Single target acuity (STA) is a key measure for understanding visual object perception in harbor seals. While STA was already determined with stationary and moving compact single targets of different contrasts in air, we herein assessed underwater STA with the same stimuli as used for aerial testing for comparison. A two-alternative-forced-choice task was conducted with two trained harbor seals under controlled light and turbidity conditions. Underwater STA was determined as 0.30 deg for stationary and 0.27 deg for moving single targets, and thus matched the previously documented aerial STA for one harbor seal. This result confirms that our test individual can resolve compact objects equally well in both media under our experimental conditions. Underwater STA decreased when contrast was reduced, reaching 0.63 deg at the lowest contrast condition tested. Performance for low-contrast stimuli was likely impacted by caustic effects, resulting from the movements of the harbor seal's head in and out of the testing basin. Additionally, as it was already found for aerial STA, no difference between underwater STA for stationary and moving single targets was documented. Our findings contribute to the understanding of amphibious vision in harbor seals and are informative regarding the perception of objects, such as prey fish.

Climbing animals need to be able to adjust their heading in both vertical and horizontal directions, requiring pitch and yaw rotation of the body axis, respectively. Stick insects are climbing herbivores that dwell among leaves and branches of the vegetation they feed on. By nature, they need to adjust their 3D heading in a complex environment. Since insects in general turn towards visual landmarks, we test whether or not stick insects initiate pitch rotation in response to landmarks that reliably elicit yaw rotation. We show that this is not the case. Instead, tactile cues alone are sufficient to mask the effect of visual deprivation, whereas lack of tactile cues strongly delays body inclination and the onset of climbing, even when the same visual landmark cues are present that are sufficient to induce turning reliably. In a second set of experiments, we use a setup that constrains the onset of turning to tell whether visually induced yaw rotation is initiated by swing movements or rather by stance movements of the front legs. We show that a turn-related left-right asymmetry of front leg movement begins at least one stance phase after passing the constraint and may begin with the first swing movement thereafter. We conclude that stick insects do not exploit visual cues for initiating pitch rotation, even though they reliably initiate yaw rotation towards the exact same landmark. Moreover, we demonstrate that yaw rotation towards visual landmarks may begin with a swing movement of a front leg, much like the pitch rotation at the onset of climbing.

Animals have evolved escape behaviors to survive. Freshwater planarians have many predators, including conspecifics in cannibalistic species such as Dugesia japonica. When agitated, planarians escape via a locomotory behavior called "scrunching", whereby the planarian periodically elongates and contracts its whole body. Current understanding is that planarians move forward when they scrunch. However, when transversely cutting D. japonica, we observed that while head pieces scrunched forward, tail pieces scrunched backward instead. Previous work has shown that forward scrunching is a conserved planarian escape behavior in response to transection and adverse stimuli such as low pH, noxious heat, hydrogen peroxide, and allyl isothiocyanate. Testing these stimuli, we found that backward scrunching is more difficult to induce than forward scrunching in both intact planarians and pieces. Using electrostimulation, we show that behavior progresses with increasing voltage from turning to backward scrunching to flailing when stimulated anteriorly, demonstrating that backward scrunching is a response to moderately strong stimuli. Moreover, we show that tail pieces - originating from transection or asexual reproduction (fission) - exhibit backward scrunching when attacked by intact planarians. Backward scrunching and backward steps of tail pieces were also observed when worms were bitten into pieces by dragonfly or damselfly nymphs, natural predators of planarians. The survival of tail pieces after fission is necessary for the expansion of asexual planarian populations. Thus, we propose that backward scrunching serves as an effective escape behavior to protect planarian tails from being eaten.

