Current Biology

Spiders can maintain a wide range of free-running periods while still being entrained to a 24-hour day. To investigate the underlying mechanism of this entrainment, we constructed the phase-response curve (PRC) for the orb weaver, Metazygia wittfeldae, by subjecting the spiders to one-hour light pulses at various times throughout the circadian day. The resulting type 0 PRC showed high amplitude (> 6 hour) phase advance and delays when the light pulse was applied during circadian time (CT) 16-18, with a break point of advances to delays at CT 17. We then investigated the genetic mechanism of the phase response to light by splitting M. wittfeldae adult females entrained to 12 hours light:12 hours dark (LD 12:12) into two groups. One group received a 1-hour light pulse 5 hours after lights off (CT17), and one group did not. We then sacrificed spiders for RNA isolations 1 and 10 hours after the light pulse. We identified numerous genes that were downregulated by the light pulse 1 hour after the pulse relative to no pulse group. Intriguingly, many of these genes had a flipped pattern of expression 9 hours later - the pulse group had higher expression than the no pulse group. This pattern is consistent with the shifted phase of locomotor activity expected after the light pulse application. We also identified clock gene homologs in M. wittfeldae that had distinct expression patterns from other arthropods.

Cellularization is the coordinated division of a multinucleate cytoplasm into many cells.1-3 Multinucleation is a common life cycle strategy observed across eukaryotic lineages, including in microbial eukaryotes, fungi, plants and animals, and is associated with the ability to transition to a unicellular state through cellularization.4 In the best-studied model for this process, Drosophila melanogaster, cellularization requires the coordinated action of actin and microtubule (MT) networks to bring about the synchronous invagination of plasma membrane furrows, but the extent of conservation of these mechanisms across eukaryotes remains unknown.1,5,6 Here we investigate cellularization in the ichthyosporean Sphaeroforma arctica, a close relative of animals with a multinucleate life cycle stage.7-9 Using live cell imaging, ultrastructure expansion microscopy (U-ExM) and volume electron microscopy, we define the membrane, MT and actin dynamics that accompany cellularization in S. arctica. Using pharmacological inhibitors and centrifugation, we show that MTs, in addition to positioning nuclei, play a role in guiding nascent furrows to sustain equi-partitioning of nuclei and cytoplasm between daughter cells. Our findings indicate that cellularization is regulated through crosstalk between actin and MT networks, exhibiting mechanistic parallels with canonical cytokinesis, and establish S. arctica as a valuable model for investigating general principles of cellularization.

Biological rhythms are fundamental to survival, synchronizing physiological and behavioural processes like the sleep-wake cycle with predictable environmental cycles like the solar day1. However, the extent to which human sleep responds to the lunar cycle remains a subject of controversy, particularly given the ubiquity of artificial light and conflicting reports regarding the influence of moonlight2-5. While lunar illuminance has been the primary candidate for such modulation, it fails to account for semilunar rhythms2,6 or effects observed during the dark new moon phase2,7. Here, we show that human and non-human primate sleep timing is synchronized with the gravimetric cycles exerted by the Moon and Sun. By analysing longitudinal actigraphic recordings from urban cohorts in Seattle, indigenous Toba/Qom communities in Argentina, and captive titi monkeys with attenuated access to natural light, we found that sleep onset is consistently delayed around periods of maximal gravitational variations. Crucially, this synchronization aligns with gravimetric peaks regardless of whether they occur at the full or new moon. Furthermore, while human sleep timing is heavily influenced by social constraints and self-selected light exposure, this synchronization persists in titi monkeys, in which these confounds are absent. These findings identify lunar gravity as a distinct environmental cue that may regulate sleep-wake behaviour. Although this regulation may be mediated by other geophysical factors oscillating with lunisolar gravitational tides, the results suggest that the mechanism is an evolutionarily conserved trait that shapes biological timing beyond the influence of light.

Nuclei and mitotic spindles are actively positioned at defined locations within cells to regulate cell polarity, division and multicellular morphogenesis1-4. Forces generated by cytoskeleton networks regulate the positioning of these organelles and are commonly influenced by extrinsic cues such as cell geometry or polarity5-12. To date, however, most studies have investigated this problem in one given cell type, hampering our understanding for how mechanical systems that position nuclei and spindles may scale during multicellular development. We tracked the spatiotemporal behaviour of centrosomes, nuclei and spindles in early sea urchin embryos from the 1-cell to the [~]1000 cells blastula stage. We found that they are initially located at cell centers, but that they undergo a progressive decentration towards the embryo apical surface, as cells become smaller during development. This apical shift is mediated by microtubule (MTs) pulling forces which are influenced by both cell shapes and apical polarity domains. Using 3D mathematical models and embryo dissections, we propose that MT centering forces that derive from cell geometry decay in strength during development as a consequence of cell size reduction, allowing apical polarity decentering forces to take over. Our results support a self-organized scenario in which polarity cues progressively outcompete cell geometry, to modulate the overall balance of MT forces and pattern nuclear and spindle positioning throughout early embryo development.

