Oscine songbirds show remarkable diversity in song organization spanning from long songs composed of many different syllables to short single songs. All of these likely arose through sexual selective forces and therefore are thought to reflect a singer's skill, often described as vocal performance. It is therefore important to gain insight into the song production mechanisms in species that sing a single, short song. Here we investigated the physiological control underlying learned song and other song-like vocalizations in the white-crowned sparrow (Zonotrichia leucophrys) by recording air sac pressure, tracheal and bronchial airflow and sound during spontaneously generated vocal behavior in 19 males (11 tutored, 8 untutored). The left side of the syrinx tends to produce more contributions to most song syllables than the right side, while both sides generate similar and overlapping frequency ranges and interact in the production of buzzy syllables. Two other song-like vocalizations, trills and twitter song also require sophisticated respiratory and syringeal movements. Trills display the most rapid temporal pattern with mini-breath rates of > 20 Hz. This illustrates that vocalizations other than typical song can also inform us about vocal performance. The basic production mechanism and syringeal lateralization was consistent between tutored and untutored birds, as well as across the different vocalizations studied here, suggesting innate development of the respective contributions of the two sound sources.

The magnetic compass has been shown in several classes of vertebrates, including anuran amphibians. Frogs obtain information from the magnetic field (MF) to follow migratory directions during their movements between wintering and breeding sites. In birds that are most studied in this respect, the magnetic compass sensor is thought to be located in the retina, and we explored this possibility in anurans. We previously reported the effect of the MF on the avian retina by electrophysiological methods; in the present study, we performed similar research in amphibians. Marsh frogs were captured in southern Russia in early autumn, and subsequently induced into a breeding migratory state through exposure to a spring-like photoperiod and temperature. Electroretinograms (ERGs) were recorded from isolated retinas that were carefully oriented in the sample holder to ensure consistent application of the MF. ERGs in response to red, blue, and ultraviolet light flashes were recorded under different MF directions: baseline (field passing through the eye during eastward migration, the predominant migratory direction for this frog population) and inverted inclination. Data were also examined by MF orientation relative to the retinal preparation (near‑perpendicular/near‑parallel). Our analysis revealed no significant effect of MF direction on the amplitudes of the a‑ or b‑waves of the ERG in response to light of any wavelength. This suggests that the sensory mechanism of the magnetic compass in frogs is either not located in the retina or that the reaction is so subtle that it cannot be recorded using the total ERG from the entire retina.

More than half a century ago, Buchner (1971) evaluated the visual axes of the ommatidia in a Drosophila's neural superposition eyes, using the pseudopupil method. The spatial distribution of the visual axes was reported in a stereographic projection chart. Analysis of this chart shows that the ommatidial lattice is well described by a horizontal-vertical (H-V)-coordinate system, which allows assessment of the partial interommatidial angles between the vertical columns and horizontal rows of ommatidia, Δφh and Δφv, respectively. Their angular ratio ρa = Δφh/Δφv is expected in an ideal neural superposition eye to be √3, but this appears to hold only in a central band of the eye. Dorsally and ventrally ρa is much smaller, while posteriorly it is much larger. The quite different gradients of Δφh and Δφv over the eye cause distinct regional deviations from ideal neural superposition. Instead of the interommatidial angle Δφ, considered to be the central factor determining the eyes' spatial resolving power, the local values of Δφh and Δφv will presumably be the important determinants for the spatial resolving power, at least for the vertical and horizontal motion-sensitive neurons in the fly brain. Various ways to chart the visual space of a compound eye are demonstrated and discussed.

Social context is a key modulator of behaviour and cognition across taxa, yet the effects of social isolation (SI) and subsequent recovery remain poorly characterised in invertebrate systems. Here, we developed a longitudinal behavioural procedure to examine how SI and social reintroduction (SR) influence feeding, exploration, and operant conditioning behavioural assays in the pond snail Lymnaea stagnalis. To capture biologically relevant variation, we compared two populations with differing environmental backgrounds: a long-established laboratory strain (W) and a "wild" population (TC1). Isolation was associated with reproducible changes across multiple behavioural domains, including reduced feeding and impaired memory performance in an operant conditioning assay. These effects emerged more rapidly in laboratory-inbred snails, whereas the "wild" ones required a longer isolation period to exhibit comparable behavioural alterations, indicating differences in response dynamics between populations with distinct environmental backgrounds. Following SR, behavioural recovery was modulated by social context. In W snails, social reintroduction with familiar conspecifics was associated with substantial recovery, whereas social reintroduction with unfamiliar conspecifics produced more limited improvement. In contrast, TC1 snails showed a delayed onset of behavioural disruption and less complete recovery after social reintroduction within the tested Timeframe, irrespective of conspecific familiarity. Together, these findings demonstrate that responses to social isolation in L. stagnalis are strongly influenced by population background and the social environment during recovery. By integrating laboratory-reared and "wild" populations within a multi-behavioural approach, this study establishes a tractable framework for future investigations linking social context to the neural and molecular mechanisms underlying behaviour and learning.

