Current Biology

Male Drosophila courtship includes two communication signals: airborne song and substrate-borne vibrations. While the neural control of song has been extensively characterized, little is known about the circuits underlying vibration production. Here, we identify neurons expressing the Hox gene abdominal-B (abdB) as a driver of vibration production. Optogenetic activation of abdB neurons selectively elicited vibrations in both males and females without inducing courtship song, whereas silencing these neurons did not impair vibration production during natural courtship. The vibration-driving abdB neurons are neither doublesex-nor fruitless-positive, defining a previously unrecognized component of the courtship circuit. Although abdB activation produced only stimulus-locked vibrations, co-activation of the persistence-promoting neuron cluster pCd converted this transient signal output into sustained vibration trains. Together, our results identify a dedicated pathway for vibration production and show that signal identity and persistence can be independently specified by distinct circuit components.

While the external cues that generate behavioral responses have been extensively studied, behavioral changes in response to internal stimuli are much less understood. C. elegans hermaphrodites are self-fertile until they exhaust their supply of self-sperm, after which time they can only produce more progeny via mating with a male animal. Fertile hermaphrodites are less likely to be mated by males than sperm-exhausted hermaphrodites. We report that sperm-dependent hermaphrodite escape is facilitated by an aversive response to physical contact (touch stimulus) by males, specifically male turns around the hermaphrodite nose and male contact at the vulva. Using germline masculinizing and feminizing mutants, we found that sperm are both necessary and sufficient to induce contact-dependent mating evasion. Surprisingly, loss of the entire somatic gonad resulted in ectopic evasion behavior, via an oppositional monoaminergic signal. Hermaphrodites lacking the HSN neuron are constitutively receptive to male mating touch both at the vulva and at the nose, suggesting that HSN transmits fertility status to the nervous system. HSN also modulates other downstream circuits, such as the nose touch sensory neurons ASH and FLP, which are required for evasion of male contact at the nose. Taken together, we identified a signaling cascade wherein presence vs. absence of sperm is transmitted via monoaminergic signaling from the somatic gonad to the nervous system. This demonstrates how changes in internal state, such as fertility status, act to modulate neural circuits and alter the valence of sensory input.

Understanding how cells specialize is essential for reconstructing the diversification of life on earth. Cnidocytes (stinging cells) have a single origin in the stem cnidarian ([~]800mya) and have since specialized into extremes in morphology and function. Using single-cell RNA sequencing and transcriptional lineage reconstruction in a coral and a sea anemone, we show that a single gene (FoxL2) controls a critical switch point in the evolution of cnidocyte diversity: the decision to be a piercing cell or an ensnaring cell. Surprisingly, ensnaring cells are one of the most highly conserved differentiated cell types. This suggests spirocytes reached an adaptive peak early and have changed little during the 600 million years since corals and sea anemones last shared a common ancestor, making them living fossil 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.

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 exhibit invariant chirality. Snails are the exception because some wild-living species show abundant chiral variation, yet the existing knowledge is from snails in which the chirality mutation is rare and causes pathology. Here, we show that a chiral polymorphism in Japanese Euhadra snails is due to functional variation in an unconventional myosin I a/b, an isoform 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 pathological. Phylogenetic and structural modelling suggests that dominant-acting amino acid substitutions in the myosin actin-binding domain and/or motor-level junction were enabled by relaxed selection. These results broaden the known molecular repertoire underlying LR asymmetry, suggest key mutations and positions that should be explored in other model animals, and highlight snails as a powerful model for understanding the origins of animal LR asymmetry.

Cryptic female choice - female-mediated bias in fertilization after mating - is well established in animals and can also occur in plants when multiple pollens compete on the same pistil. However, whether interactions between pollen and pistil tissues after pollen deposition contribute to this process remains unknown. Here, we experimentally test whether such interactions mediate cryptic female choice in the angiosperm Brassica rapa. We quantified fertilization success of pollen donors competing on the same pistil using paternity analyses, and in parallel, made semi-in vivo assays to measure pollen tubes trajectories emerging from the excised styles and growing toward unfertilized ovules for each donor-recipient pair. We show that pollen tube growth towards ovules predicts higher fertilization success under pollen competition. Thus, we document a previously unobserved mechanism of cryptic female choice based on physical interactions between male and female components of reproduction. In addition, different recipient plants favour different pollen donors, consistent with non-directional female choice. Plants with longer styles bias paternities more strongly towards the most successful pollen donor. Overall, our study demonstrates that interactions between pollen tubes and pistil tissues after pollen germination enable plants to bias paternity toward particular donors.