Mosquitoes undergo development as aquatic larvae and pupae before emerging as terrestrial adults. Accordingly, blood-fed and mated female mosquitoes must select an appropriate egg-laying site to maximize the fitness of their offspring. Female yellow fever mosquitoes (Aedes aegypti) lay their eggs above the waterline of small containers or natural bodies of water, where they can remain dormant for many months until they are submerged and hatch. Here, we show that female mosquitoes use surface texture as a powerful cue to guide egg-laying decisions, selecting rougher textures over smooth when choosing among containers and when selecting specific sites within a given substrate. In addition, we identify an interaction between substrate texture and water salinity with respect to egg-laying decisions, demonstrating that female mosquitoes integrate competing cues to determine the ultimate suitability of an egg-laying site. Finally, we explore the dynamics of local egg-laying search behaviour, demonstrating that texture modulates traversal speed while mosquitoes search for appropriate egg-laying sites.

Sensory systems provide animals with essential information about their environment and are critical for generating appropriate behaviours. Mechanosensation is a fundamental component of this sensory repertoire, and disruption of mechanosensory pathways can have severe functional consequences. In the nematode Caenorhabditis elegans, mechanosensory circuits have been extensively characterized and mediate touch-driven navigation and avoidance. These circuits rely on conserved molecular components including the stomatin-like protein MEC-2 along with MEC-6, which function together in the mechanotransduction complex. In contrast, the predatory nematode Pristionchus pacificus has repurposed mechanosensory pathways to also enable prey detection, a derived ecological behaviour. As we previously demonstrated that Ppa-mec-6 is required for efficient predation, here we assessed if Ppa-mec-2 plays a similar role in P. pacificus prey detection. We find that while Ppa-mec-2 is required for the aversive touch response, it is dispensable for prey detection. This functional divergence reflects differential neuronal expression as Ppa-mec-2 is absent from the IL2 neurons that mediate prey detection and also robustly express Ppa-mec-6. These findings reveal that partitioning of mechanosensory components across neuronal types enables functional specialization, demonstrating how conserved sensory machinery can support distinct behavioural functions across evolution.

During sleep, we functionally disengage from our external environment. Our eyes close, profoundly reducing visual input to the brain. However, some light passes through the eyelid, and luminance changes are perceived even through closed eyes during wakefulness. Although the relay of sensory information is thought to be gated by the thalamus during sleep, sensory information can still reach the cortex. To elucidate how visual inputs are modulated at each stage of thalamic and cortical processing during sleep, we used simultaneous EEG-fMRI while presenting luminance-modulated visual stimuli to sleeping humans. We discovered that responses to light remained intact in the visual thalamus during N1 and N2 sleep. However, stimulus-evoked responses in early visual cortex were profoundly suppressed, exhibiting an inverted pattern in which high-intensity visual stimulation evoked visual cortical deactivation. These findings suggest a cortical mechanism where inhibitory circuits regulate stimulus-driven deactivation in visual cortex, facilitating sensory isolation during early stages of sleep.

The ability of flying insects to locate distant food and mates by tracking odor plumes through turbulent and unsteady flow represents a remarkable feat of sensorimotor integration. Successful navigation requires not only extracting a reliable directional estimate from an intermittent olfactory signal, but also contending with the challenging dynamics of variable winds. While prior work has established that insects integrate the history of odor encounters to shape search decisions, whether they also retain a working memory of recently experienced wind conditions has remained unknown. Here, we use optogenetics combined with controlled wind perturbations in a free-flight wind tunnel to investigate how wind history modulates the olfactory search behavior of Drosophila melanogaster. By introducing lateral "gust" flow via auxiliary fans and independently delivering olfactory stimuli, we show that the wind experienced during an olfactory stimulus shapes both the immediate surge response and the subsequent spatial search. Flies that received an olfactory stimulus while being displaced by a crosswind gust were significantly more likely to return to the gust zone during the post-stimulus search phase compared to flies that received the same odor cue in steady laminar flow. Meanwhile, surge responses and course directions exhibited during search indicate that moment-to-moment flight kinematics may be driven more by instantaneous flow. These results reveal that wind experience is tracked in addition to olfactory experience, and provide evidence that Drosophila maintain a short-term working memory of ambient wind conditions to guide olfactory navigation.