In arid environments or during prolonged drought periods, maintaining hydration becomes increasingly challenging, often requiring organisms to reduce investment in costly behaviors. Vocal performance is sensitive to hydration status because systemic dehydration can alter vocal fold mechanics and reduce vocal efficiency. In many mammals, vocalizations are produced when expiratory airflow induces self-sustained vibration of the vocal folds, making this mechanism vulnerable to systemic water imbalance. This study tested whether dehydration alters singing rate and acoustic song parameters in adult California mice (Peromyscus californicus). Mice were recorded over three days of water deprivation. Baseline variation was first assessed in a control group of ten animals with unrestricted water access; vocal activity and seven acoustic parameters showed no consistent daily trends. Vocal activity and acoustic parameters were then evaluated in 14 mice subjected to 72 h of water deprivation. Vocal activity did not decline during dehydration. Fundamental frequency, sound intensity, and syllable repetition rate decreased significantly during late-stage dehydration but recovered toward baseline after water restoration. Changes in fundamental frequency and sound intensity are consistent with altered vocal fold biomechanics associated with reduced tissue hydration, whereas reduced syllable repetition rate without changes in syllable duration suggests an additional effect on temporal control of vocal output. These findings demonstrate that systemic dehydration affects multiple components of vocal production and that vocal performance recovers following rehydration.

Insect photoreceptors are non-spiking neurons that encode visual information with graded voltage responses produced by stochastic activation of the phototransduction cascade in the microvilli. However, light-evoked, voltage-gated sodium channel (NaV) dependent axonal spikes have been reported in several species, where they are thought to support downstream signal transmission. Here we report a new mode of electrical activity in rhabdomeric photoreceptors: spontaneous trains of small, fast spikes appearing in darkness immediately after piercing the membrane. These spike trains differed from both quantum bumps and conventional axonal spikes. They occurred without light stimulation, persisted for tens of seconds to minutes, exhibited several millivolt amplitudes, and had kinetics and waveforms resembling NaV-dependent regenerative action potentials. Several lines of evidence indicated that spikes are generated in distal parts of the axon. First, spiking was suppressed by off-axis illumination that produced minimal somatic hyperpolarization, consistent with the effects of lateral interactions on axon terminals in the neuropil. Second, observation of spike superposition indicated that they can arise from multiple electrotonically separated loci and summate at the soma, suggesting distal, spatially separated spike-generating sites. Third, while spiking was sensitive to experimentally imposed changes in somatic membrane potential, spike frequency and duration often changed spontaneously and independently of it. Spiking spontaneously and irreversibly terminated through a gradual decline in spike frequency and often amplitude, consistent with a progressive reduction in NaV channel availability. Our results suggest that spontaneous spike trains reflect a transient shift in axonal excitability, possibly triggered by electrical perturbations associated with membrane penetration.

Medicinal leeches have long served as classic systems in comparative neuroethology because individual neurons can be identified across animals and linked to well-defined behaviors. This review argues that Hirudo verbana is now positioned for a new phase in which this identified-cell framework can be connected directly to molecular mechanisms. We first outline the organization and experimental accessibility of the leech nervous system, then evaluate genomic and transcriptomic resources as tools for testing physiologically constrained hypotheses rather than as endpoints in themselves. We focus on selected problems in which behavior, identified neurons, and molecular candidates can be brought into close alignment: sensory encoding, serotonergic state-dependent gating, multifunctional behavioral circuits, heartbeat rhythm generation, and endocannabinoid-dependent plasticity. Across these examples, the comparative value of Hirudo verbana lies not in nervous-system simplicity alone, but in interpretability: receptors, ion channels, pumps, peptides, gap-junction proteins, and metabolic enzymes can be examined in relation to cellular and circuit operations already defined by physiology. Future progress will require tighter integration of circuit-defined phenotypes with cell-resolved transcriptomics, spatial localization, targeted perturbation, and quantitative modeling. This circuit-constrained strategy positions Hirudo verbana as a valuable bridge between classical identified-cell neuroethology and molecular tests of circuit physiology.

Physiological biologging is a flourishing field enabling researchers to answer fundamental questions about animal behaviour and physiology in their natural environment. As biologging devices are further miniaturised their use on small species (< 1.5 kg) is increasing-making this a pivotal time to review how this technology is being used, and what technological limitations and practices users must be aware of, to answer questions in small animals. Here we focus on the applications of devices that measure heart rate and their use as a proxy for energy expenditure in small terrestrial species. We outline essential considerations for programming (i.e. ECG sampling frequency) and placement of devices, and strongly advocate for the verification of heart rate measurements via ECG analysis where possible. As devices become smaller, cheaper, and more effective there is a growing capacity for integration of multiple sensors on a single device. This has broad implications for the study of energy budgets, stress and conservation management in small species. We encourage users of biologging technology to thoughtfully consider our recommendations to make the most of what this technology can offer.

