Current Biology最新文献

Torpor is a controlled physiological state of reduced metabolism and typically body temperature (T_b) used by some endothermic animals to reduce their resting energy expenditure^1,2 and increase survival during unfavorable environmental conditions.^3,4,5,6 Passerine birds, the largest avian order, have long been considered limited to shallow reductions of T_b (min. T_b usually >30°C; undocumented <23°C) during part of their rest phase,^7,8 with deeper and longer torpor restricted to a few non-passerine bird groups.⁹ Here, we used temperature telemetry to record the skin temperature (T_s; as a close proxy for core T_b) of free-living white-backed swallows (Cheramoeca leucosterna; 15 g) during winter in inland Australia. This species is an aerial foraging passerine bird that roosts in burrows. On most nights, we measured only shallow reductions in T_s; however, during and after rainfall events, tagged birds remained inactive in their burrows during the daytime and employed bouts of torpor that were relatively deep (min. T_s: 18.8°C) and long (max.: 17.5 h). The depth of torpor and extension of torpor beyond the nocturnal rest phase expand the known capabilities for heterothermy within passerine birds. For aerial foraging swallows, torpor is presumably an important adaptation for reducing starvation risk during weather events that reduce prey availability. Our findings have implications for understanding avian thermoregulatory strategies, the evolution of torpor, and how endothermic animals cope with extreme weather events. They also highlight the power of biologging to reveal previously unknown physiological capabilities and provide insight into the adaptive importance of animal responses to natural environmental conditions.

Electric eels are famous, and rightly so. They have a storied history as perhaps the first model species in science, having been used to explore the link between biology and electricity since the 1700s. In 1775, John Walsh obtained the all-important 'spark' from an electric eel, suggesting man-made electricity and animal electricity are equivalent. In the year 1800 Alessandro Volta invented the first battery based on the anatomy of the eel's biological batteries (electrocytes). In the same year Alexander von Humbolt purportedly observed the extraordinary spectacle of South American fishermen herding horses into a pool containing electric eels. His description of the ensuing battle was published in 1807, catapulting electric eels (and Humbolt) to world fame. Later, in 1838, Michael Faraday - the father of modern electrostatics - published an extensive investigation of electric eel discharges, sealing the case for biologically generated electricity and kicking off modern studies of physiology. These and other studies presaged Krogh's principle in biology - that there is an animal of choice best suited for a particular biological problem - long before August Krogh was born.

Identifying individuals within a species is a cornerstone of ecological and biological research, holding the key to understanding behavior, population dynamics, and conservation needs. However, conventional identification methods such as genetic sampling and physical tags come with significant trade-offs, including invasiveness, high costs, and limited scalability. Despite remarkable advances in computer vision that have transformed the identification of patterned species, reliably distinguishing individuals in unmarked species remains an open challenge. Here, we curate a novel dataset of visually identified individual Alaskan coastal brown bears (Ursus arctos). This 72,940-image dataset contains high-resolution images of 109 known individuals from multiple seasons and in varied conditions (e.g., fur shedding, substantial weight gain). Identification of these bears is notoriously difficult, yet our new pose-aware metric-learning-based AI model is able to leverage biometric information that enables individual re-identification (ReID) with promising accuracy for future research and conservation efforts. Our findings indicate that it is possible to reidentify individual brown bears across years and to detect unknown individuals in a "real-world" open dataset. PoseSwin presents a promising approach to the challenge of non-invasive ReID of other unmarked species, as well, and points toward an expanded range of possible questions in wildlife and ecological research.

Animal nervous systems must coordinate the sequence and timing of numerous muscles-a challenging control problem. The challenge is particularly acute for highly mobile sensing structures with many degrees of freedom, such as eyes, pinnae, hands, forepaws, and whiskers, because these low-mass, distal sensors require complex muscle coordination. This work examines how the geometry of the rat whisker array simplifies the coordination required for "whisking" behavior.^1,2,3 During whisking, 33 intrinsic ("sling") muscles are the primary drivers^{4,5,6,7,8,9,10,11,12} of the rapid, rhythmic protractions of the large mystacial vibrissae (whiskers), which vary more than 6-fold in length and 3-fold in base diameter.^13,14,15,16 Although whisking is a rhythmic, centrally patterned behavior,^{17,18,19,20,21,22,23,24} rodents can change the position, shape, and size of the whisker array, indicating considerable voluntary control.^{25,26,27,28,29,30,31,32,33,34} To begin quantifying how the array's biomechanics contribute to whisking movements, we used three-dimensional anatomical reconstructions of follicle and sling-muscle geometry to simulate the movement resulting from uniform contraction of sling muscles across the array. This simulation provides a geometric baseline for whisker protraction when driven purely by intrinsic sling muscles. It does not isolate neural from biomechanical contributions but helps identify deviations that suggest active control. Simulations reveal that all follicles rotate through approximately equal angles, regardless of size. The maximum distance between whisker tips occurs at approximately 90% of resting muscle length, after which whisker tips converge and sensing resolution increases monotonically during protraction.

Diurnal hawkmoths perform flight maneuvers with exquisite control. How do they process sensory cues to generate such fast and precise motor outputs? New work has revealed the neural architecture that underlies their early visual processing.