Courtship in frogs can mediate the final approach between the sexes before amplexus and spawning. It can involve male and female calling, touching, and guidance to the spawning site. Courtship behaviors have been described for several species in nature but little experimentation has been done to uncover the biological mechanisms that control them. We characterized the close-range courtship (within 10 cm) interactions in the túngara frog, an emerging model organism, to provide a quantitative baseline in a neutral arena in support of future experiments. In this initial assessment, we isolated each pair to examine only the social stimulation that is intrinsic to the pair. Among 81 pairs, 80% entered amplexus and of those 57% laid eggs. Males called before amplexus in 86% of the trials in spite of the female's proximity. The female was inferred to execute the final approach before amplexus in 79% of the events. Egg laying was concentrated in the period 6-8 h after sunset and it could be followed by calling. Multiple bouts of egg nest building were observed in 1/4 of the trials and physical contact other than amplexus was common. Male strategy, the last approach before amplexus, and egg laying were not influenced by age or body size but females with high body condition were more likely to lay eggs. Our data revealed that courtship in the túngara frog is not necessarily terminated when the male is approached by the female, but additional close-range interactions may mediate the onset of amplexus and reproductive success.

The Surinam toad (Pipa pipa) is a fully aquatic, tongueless pipid frog that captures prey using rapid suction feeding coordinated by the forelimbs. The digit tips bear distinctive lobed structures whose function has been unknown. Here we characterize the morphology, mechanical sensitivity, peripheral innervation, central representation, and behavioral function of these digit tip lobes using scanning electron microscopy, von Frey threshold measurements, in vivo electrophysiology of the brachial nerve and optic tectum, and high-speed video analysis (1000 fps). SEM reveals a progressive quadrification yielding 128 terminal lobules per frog, bearing dome-shaped papillae at 142 ± 18/mm[2]-nearly fourfold the density on adjacent digit shaft skin. Distal lobule tips have the lowest mechanical thresholds on the forelimb (median 0.07 mN). Brachial nerve recordings reveal disproportionately represented, low-threshold, predominantly rapidly adapting mechanoreceptive afferents with small receptive fields confined to the lobules, some also responsive to water current stimulation. Tectal mapping shows the digit tips are somatotopically represented and disproportionately magnified, occupying 34% of the forelimb representation despite comprising only 8% of forelimb surface area (magnification factor: 4.3×). High-speed behavioral recordings under visible light, infrared, and cobalt-blocked lateral line conditions demonstrate that frogs initiate suction feeding before prey fish contact the digits, indicating detection of hydrodynamic disturbances at short range (~ 5 mm). These results establish the digit tip lobes of Pipa pipa as somatosensory foveae-specialized mechanoreceptive organs analogous to the tactile fovea of the star-nosed mole.

Analysis of flash-induced quantum bumps (QB) recorded in vivo from photoreceptors of the blow fly Protophormia terraenovae, which were light-adapted by stimuli of varying duration and intensity, revealed that a subset of trials contained a secondary QB-like transient occurring after the primary QB. By averaging traces with onset-aligned light-induced QBs, we discovered secondary signals with the following properties: (1) The relative magnitude of the secondary signal increased with both the intensity and the duration of the adapting stimulus. The secondary signal was absent in dark-adapted photoreceptors, but following bright 10 s adapting pulses its size approached ~ 40% of the primary QB. (2) The interval between the peaks of the primary QB and the secondary signal decreased with increasing adaptation: from ~ 100 ms in minimally light-adapted photoreceptors to ~ 40 ms after the strongest stimulation. (3) The larger was the secondary signal, the sooner it appeared after the primary QB. (4) Following strong light adaptation, in five experiments we observed two and in one experiment three evenly spaced secondary peaks with progressively decreasing amplitudes. Together, these observations indicate that the secondary signal likely represents a QB arising from incomplete termination of phototransduction in some microvilli during strong light stimulation. The systematic, strong shortening of the secondary peak interval with increased adaptation implies that the microvillus refractory period in P. terraenovae is itself subject to light adaptation. Because refractory period shortening increases the pool of microvilli available for transduction, this effect would raise the effective signal-to-noise ratio of the photoreceptor in bright light.

