PLOS Biology

Compositional syntax - the ability to combine meaningful units into structured sequences whose overall meaning depends on both the meanings of the parts and their combination - is a hallmark of human language. Recent work suggests that chimpanzees may exhibit similar capacities, raising the possibility that compositionality predates the emergence of language in humans. However, a key challenge has been to exclude simpler explanations in which call combinations are processed as independent utterances rather than integrated structures. Here, we address this issue using a source-manipulation paradigm in playback experiments with captive chimpanzees (n = 6) at the Sigean African Reserve, France. We presented sequences combining alarm and recruitment calls either from a single source (one loudspeaker) or from two spatially distinct sources (two loudspeakers). If sequences are interpreted as independent calls, responses should not differ between conditions. Instead, chimpanzees responded significantly faster when sequences originated from a single source. Bayesian survival analyses confirmed this effect. These results support a non-trivial form of compositionality, whereby the meaning of call combinations depends on their integration into a unified sequence produced by a single individual. Our findings provide experimental evidence that key features of linguistic compositionality may have evolutionary roots in the primate lineage.

Venom systems are key evolutionary innovations that have contributed to the ecological success of numerous animal lineages. In ants (Formicidae), venom exhibits an exceptional diversity in both chemical composition and delivery mechanisms. Here, we combine a synthesis of current knowledge on the evolution of ant venoms with new phylogenetic comparative analyses, integrating chemical, morphological, and phylogenetic data at the genus level. Comparative analyses across Formicidae support the hypothesis that peptide-rich venoms represent the ancestral condition in ants, as they are widely distributed across basal and derived lineages. Despite this ancestral state, we identify seven independent evolutionary transitions toward non-peptidic venom, occurring in major clades including Dolichoderinae, Formicinae, Stenammini, Solenopsidini, Crematogaster, Pheidole, and fungus-growing ants. Ancestral state reconstruction and tests of correlated evolution across 114 genera show that these seven shifts away from peptide-based venom were almost irreversible and tightly coupled with the loss of stinging capacity and a dietary shift away from predation. These transitions are consistently associated with profound morphological modifications of the venom apparatus, such as reduction or complete loss of the sting, or its transformation into non-injecting structures. Chemically, these systems are dominated by alkaloids, iridoids, formic acid, esters, and terpenoids. These repeated transitions reflect major ecological and evolutionary shifts. Lineages that rely less on individual predation and more on collective foraging or plant-based diets tend to exhibit reduced reliance on injectable peptide toxins. Instead, they favor metabolite-based venoms that can be co-opted from existing biochemical pathways and deployed in diverse ecological contexts. Conversely, peptide-rich venoms are retained in lineages subjected to strong selective pressures for rapid prey immobilization or defense against vertebrate predators. Overall, ants represent a unique model for understanding venom evolution, illustrating how shifts in chemistry, morphology, and ecological strategy can drive repeated and convergent innovations. Future integrative studies combining genomics, metabolomics, and functional assays will be essential to unravel the mechanisms underlying these transitions and their role in the extraordinary diversification of ants.

The evolutionary origins of cognitive monitoring remain contested. Metacognition, the capacity to monitor one's own cognitive states, has long been linked to complex vertebrate brains, yet whether a miniature brain can evaluate the reliability of its internal representations is unknown. Here we demonstrate that bumble bees engage in uncertainty-guided decision-making. Bees dynamically adjusted opt-out choices according to perceptual difficulty, settling for a smaller guaranteed reward to avoid errors, and actively paid a reward cost to seek information under uncertainty. Without any retraining, bees transferred this 'opt-out-under-uncertainty' rule to novel tactile and working-memory tasks under an all-probe design. This strategy was stable across individuals and accurately captured by a confidence-based decision model. Our findings suggest that a brain of approximately one million neurons can support an abstract domain-general uncertainty-monitoring policy, indicating that the neural substrates for uncertainty-guided decision-making may be far more ancient and widely distributed than previously assumed.

