Left-right (LR) asymmetry is a fundamental feature of animal development, yet progress in understanding its establishment has been limited by the fact that almost all animals do not ordinarily vary in the direction of their asymmetry. Snails are an exception because some wild-living species show abundant variation-externally visible in the shell coiling direction or "chirality"-yet the existing knowledge is from species, including the pond snail Lymnaea stagnalis, in which the sinistral mutation is rare and causes pathology. Here, we show that chiral polymorphism in Japanese Euhadra snails is due to functional variation in an unconventional myosin I a/b, a myosin family member not previously implicated in LR specification in any animal. Both the sinistral and dextral gene variants are ancient, impart minimal transcriptional differences in the single-cell embryo, and are not associated with pathology. Analyses show that relaxed selection enabled dominant-acting amino acid substitutions in the sinistral version of the Euhadra myosin motor domain and motor-lever junction, potentially affecting actomyosin interactions. For comparison, in the pond snail, we found that thousands of genes are differentially expressed between dextral and sinistral embryos due to the frameshift mutation in a formin gene. Overall, these results reinforce the role of myosin and actin-driven processes in LR symmetry breaking, broaden the known molecular repertoire, and highlight key mutations and positions in myosins that should be explored further, including in other animals.

Arabidopsis thaliana, a widely used genetic model species, is considered incapable of forming mycorrhizal associations, which support nutrient acquisition in most other land plants. Mucoromycotina "fine root endophytes" (MFREs) are a recently characterized group of mycorrhizal fungi capable of forming nutritional mutualisms with a wide range of plants, supplying nitrogen and phosphorus to host plants and gaining access to photosynthetically derived carbon. Here, we demonstrate that a wild-isolated MFRE strain, Lyc-1, successfully colonizes Arabidopsis roots under monoaxenic conditions without affecting plant growth. Using a combination of conventional light and epifluorescence microscopy, we demonstrate extensive extra- and intraradical colonization of the root cortex. Stable- and radio-isotope tracing further revealed bidirectional nutrient exchange between the host plant and the fungus. To our knowledge, this is the first demonstration of a functional, mycorrhiza-like nutritional mutualism in Arabidopsis. As Arabidopsis lacks a complete set of common symbiosis signaling pathway genes, our findings suggest that Arabidopsis-Lyc-1 symbiosis may be controlled by an alternative, so far uncharacterized, symbiotic pathway. Thus, our study not only supports the existence of multiple evolutionary routes to plant-fungal nutritional mutualisms but also establishes Arabidopsis as a genetically tractable model to study plant-fungal symbiosis, thereby opening new opportunities to dissect the molecular basis and evolution of mycorrhizal symbioses.

While artificial light and digital technologies are widely assumed to delay and curtail sleep, direct, longitudinal evidence documenting these changes is remarkably scarce. From 2012 to 2024, we conducted a longitudinal study of native Toba/Qom communities in northern Argentina, including rural groups newly introduced to electricity and semi-urban groups with earlier access to electricity. Using linear mixed-effects models on a dataset of over 12,000 actigraphically recorded sleep events from 156 participants at different times, we observed striking shifts in sleep dynamics. Remarkably, both groups showed delays of close to 1 h in sleep timing, and participants from rural communities lost 35 min of sleep within the course of a decade. These changes occurred across a period that included, first, the introduction of electricity to rural communities after 2016, and, in more recent years, the spread of the internet and smartphone use among the Toba/Qom. While previous work in these and other populations has shown that both factors are associated with changes in sleep habits, our analyses suggest that they cannot fully explain the reported shifts in sleep timing across time by themselves, which may therefore be consistent with concurrent broader processes of modernization and acculturation. These transformations highlight the rapid changes that can take place in communities going through the early stages of the adoption of modern technologies, offering a contemporary parallel to the shifts in human sleep hypothesized to have accompanied global industrialization.

In most flying species, legs and wings mediate earthbound vs. aerial locomotion, respectively. During terrestrial social displays such as threat or courtship, however, species-typical movements of these appendages are coordinated in a stereotyped manner. How such appendicular control is integrated is poorly understood. Threat behavior in Drosophila consists of four types of leg and wing actions, which can be performed singly or in combination. Using a large-scale functional screen, we previously identified a cluster of 4-5 AIP (CL062) neurons whose optogenetic activation can evoke all threat actions and which are essential for natural threat displays. To understand how this threat command module functions, we have mapped AIP neurons into the male fly connectome and identified split-GAL4 drivers for four major downstream targets, whose functional connectivity and behavioral roles we have tested. Surprisingly, we find that distinct threat-specific actions are not controlled by parallel connections from different subsets of AIP cells to different action-specific descending neurons (DNs), a parsimonious circuit architecture. Rather, AIP neurons collectively activate two parallel downstream modules comprising pairs of neurons that control wing vs. leg movements, respectively. Wing movements are controlled via direct projections to two specialist DNs that act synergistically, while leg movements are controlled indirectly via two interneurons that act antagonistically to pattern the activity of multiple DNs, which are likely used in other locomotor contexts. These data elucidate a hierarchical circuit for appendicular coordination during a terrestrial social display and provide insight into how the brain has repurposed appendage-specific locomotor control for social communication, a form of exaptation.

