Current Biology

Habits are automatic actions shaped by prior experience, enabling efficient and fast responses in stable environments. While habitual gaze rapidly directs the eyes toward valuable objects, the mechanisms underlying habitual manual choice for reaching and grasping remain unclear. Here we show that macaque monkeys develop habitual manual choices toward previously rewarded objects through multi-day object-value learning, driven by learned value and spatial preferences. This reaching habit persisted without reward and showed shorter latencies than in value-deliberative tasks, consistent with automatic control. Regression analyses further revealed that manual choice was guided by learned object values, whereas visual salience had no effect, unlike gaze habits. Instead, intrinsic spatial preferences continued to bias reaching behavior even after long-term value learning. These findings demonstrate that habitual manual choice arises from the integration of spatial preferences and long-term value memory, defining a distinct mechanism of automatic behavior beyond habitual gaze.

Temporal niche partitioning is a strategy for reducing interspecies competition and strengthening reproductive isolation. It relies on animals confining their daily activity to distinct diurnal, crepuscular, or nocturnal windows. However, a hardwired temporal niche is only advantageous under stable, predictable ecological regimes; surviving dynamic environments demands behavioral flexibility. Yet, it remains unclear how animals override rigid biological constraints to rapidly exploit transiently available fitness-critical time windows. To address this, we leveraged the twilight-active, species-rich Drosophila genus and monitored their daily activity under naturalistic conditions. Here, we show that intense sociosexual interactions rapidly drive a species-specific reformatting of their canonical crepuscular niche. The dominant sensory modality used for sexual communication predicts niche shift direction: reliance on chemosensation for courtship redirects behavioral activity into the night, while visual reliance shifts it into the day. This temporal plasticity bypasses the circadian clock, instead operating via a conserved dopaminergic pathway. Dopamine operates a dual-output brain circuit that simultaneously inhibits sleep and sustains sexual motivation. Our results reveal how mating imperatives decouple behavioral timing from circadian command, enabling conditional colonization of otherwise restricted temporal windows. Ultimately, by driving the divergence of previously overlapping niches, sociosexually induced temporal plasticity provides a powerful mechanism for sympatric coexistence in crowded environments.

Cnidae are explosive harpoon-like organelles localized within stinging cells, or cnidocytes, of the phylum Cnidaria (jellyfish, hydroids, sea anemones, and corals). These unique Golgi-derived vesicular structures define the phylum and are prominent examples of an evolutionary cellular novelty. While recent studies have focused on the developmental specification and regulation of cnidocytes more broadly, less is understood about gene expression patterns, structural variations, and toxin repertoires within distinct cnidae subtypes. Here, we determine the transcriptional profile of two major cnidae subtypes in the sea anemone Nematostella vectensis, nematocytes and spirocytes, using the cnidae-specific structural family of proteins called minicollagens. We first define the in vivo expression patterns for three known and three uncharacterized minicollagen orthologs. We show that four minicollagens are broadly expressed throughout ectodermal cnidocytes in developing larvae and primary polyps while two others are restricted to tentacular cnidocytes. Leveraging whole adult scRNA-seq data and two novel transgenic reporter lines, we then demonstrate that the tentacle-restricted cnidocytes are developing spirocytes that are distinguished by expression of the minicollagen NvNcol5. To deepen our analysis of cnidocyte gene expression, we used a customized RNA-FACS-seq pipeline to determine global transcriptional differences between these two subtypes. This approach identified a suite of differentially expressed genes, illuminating spatial and temporal gene expression dynamics across both developing nematocytes and spirocytes. Altogether, our experiments provide fundamental and novel insights into the specialization of cnidarian stinging cells while establishing a rich set of resources for further investigation.