A fundamental challenge in drug development is the frequent failure of early laboratory research to translate into clinical benefit. One promising solution is to confirm findings from exploratory single-laboratory studies across multiple laboratories before clinical testing. We investigated this approach following the conduct of preclinical multi-laboratory studies across different fields of medicine. For this, we evaluated effect sizes, experimental rigor, and a set of criteria to identify determinants of confirmation success. When tested under increased rigor, only a fraction of multi-laboratory studies confirmed the initial results. The underlying effect size reduction was associated with outcome-relevant experimental differences between exploratory and confirmatory stages. In summary, multi-laboratory studies proved highly informative and served as an effective filter for promising treatments.

Bats are recognized reservoirs for several zoonoses and have an exceptional tolerance to viruses, likely linked with strong evolutionary selection in immune genes. Notably, in light of the emergence history of severe acute respiratory syndrome coronavirus (SARS-CoV), SARS-CoV-2 is hypothesized to have originated from Rhinolophus bats as well. In-depth studies are still needed, however, to unravel how SARS-related coronaviruses (SARSr-CoVs) persist and thrive in nature through evolution, virus-host interactions, and cross-species transmission. Here we present a pioneering 10-year longitudinal study of BBCoV-EPI1, a SARSr-CoV in Rhinolophus bats that revealed the complexity of virus-host interactions and the tempo at which new viral lineages emerge. Our results demonstrated the impacts of host life cycles (hibernation, female gathering, weaning juveniles, and mating periods) on strong seasonal oscillations in viral prevalence. These pronounced fluctuations drove viral diversification through bottlenecks, founder effects and Darwinian selection, counterbalanced by high mutation rates, fast gradualism, and recombination. We also found that host-cell enzymes are major contributors to BBCoV-EPI1 evolution in bats. The antiviral effect of APOBEC3 detected here in bats is weaker than it is in humans. Conversely, the ADAR enzyme had an unexpectedly strong and beneficial influence on viral evolution, even though the high mutation rate of RNA viruses is usually attributed to viral polymerases' low replication fidelity. We discovered that key BBCoV-EPI1 innovations in Rhinolophus bats were mostly located in proteins involved in cell-cycle hijack and in blocking bat cells' antiviral response, rather than in the Spike (S). We also showed that the BBCoV-EPI1 S protein efficiently uses angiotensin-converting enzyme 2 (ACE2) receptor to enter Rhinolophus bat cells, but not to enter human or sympatric species cells, due to amino-acid differences at the S-ACE2 interface. Last, this work identifies 101 critical amino-acid changes frequently associated with viral fitness shift, and paves the way for future experimental studies focusing on the capacity of SARSr-CoVs to adapt to hosts and cross the species barrier.

Communication signals often contain behaviorally relevant structure on multiple temporal scales. Short-timescale features are commonly thought to be recognized first and then integrated into longer-timescale representations. Whether a shared circuit can instead recognize multiple timescales remains unclear. Cricket calling songs provide a tractable test because millisecond-scale pulses are grouped into chirps lasting hundreds of milliseconds. We combined female phonotaxis with a mechanistic model of the identified pulse-recognition network to ask whether this circuitry can also generate chirp selectivity. In Gryllus bimaculatus, the model, originally parameterized from pulse-scale electrophysiology and behavior, recovered the main boundaries of chirp preference without fitting to chirp behavior. Coincidence detection generated the minimum chirp-duration requirement, whereas suppressive computations in the networks input neuron shaped the upper boundaries for chirp duty cycle and period. Across 14 species, varying these suppressive computations captured major differences in chirp tuning. These findings reveal a temporally interleaved serial circuit in which long-timescale selectivity begins upstream of completed short-timescale selectivity, offering an alternative to both conventional short-first hierarchies and parallel pathways.