Soil zinc (Zn) pollution, largely caused by anthropogenic activities such as mining and metal processing, can disrupt metabolism and reproduction, often leading to death. Some fungi can tolerate elevated Zn concentrations, but the mechanisms of Zn tolerance and if and how they affect symbionts are still unclear. To fill these gaps in knowledge, we investigated Zn tolerance in the ectomycorrhizal fungus Suillus tomentosus and its host pine Pinus contorta, two widespread symbiotic partners in American Western forests. Using a combination of whole-genome resequencing, in vitro Zn fungal assays, fungal-pine partner bioassays, transcriptomics, and metabolomics, we found an absence of S. tomentosus population structure based on Zn tolerance, and that the trait is highly polygenic, constitutive, and associated with Zn exclusion and antioxidant responses to mitigate toxicity. We also found that S. tomentosus protects P. contorta from Zn toxicity by increasing seedling performance under Zn stress, with Zn-tolerant S. tomentosus providing slightly more benefit compared with Zn-sensitive S. tomentosus. Our results illustrate that fungal metal tolerance is a complex trait, and that intraspecific variation should be considered for understanding the impacts of environmental stress on biodiversity, as well as for designing effective biotechnological tools and conservation/reforestation strategies.

Transverse asymmetric cell divisions (ACDs) in grass leaf epidermal development produce large basal pavement cells and small apical specialized cells. These "patterning divisions" generate the long-short epidermal cell pattern that is distinctive of grasses. Here, we show that patterning divisions require premitotic basal polarization of BdPOLAR-LIKE1 (BdPL1) in the model grass Brachypodium distachyon. Loss of BdPL1 disrupted division-plane orientation and postmitotic cell-size asymmetry in all cell files, which resulted in epidermal patterning defects. Ectopic expression analyses demonstrated that BdPL1 polarization was independent of cellular context and sufficient to promote supernumerary transverse divisions. Furthermore, the developmental regulators BdBREVIS RADIX-solo and BdYODA1 formed a post-division polarity domain that enforced cell fate asymmetry independently of BdPL1. We propose that the premitotic BdPL1 module enforces physical cell division asymmetry contributing to medio-lateral patterning of cell types, whereas the postmitotic BdBRX-solo/BdYDA1 module enforces within-file cell fate asymmetry. Together, they robustly pattern the grass leaf epidermis.

The amphibian chytrid fungus Batrachochytrium dendrobatidis (B. dendrobatidis) has caused catastrophic biodiversity loss worldwide.[1][,][2][,][3] Although B. dendrobatidis is now widespread across environmentally suitable regions,[4] the absence of amphibian declines in some high-suitability areas suggests the existence of refuges supporting epidemiologically naive communities. Epidemiologically naive refuges have not experienced past B. dendrobatidis epizootics despite suitable environmental conditions and may be B. dendrobatidis-free, harbor less virulent B. dendrobatidis lineages, or contain resistant host communities. As eradication of virulent B. dendrobatidis lineages is rarely successful after establishment, identifying epidemiologically naive refuges is imperative.[5][,][6] Here, following extensive multi-year disease surveillance, we report a major epidemiologically naive refuge in the Neotropical highlands, the Sierra Nevada de Santa Marta (SNSM) in northern Colombia. We found no evidence for contemporary B. dendrobatidis presence, despite detecting the hypervirulent Global Panzootic Lineage in a neighboring Andean mountain range. Population genomic analyses in SNSM-endemic harlequin toads found no demographic signatures indicative of cryptic epizootic decline. Niche modeling predicted high suitability for B. dendrobatidis occurrence and B. dendrobatidis-induced declines throughout the SNSM, with climatic conditions in lowland regions surrounding the SNSM likely acting as a dispersal barrier and preventing B. dendrobatidis invasion, creating a "sky island." Infection trials using three SNSM-endemic amphibian species revealed tolerant and susceptible species. Together, our results indicate that the SNSM is an epidemiologically naive refuge at risk of invasion by hypervirulent B. dendrobatidis, which could result in the loss of 25 endemic amphibian species. We highlight the urgent need for proactive conservation action and the strict implementation of biosecurity to safeguard the unique and vast amphibian diversity of the SNSM.