Pennaceous feathers are fundamental to avian flight, yet their early function in non-volant dinosaurs remains unknown. Early-diverging pennaraptorans had simple pennaceous feathers on proto-wings and tails, which were unsuitable for flight but may have enhanced visual signals. However, the visual display hypothesis has not been empirically tested. To address this, we used computer animations of early pennaraptoran displays to measure responses in a well-established animal model of a visually sensitive neural pathway. We show that pennaceous proto-wings and tails enhance the efficiency of motion-based displays across a range of anatomically plausible movements. Integrating these results with comparative and paleontological evidence, we suggest that early pennaceous feathers functioned in diverse signaling contexts and were subsequently exapted for aerodynamic use.

Visual motion processing in flying insects is strongly modulated by behavioural state, yet the mechanisms by which mechanosensory feedback contributes to this modulation remain poorly understood. Here we show that wing mechanosensation alone is sufficient to modulate a subset of optic-flow-sensitive descending neurons (WFDNs) in butterflies. Airflow stimulation of the wings, mimicking flight conditions, increased baseline firing rates and reduced response latencies in WFDNs, without altering response gain or temporal frequency tuning. These effects indicate that mechanosensory modulation acts through mechanisms distinct from those governing other state-dependent changes in visual processing. Consistent with this interpretation, previous work has shown that baseline firing and response latency can be rapidly modulated, whereas gain changes arise through slower neuromodulatory pathways. Mechanosensory modulation was cell-type specific: the horizontally tuned WFDNL neuron was consistently affected across individuals, whereas other WFDN types were largely insensitive, likely reflecting the unilateral airflow stimuli used here. Interestingly, WFDNL modulation arose exclusively from mechanosensory input from the proximal area of the wing, not from distal wing deformation. This suggests that descending visual pathways require only coarse gain or excitability modulation rather than detailed information about wing shape or strain, leaving fast reflexive control of distal wing deformation to local ganglionic circuits. Together, our results demonstrate that wing mechanosensation selectively modulates visual descending pathways by altering excitability and timing rather than visual feature encoding, supporting the existence of multiple, parallel mechanisms for state-dependent visual modulation during flight.

Many animals navigate their world largely by seeing and feeling it. To disentangle these visual and mechanosensory contributions, we developed a virtual reality assay targeting the optomotor response in adult wild-type zebrafish swimming against flow. By projecting dynamic visual patterns onto the walls of a variable-speed flow tank, we decoupled wide-field optic flow from hydrodynamic velocity. We then tested fish responses to abrupt visual perturbations while they held station in the unsteady wake behind a bluff body. These perturbations reliably elicited compensatory optomotor responses, with fish aligning to the direction of the moving stimulus. Notably, this behavior was absent in uniform flows, suggesting that fish prioritize visual input when predictive lateral line signaling is compromised. We propose that this sensory shift serves to optimize swimming energetics in turbulent wakes. Extending this framework, we further show that zebrafish swimming against flow, whether alone or in groups, exhibit heightened escape responses to looming visual stimuli. Together, our findings reveal that fish sensory strategies are not fixed but dynamically tuned to hydrodynamic context: favoring visual cues in turbulent environments and lateral line input in uniform flows. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=84 SRC="FIGDIR/small/715425v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@1d7ba00org.highwire.dtl.DTLVardef@1f456f1org.highwire.dtl.DTLVardef@7826c4org.highwire.dtl.DTLVardef@391a68_HPS_FORMAT_FIGEXP M_FIG C_FIG

Hybridisation is ubiquitous amongst plants and has important evolutionary consequences ranging from the collapse of distinct lineages through to the generation of new species. Here, we develop a phylogenetic hypothesis for the Austral podocarps (Podocarpus), a monophyletic group of six species distributed in Tasmania, mainland Australia, New Zealand and New Caledonia, and identify a putative hybrid lineage. Using a targeted capture approach to generate DNA sequence data, we find discordance between nuclear and plastid derived phylogenetic estimates and in particular, the relationships of the New Zealand species Podocarpus nivalis and Australian P. lawrencei are significantly discordant. Species network analyses largely resolve this incongruence and indicate that P. nivalis is a hybrid lineage, with P. laetus (New Zealand) and P. lawrencei as parents. We hypothesise that P. nivalis has arisen following trans-Tasman dispersal of P. lawrencei, and shows eco-geographic divergence from P. laetus, which could facilitate reproductive isolation. We suggest that introgression from P. laetus to colonising P. lawrencei could significantly reduce founder effects while cold tolerance inherited from P. lawrencei has enabled P. nivalis to occupy alpine environments. Our findings highlight the importance of reticulate evolution in Southern Hemisphere conifers and demonstrate the value of phylogenomic network approaches for resolving recent and complex radiations.