Understanding the evolution of cognition is fundamental to understanding the origins and nature of our own cognitive abilities, with cross-species comparisons providing a cornerstone of this endeavor. Yet, comparative cognition so far has largely focused on endothermic vertebrates, particularly mammals and birds, while ectotherms--representing a substantial proportion of vertebrate diversity--remain relatively understudied. Moreover, variation in experimental methods makes existing data difficult to compare across species. Big-team science offers a way to overcome these limitations by enabling standardized cognitive testing across broad taxonomic scales. Here, we apply this approach to fishes, using inhibitory control as a proof of concept for standardized comparative testing in 444 individuals across 22 teleost species spanning 19 genera. We demonstrate that standardized cognitive testing across such diversity is feasible, while also revealing substantial heterogeneity in the sample. Performance varied markedly among species, but, strikingly, showed only a weak phylogenetic signal, contrasting with patterns previously reported in mammals and birds. In addition, we detected great within-species variation, including differences across research groups, suggesting that performance may reflect not only species-level evolutionary history but also ontogenetic experience and the capacity to adjust decision rules to local conditions. Together, our findings highlight the importance of both evolutionary and environmental sources of cognitive variation and demonstrate that extending standardized comparative approaches beyond traditionally studied endotherms can reveal a more dynamic and complex picture of cognitive evolution across the vertebrate lineage.

Ant larvae are blind and immobile, depending heavily on the adults for care in the form of feeding, grooming, and transport. However, they are not inactive colony members but play a central role in the organization of ant societies by modulating adult behavior and physiology. While adult ants have been studied extensively, we still know little about what sensory modalities larvae use to perceive their environment. Here, we provide a molecular and circuit-level characterization of the chemosensory system of the clonal raider ant larva. Combining scanning electron microscopy and confocal imaging, we show that dome sensilla in the maxillary and labial palps are innervated by odorant receptor (OR) neurons. A larger population of ionotropic receptor (IR) neurons innervate papilla sensilla across various regions of the larval head: the antennae, the labrum, the maxillary palps and galeae, as well as the labial palps and the ventral labium. This suggests that IRs, which can have various functions, from taste and olfaction to temperature and humidity sensing, constitute the predominant chemosensory modality in ant larvae. To investigate projections into the central brain, we imaged transgenic lines that fluorescently label OR- and IR-expressing neurons. We found that OR- and IR-expressing neurons in the labium and maxilla project along the labial and maxillary nerves through the subesophageal ganglion to the deutocerebrum, whereas IR-expressing neurons from the labrum project to the tritocerebrum and those from the antenna project to the posterior deutocerebrum. Together, our findings establish a structural and molecular framework to study larval chemosensation in ants.

Across animal phyla, odor information is represented in the first olfactory processing center by combinatorial activation of discrete glomeruli. To examine how this organization of olfactory processing channels emerges during development we combined 2-photon calcium imaging, volume electron microscopy, and large-scale automated neuron reconstruction in zebrafish larvae. We focused on a developmental stage (130 hours post fertilization) when the olfactory bulb (OB) is structured into ~16 large neuropil regions referred to as protoglomeruli but most glomeruli are not yet differentiated. Our ultrastructural reconstructions revealed that protoglomeruli are organized into smaller units referred to as microglomeruli, each of which is defined by a distinct set of mitral cells with overlapping, spatially confined dendritic arbors. Neighboring microglomeruli were innervated by distinct subsets of sensory axons and activity was more highly correlated among mitral cells associated with the same microglomerulus than across microglomeruli of the same or different protoglomeruli. These results reveal a precise subcellular organization of the neuropil in the developing OB into distinct processing channels, indicating that the layout of the adult glomerular array is established already early in development.

We used Scopus data on 243949 top-cited scientists to map scientific cosmopolitanism defined as having at least two different countries that contribute alone at least 10 percent of an author published record as indexed in Scopus. 20.4 percent of the top-cited authors were cosmopolitan based on this definition. Based on current author affiliation, rates varied widely from 9% to 76% across countries with at least 250 top-cited authors. Countries with few top-cited authors had almost always high rates of cosmopolitanism. The proportion of top-cited authors who are cosmopolitan has steadily increased over time in younger generations among those who started publishing after 1965 reaching 43% recently. Large differences were also seen across scientific subfields from 1% in General Psychology and Cognitive Sciences to 46% in Econometrics. Across the 30 country pairs that were most over-represented, countries shared borders, languages, most common religion pairs, or any of these features in 15, 19, 26, and 29 cases, respectively. The map of cosmopolitan authors reveals a large and increasing proportion of the most influential scientists who share two or more scientific homes that each has made a substantial contribution to their career. Cosmopolitanism among scientists requires better study to help facilitate its potential positive contributions not only to individual scientists but to science and society more broadly.