Hippocampal spatial representations emerge within minutes of first exposure to novel environments, challenging models based solely on gradual synaptic plasticity. Here, we show that CA1 spatial coding is organized according to a dual-mode architecture comprising a pre-organized backbone and an experience-dependent component. Backbone cells expressing immediately emerging place fields form a stable spatial scaffold and dominate positional decoding from the first traversal, whereas experience-dependent cells bearing gradually emerging fields are progressively incorporated to refine spatial representations. Analyses of ensemble activity further reveal that offline dynamics prospectively organize future spatial coding. In backbone cells, latent tuning aligns with their future place fields prior to task engagement, while in experience-dependent cells this alignment strengthens before overt place-field expression. Together, these findings identify a dual-mode organization of hippocampal populations in which offline dynamics pre-organize network activity to enable rapid and precise spatial coding in novel environments.

During early visual cortex development, the onset of visual experience initiates a period of rapid dendritic growth and excitatory synapse formation that coincides with the functional maturation of visually driven neuronal response properties. How this surge in the number of excitatory synaptic inputs refines the initial functional network structure to generate coherent, yet adaptable, single-neuron responses remains unclear. To address this issue, we examined the functional properties and spatial organization of individual dendritic spines of layer 2/3 neurons in ferret visual cortex before and after the onset of visual experience. Our findings indicate that this initial period of visual experience is marked by a dramatic and selective functional and spatial recomposition of the visually naive excitatory synaptic network. This reorganization leads to an increase in the proportion and tuning strength of orientation- and direction-selective inputs and markedly expands the population of binocular inputs, particularly those with highly aligned responses across both eyes. This refinement follows distinct developmental trajectories of contralateral vs. ipsilateral inputs, as well as monocular vs. binocular inputs, that reshape the functional organization of excitatory synaptic inputs to individual neurons. In parallel, synaptic inputs are spatially reorganized, with co-tuned inputs becoming locally clustered along dendrites as a coarser branch-level organization present at eye opening is remodeled. Together, these rapid changes appear to be organized as a scaffold-and-integration process through which visual experience expands and reorganizes the excitatory synaptic network. This process enhances tuning selectivity and supports the emergence of a robust binocular representation while maintaining functional input diversity.

Host-associated prokaryotes can undergo extreme genome reduction, but the most reduced genomes belong to mutualistic endosymbionts whose hosts compensate for lost functions, eroding the symbiont's identity as an autonomous cell. Whether comparable reduction can occur while preserving the informational autonomy of a cell remains unclear. Here, we report the discovery of Candidatus Sukunaarchaeum mirabile, an archaeon with a genome of only 238 kbp (less than half the size of the smallest known archaeal genome) obtained by single-cell genomics from a dinoflagellate cell. Phylogenetic analyses reveal Sukunaarchaeum as an extremely divergent lineage that cannot be placed within any recognized archaeal phylum, although its precise branching position remains unresolved; environmental surveys indicate a diverse, geographically dispersed, and previously overlooked clade. Its genome lacks virtually all recognizable metabolic pathways yet retains the catalytic cores of the machinery for DNA replication, transcription, and translation, with losses largely confined to auxiliary and regulatory subunits. This profile contrasts with that of highly reduced mutualistic endosymbionts, in which informational genes are lost alongside metabolic ones, eroding autonomous cellular identity: Sukunaarchaeum encodes no recognizable metabolic pathway that could benefit a host, and instead dedicates ∼25% of its genome to large membrane proteins of unknown function, a feature paralleled by host-invasion proteins in parasitic archaea. These observations argue against a mutualistic mode of host dependence and reveal a second, distinct endpoint of cellular reduction: the informational core may represent the practical lower bound for a cell that retains the capacity to replicate and express its own genome.

The animal fossil record is a non-uniform archive of evolutionary history in which exceptional preservation diminishes toward the present,[1][,][2][,][3] with biomineralized skeletal elements constituting the majority of the fossil record. Preservation of soft tissues requires rare combinations of chemical, biological, and physical conditions that preclude or delay decay until biological substrates can be geologically stabilized via mineralization or maturation.[4] However, during the late Ediacaran Period (∼579-539 mya) fossilization of soft-bodied macroorganisms was common across a wide range of depositional settings.[5][,][6] Taphonomic models seeking to explain Ediacaran exceptionalism typically appeal to unusual mineralogical and geochemical conditions or microbiological influence (e.g., Gehling,[7] Tarhan et al.,[8] Bykova et al.,[9] and Bobrovskiy et al.[10]), and the Paleozoic decline in exceptional preservation has invariably been explained in terms of expansion of the oxic zone through metazoan bioturbation (though see Cribb et al.[11]) and enhanced scavenging.[12] We explore the hypothesis that temporal heterogeneity in metazoan exceptional preservation is a consequence of the origin and/or proliferation of microbial collagenases.[13] Collagenase gene trees reconciled with a time-calibrated phylogeny show that collagenases arose and were produced by obligate anaerobes billions of years before proliferating by lateral gene transfer, approximately coincident with the diversification of early animals. These results support a link between the evolution of collagenases, animals, and the non-uniformity of the fossil record. Proliferation of collagenase-producing microbial lineages occurred in concert with early animal evolution. Evidence also indicates a shift in the locus of collagen degradation within the sediment redox profile, coincident with the decline of exceptional soft-tissue preservation in the marine realm.