Seasonality drives the evolution of reproductive plasticity in butterflies. An extreme form is reproductive diapause, where individuals halt reproduction during unfavourable seasons through cascades translating predictive environmental cues into reproductive phenotypes. How diapause evolves from milder forms of plasticity through changes in those cascades is poorly understood. In the tropics seasonality is common, but it is unclear how phylogenetically widespread reproductive diapause is, and exactly how seasonal tropical climates drive reproductive plasticity. Here, we study reproductive plasticity in Amazon butterflies using a multi-year monthly time series of reproductive phenotypes. Sampling 4 subfamilies across Nymphalids, we observe a phylogenetically widespread occurrence of diapause, suggesting repeated evolutionary changes in reproductive plasticity. Detailed analyses of two Catonephele species reveal a shared temperature response, but dry season diapause only in C. acontius. Thus, evolution of diapause combines cue conservation with species-specific divergence of trait plasticity, suggesting gradual and modular evolution of reproductive plasticity.

The zygote is the origin of development, and in most angiosperms, it divides asymmetrically to establish the apical-basal axis. In Arabidopsis thaliana, the zygote undergoes tip growth-like polar elongation, using a subapical transverse microtubule band (MT band). Because canonical tip-growing cells rely on longitudinal actin filaments (F-actin), it remains unclear whether and how the zygote employs conserved tip-growth mechanisms. Here, using quantitative live-cell imaging, pharmacological perturbations, and mechanical simulations, we found that oscillatory Ca{superscript 2} waves, a hallmark of tip growth, are coupled to zygote elongation through a bidirectional feedback loop, as in other tip-growing cells. However, Ca{superscript 2} waves were dispensable for overall F-actin alignment but promoted MT band turnover. Our study provides a model showing that the zygote uses a conserved tip-growth module, in which Ca{superscript 2} oscillations and cell elongation reinforce each other, but redirects the target cytoskeleton to the MT band, enabling zygote-specific tip growth for axis formation.

Selecting an appropriate behavioral response according to ones internal state is essential for well-being. Across the reproductive cycle, fluctuating levels of sex hormones align female behavior with reproductive capacity by modulating neuronal circuits that express hormone receptors. Sex hormone receptor-expressing neurons present along the anterior-posterior axis of the ventrolateral region of the ventromedial hypothalamus (VMHvl) are key regulators of female sexual behavior. While posterior progesterone receptor-expressing neurons of the VMHvl (pVMHvlPR+) are fundamental for female sexual receptivity during the receptive phase of the reproductive cycle, we have recently shown that anterior VMHvlPR+ (aVMHvlPR+) neurons are involved in rejection behavior when non-receptive. Here, we mapped the connectional architecture of aVMHvlPR+ neurons using viral tracing approaches. As expected, these neurons strongly project to several hypothalamic areas. Furthermore, consistent with previous reports, we show that aVMHvlPR+ neurons robustly project to several columns of the periaqueductal gray (PAG) along its anterior-posterior axis. Artificial activation of aVMHvlPR+ somas selectively recruits the dorsomedial PAG (dmPAG). Optogenetic activation of aVMHvlPR+ axons in the dmPAG partially recapitulates the rejection phenotype observed upon activation of aVMHvlPR+ somas, increasing the rate of rejections in receptive females. These findings reveal a putative pathway regulating female rejection behavior within a more complex circuit, ensuring that mating does not occur during non fertile periods.