The maintenance of body temperature (Tb) and hydration state within tolerable ranges is crucial for effective physiological functioning and thus survival. It is well established that deviations in Tb and hydration state can have immediate effects on organismal health, and recent work has demonstrated that, despite surviving the initial impacts of such challenges, individuals may experience profound long-term impacts on fitness, though the mechanisms driving these long-term impacts remain unclear. One potential mechanism underlying detrimental long-term effects is oxidative stress, yet the relationships among increased Tb, dehydration, and oxidative stress dynamics, as well as whether these relationships can be altered through adaptation, are mostly unexplored. Accordingly, we conducted complementary field and lab experiments to investigate seasonal, behavioral, thermal, and hydric effects on oxidative stress in two species of arid-adapted Crotalus rattlesnakes representing three populations from two xeric locations with differing aridity. Regardless of experiment or treatment, we found that C. pyrrhus, the most abundant species in the more arid location, had consistently lower reactive oxygen metabolite (ROM) concentrations than did C. atrox from the same and the less arid locations. Furthermore, the C. atrox population from the more arid site had ROM concentrations intermediate and often significantly different from the other two populations. Interestingly, when Tb and activity were similar between the C. atrox populations (e.g., in Spring), ROM concentrations were similar. Contrary to our hypotheses, we found no consistent patterns relating antioxidant capacity to any environmental or phylogenetic variable. Lastly, hydration state did not influence either ROM concentration or antioxidant capacity. Overall, our study demonstrates that while water deprivation and increased temperatures don't necessarily induce oxidative stress in species tolerant of these conditions, results are consistent with the hypothesis that species that are more specialized for extremely arid environments have reduced ROM concentrations. Such insight is critical as we attempt to understand how species have adapted to arid conditions and how species may respond to a warming and drying globe.

Echolocating big brown bats broadcast downward-sweeping, frequency-modulated (FM) biosonar sounds and process the returning echoes to track and capture flying insects. Neurons in the inferior colliculus are tuned to different frequencies along the FM sweep and form a representation of target azimuth largely on the basis of sensitivity to interaural differences in intensity, with canonical interaural time difference cues by themselves less reliable. Here, we reanalyze neurophysiological data on binaural sensitivity of inferior colliculus neurons consistent with a signal-processing model used in engineered sonar for generating directional beams. Model inputs are the times-of-occurrence of phasic-on responses to FM sweeps presented at a range of interaural intensities and azimuths. Tuning curves for interaural intensity were computed, and the slopes of these tuning curves plotted against neuronal best frequency and sound azimuth. The resulting aggregate plots suggest that the bat forms two distinct beams, one encompassing the entire FM sweep for a narrow zone of azimuths straight ahead and the other restricted to lower frequencies and offside to the left and the right. When interpreted with respect to psychophysical data, these analyses suggest that the forward beam allows for acute target perception, while the offside beams allow for perception of multiple objects that constitute clutter. The distribution of azimuths further suggests the formation of numerous detailed offside beams pointing in different directions to accommodate the width of the spatial arrangement of the clutter.

The pond snail Lymnaea stagnalis displays clear photoperiodism; it lays more eggs in long-day conditions than in short to medium-day conditions. The lateral lobes (LLs) are paired small budding structures of the cerebral ganglia and regulate egg laying as a coordinating center between reproduction and body growth, and LL ablation causes gigantism and attenuates egg laying. Our previous study demonstrated that the canopy cell (CC) in LL photoperiodically changes the excitability; it excites more in long-day conditions than in medium-day conditions. Here, we examined the function of CC in egg laying by the microsurgery. As a result, in long-day conditions, snails without CCs exhibited smaller albumen gland somatic index (ASI, proportion of the albumen gland/soft body) and smaller total number of egg masses laid than intact snails. In contrast, in medium-day conditions, there were no significant differences in ASI among intact, sham and CC ablation groups. Since the albumen gland produces galactogen-rich perivitelline fluid and supplies eggs with it, the CCs seem to promote egg mass production via acceleration of the perivitelline fluid production in long-day conditions. It is noteworthy that CC ablation had no effects on gonadal somatic index (GSI, proportion of the ovotestis/soft body). Besides, CC ablation caused slight increase in shell size and body weight. These imply that CCs are at least partially responsible for gigantism and decrement of egg laying caused by LL ablation, and we revealed another regulator in photoperiod-dependent egg laying in L. stagnalis. Our findings contribute to understanding neuroendocrine mechanisms underlying molluscan photoperiodism.