Foraging in naturalistic environments is often challenging, as animals must evaluate varying sensory cues to locate optimal food sources. To successfully navigate a taste gradient, where perceived concentrations change over space and time, animals need to compare previously encountered taste qualities with current information. How such short-term taste memories are implemented in the brain and used to guide navigation remains poorly understood. Due to their powerful genetic toolkit and whole-brain connectome, Drosophila larvae are an excellent model organism for investigating the neural basis underlying taste gradient navigation. Using linear fructose and salt gradients, we show that larvae are attracted to high fructose concentrations, whereas they avoid high salt concentrations. To identify the neural basis underlying taste gradient navigation, we tested the role of cell types from the peripheral chemosensory system to higher brain regions. Contrary to conclusions from simple two-choice preference assays, we show that gradient navigation depends on different cell types across multiple layers of chemosensory processing and associative learning circuits, including mushroom body neurons. Attractive and aversive taste signals are conveyed through parallel, partially overlapping pathways that converge onto mushroom body output neurons, where they are integrated to shape motor behaviors during chemotaxis.

The eukaryotic cytoskeleton generates remarkable diversity in cellular architecture despite being built from deeply conserved actin and tubulin polymers. Diversification of cytoskeletal regulators, motors, and filament-organizing proteins produces highly varied cellular morphologies across eukaryotes, yet certain higher-order architectures repeatedly emerge in distantly related lineages. One notable example is cytoskeletal arborization, which occurs not only in metazoan neurons but also in amoeboid lineages distributed throughout the eukaryotic tree. Whether these similar branched architectures arise through conserved cytoskeletal organization, independent reuse of shared molecular systems, or convergence driven by common physical constraints remains unresolved. Here, we investigate the rhizarian amoeba Filoreta ramosa, which forms a multinucleate reticulated network through branching and anastomosis. Using live imaging, immunofluorescence, morphometric analyses, and cytoskeletal drugs, we define how actin and microtubule systems organize branch formation, intracellular transport, and large-scale network architecture. Actin-rich protrusions initiate exploratory branchlets that become selectively stabilized through microtubule incorporation. Longitudinal microtubule arrays reinforce mature branches and support rapid bidirectional organelle transport, while branch nodes function as distributed sites of microtubule nucleation. These cytoskeletal features parallel key mechanisms underlying neuronal arborization, including actin-driven exploration, microtubule-dependent branch stabilization, and transport systems that scale with increasingly extended cytoskeletal networks. However, unlike neurons, Filoreta develops a decentralized reticulated network through repeated anastomosis and distributed microtubule organization, demonstrating that similar arborized morphologies can emerge through distinct architectural strategies. Our findings indicate that arborization can arise through multiple evolutionary adaptations to common cellular constraints. Shared cytoskeletal mechanisms repeatedly support branching architectures, but distinct topologies and modes of cellular organization demonstrate that evolution can reach arborization through different routes. Similar cytoskeletal networks may repeatedly emerge in diverse lineages when cells face the challenges of exploration, stabilization, and transport across increasingly larger scales. Filoreta therefore provides an experimentally tractable model for investigating how conserved cytoskeletal systems generate diverse arborized cellular architectures across eukaryotic evolution.

Late Pleistocene sea-level fluctuations and glacial corridors intermittently connected the island of Ireland to Britain and continental Eurasia, shaping patterns of megafaunal dispersal and occupation. However, the scarcity of genetic data from ancient Irish fauna has limited our understanding of their demographic histories and relationships to continental populations. To address this, we generated sedimentary ancient DNA sequences from Castlepook Cave in southwest Ireland, detecting twelve ancient taxa, including two without zooarchaeological records at the site. We recovered the first mitochondrial sequences from Irish cave hyenas and woolly mammoths, providing new insights into their maternal population history: cave hyenas carried mtDNA haplogroup A1, previously identified in Late Pleistocene European populations, while woolly mammoths belonged to clade III/B2, which was replaced in Europe at approximately the same time. We also identify two mitochondrial clades (1b and 2), consistent with pre-Last Glacial Maximum mitochondrial lineage turnover in Ireland. Together, these results indicate that Irish megafauna formed a biogeographical continuum with their conspecifics in Europe, extend the known geographical range of several mtDNA lineages, and support faunal connectivity at the northwestern edge of Europe prior to the Last Glacial Maximum.