Predator removal can destabilise and devastate ecosystems, particularly if a species released from top-down control can itself fundamentally alter the system¹. On Indo-Pacific reefs, coral-eating crown-of-thorns starfish (CoTS, Acanthaster spp.) threaten ecosystem function and resilience due to their propensity to undergo destructive population outbreaks that cause widespread coral loss^2,3. One of the foremost hypotheses to explain these outbreaks centres around the overfishing of their putative predators^4,5. Notably, outbreaks of CoTS seem to be less prevalent on reefs protected from fishing^4,5, but the risk of predation has never been quantified. Here, we show that the predation risk for CoTS inside no-take marine reserves on Australia's Great Barrier Reef is 3.6- and 2.8-times higher than in areas where fishing is permitted and limited, respectively. Moreover, the elevated predation risk inside no-take reserves is directly attributable to a single fish species, the spangled emperor (Lethrinus nebulosus), a fishery species that shows up to 6.3-times greater biomass on no-take versus fished reefs. These findings may explain how no-take reserves protect reefs from CoTS outbreaks⁴ and highlight targeted conservation of L. nebulosus as a promising management strategy to mitigate reef degradation by CoTS outside of no-take reserves.

From tiny mosses to giant redwoods, around 450,000 species of land plants show a huge variety of forms, yet all land plants develop from stem cells in proliferative meristems. What makes a meristem? Two new papers suggest that low auxin signalling holds the key.

Motor proteins perform essential roles in spindle assembly and division, but little is known about the forces that motors produce in spindles. Here, we report new tension sensors designed to measure loads across a kinesin-14 motor protein that both slides and crosslinks microtubules in spindles. The new tension sensors are motors that show active motility in vitro-they also produce fluorescence in spindles that is sensitive to loads across the motor. We find that assembling and mature spindles respond differently to increased loads caused by osmotic shock and show differences in binding by the tension-sensor motors. Binding to spindles that are still forming is dominated by rapid, transient microtubule binding and unbinding and sliding interactions. By contrast, the motors bind tightly to mature spindles, crosslinking microtubules and resisting opposing forces, bearing higher loads. Tension sensors created from motor variants or mutants that bind more tightly to microtubules than wild type bear even greater loads. The higher motor loads in mature spindles greatly exceed the forces that the wild-type motor produces-this implies that the motor in mature spindles acts primarily to oppose forces from microtubule dynamics or other motors rather than producing force as a motor. Thus, our studies define mechanical states of a spindle motor that are characterized by loads and microtubule-binding interactions and dominated by microtubule sliding or crosslinking, resisting opposing forces. These findings provide a new way of thinking about how motors create tension and contribute to forces in the spindle.

To adapt behavior in changing environments, animals must continuously re-evaluate previously learned associations. This flexibility of memory systems has been identified as a promising strategy to target maladaptive memories. Here, we show that re-exposure to an unconditioned stimulus (US) alone, a sugar reward, can re-evaluate appetitive memories in Drosophila melanogaster. Using olfactory conditioning, we demonstrate that unpaired US exposure after memory formation reduces conditioned responses to multiple odor-reward associations. This reduction is specific to the re-exposure of the trained US and does not result from an altered motivational state or generalized behavioral suppression. Importantly, this US-induced memory devaluation engages mechanisms distinct from dopamine-driven modulation of memory accessibility, indicating a separate process of memory re-evaluation. Moreover, we find that sugar re-exposure diminishes both short- and long-term memory phases and can act on consolidated memories, suggesting broad temporal applicability. Notably, this devaluation does not change the reward-memory trace in specific mushroom body output neurons, implying that the underlying memory trace remains intact despite behavioral suppression. Our findings reveal a mechanism by which reward re-experience pervasively devalues associated memories, offering a potential approach to target multiple memories without requiring re-exposure to individual cues. This work provides insight into how experience can broadly reshape memory networks and may inform future approaches for persistent memory modification.

Thorns are modified branches that have evolved independently multiple times as defenses against herbivores. We previously identified the TCP transcription factors THORN IDENTITY1 (TI1) and TI2 as key regulators of thorn development in Citrus; however, how these genes are regulated remains unclear. In this study, using comparative transcriptomics, we identified TI3, encoding a SHORT INTERNODES/STYLISH (SHI/STY) family transcription factor that is specifically expressed in thorns. We found that TI3 binds to a previously undefined CTAG core element in the promoters of TI1 and TI2, activating their expression to promote stem cell arrest in the thorn meristem. CRISPR-Cas9-mediated disruption of TI3 function converted thorns into branches. Conversely, the PEBP family protein CsCENTRORADIALIS (CsCEN) represses TI3 expression in the axillary meristem to maintain stem cell activity and promote branch development. Mutations in CsCEN resulted in branch-to-thorn conversions, whereas cscen ti3 double mutants exhibited the ti3 mutant phenotype, supporting the idea that CsCEN regulates TI3 expression. The thorn-specific expression pattern of TI3 homologs across three Rutaceae species suggests that TI3 might have a conserved role in thorn development. Thus, TI3 represents a new regulator of meristem identity, and manipulating its activity is a promising approach for breeding thornless cultivars.