Migrating animals can track resources to maximize energy intake, but moving may also expose them to rapid changes in weather that require thermogenic defense. The Migratory Flexibility Hypothesis predicts that migrants exposed to variable conditions may need to be more flexible in thermogenic response. Here, we investigate metabolic flexibility of the red crossbill (Loxia curvirostra), an altitudinal and latitudinal nomad that experiences wide variability in climate, to determine how flexibility in migration relates to thermogenic flexibility. Two ecotypes of captive red crossbill (Type 3 and Type 5) that vary in degree of nomadism were transferred to thermoneutral (21 °C) or cold (6 °C) temperatures during their spring migratory period. Metabolic rates and baseline corticosterone levels were repeatedly measured across nine days during acclimation. Both ecotypes of red crossbill showed the fastest increase in thermogenic capacity (Msum) yet documented in songbirds, and this change was accompanied by higher basal maintenance costs but not upregulation of baseline corticosterone, suggesting that acclimation did not induce allostatic overload. Furthermore, crossbills in thermoneutral temperatures, that were exposed to only a single 90-minute cold exposure during Msum measurement, transiently upregulated Msum, demonstrating high sensitivity to even brief cold exposure. Type 5 red crossbills, which frequently live at very high elevations, showed slightly steeper increases in Msum despite being considered less nomadic. These findings indicate that metabolic flexibility may be advantageous for species that experience rapid temperature oscillations during migration, but the ability to upregulate may be most related to duration and extent of temperature extremes.

This study evaluated the effects of varying dietary carbohydrate (CBH) levels on growth performance, body composition, hematological parameters, metabolism, and intestinal and hepatic enzyme activity in juvenile red-bellied pacu (Piaractus brachypomus). Fish (initial weight 70.25 g) were fed three times daily to apparent satiety for 45 days with diets containing 371.80-378.20 g kg-1 crude protein and 17.00-17.42 MJ kg-1 gross energy, and supplemented with 230, 260, 290, 320, or 350 g CBH kg-1. Fish were distributed among 15 tanks (practical volume of 800 L; stocking density of 0.878 g L-1), with treatments replicated 3 times. Optimal growth performance, feed conversion ratio, and whole-body nutrient deposition were observed in fish fed diets containing 260-290 g CBH kg-1. Fish fed the highest CBH level (350 g kg-1) exhibited reduced erythrocyte counts but increased hemoglobin concentration. Increasing dietary CBH levels resulted in higher hepatosomatic index, plasma triglyceride concentration, and liver and muscle glycogen stores, while reducing the viscerosomatic index and hepatic aspartate aminotransferase activity, with no effect on glycemia. Intermediate CBH levels (260-320 g kg-1) increased intestinal amylase and lipase activities but reduced alkaline protease activity. In the liver, high-CBH diets stimulated the activity of key enzymes involved in glycolysis (6-phosphofructo-1-kinase, PFK1; and pyruvate kinase, PK), the pentose phosphate pathway (6-phosphogluconate dehydrogenase, 6PGDH), and the tricarboxylic acid cycle (isocitrate dehydrogenase, ICDH), while decreasing the activity of rate-limiting enzymes in gluconeogenesis (fructose-1,6-bisphosphatase 1, FBPase1) and amino acid deamination (glutamate dehydrogenase, GDH). In conclusion, dietary CBH levels between 260 and 290 g kg-1 are recommended to optimize growth performance and enhance digestive and hematometabolical efficiency in juvenile red-bellied pacu. Exceeding this range may impair performance and welfare, highlighting the importance of precise dietary formulation in aquaculture.

Sleep is a widespread biological state found across both vertebrates and invertebrates, yet its expression and functions remain incompletely understood. Comparative research shows that invertebrates, including insects, exhibit behavioral and neurophysiological features that parallel vertebrate sleep, such as immobility, increased arousal thresholds, homeostatic rebound, and state-dependent neural activity. Insects combine compact nervous systems with well-characterized learning behaviors, making them powerful models for uncovering the mechanisms and functions of sleep. Here, we review sleep in insects with a focus on Apis mellifera and new data on polyphasic sleep patterns revealed by automated video analyses of antennal movement over day-long experimental periods. By comparing invertebrate and vertebrate sleep, we highlight both conserved and divergent features that inform hypotheses about sleep's adaptive roles in memory consolidation, energy regulation, and behavioral architecture. These insights underscore the value of invertebrate models for advancing comparative neuroscience and for inspiring computational approaches to challenges such as catastrophic forgetting in artificial neural networks.