When an animal consumes a new food and consequently feels ill, it rapidly and robustly learns to avoid this food in the future, a form of learning termed conditioned flavour avoidance (CFA). Postingestive malaise often occurs long after novel food consumption, necessitating a neural mechanism that can facilitate plasticity between temporally distant events. Neuromodulators, acting through G-protein-coupled receptors (GPCRs) that can influence neuronal excitability on extended timescales, may underlie this process. The projection of parabrachial (PB) Calca neurons to the central amygdala (CeA) is critical for formation of CFA. Here, we demonstrate that these neurons overlap with a PB population that releases acetylcholine (ACh) in the CeA. ACh is released in CeA during consumption of a novel solution and subsequent visceral malaise, consistent with a role in CFA acquisition. Two-photon calcium imaging in brain slices reveals that ACh widely activates CeA neurons and enhances glutamatergic responsivity on a timescale consistent with CFA learning. CRISPR-Cas9-mediated genetic knockdown and optogenetics demonstrate that ACh from PB facilitates CFA behavior. Large-scale neuronal recordings in the CeA along with our CRISPR approach reveal that loss of ACh signaling to CeA blocks key signatures of CFA-associated plasticity. Together, these data point to the cholinergic input from PB to central amygdala as a critical neuromodulatory signal that links activity over long timespans to facilitate associative learning in CFA.

Female reproduction is an energetically expensive process, so species evolve to balance survival with reproductive output. Many female organisms can temporarily pause their reproduction, including egg development, in response to physiological stress. The cellular mechanisms initiating and maintaining a stress-induced pause in oogenesis have been most extensively studied in Drosophila melanogaster. While the molecular control of paused oogenesis in response to starvation have been well characterized in flies, it remains unknown if these mechanisms are shared by other species with regulated pauses in oogenesis. Eusocial insects are characterized by a reproductive division of labor, with colonies of reproductive queens and sterile female workers. The social paper wasp, Polistes, has a dynamic dominance-based hierarchy for queen status. Worker Polistes are kept sterile by a combination of social and nutritional stressors. Here, we establish Polistes as a model to explore adult female reproductive plasticity. Through immunohistochemistry we have directly compared the Drosophila and Polistes ovarian structure and identified critical regions of the ovary in wasps that undergo regulated cell elimination during reproductive pause in flies. By comparing tissue structure, cell organization and rates of cell death between Polistes queens and workers we identified apoptosis as a key regulator maintaining worker sterility. Critically, this mechanism appears to be partially conserved with that in Drosophila. Finally, we find that changes in the timing and location of cell death in Polistes workers implicate oocyte identity and oocyte growth as additional potential regulators of temporary disruption of oogenesis.

Sleep is regulated across multiple timescales. Transitions between sleep and wake happen within seconds; individual sleep bouts last minutes to hours; and homeostatic sleep need has classically been tracked across multiple bouts. Rapid sleep-to-wake transitions are driven by identified neurons, circuits, and neuromodulators, while slow wave activity correlates with sleep need across hours. However, no signal has been shown to encode sleep history within individual sleep bouts, the timescale at which the brain must continuously monitor how much sleep has occurred and how likely waking is at any given moment. Biochemical signals downstream of sleep/wake-associated neuromodulators display slower dynamics than the neuromodulators themselves, making them candidate encoders of within-bout sleep history. Here, by measuring protein kinase A substrate phosphorylation (PKA-SP) in real time in freely behaving mice, we show that membrane PKA-SP decreases exponentially within each sleep bout with consistent kinetics across bouts, integrates sleep duration and sleep interruption, and continuously forecasts moment-to-moment waking probability. Following sleep deprivation, PKA-SP reaches lower levels at the end of sleep bouts, correlating with increased sleep need dissipation. These findings identify a molecular signal encoding within-bout sleep history, revealing how biochemical dynamics bridge fast arousal circuits and the slow timescale of classical sleep homeostasis.

