments. We show that mechanosensation dominates in the larval peripheral nervous system, as most sensilla have corresponding structural properties. The result of this work, the construction of a complete structural and neuronal map of the external larval sensilla, provides the basis for following molecular and functional studies to understand which sensory strategies the Drosophila larva employs to orient itself in its natural environment.

Chagas disease vectors can ingest several times its own volume in blood with each meal. This ad libitum feeding causes an intense process of diuresis inducing the insect to eliminate a large quantity of urine during the next few hours. This process, which is under the control of endocrine and neuroendocrine systems is necessary to restore homeostasis, and to begin physiological mechanisms leading to growth and reproduction. To ensure diuresis, the speed of circulation of the hemolymph must be increased to allow the Malpighian tubules to produce the urine. Behind this acute phenomenon, triatominae insects can spend several weeks without feeding. In this way, it could be assumed that during most of the time of life the insect is in a resting condition. Triatominae circulatory system is quite simple, including a dorsal vessel which pumps hemolymph in an anterograde direction. The return is caused by peristaltic contractions of the anterior midgut. While the mechanisms controlling the circulation of the hemolymph during post-prandial diuresis was largely analysed, the mechanisms controlling it during resting conditions is poorly understood. In this study we analyse several canonical pathways (i.e. L-type VGCC; GPCR; RyR; IP3R) and a novel system represented by the recently characterized Piezo proteins. Our results show that during the resting condition hemolymph circulation depends on a cross-talk between myogenic activity, inhibitory and stimulatory cell messengers, and also Piezo proteins. We present for the first time the existence of a putative Piezo protein in Hemiptera.

Activation and modulation of sensory-guided behaviors by biogenic amines assure appropriate adaptations to changes in an insects environment. Given its genetic tool kit Drosophila melanogaster represents an excellent model organism to study larger networks of neurons by optophysiological methods. Here, we studied stationary crawling movements of 3rd instar larvae and revealed how the octopaminergic VUM neuron system reacts during crawling behavior and tactile stimulations. We conducted calcium imaging experiments on dissections of the isolated nervous system (missing all sensory input) and found spontaneous rhythmic wave pattern of neuronal activity in VUM neuron clusters over the range of thoracic and abdominal neuromeres in the VNC. In contrast, in vivo preparations (semi-intact animals, receiving sensory input) did not reveal such spontaneous rhythmic pattern. However, tactile stimulations activated different clusters of the VUM neuron system simultaneously in these preparations. The activation intensity of VUM neurons in the VNC was correlated with the location and degree of body wall stimulation. While VUM neuron cluster near the respective location of body wall stimulation were less activated more distant cluster showed stronger activation. Repeated gentle touch stimulations led to decreased response intensities, repeated harsh stimulations resulted in increasing intensities over trials. Optophysiological signals correlated highly with crawling behavior in freely moving larvae stimulated similarly. We conclude that the octopaminergic system is strongly coupled to the neuronal pattern generator of crawling movements and that it is simultaneously activated by physical stimulation, rather intensity than sequential coded. We hope that our work raises the interest in whole biogenic network activity and shows that octopamine release does not only underlie "the more the better" principle but instead has a more complex function in control and modulation of insects locomotion.

Vestibular neurons are core elements of the pathways involved in vestibulo-motor functions, such as vestibulo-spinal and vestibulo-ocular reflexes. To meet behavioral needs, electrophysiological neuronal properties are adequately adapted to the sensory-motor computation sustaining these distinct vestibular reflexes. During frog metamorphosis, there is a complete reorganization of the posturo-locomotor system while the oculomotor system remains minimally changed, probably associated to so far unknown changes in vestibular neuronal properties. We used this unique model to investigate the central developmental mechanisms underlying such a reconfiguration of vestibular-associated behaviors. Central vestibular neurons exhibit two types of electrophysiological phenotypes: tonic neurons with a continuous discharge and phasic neurons with a transitory discharge mainly due to the activation of Kv1.1 channel. Electrophysiological recordings and Kv1.1 immunolabeling of vestibulospinal (VS) and vestibulo-ocular (VO) neurons at both larval and juvenile stages revealed that the majority of VS neurons exhibited a tonic discharge in larvae but a phasic discharge in juvenile, while VO neurons remained mainly tonic throughout development. Changes in phasic and tonic neurons proportions in VS population are partly explained by neurogenesis. But we provide evidences that an electrophysiological phenotype switch is a concomitant developmental mechanism participating in the maturation of these central vestibular neurons. All together our results showed that the maturation process in central vestibular neuronal groups is highly related to the metamorphosis-induced remodeling of vestibulo-motor functions they are involved in, with the ultimate purpose of ensuring an adequate adaptation of neuronal elements properties to the developmental changes of behavioral constrains.