Reconstructing locomotor performance of extinct animals is fundamental to understanding paleoecology, yet the soft tissues that control movement rarely fossilize, leaving performance poorly constrained for extinct taxa[1]. Burst locomotion is a key determinant of predatory and escape success[2][,][3] and is governed by well-established fluid dynamics and kinematic principles, meaning it can be modeled from skeletal morphology alone. Here, we apply a drag-based fast-start framework, which we term a "slam-start," to estimate lunge velocity in four mosasaurs, dominant seagoing predators of Late Cretaceous oceans,[4] spanning Mosasaurinae and Russellosaurina, using skeletal and caudal muscle reconstructions to parameterize tail excursion amplitude, muscle power output, and hydrodynamic drag across a range of plausible parameters. Across all modeled conditions, lunge velocity increases with tail curl amplitude and power output, while increasing drag coefficient produces only modest reductions in performance. Russellosaurine mosasaurids (Platecarpus tympaniticus and Tylosaurus proriger), which have longer tail displacement areas, exhibit higher normalized lunge velocities than mosasaurines (Mosasaurus sp. and Plotosaurus bennisoni), and these relative differences are consistent across a wide range of drag regimes. These results support distinct hunting strategies within Mosasauridae: the faster-lunging russellosaurines were likely ambush predators, whereas the slower mosasaurines were likely pelagic cruisers. As a case study, this work demonstrates that physics-based biomechanical modeling can generate quantitative, directly comparable locomotor estimates for extinct taxa using preserved morphology as input, offering a transferable protocol for studying burst performance across marine reptiles, taxa with no living analogs, and through deep evolutionary time.

Filamentous fungi, such as Aspergillus species, use microtubule transport to move early endosomes. Other cargos, such as peroxisomes and mRNAs, "hitchhike" on early endosomes to move throughout the long hyphae of these organisms. In Aspergillus nidulans, peroxisomes hitchhike on early endosomes using the endosomal protein PxdA and the peroxisomal protein AcbdA. The HookA adaptor protein links endosomes to microtubule motors. Here, we set out to explore the physiological functions of peroxisome hitchhiking and endosome motility. A. nidulans has a complex life cycle that includes asexual and sexual reproduction. A. nidulans and other fungi within the Pezizomycotina subphylum are also notable for the vast number of secondary metabolites they produce. Light and other environmental conditions influence developmental decisions and secondary metabolite production. Here, we found that sexual reproduction is favored in the absence of endosome motility, even in the light, which normally promotes asexual reproduction. RNA sequencing of strains lacking PxdA-marked motile early endosomes showed altered expression of genes involved in development. Unexpectedly, we also observed altered expression of genes involved in secondary metabolism in strains lacking endosome motility and peroxisome hitchhiking. Using mass spectrometry, we found that the loss of endosome motility affected the biosynthesis of secondary metabolites, including sterigmatocystin, a carcinogenic mycotoxin that is a food contaminant. Finally, in a pathogenic species, Aspergillus fumigatus, we found that deletion of its pxdA homolog significantly altered secondary metabolite production. Our work uncovers an unexpected link between organelle motility, developmental decisions in response to light, and secondary metabolite production in filamentous fungi.

Miniaturization, or an extreme reduction in body size, is present in both the plant and animal kingdoms. In animals, this concept has been studied across a range of systems, where it has been associated with the vestigialization or loss of structures such as the reduction of lungs in miniature frogs[1] and the loss of body segments in tardigrades.[2] By contrast, the morphological mechanisms underlying plant miniaturization remain poorly understood. The Araceae exhibits a striking evolutionary breadth, encompassing both the smallest flowering plants and some of the largest herbaceous species known, making it an ideal family for exploring the concept of miniaturization. Here, we focus on the rooted species of duckweeds, which measure just a few millimeters and have an aerial body plan consisting of a single, cryptically defined structure, called a frond. Transcriptional dissection of the duckweed frond revealed distinct zones, one with homology to aroid leaf blades and the other with both stems and petioles, indicating that the duckweed frond is a hybrid organ arising from the fusion of stem and leaf parts. The identities of these zones are further supported by patterns of cell division comparable to those in monocot leaves and by secondary cell wall staining consistent with stem tissue. Collectively, our data support the hypothesis that miniaturization in duckweeds has not arisen through the loss of body components,[2] as seen in some animal lineages such as tardigrades, but through a restriction in cell division and the fusion of organs.