Understanding how neural populations support natural behaviour requires knowing what a population does while an animal performs a specific, self-initiated action. For responses evoked by an experimenter-delivered stimulus, the signal can be aligned by the trigger itself, and no behavioural scoring is needed to define the event. Complex behaviours such as parental care and social interaction provide no such trigger. They are defined from the video record, usually offline and post hoc, and are conventionally scored in one program and exported to another for analysis. In this study we developed EthoTrace, a single self-contained HTML file that runs in a desktop browser without installation, server or network access and carries a session from behaviour and calcium signal through to the statistical comparison. Behaviour is annotated on a timeline shared with the {Delta}F/F trace, the signal is corrected and scaled under a stated baseline convention, single bouts stay inspectable in their behavioural context, and repeated bouts are aligned without filling absent data. We demonstrate the complete workflow on a parenting behaviour experiment, in which behaviour was scored and the photometry signal analysed in a single session folder. We expect EthoTrace to facilitate integrative analysis in neuroscience, where behavioural observation and fiber photometry signals are interpreted together.

Recent reanalyses of major lipid-lowering trials have reported substantially greater treatment benefit in individuals with higher polygenic risk scores (PRSs) for coronary artery disease (CAD). We tested whether trial eligibility criteria could generate this pattern through collider bias. In simulations where the true PRS-by-treatment interaction was set to zero, we reproduced apparent PRS-dependent treatment effects similar to those observed in reanalyses of three trials. This included FOURIER-like hazard ratios for lipid-lowering treatment versus placebo of 0.77 in the high CAD PRS stratum and 0.95 in the low CAD PRS stratum. In the Helix Research Network (n = 175,106) and UK Biobank (n = 92,859) cohorts, where we did not apply the trial eligibility criteria, the CAD PRS showed little evidence of modifying the effect of statin use on acute coronary events. We then used LDL cholesterol response as a better-powered test of collider bias: we found no evidence that LDL PRS modified statin response in population cohorts, yet stratifying on baseline LDL cholesterol induced apparent PRS-dependent response matching the simulations. Importantly, treatment randomization does not protect against eligibility-induced collider bias. PRS-dependent response may therefore reflect bias from eligibility rather than biology. These results should inform the planning and execution of clinical trials for precision medicine.

When human beings navigate through an environment, a conceptual space, memories or even imagined spaces, fMRI signals in select brain regions vary with movement direction, alternating in strength with a periodicity of 60 degrees. At the cellular level, certain neurons called grid-cells form a hexagonal lattice representation of physical space. Given that the axes of the lattices align across neurons, the concerted directional and spatial firing of populations of these neurons may form the basis of the hexadirectional modulation of the fMRI signal. However, the exact link between the two remains unclear. Multiple mechanisms have been proposed that could couple neuronal activity to the fMRI signal. These include (1) preferential neuronal discharge when the direction of motion coincides with the lattice axes, (2) repetition suppression when multiple fields are traversed in succession, or alternatively, (3) a nonlinear transduction step. Here, we propose targeted experiments that can distinguish these mechanisms, for which we assess the expected effect sizes via simulations. In particular, by introducing calibrated pauses between linear path segments, it is possible to differentiate the repetition-suppression hypothesis from the nonlinear transduction model. By additionally varying the subjects movement speed and path lengths, the proposed protocol can distinguish conjunctive neuronal tuning (in which neurons respond to both speed and location or direction and location) from the other hypotheses. Crucially, if either the repetition-suppression or the nonlinear-transduction hypothesis holds, then the scale of the lattices will play a role. According to our analysis, hexadirectional signals should emerge only when a linear path segment is longer than half of the spatial lattice period. As grid cells with different scales are grouped into distinct modules along the dorso-ventral axis of the entorhinal cortex, this may make it possible to non-invasively measure the hierarchy of grid scales in the human brain.