Anthropogenic noise pollution has become a threat for the fauna with possible effects on animal physiology and behaviour. We explored the effects of anthropogenic vibrational noise on honey bees (Apis mellifera). The intensity of substrate borne vibrations generated by trains on the ground, on the front comb of a hive and on its base as well as the airborne sound pressure were recorded at different distances and sites. Vibrational noise of amplitudes that can be detected by honey bees is present on the ground surface, on the comb and on the base over distances up to 20 m from the railway track and the attenuation of the airborne sounds is higher than the attenuation of the substrate borne vibrations. Bees placed in an observational hive and exposed to simulated substrate borne vibrations caused by a cargo train show significant behavioural reactions. The same substrate borne vibration was presented to bee colonies every 5 minutes continuously for six months at realistic amplitudes. On the colony level no differences are found for capped and open worker brood, worker eggs, adult drone population, capped and open drone brood, brood development, varroa mites, collected pollen and honey production; while some significant differences are present for worker population and pollen collecting foragers. We conclude that honey bee colonies in the vicinity of railroads are exposed to substrate borne vibrational noise above their threshold of sensitivity up to 20 m. At the individual level bees show reactions to the vibrations; however, at the population level bees seem to cope with the disturbance. As higher amplitudes and additional stress factors might affect the colonies, it seems to be anyways advisable to generally avoid placing bee colonies close to anthropogenic vibrational noise sources.

O_LIThe metabolic rate of an organism is intrinsically linked to key traits such as reproductive output and lifespan. While the drivers of individual differences in metabolic rate are poorly understood, previous research in insects has shown that metabolic rate can change substantially in the initial hours and days post-eclosion as adults. C_LIO_LIHere we repeatedly measured the resting and active metabolic rate of individual adult honeybees (Apis mellifera) for up to 48 hours from the time of eclosion. We combined flow-through respirometry with automated behaviour tracking, permitting us to obtain active (AMR) and true resting metabolic rate (RMR) from freely moving animals. We compared these recordings to the more conventional approach of obtaining resting metabolic rate by restraining animals. C_LIO_LIBoth active and resting metabolic rates and mass-specific metabolic rates increased significantly in the first 48-hours post-eclosion, whereas metabolic scope did not change. Mass-specific water loss was highest in active bees and changed non-linearly with time post-eclosion, increasing in the first 24 hours before decreasing again. A similar quadratic relationship with time was also observed for bees movement speed. Speed- and mass-specific metabolic rate and scope increased with time post-emergence, whereas speed- and mass-specific water loss did not. C_LIO_LIThe metabolic rate of restrained bees was consistently significantly higher than the true RMR at all time points, likely due to the stress associated with being restrained. Therefore, we recommend future studies of insect resting metabolic rates avoid restraining organisms to restrict movement and consider employing behaviour tracking as a means to extract metabolic rate data from periods of true rest. C_LIO_LIThis study provides important insights into the previously overlooked changes in metabolism exhibited by newly emerged honeybee workers. The high mortality rate beyond 48 hours, coupled with significant changes in metabolic rates, body mass, and water loss, underscores the importance of this early post-eclosion period for survival and metabolic stabilization. C_LI