The ability of an organism to attend to, and orient towards, relevant stimuli is critical for survival. In the mammalian brain, a principal brain region performing this function is the superior colliculus (SC). Despite its important role in attention and orienting movements, little is known about the role the SC plays in sensory decisions. Using Neuropixel recording and optogenetic perturbation of neuronal activity in awake behaving mice, we provide a quantitative link between the activity of neurons in the SC and the behavioural outcome during a whisker-dependent sensory detection task. Consistent with the idea that the SC contributes to sensory decision-making, the activity of SC neurons was correlated with behavioural performance. Furthermore, we found that optogenetic inhibition of the SC during the whisker-dependent detection task reduced behavioural performance. These findings indicate that the SC both encodes and causally shapes sensory decisions during a whisker-dependent task.

Phasic striatal dopamine has been implicated in the initiation of well-trained action sequences in reward-guided tasks. Whether such signals also support natural skills learned without explicit cues or immediate rewards remains unknown. Using birdsong as a model of a naturally learned, skilled vocal behavior, we found that dopamine transients accompany the initiation of song sequences. These transients emerged during learning, shifting from later phases of the sequence toward sequence onset as song matured. Temporally targeted optogenetic inhibition of dopamine signaling at sequence onsets disrupted the maintenance of learned song, resulting in the gradual and severe deterioration of adult song. Thus, phasic dopamine signaling at sequence initiation develops during learning of a natural skilled behavior and is required for its long-term maintenance.

Active sensing allows organisms to shape incoming sensory information through self-generated actions, and saccadic eye movements provide a key readout of this process in vision. In primates, saccades are strongly modulated by cognitive variables such as uncertainty, value, and behavioural goals, particularly in complex, naturalistic settings. In rodents, by contrast, saccades have largely been interpreted as reflexive components of head-eye coordination, and evidence for goal-directed visual sampling has remained sparse. Here, we examined how mice use saccades during a vision-dependent foraging task in a traversable immersive virtual environment with naturalistic stimuli. We correlated their saccade dynamics with behavioural strategies observed within the virtual environment. Target-directed saccades emerged specifically when informative sensory evidence was available, but also occurred anticipatorily when animals could rely on previously learned spatial contingencies, indicating that saccades were guided not only by immediate visual input but also by internal representations. Strikingly, the temporal structure of inter-saccade intervals resembled signatures previously reported in primates and lengthened with increased processing demand following changes in task contingencies. Together, these findings show that mouse saccades are not merely reflexive gaze corrections, but form part of a cognitively modulated active sampling strategy. More broadly, they suggest that key principles of active visual sensing may be conserved across species and establish mouse oculomotor behaviour as a tractable readout of internal cognitive state.

The polarization of motile cilia requires that the centrioles, from which cilia are formed, display rotational asymmetry. This property is manifested in the presence of asymmetrically distributed appendages and relies on evolutionary conserved mechanisms. These mechanisms are also at play in cells that form primary cilia despite the lack of ciliary motility and asymmetric centriole appendages in this context. Here, we find that a complex consisting of CCDC61, KIAA1328 (K1328), and Centlein (CNTLN) contributes to the establishment of centriole rotational asymmetry. In cells with a primary cilium, this complex is required for assembling a linker that repositions the daughter centriole close to and orthogonal to the proximal end of the mother centriole/basal body. The CCDC61/K1328/CNTLN complex also triggers the asymmetric recruitment of pericentriolar matrix components around newly assembled centrioles, which likely facilitates the later attachment of the basal body-daughter centriole linker. Overall, our results establish that rotational asymmetry relies on the coordinated recruitment of asymmetric landmarks along centrioles and is necessary for positioning the centrioles in a configuration that is widely conserved in ciliated cells.