Animals inhabiting aquatic or terrestrial habitats experience different constraints on their physiology and locomotion, and are exposed to fundamentally different sensory environments. Across evolutionary timescales, most species have adapted to live exclusively either in water or on land. Newts are among the vertebrates that defy this rule and split their adult lives between freshwater ponds and terrestrial habitats. In these amphibians, transitions across environments cause remarkable phenotypic plasticity in their body morphology. But whether and how the nervous system and behavior also adapt to these environmental changes remains poorly explored. Here, we establish the Iberian ribbed newt Pleurodeles waltl as a new model to study the neurobiology of environmental plasticity in a vertebrate. We first show that experimental transitions between aquatic and terrestrial laboratory settings recapitulate morphological changes observed in the wild. Furthermore, aquatic and terrestrial newts display plasticity in sensory and motor behaviors, including differences in walking gait and odor responsiveness. In the olfactory system, the transition from water to land involves a profound remodeling of the nasal epithelium, including reversible transcriptomic changes in secretory and support cells, and an increase of neurogenesis. Together, our findings reveal how plasticity of specific cell types in the nervous system supports behavioral adaptations across environments. More broadly, this work establishes newts as a model to study the functional constraints and convergent adaptations that may have shaped the evolution of vertebrate nervous systems in water and on land.

Septins are conserved polymer-forming proteins that scaffold the actomyosin cytoskeleton, its regulators, and other factors to cellular membranes. Septins also sense micron-scale curvature, bind microtubules, and establish membrane diffusion barriers. C. elegans is a powerful animal model to study septins roles because there are only two septin genes: unc-59 and unc-61. In many fungal and animal cell types, septins are required for proper cytokinesis. In the C. elegans zygote, septins scaffolding roles in cytokinesis manifest during the chiral rotation of the cell cortex and the asymmetry of cytokinetic ring closure. Originally named for the uncoordinated movement exhibited by hypomorphic alleles, UNC-59 and UNC-61 are also required for normal postembryonic development, germline development, and fertility. To study C. elegans septins in these various contexts, we sought a fluorescent-protein tagging strategy that minimally perturbed septin function. We examined strains in which GFP, mKate2 or wrmScarlet had been inserted at the unc-59 locus, or coupled to unc-61b/c at an exogenous locus, to encode fluorescently tagged fusion proteins. We compared these tagged septins to classical hypomorphic alleles, and to new null alleles. Null alleles phenocopied hypomorphic alleles in all our assays. Strains bearing fluorescently tagged septins exhibited defects in zygote cytokinesis, qualitatively phenocopying both hypomorphic and null alleles. These findings agreed with recent work with fission yeast, demonstrating the sensitivity of septin function to tagging. Interestingly, tagging septins did not perturb postembryonic development including animal mobility. This suggests that septins play distinct functions in the zygote versus later in development.

Sexual processes in microbial eukaryotes are often cryptic, obscuring the diversity and evolutionary history of sex across major eukaryotic lineages. Within Amoebozoa, trophic-cell fusion has been associated with sexual development in distantly related taxa, but evidence from Tubulinea, one of the three major amoebozoan lineages, has been lacking, leaving a major gap in the known distribution of fusion-associated sexual development. Here, we combine long-term behavioral observations with transcriptomic analyses to uncover an extensive fusion-associated developmental program in the testate amoeba Arcella vulgaris. Individual trophic cells progressively fused with neighboring amoebae to form large multinucleate aggregates exhibiting coordinated movement and cytoplasmic streaming. Transcriptomic analyses identified a distinct meiosis-enriched state characterized by elevated expression of conserved meiotic genes, including DMC1, HOP1, HOP2, MER3, MSH5, REC8, ZIP4, and PCH2, together with genes involved in homologous recombination and chromosome maintenance. Morphologically similar fused aggregates occurred in both meiosis-enriched and meiosis-reduced transcriptomic states, revealing substantial molecular differentiation within the fusion process and suggesting a dynamic developmental continuum. The coordinated activation of conserved meiotic pathways strongly supports a role for trophic-cell fusion in sexual development. By extending fusion-associated sexual development to Tubulinea, our findings fill a major phylogenetic gap and establish the occurrence of this developmental phenomenon across all three major amoebozoan lineages. This broad phylogenetic distribution raises the possibility that fusion-mediated sexual development is an ancient and widespread feature of Amoebozoa and provides new insight into the evolution and diversity of sexual programs in microbial eukaryotes.

