Journal of Experimental Biology最新文献

Supervised machine learning is commonly used to classify fine-scale behaviours from animal-borne accelerometers, assigning new data to predefined behaviour categories seen during training. These models cannot recognise novel behaviours as 'unknown', however, and, when exposed to new behaviours, will continue to overpredict the known classes. This issue - known as open-set recognition - is an inevitable, but underexplored, limitation in accelerometer-based behaviour classification. Here, we describe the problem and assess four solutions: (1) a multiclass model with an 'other' category, (2) threshold-based models, (3) one-class models and (4) binary one-versus-all models. We show that traditional multiclass models produce high false-positive rates when exposed to behaviours not present during training. We instead suggest the implementation of binary one-versus-all models as a more conservative method, particularly in cases where a single or limited set of behaviours are of interest. Awareness of this challenge will enhance recognition of often unreported uncertainty in real-world applications.

Understanding the neural basis of animal behaviour requires a thorough description of the associated sensory inputs. This is especially important when behaviour actively shapes incoming sensory information. Weakly electric fish use perturbations in a self-generated electric field as a basis for an electric sense, and these field perturbations are encoded by electroreceptors distributed over their bodies. Thus, swimming movements and body pose shape not only the field but also the orientation of the receptor array. Previous modelling in this context has focused primarily on the so-called electric image in stationary fish and has not addressed how natural electrosensory inputs are generated in freely swimming fish. Here, we present fish2eod, an open-source finite-element-based modelling framework that describes the dynamics of electrosensory inputs during natural behaviours, including social interactions, in complex environments.

Freshwater ecosystems play a critical role in supporting biodiversity and providing essential environmental services. However, these ecosystems are increasingly threatened by human activities, including habitat loss, pollution and climate change. Traditional assessment methods focus on water properties, but biomonitoring approaches, particularly those examining behaviour and cognition, provide valuable insights into the ecological effects of pollutants. This study examines the effects of three common pollutants (glyphosate, atrazine and paracetamol) on the cognitive abilities of Aedes aegypti mosquito larvae, a vector for several diseases. We used an automated bioassay to study habituation learning and the effects of the three pollutants alone or in combination, at sub-lethal doses ranging from field-realistic to commercially recommended levels. Our results show that the three compounds modulate individual spontaneous activity and impair habituation and memory retention. These changes may alter the perception or the behavioural response of mosquito larvae to signals of their environment as indicating the presence of conspecifics or predators, and suggest that other organisms living in freshwater ecosystems may also be affected. Incorporating behavioural and cognitive assessments in ecotoxicological studies provides a more comprehensive understanding of the ecological effects of pollutants, which is needed to address economic challenges in fragile ecosystems.

Southern right whales (Eubalaena australis; SRWs) are well adapted to cold waters because of their large body size and thick blubber. Each year, they migrate from high-latitude feeding grounds to warmer breeding grounds where they give birth. To assess thermal benefits of this migration, we modelled the effects of body size, condition and water temperature on heat loss. Using unmanned aerial vehicle photogrammetry at the Península Valdés calving ground in Argentina, we measured body length, volume, condition and surface area of living SRWs. Blubber thickness was predicted from a blubber-mass model and validated using necropsy/catch data. Sensible heat loss was estimated using a model incorporating blubber thermal conductivity and body temperature, whereas respiratory heat loss was based on respiration rate and tidal volume models. We compared heat loss in Península Valdés with that in South Georgia/Georgia del Sur (SG/GS), a key feeding ground. Body size had a strong positive effect on both heat loss values, but mass-specific loss decreased as surface-area-to-volume ratio declined. Increased body condition reduced sensible heat loss. Migration from SG/GS to Península Valdés reduced calf heat loss by 26% during early lactation. However, total heat loss remained low relative to field metabolic rate (FMR), indicating limited thermoenergetic benefit from migration. Only at poor body condition (<-0.35) did heat loss exceed FMR, threatening survival. Notably, gull-inflicted lesions significantly increased heat loss in small and poorly conditioned calves, but had no effect on larger or better-conditioned calves. These findings highlight body condition as a key regulator of heat loss in baleen whales.

Positive phototaxis in diurnal bees is modulated by the wavelength and intensity of light. Unlike diurnal bees, nocturnal bees such as Megalopta aegis forage exclusively during twilight, when light intensity drops rapidly and irradiance peaks in the blue spectrum. How light parameters influence phototaxis in these nocturnal bees remains unclear. We evaluated the phototactic responses of M. aegis in a dark circular arena using UV, blue and green monochromatic lights presented at six absolute intensities. In contrast to diurnal bees, M. aegis was not always attracted to light. When attracted, they showed stronger attraction to UV than to blue or green. Paths toward UV were shorter, faster and straighter, suggesting a greater involvement of UV photoreceptors in this phototactic behaviour. Compared with honeybees tested in similar experimental setups, M. aegis exhibited slower but more directed paths. These results align with their highly light-sensitive eyes, which trade off temporal resolution for improved reliability in dim light.