Saturated cultures of the pathogenic yeast, Cryptococcus neoformans, arrest as unbudded cells in the G2 phase of the cell cycle. As cells divided and cultures saturated, we found that oxygen levels in the culture medium dropped nearly tenfold. When saturation-arrested cultures were re-oxygenated without adding fresh growth medium, cells immediately formed a bud and then underwent mitosis. Thus, the arrest is due to low oxygen concentration rather than nutrient depletion. Because the G2 arrest was associated with unbudded cells, we asked whether C. neoformans cells have a morphogenesis checkpoint that blocks mitosis until cells can form a bud. Inhibition of budding by treatment with Latrunculin A also led to G2 arrest, and we determined that this arrest is dependent on the CDK inhibitory kinase, Swe1. This finding suggests that C. neoformans possesses a morphogenesis checkpoint analogous to that in the distantly related Saccharomyces cerevisiae. We also demonstrated that Swe1 is required to enforce the hypoxia-induced G2 arrest. We propose that hypoxia inhibits budding in C. neoformans, which in turn triggers a morphogenesis checkpoint to arrest cells in G2 even when nutrients are plentiful.

Hippocampal ripples are transient, high-frequency oscillations linked to memory replay and consolidation. Ripples are well-characterized in rodents to occur during periods of behavioral inactivity (i.e., sleep, rest), viewed as "offline" states where replay can emerge with limited sensory interference. However, human studies have increasingly observed ripples during active tasks, raising the questions of whether ripple genesis and function have been misunderstood or whether there are fundamental species differences. We propose that low arousal states--predominant during offline sleep and transient during wake--may constitute a common mechanism of ripple genesis that reconciles these observations. We recorded directly from human hippocampus during sleep and wake, measuring arousal via sleep staging, pupillometry, and heart rate. Ripple occurrence consistently tracked low arousal: rates were maximal in NREM sleep, small-pupil wake states, and slow heart rate periods across sleep and wake. This modulation was stronger in anterior than posterior hippocampus and was hippocampus specific: ripple-like activity outside the hippocampus showed an opposite modulation, increasing with high arousal. These results resolve apparent species differences and provide a unifying view of offline periods as arousal dips that can emerge across behavioral states, including transiently during active wake, suggesting hippocampal ripples, and memory consolidation, occur continuously intermixed with cognition.

The reliable execution of learned motor sequences poses a challenge: they require reproducible neuron activity patterns for behavioral consistency yet must retain flexibility for modulation that depend on internal states and adaptation to external contingencies. The zebra finch, a songbird, provides an ideal system to examine this problem because their vocalizations are highly stereotyped and are associated with precisely time-locked bursts in HVC, a key nucleus involved in song production. However, their songs are not immutable /totally fixed, as they can be modulated during social interactions and can recover after brain lesions. Here, we used calcium imaging of HVC projection neurons during freely produced songs to track activity across repeated renditions of the same song from seconds to weeks. We first confirmed that song-locked calcium-event timing was stable across days. Surprisingly, not every neuron showed a calcium event on every rendition of the song. We referred to the presence of such an event as participation. This participation was a stable, neuron-specific property that varied with the past and future renditions of the songs within an utterance and depended on social context. Song recovery after brain lesion and refinement during learning further revealed that neural participation could change while sequence timing remained stable. These results suggest that stable motor sequences need not rely on rigid repeated activation of the same cellular ensemble but can preserve temporal order while flexibly selecting which neurons contribute to each expression of the behavior. This provides a cellular solution to the reliability-flexibility tradeoff in learned motor control.

The transition to metazoan multicellularity required the evolution of cell-surface receptors that coordinate adhesion and signaling under changing environmental conditions. We investigated potential regulators of cell interactions in the choanoflagellate Salpingoeca rosetta, one of the closest living relatives of metazoans. Here, we identify Cupidon, an adhesion G protein-coupled receptor that acts as a dual-function regulator of cell adhesion and mating. Under well-fed (i.e., nutrient-replete) conditions, Cupidon suppresses cell aggregation by inhibiting N-acetylglucosamine-dependent collar-mediated adhesion. Starvation of S. rosetta triggers gametogenesis, resulting in anisogametes: female gametes with an elongated collar and male gametes that form a basal protrusion, the "fertilopod." Cupidon undergoes concurrent changes in proteolytic processing and localization, ultimately concentrating at the gamete contact interface, where it promotes gamete fusion. Together, our findings reveal that aGPCR-mediated regulation of cell adhesion predates the origin of metazoans.