Photoreceptors are retinal neurons whose subtype-specific opsin expression and mosaic organization enable parallel encoding of spectral and spatial visual information. Yet, the transcriptional mechanisms establishing and maintaining subtype identity remain poorly understood. We investigated the role of the T-box transcription factors tbx2a and tbx2b in zebrafish photoreceptor development and found evidence for paralog subfunctionalization across photoreceptor lineages. Tbx2b is required for UV-cone generation and prevents fate switching toward rods, while Tbx2a is constrained to UV-cone generation without involving rods. These factors also maintain cone identity by repressing inappropriate M-cone fate. Despite major changes in photoreceptor composition, tbx2 mutants retain luminance- and motion-driven vision, whereas prey capture is abolished only in tbx2b mutants and not tbx2a mutants. Our findings identify the tbx2 paralogs as key regulators of cone-subtype generation and maintenance and reveal how developmental programs diversify photoreceptor fate to appropriately support visually-guided behaviors important for survival.

Animals may fail to respond to reliable sensory stimuli because of noise in the neural circuits or modulation by internal states. In locusts, looming-evoked jump escape response (JER) fails in [~]40% of trials, and this failure correlates with multiplexed features of the descending contralateral movement detectors (DCMD) response. Using Hieroglyphus banian, we show that these failures arise from a competing behavioral state, grooming. A light-to-dark transition (LDT) in the JER assay induced prolonged grooming and suppressed JER. Reducing the amplitude of this transition decreased grooming and rescued JER. Electro-mechanical induction of grooming was sufficient to cause JER failure. The grooming state induced by either LDT or electro-mechanical stimulation reduced looming-evoked DCMD responses through divisive gain modulation. Grooming was rare under natural field conditions. Thus, behavioral failures can arise from internal state modulation driven by unobserved stimulus history, rather than stochastic noise in the nervous system. HighlightsO_LIAn unobserved prior sensory event drives failure of escape responses. C_LIO_LILight-to-Dark Transition (LDT) induces a long-lasting grooming state in grasshoppers. C_LIO_LIGrooming state causes divisive gain reduction in the DCMD neuron and escape failures. C_LIO_LIFailures of survival-critical behaviors may reflect state rather than neuronal noise. C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=68 SRC="FIGDIR/small/739074v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@1f8733eorg.highwire.dtl.DTLVardef@561eb8org.highwire.dtl.DTLVardef@1fae92forg.highwire.dtl.DTLVardef@1e32231_HPS_FORMAT_FIGEXP M_FIG C_FIG Unobserved prior events, rather than neuronal noise, can cause JER failure. Locusts and H. banian fail to evoke JER in response to the looming stimulus in [~]40% of the trials. We show that these failures, correlated to grooming, were caused by the LDT and were rescued when lit. Grooming was sufficient for JER failure, and it was mediated by shunting-inhibition-like modulation of the DCMD response.

Mammalian circadian rhythms are primarily entrained by light, but nonphotic cues can also reorganize behavioral timing through mechanisms that remain poorly understood. Nocturnal foot shocks delivered to rodents while they forage away from the safety of their nesting area have been shown to entrain circadian behavioral rhythms and shift foraging and feeding to the daytime. To identify the neural circuits underlying this nonphotic fear entrainment, we optogenetically stimulated tachykinin 1-expressing neurons in the parabrachial nucleus (Tac1PBN) during the subjective night while the animals foraged outside of their nest, which recapitulated the total activity-rest phase switch in circadian behaviors induced by foot shocks. Furthermore, selective stimulation of Tac1PBN projections to the central amygdala (CeA) produced a significant but reduced phase shift compared to direct stimulation of Tac1PBN cell bodies. When Bmal1, a core clock gene, was conditionally deleted from the CeA, mice failed to fear-entrain, implicating the CeA molecular clock as a necessary component for fear entrainment. Together, these experiments demonstrate that activation of a defined neuronal population outside of the suprachiasmatic nucleus (SCN) can reorganize circadian behavior by engaging a non-SCN circadian oscillator network that requires an intact CeA molecular clock.