The Otsuchi Coastal Research Center (OCRC), a field station belonging to the Atmosphere and Ocean Research Institute at the University of Tokyo, was established in 1973 in Otsuchi, a coastal town on the Sanriku coast of Honshu, Japan. Located near a site where warm and cold ocean currents converge, OCRC facilitates research in biology, chemistry, physics and geoscience within a unique marine environment shaped by a complex rocky coastline and river-fed bays. The centre is staffed by resident researchers and technicians, provides research vessels and a dormitory, and supports around 2000 person-days of visiting scientists annually for field observations, aquarium-based experimentation and instrumental analyses. Since 2004, we have pursued biologging studies at OCRC with graduate students and collaborators from Japan and abroad. This research has focused on loggerhead and green turtles, streaked shearwaters, chum salmon and ocean sunfish, producing insights into physiology, behaviour, ecology and environmental science. In 2011, the original research building and dormitory were severely damaged by an earthquake and tsunami, resulting in the loss of field notes, materials and some data. Fortunately, there were no casualties, and a new research building and dormitory were rebuilt on higher ground in 2018. To enhance data preservation, the biologging intelligent platform (BiP) was established to archive biologging datasets with their associated metadata. To better understand how marine animals respond to ongoing environmental changes, continued long-term field research and historical data comparison are essential. With access to diverse ecosystems and robust technical infrastructure, and its collaborative research culture, OCRC is uniquely positioned to potentially meet that demand.

Weakly electric fish rely on electrosensory, visual and mechanosensory (lateral-line) cues to guide behavior in flowing water, yet the effects of ambient currents on multisensory tracking and active sensing remain poorly understood. We tested the weakly electric knifefish Apteronotus albifrons (n=4) tracking a moving refuge in a recirculating flow tunnel while systematically varying flow speed (0-16 cm s-1), illumination (light versus dark) and refuge structure (windowed versus non-windowed). Tracking performance was quantified with time- and frequency-domain measures (root-mean-square error; gain-phase analyses), and active sensing as movement power outside stimulus frequencies (mean active sensing power, MASP). Increasing flow degraded tracking: relative to still water, RMSE rose by ∼46% at 16 cm s-1. Deficits were largest in darkness and with the windowed refuge, and were concentrated at low stimulus frequencies. Under higher flows, fish showed a trend toward increased off-frequency movement power (by ∼33%), consistent with compensatory active sensing to sustain sensory acquisition. The effects were non-linear and context dependent. This pattern indicates that increasing hydrodynamic noise may drive dynamic reweighting among visual, electrosensory and mechanosensory inputs. Collectively, our data indicate that ambient flow degrades low-frequency tracking and may elicit compensatory active sensing in A. albifrons, extending recent demonstrations of context-dependent sensing and control switches in this species and bridging rheotaxis with electrosensory refuge tracking.

Sensory systems adapt to environmental change through behavioral and neurogenic plasticity. We examined brain cell proliferation in sensory structures in response to long-lasting sustained darkness. Female Austrolebias reicherti were exposed to continuous darkness or a natural light:dark cycle for 45 days. At the end of this conditioning period, sensory clues involved in sexually oriented behaviors and brain proliferation were compared between groups. To assess functional implications, a dual choice test was performed under different sensory conditions (visual and olfactory) using conspecific or heterospecific (same genus) males. To evaluate proliferation, individuals received a single BrdU injection 3 days before fixation. BrdU+ cells were evaluated in the brain and their density distribution was quantified in the optic tectum (TeO), torus longitudinalis (TL) and olfactory bulb (OB). Cell proliferation in dark-maintained females was greater in the OB, whereas cell proliferation in light-maintained females was greater in the TeO and TL. Concordantly, females in the darkness condition were better at identifying conspecifics using smell than those in the light condition, whereas those in the light condition were better at identifying conspecifics using vision than those in darkness. The brain optimized to function most effectively under specific light conditions, adjusting cell proliferation to reinforce neural sensory circuits with the greatest demand. In conclusion, the average strength of sustained darkness conditions modulates neurogenesis in key sensory brain regions and influences the ability of females to discriminate between conspecifics and heterospecifics. Sensory plasticity in response to environmental variability may play a crucial role in adaptive and evolutionary processes in this species.

Many animals form behavioral collectives, and optimal interaction strategies often differ across social contexts. Sensory scenes generated by many interacting conspecifics are complex. Thus, maintaining socially calibrated responses requires individuals to distill key features from conspecific scenes to guide continued adjustments to social fluctuations. Túngara frogs produce mating calls in choruses varying in size, and interaction patterns differ across social environments; rivals alternate their calls in smaller choruses, but increasingly overlap one another's calls in a stereotyped fashion as chorus size increases. We used automated playback to investigate the cues guiding this socially mediated shift in interaction modes. We played conspecific stimulus calls to males at various delays relative to their own calls, preceded by various acoustic motifs that mimicked conspecific stimulation patterns males will hear in different social environments. Males almost never overlapped isolated stimulus calls at any delays. However, their probabilities of overlapping stimulus calls increased markedly when stimulus calls were preceded by motifs characteristic of larger choruses, i.e. those exhibiting intense conspecific stimulation patterns. Furthermore, the escalatory effects of motifs became increasingly pronounced as motif/stimulus combinations were played at later delays. Thus, interaction strategies are calibrated to current social dynamics each call cycle in response to a multifaceted cue that incorporates both the nature of conspecific stimulation experienced and how the timing of this stimulation interacts with endogenous responsiveness rhythms. Our results highlight that inactive phases within behavioral rhythms provide repeated opportunities to sample current social dynamics, allowing response patterns to be continually calibrated to social fluctuations in behavioral collectives.