In invertebrates, hemocytes are the principal effector cells of innate immunity, and a growing body of evidence indicates that the circulation of immune cells is under circadian and nycthemeral control across both vertebrate and invertebrate taxa. Yet whether such temporal organisation extends to terrestrial gastropods, increasingly used as comparative models in physiology and ecotoxicology through hemocyte-based biomarkers, remains poorly documented. This study investigated nycthemeral variations in hemocyte-related parameters in juvenile, sub-adult and adult Cornu aspersum maintained under controlled laboratory conditions. Snails were sampled at four time points over a 24 h cycle (06:00, 12:00, 18:00 and 24:00; n = 20 per developmental stage and sampling time). Circulating hemocyte concentration, hemocyte viability, proportions of hemocyte types I and II, and micronucleus frequency were assessed following standardised procedures. Significant temporal variations were observed in circulating hemocyte concentration, with lower values generally recorded during evening and nocturnal sampling periods (18:00 and 24:00). Similar nycthemeral patterns were observed across developmental stages, although they were less pronounced in juveniles. In contrast, hemocyte viability, hemocyte profile distribution and micronucleus frequency remained comparatively stable throughout the 24 h cycle, suggesting the absence of marked cytogenomic fluctuations associated with sampling time under the tested conditions. These findings indicate that nycthemeral physiological rhythms may substantially influence hemocyte circulation dynamics and hemolymph accessibility in terrestrial gastropods, while exerting limited effects on basal cellular integrity. The study highlights the importance of temporal standardisation in hemocyte-based biomarker protocols and supports the integration of chronobiological considerations into ecotoxicological and comparative physiological investigations involving terrestrial molluscs.

Acoustic distance estimation in vocal species is fundamental for effective decision-making for territory defense, mate attraction, and eavesdropping predators and parasites. The most straightforward distance cue is sound pressure level. However, variation in sound pressure level within individuals is not well documented, even less the call-by-call variation that may occur within individuals, even though modulation of call amplitude will promote responses to fluctuating ecological contexts and challenges. In this study, I report on the variable and unpredictable pattern of sound pressure levels in the advertisement calls of individual running frogs, Kassina fusca. The sound pressure levels of all advertisement calls within a single calling bout were recorded for nine males. Median peak SPL between males varied between 89.5 and 98.4 dB and showed highly significant differences between males. Furthermore, the maximum change in SPL between successive calls of a male ranged between 1.7 and 12.7 dB. Run charts of each male indicated random patterns of variation in SPL's during the recorded call bout. The results of this study are best explained as a mechanism to interfere with accurate distance estimation, either by competitors, parasites, or predators.

Communication systems shape behavioral interactions that are crucial for recognition, territoriality, and reproduction across animals. In many anuran species, acoustic communication drives reproductive and defensive behaviors as males produce advertisement calls to establish territories and attract females. Understanding the temporal dynamics in vocalizations and their variation between and within males can provide crucial insight into the mechanisms that generate call patterning and communication. Here, we examine such dynamics in the call patterning of male Boana pulchella, a South American treefrog species that produces temporally-variant call series over time. Using rhythm analysis, we quantify the rhythmic structure of these vocalizations and characterize the variability in their temporal patterning between males. We find that rhythmic isochrony is timescale-dependent - call series are produced isochronously while the patterning of calls and notes within these series is non-isochronous yet periodic. The isochronous rhythm is maintained through an inverse relationship between series duration and the silence interval that follows it, such that longer series are followed by shorter silence intervals. Temporal features of calls and notes as well as their variation vary depending on within-series patterning dynamics and across timescales. Taken together, these results suggest that B. pulchella vocal timing is generated by hierarchically organized oscillators that produce isochronous vocalizations over a calling bout through flexible modulation at finer timescales.