Many arthropods (insects and crustaceans) rely on their antennular chemosensory system to detect key environmental resources like food. While odor mediated food search is well studied in insects, characterization of crustacean chemosensory behavior has been limited by the long lifespans and large size of traditional crustacean model species. Here, we report the first characterizations of the food search behaviors of the genetically tractable amphipod crustacean, Parhyale hawaiensis. We find that Parhyale can locate an odorous food pellet, and predominantly approach food using direct, targeted swims from the arena walls. Removal of both first and second antennae dramatically reduced foraging success and impaired Parhyales ability to control take-off angle and maintain a stable heading during swims. Removal of the first or second antenna alone did not significantly disrupt foraging, and resulted in mild disruption of orientation phenotypes. Intact animals performed sharp turns near the location of the food pellet, which were observed when either first or second antenna were present, but not when all antennae were removed. Turns were longer and had higher average angular velocities following removal of either set of antennae, with full antenna removals representing the most extreme phenotype. In contrast with the long-held theory that the crustacean second antennae exclusively mediate contact chemosensation, we report that first- and second- antennae both contribute similarly to food localization and stabilization of locomotion in Parhyale in our behavioral paradigm. This work establishes Parhyale as an accessible model for studying olfactory behaviors in an aquatic arthropod.

In an early phase of life, most animals are behaviorally and physiologically not yet able to reproduce but show adaptations specific to a juvenile state. In Drosophila females, sexual maturation after metamorphosis is achieved by acquiring receptivity to male courtship and completing oogenesis, a transition that is under hormonal control and requires coordinates changes in the nervous system. Here, we show that immature females display a transient signaling behavior during the time window of asexuality by flicking their wings in response to and dependent on male courtship stimuli. Immature wing flicks require the activity of Doublesex (Dsx) expressing central brain pC1a neurons that mediate receptivity in mature virgins. Immature wing flicks generate patterned sound pulse trains that differ from other intraspecific acoustic signals, but resemble pulses produced during mature male agonistic interactions. Courting males exposed to immature flicks shorten courtship singing and abstain from copulation attempts, indicating that immature wing flicks serve as an effective rejection signal of asexual females to minimize futile male mating pursuits.

Animals must constantly calibrate the costs and benefits of exploration of an environment based on expectations of danger. These decisions are strongly shaped by past experience of perceived threats within that environment and by internal state, which is strongly modulated by circulating gonadal hormones. Although the circuits underlying threat detection are relatively well characterized, how sex hormones shape the long-term behavioral consequences of prior threat experience, and whether this differs across sexes, remains unknown. Here, we show that female mice, like males, exhibit robust long-term threat avoidance (LTTA), avoiding a location where they previously experienced a single visual threat. However, we find that in females this behavior shows strong modulation by the estrous cycle. Surprisingly, we find that though male and female LTTA is driven through glutamate release by the melanopsin-projecting intrinsically photosensitive retinal ganglion cells (ipRGCs) in the thalamic perihabenular nucleus, disruption of this circuit drives completely opposing effects on male versus female LTTA. Moreover, hormonal modulation of LTTA in females requires functional ipRGC input. Thus, despite similar circuit architecture and behavioral outcomes, the individual components of the LTTA circuit play opposing roles in shaping this behavior in males and females, and female LTTA is further tuned by hormonal status.

Aquatic animals deploy adhesives, in numerous essential functions, and reversibility is a key adaptation. The molecular mechanisms of reversible wet adhesion remain poorly understood. Using a model organism, the freshwater cnidarian Hydra vulgaris, we dissect the mechanism of molecular assembly in a secreted adhesive and uncover a glycan and protein-based architecture organized by a lectin-like protein, Hydra vulgaris adhesive protein 1 (HvAb1). We identify HvAb1 as a nonredundant organizer of the adhesive matrix, being basal-disc specific and secreted. Knockdown of HvAb1 severely impaired attachment and disrupted footprint architecture in a mosaic pattern, with only HvAb1-positive regions of the adhesive footprint retaining their normal structure. The adhesive is wheat germ agglutinin (WGA)-reactive and contains a fibrillar chitin-based sub-network, synthesized by a basal-disc-specific chitin synthase. Applying exogeneous chitinase abolished both WGA staining and Hydra attachment, indicating that WGA-positive components perform essential roles in adhesion. Our results therefore describe a glycan-dominated matrix, organized via a lectin-like protein (HvAb1), which is reinforced by chitin and enables reversible adhesion underwater. This establishes Hydra as a tractable model to better understand the principles of reversible adhesion underwater and, potentially, inform future bioinspired, sustainable adhesives.