Gut microbes convert cholesterol into coprostanol, a poorly absorbed sterol that is largely excreted in feces and is linked to lower serum cholesterol levels. However, the enzymes responsible for this process remain poorly characterized. The second step of the pathway, cholestenone reduction into coprostanone, has long been established, yet the enzyme(s) responsible were unknown. Here, we use comparative genomics to identify SpiE, a cholestenone (4-cholesten-3-one) reductase that is part of the steroid processing (spi) pathway with SpiR. We confirm that SpiE binds to and reduces both cholestenone and progesterone into 5{beta}-reduced forms. SpiR and SpiE together convert cholesterol into coprostanol, indicating that both enzymes are sufficient for coprostanol formation. SpiE belongs to the short-chain dehydrogenase (SDR) family and represents an evolutionarily distinct lineage of SDR ene-reductases. Metagenomic analyses reveal that spiE relative abundance is strongly correlated with stool coprostanol (Spearman's {rho}=0.81, p=5.99e-65). In longitudinal patient cohorts, antibiotic treatment coincided with loss of SpiE and coprostanol production. Post antibiotics, the emergence of distinct SpiE-encoding genera rescued coprostanol production in some individuals. Our findings provide the biochemical basis of the cholesterol to coprostanol pathway and lay the groundwork for future studies linking it to host physiology.

Many animals use the Earth's magnetic field to orient and navigate over long distances, yet the sensory mechanism that underlies this ability remains unresolved. A central question is whether the compass depends on light: a cryptochrome-based radical-pair mechanism, best characterised in birds, requires a photon to generate the magnetically sensitive species, whereas magnetic particle-based and inductive mechanisms do not. In mammals, which lack the light-sensitive cryptochromes that the avian model requires, this question is unresolved. Here we tested whether migratory bats, Pipistrellus nathusii, require light for migratory orientation, studying wild migrants at a major flyway under laboratory-controlled light conditions, including verified total darkness. Bats were acclimated to starlight-level illumination or to total darkness before release into a circular arena in which take-off direction was recorded, and take-off latency was taken in every trial as a control for behavioural state. Bats released under starlight-level illumination, and bats released in total darkness after starlight acclimation, both oriented in the south-westerly direction typical of free-flying bats at this flyway; their mean headings lay 11 degrees apart and did not differ in direction, in angular concentration, or in take-off latency. Bats released in total darkness after prolonged darkness produced the same mean heading but did not reach significance under a Rayleigh test, and did not differ from either other group. To our knowledge, this is the first demonstration that a migratory mammal expresses its seasonally appropriate migratory heading in total darkness. Bats orienting in darkness took off five to eight minutes after their last photon exposure, seven to eight orders of magnitude beyond the microsecond lifetime of the only cryptochrome radical pair demonstrated to exist and to be magnetically sensitive. Because a compass reading is informative only at the moment of the directional decision, a signal generated before a bat entered darkness could not encode its heading at take-off; the magnetically sensitive species must therefore form without photons. The radical pairs capable of doing so have not been shown to exist, even in vitro. A migratory mammal thus expresses its seasonal heading without concurrent light, in a lineage lacking the photoreceptor on which the light-dependent compass in birds relies.

Multisensory synchrony judgments depend on recent history: the point of subjective simultaneity (PSS) shifts toward recently experienced timing relationships. This shift, known as rapid temporal recalibration, is almost always interpreted as perceptual, a change in when events appear simultaneous. Yet serial dependence in such judgments can arise from two mechanistically distinct sources that a raw PSS shift cannot separate: a genuine perceptual realignment, which slides the psychometric function sideways along the multisensory asynchrony axis (an odd effect), and a decisional carryover, a bias to repeat the previous verdict, which lifts the function vertically without moving the PSS (an even effect). We re-analysed eight published datasets investigating rapid recalibration spanning audiovisual, audiotactile, and visuotactile pairings and audiovisual speech, decomposing serial dependence into these two components within a single mixed-effects model. The components dissociated by modality: perceptual recalibration was robust for audiovisual pairs but weak for audiotactile and absent for visuotactile pairings, whereas the decisional carryover was largest for the tactile pairings and weak for audiovisual pairings, so that the two traded off across the senses. In audiovisual speech, the decisional carryover was gated by the spoken syllable but not by the talkers identity and did not persist beyond one trial, identifying it as a content-specific, one-step decision memory rather than a motor habit or a multi-trial store. Separating the perceptual and decisional contributions to a timing judgment thus re-draws the map of temporal recalibration and revises several conclusions drawn from the undecomposed PSS.