Odorants stimulate olfactory sensory neurons (OSNs) to create a bilateral sensory map defined by a set of glomeruli present in the left and right olfactory bulbs. Using Xenopus tropicalis tadpoles we challenged the notion that glomerular activation is exclusively determined ipsilaterally. Glomerular responses evoked by unilateral stimulation were potentiated following transection of the contralateral olfactory nerve. The gain of function was observed as early as 2 hours after injury and faded away with a time constant of 4 days. Potentiation was mediated by the presence of larger and faster calcium transients driving glutamate release from OSN axon terminals. The cause was the reduction of the tonic presynaptic inhibition exerted by dopamine D2 receptors. Inflammatory mediators generated by injury were not involved. These findings reveal the presence of a bilateral modulation of glomerular output driven by dopamine that compensates for imbalances in the number of operative OSNs present in the two olfactory epithelia. Considering that the constant turnover of OSNs is an evolutionary conserved feature of the olfactory system and determines the innervation of glomeruli, the compensatory mechanism here described may represent a general property of the vertebrate olfactory system to establish an odor map.

Floral displays attract pollinators through a finely tuned interplay of colour, pattern, shape, and scent. Yet, the question remains: how do bees respond when these traits are stripped to their simplest form, with only visual cues at play? In this field study, we examined the foraging behaviour of Apis mellifera on artificial flowers differing solely in background colour (white or yellow) and UV patterning, while shape and scent were held constant. Across three summer days, standardized stimuli were placed within a natural meadow, and bee-flower interactions were recorded and analyzed by Bayesian hierarchical models. The results reveal a clear preference for yellow over white backgrounds and prolonged visitation in the presence of ring-shaped UV patterns, whereas full UV coverage acted as a deterrent. These effects, though moderate, were consistently modulated by abiotic covariates, particularly radiation, temperature, and time of day. Negligible inter-individual variation and a substantial share of residual variance further underline the context-dependent complexity of foraging. In sum, our findings demonstrate that visual floral traits, while influential, are interpreted through the dual lens of environmental contingency and the bees inherent cognitive machinery.

Bees rely heavily on vision during most of their interaction with the environment, but so far, visual abilities have not been included into functional investigations of these crucial pollinators. This is probably due to the lack of comprehensive and phylogenetically-controlled quantification of visual traits across species. In the present study, we used high-throughput micro-CT tools to quantify, compare and understand the diversity of visual traits of compound eyes in bumblebees. Visual systems of bumblebees were far from identical, with variations across sizes, castes and species. While phylogenetic proximity poorly supported interspecific variations, these were better explained by two ecological factors: social parasitism and habitat. The eye parameter - a metric that measures the relative investment of a compound eye into resolution or sensitivity - was lower in queens of social parasitic species than of non-parasitic species. Workers of species associated with forested habitat had distinct visual traits, including a higher eye parameter, than those of species living in open landscapes. These diverse visual traits are likely to provide selective advantages to bumblebees given their specific ecological requirements. We thus propose that social parasitism and forest habitat are drivers of the diversification of compound eyes in bumblebees. Finally, we discuss how the present study can inspire trait-based approaches in ecology and conservation biology.