Corals form important ecosystems that serve as habitat for numerous marine species. Being sessile, adult corals are exposed to changing environments without the means to relocate. Species dispersal is therefore restricted to the motile larval lifestage. How do microscopic larvae achieve reliable dispersal and conquest of novel habitats under time pressure and unpredictable environmental conditions? Here we show an unexpected diversity of behaviors in the cold-water coral Lophelia pertusa. Anatomical and behavioral changes of coral planula promote a change from neutral, passive buoyancy in the dispersal phase, to active swimming and search behavior during competency. As lipids are metabolized and sensory abilities develop, the coral larvae drastically change their motility patterns. Comparative analysis with a poorly dispersing, lecithotrophic anthozoan larvae reveals that developmentally timed sensory integration is conserved between species, but the behavioral modes and sensory responses are adapted to their particular ecology.

During meiosis, chromosomes face a paradox: the machinery that ensures reductional chromosome segregation also destabilizes centromeres by dismantling kinetochores, risking chromosome missegregation. Here we show how cells resolve this crisis through an unexpected activity of the telomere bouquet. We demonstrate that the bouquet transfers heterochromatin components to pericentromeres, which in turn recruit the Aurora B kinase to direct centromere reassembly. The heterochromatin protein Swi6HP1 relocates from telomeres to centromeres, enabling Haspin kinase-dependent phosphorylation of histone H3 and consequent enrichment of the chromosomal passenger complex, which includes the Aurora B kinase. Aurora B then phosphorylates core centromere proteins, including CenpA and CenpC, to promote kinetochore reassembly. Phosphomimetic mutants of CenpA or CenpC bypass the telomere-heterochromatin-Haspin pathway, demonstrating that Aurora B-mediated phosphorylation is sufficient for reassembly. This function is conserved in mitotically proliferating cells subjected to centromere dismantlement. Our findings establish a safeguarded system that couples meiotic nuclear architecture to centromere identity and reveal a fundamental role for the Aurora B kinase in centromere assembly, beyond its canonical function in correcting kinetochore-spindle attachment errors.

Spatial navigation depends on integrating multiple cue sets whose influence is determined primarily by their inferred reliability. Here we investigated how cue weighting in the medial entorhinal cortex is updated based on previous experience at different time scales (minutes vs. days). In mice recorded in light and darkness while manipulating coherence between distal room cues and local arena cues, grid cells displayed stable firing fields in darkness only when prior light experience maintained coherent cue relationships. Grid activity remained anchored to local cues, and stability continuously increased by repeated exposure. In contrast, mice that experienced cue mismatch in light showed markedly reduced grid stability in darkness. Strikingly, re-establishing cue coherence produced only partial recovery, whereas a single exposure to cue mismatch abolished reliance on local cues. The reference frame shift at different time scales reflects a dynamic balance between flexibility and stability determined by a conservative cue weighting strategy.

Coral reefs are constructed by colonial cnidarians whose survival depends on the coordinated growth and physiological integration of thousands of interconnected polyps. While coral skeletons have been extensively studied, the internal three-dimensional organization of coral tissues remains poorly resolved, limiting our understanding of how reef-building corals function as integrated modular organisms. In this study, we established a contrast-enhanced X-ray tomography (XRT) workflow for decalcified coral tissues, enabling detailed visualization and quantitative comparison of internal polyp architecture across four reef-building species with distinct colony forms: Acropora cervicornis, Acropora millepora, Montipora capitata, and Pocillopora damicornis. Importantly, this methodology resolved previously inaccessible patterns of tissue organization and structural connectivity among neighboring polyps. The two Acropora species shared a conserved axial - radial organization but differed in mesenterial morphology, whereas M. capitata exhibited complex, entangled mesenterial networks that connected both neighboring and distant polyps. In contrast, P. damicornis displayed superficial connectivity restricted to the coenosarc. Together, these results suggest that internal tissue architecture is an evolutionarily flexible trait, shaped by ecological and developmental pressures rather than strictly by shared ancestry. Our XRT workflow thus provides a new comparative framework for understanding how corals function as integrated living colonies.