Nocturnal activity in bats is defined by the timing of flight initiation at dusk and flight termination at dawn. In addition to the endogenous 24-hour circadian rhythm, these flight activities are influenced by environmental cues operating over longer timescales, particularly lunar phases and seasonal variation. Although the influence of lunar phases on the flight activity of Rousettus leschenaultii has been reported, little is known about their effects on Rhinolophus rouxii or about how seasonal variation influences the emergence and return times of these two co-roosting bat species over an annual cycle. The abandoned temple-like structure, Gaddige Maṭha, located between forests and village settlements in Western Ghats, provides a unique opportunity to compare the flight activities of two species with contrasting foraging guilds in a shared roosting environment. We investigated the effects of 12 consecutive lunar cycles (comprising four lunar phases) and three seasons (winter, summer, and monsoon) on bat emergence and return flight timings. Emergence and return surveys were conducted from October 2024-September 2025, and the data analyzed using Generalized Linear Models. Contrary to previous reports indicating a lunar influence on the flight activity of R. leschenaultii, our findings revealed that lunar phases had no significant effect on the flight activity of either R. leschenaultii or R. rouxii. In contrast, seasonal variation, particularly during the monsoon, was the primary driver of flight activity in both species. These findings highlight the importance of considering both species-specific responses and region-specific environmental conditions when developing conservation strategies for bats.

The striped murrel (Channa striata) is a high-value food fish in Southeast Asia; however, captive breeding success has remained limited due to a lack of knowledge about its reproductive physiology. This study examined the impact of synthetic gonadotropin-releasing hormone analogue (sGnRHa) on the reproductive biology of females. Brooders (450-650 g) were administered sGnRHa at 0.4 mL/Kg for male and 0.6 mL/Kg for female brooders (n = 18) and 0.9% saline as a control (n = 6). To assess temporal steroidogenic responses, samples were collected at 0, 6, and 12 h post-injection. qPCR analysis was used to examine the expression of key steroidogenic genes, while enzyme immunoassay measured serum concentrations of estradiol, vitellogenin, and progesterone. Results indicate significant temporal responses to sGnRHa treatment. The StAR gene exhibited the most pronounced response at 6 h of post-injection. Cyp17α and Hsd17β showed peak expression at 6 h, coinciding with maximum serum estradiol (380 ± 18 pg/mL) and vitellogenin (28 ± 3 ng/mL) concentrations. Cyp19a and Hsd3β demonstrated delayed responses, reaching peak expression at 12 h. Progesterone levels were elevated at 6 h of post-injection, from a baseline of 240 ± 15 pg/mL to 310 ± 18 pg/mL. Histological examination revealed partial induction and did not show a significant change after treatment. The coordinated temporal regulation indicates that sGnRHa effectively stimulates the steroidogenesis. Early up-regulation of StAR, Cyp17α, and Hsd17β drives estrogenic activity and vitellogenesis, while delayed activation of Cyp19a and Hsd3β facilitates maturation. These findings provide insights into reproductive physiology and contribute to optimising captive breeding protocols of C. striata for sustainable aquaculture.

Seasonal variations influence environmental factors such as ambient temperature, sunlight duration and the availability of food resources, leading many species to develop behavioral and physiological adaptations. The present study explores the effect of seasonality on locomotor activity, rest and sleep patterns in captive dromedaries. Six adult female dromedaries were studied during the four seasons. Non-invasive PSG recordings (EEG, EOG, EMG) and behavioral observations were made over 72-h periods per season for each animal. The photoperiod varied seasonally from approximately 12.4 h in spring, 14.2 h in the summer, 12.4 h in autumn and 10.1 h in winter. The results reveal a robust diurnal activity pattern in dromedaries, with activity mainly concentrated during the day and rest dominating at night. The duration of motor activity shortened between summer and winter (17.1 h vs. 11.6 h). Seasonal differences were observed in vigilance states. In winter, the percentage of wakefulness was lower (52. 9%) than in summer (59. 8%), while drowsiness was higher in winter (10.1%) than in summer (6.8%). During the day, rumination was observed to be higher in summer (14.4%) than in winter (8.6%). Furthermore, total sleep time (TST), defined as the sum of drowsiness, NREM sleep and REM sleep, was significantly higher in winter (4.8 h) than in summer (3.6 h). This study demonstrates that the duration of activity, rest and sleep in dromedaries varies according to the season in outdoor captivity. The longer winter dark phase (~ 14 h) was accompanied by an increase in total sleep duration compared to the shorter summer dark phase (~ 10 h). These findings underscore the pivotal role of photoperiodic changes in regulating the locomotor activity/rest and sleep/wake cycles of desert species.