Lifespan varies widely among individuals, yet the extent to which such variation persists when genetic and environmental differences are minimized remains unclear. Here we quantify such stochastic lifespan variation in a naturally clonal vertebrate and test whether and how this variation is linked to early-life behavioral individuality. We followed N = 33 genetically identical Amazon mollies (Poecilia formosa), separated on day 1 of their life into highly standardized environments, from birth to death. Despite genetic uniformity and environmental standardization, lifespan varies markedly, spanning 502 - 826 days. Continuous high-resolution behavioral tracking during the first four weeks of life reveals that seemingly stochastic early-life activity differences explain 32.5% of this variation. Higher activity predicts shorter lifespan during the first two weeks, but as activity levels and among-individual variation in activity decline over early development, a U-shaped relationship emerges, with both low- and high-activity individuals outliving those with intermediate activity. These findings show that signatures of lifespan emerge within days of birth, even among genetically identical individuals, highlighting developmental stochasticity and early-life contingencies as major contributors to variation in life-history outcomes.

The vascular system is central to plant ecology and evolution. Here, we show that more than 100 species across 27 genera and four subfamilies of Fabaceae have evolved atypical vascular architectures and that these species occur in all biogeographical regions except Antarctica. Because Fabaceae includes many ecologically and economically important species exhibiting these novel vasculatures, the family emerges as an ideal system for assessing the implications of vascular innovation in both fundamental and applied research.

How photosynthetic endosymbionts reorganize host daily regulation remains unclear. Paramecium bursaria displays pronounced day-night behaviors, but whether its algal symbionts drive host temporal programs has been unresolved. We compared host gene expressions across a 24-hour light-dark cycle in symbiotic and aposymbiotic cells. Symbiotic cells exhibit an expanded and highly temporally ordered diel transcriptome compared with aposymbiotic cells. These rhythmic programs encompass motility, signaling, metabolism, and growth regulation, consistent with observed behaviors. Symbiosis-associated rhythmic programs recruit gene families encoding post-translational regulatory domains, including kinases, ubiquitin-related factors, WD40 scaffolds, and calcium-binding proteins, despite lacking recognizable canonical clock genes. Disrupting photosynthesis with paraquat altered these temporal profiles, shifting them toward an aposymbiotic-like state. A distantly related ciliate, Tetrahymena utriculariae, with an independently evolved symbiosis, showed similar symbiosis-associated daily programs, suggesting that photosynthetic endosymbionts can act as important organizers of host daily gene regulation in endosymbiotic protists.

The hippocampus is widely viewed as a spatial mapping system because many CA1 neurons show location-specific activity during exploration. However, the hippocampus is also required for non-spatial learning, including trace eye-blink conditioning. Because most prior reports of non-spatial signals were obtained in immobile animals, it has been proposed that the hippocampus encodes space during locomotion and non-spatial variables during immobility. To test this directly, we used calcium imaging to record thousands of CA1 neurons while rats performed trace eye-blink conditioning during free exploration of an open field. Across more than 6,000 neurons from five rats, mean firing rates during trace-conditioning periods were [~]1.5-fold higher than during non-trial periods, and this difference persisted after controlling for locomotor speed. At the single-cell level, task-related modulation was widespread and strongly biased toward increased firing. Task-enhanced neurons outnumbered spatially selective neurons by more than threefold, indicating that trace coding predominated over place coding. Although trace-conditioning events occurred at random spatial locations and during continuous locomotion, trace-related activity remained robust at both single-cell and population levels. In contrast, spatial coding was reduced during trace periods, with lower spatial information and decreased similarity between task and non-task rate maps. These findings show that during active behavior, trace coding dominates and disrupts place coding, challenging the view that the hippocampus functions primarily as a stable spatial map.

Visual experience is organized in time. When riding the same bus route each day, the visual scene unfolds in a predictable order without requiring active choice. During goal-directed behavior, individuals organize actions into routines, such as repeatedly walking the same route to work even when alternatives are equally efficient. Because experience unfolds across sequences of events, identifying how it reshapes population activity requires examining representations over time. Many studies have shown that repeated experience reduces mean firing rates in visual cortex1-14. While firing rates effectively signal novelty or repetition, they are not well positioned to describe how populations of neurons represent temporal relationships. A growing body of work suggests that the geometry of population activity provides additional insight into how visual information is structured and read out15-26. We examined how experience with temporal structure reshapes the geometry of population activity in visual area V4. We recorded neuronal populations across three contexts that varied in temporal structure and behavioral relevance: repeated presentation of individual images, passive exposure to structured image sequences, and repeated execution of self-chosen visually guided action sequences for reward. Across contexts, experience constrained population responses toward a typical activity pattern. In sequence contexts, experience made temporal position more linearly accessible and, during active practice, increased the separability of task-relevant variables. These findings show that experience reorganizes the geometry of visual population activity to reflect temporal structure, constraining responses and altering how sequence-related information is represented.