How polymorphic traits are maintained despite the homogenizing forces of gene flow and recombination is a central question in evolutionary biology. While the accumulation of locally adaptive alleles within chromosomal inversions is well established, the role of sex chromosomes in local adaptation has received comparatively less empirical support. Here, we show that a male-limited color polymorphism in an Anolis distichus contact zone is anchored by a neo-sex chromosome. Across a narrow environmental gradient, an abrupt transition between yellow and orange dewlaps, extensible throat fans used for signaling, is driven by distinct pigmentation profiles we characterize via histological and chromatographic analyses. Integrating genomics and association mapping, we demonstrate this divergence relies on an additive, oligogenic architecture. Alternative neo-Y haplotypes track the phenotypic cline and combine additively with autosomal variants near a putative ketolase and a lipid regulator to determine color, jointly explaining a significant portion of the phenotypic variance. Furthermore, we identify a copy number variant near an X-linked visual processing gene, indicating simultaneous sensory divergence. This concerted evolution suggests the local light environment drives adaptation of the communication system. Ultimately, this study demonstrates that degrading neo-sex chromosomes act as non-recombining hubs for locally adaptive alleles, preserving phenotypic diversity under gene flow.

The optokinetic reflex (OKR) is an evolutionarily conserved reflexive behavior that ensures image stabilization on the retina during global motion. It consists of smooth eye tracking movements in the direction of the moving stimulus interspersed with rapid resetting saccades. This reflex is driven by retinal ON direction-selective ganglion cells (oDSGCs), which comprise distinct subtypes tuned either to vertical or horizontal motion. oDSGCs convey directional signals to the brain via precise axonal projections to specific accessory optic system (AOS) nuclei. However, the mechanisms that establish and maintain the specificity of these circuits remain poorly understood. Here, we identify a critical role for the mechanosensitive ion channel Piezo2 in refining AOS circuitry to ensure appropriate eye movement responses. Single-cell transcriptomic profiling revealed selective enrichment of Piezo2 in horizontally-tuned oDSGCs. We show that both loss and hyperactivation of Piezo2 in retinal neurons leads to cross-coupling of horizontal and vertical OKR responses, producing aberrant diagonal eye tracking movements during horizontal optokinetic stimulation. Mechanistically, Piezo2 regulates the developmental refinement of oDSGC axonal projections within the AOS, and disruption of this process results in persistent ectopic innervation that enables aberrant crosstalk between horizontal and vertical motion pathways. These findings reveal a channel activity-dependent mechanism that ensures the functional segregation of directional motion circuits underlying gaze stabilization.

Extensible body structures have evolved repeatedly across animals, yet the mechanisms underlying the deployment of extensible organs often remain unknown. Eristalinae hoverfly larvae (rat tailed maggots) possess exceptionally elongated posterior respiratory siphons, but the mechanism underlying their extension has not been experimentally investigated. Here, using wild collected Helophilus virgatus larvae, we show that posterior siphon extension is achieved through a folding unfolding mechanism revealed by fluorescence labeling. Phalloidin staining further demonstrated that, unlike Episyrphus sp. and Drosophila melanogaster, H. virgatus possesses a dense array of transversely oriented muscle fibers in the posterior siphon. Behavioral analyses further revealed that the posterior siphon functions not only in respiration but also as a propulsive organ for near surface locomotion through asymmetric rowing. Together, our findings identify the structural and kinematic basis of posterior siphon deployment and demonstrate how a specialized respiratory organ can evolve into a multifunctional appendage that supports both respiration and locomotion.