1The mating behavior of nocturnal Manduca sexta hawkmoths is under strict temporal control. It is orchestrated via circadian and ultradian oscillations in sex-pheromone stimuli as social zeitgeber. The extremely sensitive pheromone-detecting olfactory receptor neurons (ORNs) that innervate the long trichoid sensilla on the males antennae are peripheral circadian clocks. They express the transcriptional-translational feedback loop (TTFL) circadian clockwork, best characterized in Drosophila melanogaster. In hawkmoths, it is still unknown whether or how the ORN TTFL clockwork regulates the daily rhythms in pheromone sensitivity and in temporal resolution of ultradian pheromone pulses as prerequisites to the temporal regulation of hawkmoth mating behavior. We hypothesize that, rather than the slow TTFL clock, a more rapidly adaptive post-translational feedback loop (PTFL) clockwork, associated with the ORN plasma membrane, allows for temporal control of pheromone detection via generation of multiscale endogenous membrane potential oscillations. The potential oscillations of the PTFL clock could rapidly synchronize to oscillations of pheromone stimuli at different timescales, thus enabling the prediction of stimulus patterns as a mechanism for active sensing. With in vivo long-term tip recordings of long trichoid sensilla of male hawkmoths, we analyzed the spontaneous spiking activity indicative of the ORNs endogenous membrane potential oscillations. Consistent with our hypothesis of a multiscale PTFL clock in hawkmoth ORNs, spontaneous spiking was modulated on ultradian and circadian timescales, with maximum activity at night. When we blocked the evolutionarily conserved olfactory receptor coreceptor (Orco), the circadian modulation was abolished but the ultradian frequency modulation of the spontaneous activity remained. Consistent with PTFL control, Orco was not under the transcriptional control of the TTFL clock, but its modulation was dependent on cAMP. We could replicate the experimental data in a conductance-based computational model of an ORN. In this model, Orco conductivity changed as a function of fluctuating 2nd messenger levels. This study demonstrates that a PTFL clock is sufficient to impose a circadian pattern on ORN sensitivity. 2 Significance statementIt is generally assumed that all circadian rhythms in an organism are driven by a transcriptional-translational feedback loop (TTFL) clock. In this study, we demonstrate with in vivo recordings of hawkmoth pheromone-sensitive olfactory receptor neurons (ORNs) that the olfactory receptor coreceptor (Orco) is the key pacemaker channel for controlling circadian, but not all ultradian, rhythms in spontaneous spiking activity. Since Orco expression is not driven by the TTFL clock, its conductance appears to be controlled by a post-translational feedback loop (PTFL) membrane clock via 2nd messengers. Accordingly, our computational model suggests that ORN sensitivity is tuned by periodic changes in the conductivity of an Orco ion channel, which is mediated by cycling levels of cyclic nucleotides. This highlights the role of the contribution of posttranslational modifications to the generation of circadian rhythmicity.

The hexagonal structure of honeycomb maximises storage volume while minimising the amount of wax required for its construction. How honeybee builders achieve this geometry, however, remains unclear. Previously, our group identified behavioural patterns that were triggered in builders when they encountered certain sub-scale features associated with partially constructed comb, which resulted in the alignment of new cells to small concavities and the construction of cell walls between two of these stimuli. This caused new cells to be built in the proper locations without the need for explicit instructions . Here, we investigated whether the hexagonal geometry of honeycomb cells resulted from the dense packing of cells that would otherwise have been circular tubes. We hypothesised that the reaction of a builder to a cell that is not fully enclosed by other cells would be an attempt to maximise the internal space by excavating and re-forming the surrounding walls to create a cylindrical interior. However, the creation of a cylindrical cell would be thwarted by the activities of workers within adjacent cells also acting according to these rules. Eventually an equilibrium will emerge with walls that meet at a junction arranged so that the available angular range (360{degrees}) is sub- divided equally between the cells that meet at the junction (typically, internal angles of 120{degrees} when three cells meet). To test this hypothesis, we offered wax stimuli to comb-building honeybees, shaped to encourage or to constrain the construction of comb cells, recording the bees progress. We found that at an early stage cells could be an irregular shape with curved walls and unequal wall lengths and corner angles, however, when allowed further time and unconstrained access the workers reshaped the cells achieving significantly greater regularity.

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.

Nutrient absorption through the skin and gills into the organisms tissues has been documented in several aquatic invertebrates from different phyla. However, the actual absorption mechanism is still unknown. In teleost fish, as in all jawed vertebrates, intestinal absorption is considered as the sole source of nutrients. The proton-dependent peptide transporters (PepT) of the slc15a gene family are the only known mechanism for cellular absorption of di- and tri-peptides within the animal kingdom. In this study, we explored the expression and localization of PepT2 in Mozambique tilapia (Oreochromis mossambicus) larvae. Transcript levels of PepT2 in dissected yolk-sacs from larvae showed significant expression during the larval developmental period. Immunofluorescence staining of PepT2 with Na/K-ATPase (NKA) and Na+/K+/2Cl- co-transporter (NKCC) on the yolk-sac membrane revealed co-staining with NKA and differential-staining with NKCC. While NKA staining was observed on the ionocytes basolateral membrane, PepT2 staining was restricted to the apical pit of the ionocytes, facing the surrounding water. In this study, we identified a nutrient transporter located on integument-specific cells, facing the outside aquatic environment. This is the first indication of environmental nutrients absorption in teleosts, and the first evidence of a possible absorption mechanism through PepT2, in specialized yolk-sac ionocytes.

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.