Animals encounter a variety of food items and must determine their future value and preservability. Because animals in laboratory settings are typically provided with uniform food items, there is a dearth of knowledge on how animals assess natural complex food. Here, we dissect how wild agoutis-a critical seed disperser of the Neotropics-decide whether to consume or bury food in small caches, i.e. scatter-hoarding. We find that agoutis preferentially cache nuts over fresh fruits and, when foraging, undergo a sharp transition from eating to scatter-hoarding. Remarkably, agoutis scatter-hoarded empty nuts with intact shells but not filled nuts with broken shells. This decision was dependent on an oro-manual food assessment, an ecological information-seeking behavior. They used their lips and incisors - a somatosensory fovea - to navigate the surface of the nut optimally accumulating decision-critical sensory information. Together, these findings provide a mechanistic account of preservability assessment in a wild rodent, revealing how information-seeking behaviors support long-term value optimization in natural environments.

Scene- and word-selective regions in adult ventral temporal cortex occupy consistent locations across individuals and align with eccentricity biases for peripheral versus central parts of the visual field, respectively. This relationship may reflect a developmental sequence in which initial preferences for visual field location influence the emergence of category-selectivity in these regions, driven by where each category appears in the visual field. To test this account, we used fMRI in awake, behaving infants aged 2-10 months, independently manipulating stimulus size (40{degrees} versus 6{degrees}) and category (scenes versus letters). We found eccentricity gradients across early visual cortex and ventral temporal cortex. Crucially, the collateral sulcus -- a scene-selective, peripherally-biased region in adults -- showed greater responses to big over small stimuli in infants, but no reliable preference for scenes over letters. These findings suggest that an eccentricity bias could provide a scaffold for later category specialization.

Tardigrades, key ecdysozoan organisms, have poorly characterized daily behavioral rhythms linked to their molting (ecdysial) cycle. We continuously tracked the locomotor activity of the model tardigrade Hypsibius exemplaris using infrared videography and deep learning-based automated tracking under three photic regimes: a light/dark cycle, constant darkness following entrainment, and constant darkness without prior entrainment. We identified a robust endogenous circadian-like rhythm in locomotor activity that persisted in constant darkness, independent of photic input. Although the light/dark cycle enhanced the rhythm amplitude and the overall animal activity, it was not required for rhythmicity. Individual phases varied widely, indicating a lack of population-level synchronization. Furthermore, we developed a behavioral classification system based on activity level, which enables categorizing distinct behaviors. Behavioral patterns were modulated by distinct ecdysial stages, with quiescence gating premolt and time-of-day dependent patterns in feeding and wandering. These findings provide evidence consistent with an endogenous, circadian-like timing system in tardigrades that integrates daily activity with molting cycles and establish H. exemplaris as a promising model for studying ecdysozoan chronobiology.

Respiratory viruses, including coronaviruses, generally initiate infection in the upper respiratory tract, where mechanistic studies of host-virus interactions require models amenable to genetic manipulation. Human nasal air-liquid interface (ALI) cultures are realistic models of the nasal epithelium, but robust CRISPR/Cas9 engineering workflows for this primary cell system have been lacking. Here, we established an integration-free CRISPR/Cas9 workflow for genetic engineering of human nasal basal cells, which are subsequently differentiated into gene-edited ALI cultures. GFP-based sorting of RNP-transfected nasal basal cells substantially increases editing, achieving knockout efficiencies of 70-90% across gene targets (B2M, SLC35A1, ACE2, and TMPRSS2). Genetic disruption of ACE2 markedly reduces infection by SARS-CoV-2 and hCoV-NL63, confirming its important role for both viruses in the human nasal epithelium. TMPRSS2 knockout substantially reduces replication of both viruses, demonstrating SARS-CoV-2 depending on TMPRSS2 in the human nasal epithelium and providing genetic evidence in primary human cell cultures that hCoV-NL63 relies on TMPRSS2. This platform enables systematic genetic perturbation in a physiologically relevant model of the primary site of respiratory virus infection, validates ACE2 and TMPRSS2 as targets for medical countermeasures against SARS-CoV-2 and hCoV-NL63, and provides a versatile approach to identify host dependency factors for both circulating and emerging respiratory viruses.