The exact location of the dominant pacemaker site in adult bird heart continues to be ill-defined. The aim of this study was to identify the localization of the dominant pacemaker and to investigate its electrophysiological characteristics in isolated sinoatrial preparations of the adult chicken (Gallus gallus domesticus) heart. The dominant pacemaker was localized at the base of the right leaflet of the valve of the right cranial vena cava and at the base of both leaflets of the valve of the caudal vena cava. But latent pacemakers were also identified in regions around these valves. Additionally, the valve leaflets generated conducting-like APs that with high amplitude, fast maximal upstroke velocity (greater than in working myocardium) and with diastolic depolarization. The avian sinoatrial junction is electrophysiologically heterogeneous. The avian dominant pacemaker site is more extensive than that in mammals. These findings establish a foundation for understanding species-specific pacemaker mechanisms and their evolution.

Estuarine fishes experience marked environmental variability and rely on tightly regulated osmoregulatory mechanisms to maintain internal homeostasis. Settleable atmospheric particulate matter (SePM), a complex mixture of metals and metalloids, is an emerging stressor in aquatic systems and may interfere with regulatory processes. This study investigated the effects of SePM exposure on osmoregulatory homeostasis in the estuarine fish Centropomus parallelus. Fish were exposed for 96 h to either 0 g.L[-1] (control) or 1 g.L[-1] SePM, and key physiological endpoints associated with ion and water balance were assessed, including plasma osmolality and Na[+], Cl[-], and K[+] concentrations; Na[+]/K[+]-ATPase (NKA), V-type H[+]-ATPase (VAT), and total ATPase activities in the gills and kidneys; and ionocyte abundance and transporter protein levels in gill ionocytes and renal tubules. Aluminum, iron, vanadium, and chromium levels were accumulated in the gills and kidneys. SePM exposure disrupted osmoregulatory homeostasis, as evidenced by reduced plasma osmolality and decreased Cl[-] and K[+] concentrations. NKA activity was upregulated in the gills, accompanied by an increase in the density of NKA-positive ionocytes. Conversely, total ATPase and VAT activities were downregulated in the kidneys, whereas the abundance of NKA, the symporter Na[+],K[+],2Cl[-] (NKCC), and the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride (Cl[-]) channel, remained unchanged in renal tubules. These findings suggest that SePM exposure is associated with tissue-specific modulation of osmoregulatory parameters, including increased branchial Na[+]/K[+]-ATPase activity and NKA-positive ionocyte density, and reduced renal ATPase activities, accompanied by alterations in plasma osmolality and ion concentrations. The physiological disturbances associated with SePM exposure may impair organismal performance and reduce ecological fitness in estuarine fishes inhabiting metal-impacted coastal environments.

Transient receptor potential (TRP) channels mediate insect thermosensation, yet the downstream neurotransmitter pathways linking TRP activation to behavioral output remain unclear. We investigated the role of nicotinic acetylcholine receptors (nAChRs) in thermoregulatory and neural responses induced by TRP ligands in the American cockroach, Periplaneta americana. Extracellular recordings from the ventral nerve cord showed that capsaicin reduced spontaneous neuronal firing, whereas the selective α7-containing nAChR antagonist MG 624 increased baseline activity. Notably, nicotinic receptor blockade prevented the capsaicin-induced suppression of neuronal activity, suggesting an interaction between cholinergic signaling and capsaicin-induced neuronal modulation. Behaviorally, capsaicin shifted thermal preference toward cooler temperatures, consistent with TRP-mediated heat avoidance. This response, as well as the effect of the TRPV1 antagonist capsazepine, was markedly attenuated by MG 624 pretreatment. Grooming assays revealed differential modulation of antennal and leg grooming, suggesting distinct neural mechanisms and partial interaction between cholinergic and monoaminergic pathways. Despite pronounced neural and behavioral effects, neither TRP ligands nor nicotinic receptor blockade significantly altered whole-animal metabolic rate, as assessed by CO2 production. Together, these findings indicate that cholinergic signaling contributes to behavioral responses induced by TRP ligands and interacts with capsaicin-induced neuronal modulation in P. americana. The results provide new insight into the neurochemical integration of thermosensory signaling and highlight cholinergic pathways as important contributors to insect thermoregulatory responses.