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The needle nematode genus Paralongidorus Siddiqi, Hooper & Khan, 1963 currently comprises 76 species of polyphagous plant ectoparasites with global distribution. Here, we revise the taxonomic ambiguities within the genus and update the polytomous key to facilitate species identification. Integrating ribosomal (D2-D3 expansion segments of 28S, ITS, partial 18S) and mitochondrial (partial COI mtDNA) markers, we reassess phylogenetic relationships within Paralongidorus and Longidorus. Our analyses reveal that Paralongidorus is paraphyletic, consistently resolving into two distinct subclades. We describe Paralongidorus cantabronavarrus sp. nov. from northern Spain, a species characterized by both molecular placement and morphological traits, including a uniquely anterior vulval position (V = 26-29%), the most extreme reported within the genus. This feature may represent a derived developmental adaptation, with potential ecological significance. Amphidial fovea morphology also shows evidence of convergent evolution, complicating generic boundaries. These findings challenge the validity of Longidoroides, reinforce the separation between Paralongidorus and Longidorus, and highlight the value of integrative approaches in resolving long-standing taxonomic uncertainties. The phylogenetic placement of P. cantabronavarrus sp. nov. is consistent across markers and aligns with previous studies. Overall, this work expands our understanding of Paralongidorus biodiversity in the Iberian Peninsula and underscores the need for further intensive nematological surveys in this area.

To understand how sexual isolation contributes to the evolution of reproductive barriers, we examined the pre- and post-zygotic reproductive barriers between ecotypes of the three-spined stickleback (Gasterosteus aculeatus) from North Uist, where the species has undergone an adaptive radiation. Using an experimental design that separated the effects of ecotype, population of origin, and body size, we identified a pre-zygotic barrier attributed solely to ecotype; pairings within ecotypes were more likely to result in mating than those between ecotypes, regardless of population origin or relative body size of males and females. This effect was associated with reproductive incompatibilities linked to the failure of armoured females to enter the unusually small nests of armourless males, along with high levels of aggression from armoured males directed at armourless females. In vitro crosses did not reveal post-zygotic reproductive barriers associated with ecotype or population of origin. These findings indicate that sexual isolation, linked primarily to male traits and involving the coupling of barrier effects, is a significant obstacle to gene flow among the ecotypes, supporting an emerging view that pre-zygotic sexual isolation tends to evolve rapidly and at an early stage during ecological divergence.

Terrestrial organisms employ diverse camouflage strategies, yet the fluctuating humidity and light conditions of arboreal habitats demand dynamic adaptations. This study investigated a novel mechanism of dynamic camouflage in the arboreal snails Hypselostyla camelopardalis (Camaenidae) and Reinia variegata (Clausiliidae). These phylogenetically distant species exhibit a reversible hygrochromic change: their mottled shell patterns disappear upon wetting, turning uniform dark brown, and rapidly reappear as they dry. Using a multimodal approach-including confocal laser microscopy, scanning electron microscopy, and spectrophotometry, this study shows that the colour change is associated with structural modifications within the bilayered organic periostracum. In the white regions, hydration fills microscale voids and smooths surface irregularities, effectively matching the refractive index of the periostracum and increasing light transmittance. While camouflage in terrestrial gastropods was previously considered static, our findings reveal an environmentally responsive system that dynamically adjusts to ambient moisture. This mechanism parallels strategies observed in certain insects, and is consistent with functional convergent evolution. Furthermore, the water-responsive thin-film structure of the snail shell provides a biological blueprint for the development of bioinspired smart materials, such as humidity-sensitive coatings and adaptive optical technologies.

Molting in exoskeleton-bearing organisms can result in dramatic body shape transformations. While this phenomenon has been well-studied in insects, limited knowledge exists for other animals, including crustaceans. Among crustaceans, achelate lobsters, such as Palinuridae and Scyllaridae, exhibit a unique metamorphic transition from a flattened phyllosoma larva to a three-dimensional puerulus or nisto stage in a single molt. This study investigates the mechanisms underlying this transformation in the Japanese spiny lobster (Panulirus japonicus), focusing on carapace deformation through histological analysis, live imaging, and computational modeling. Three-dimensional micro-computed tomography revealed a significant reduction in body length and a shift in mouth position during metamorphosis. Live imaging captured dynamic morphological changes, including epithelial contraction and subsequent reshaping. Furthermore, observation of the transient metamorphosis phase identified a distinctive furrow structure on the carapace surface in a mid-metamorphosis specimen that died during the metamorphosis process, absent in post-metamorphosis puerulus larvae, suggesting a possible role in the transformation process. To explore the formation of this furrow pattern, a computational model was developed based on differential shrinkage rates in vertical and horizontal directions. The model successfully reproduced similar patterns observed in natural specimens, implying that controlled anisotropic contraction could contribute to morphogenesis. Furthermore, three-dimensional shrinkage simulations demonstrated that local contraction with constrained out-of-plane deformation can generate folds, which later expand to form curved structures. This study provides novel insights into the biomechanics of arthropod molting, highlighting a previously unrecognized mechanism of two-dimensional-to-three-dimensional transformation. The findings enhance our understanding of larval development in Achelata and offer broader implications for exoskeletal morphogenesis across arthropods. The online version contains supplementary material available at 10.1186/s40851-026-00265-8.

Diverse insect groups are obligately associated with and dependent on specific microorganisms as essential mutualistic partners that are usually maintained in specialized cells or organs, called bacteriocytes or symbiotic organs. Many organisms with symbiotic microorganisms have developed elaborate vertical transmission mechanisms, which are thought to be important for the evolution of intimate symbiotic relationships with microorganisms. One such case is the cockroach-Blattabacterium endosymbiosis, in which the symbiotic bacteria have been evolutionarily conserved and co-speciated with the host insects with stable vertical symbiont transmission via ovarial passage. While classical histological descriptions and recent electron microscopic observations have reported the vertical symbiont transmission processes in some cockroach-Blattabacterium associations, the full picture of infection dynamics remains unclear. In this study, we conducted detailed histological and cytological observations of the localization of the bacteriocytes and the symbiotic bacteria during the post-embryonic development of the German cockroach Blattella germanica. We found that the symbiont-filled bacteriocytes migrate into and associate with nymphal ovaries and are subsequently eliminated from adult ovaries, suggesting that symbiont infection to the ovaries may only occur during nymphal stages. We also found that the symbiotic bacteria are localized in the space between each oocyte and surrounding follicle cells, the symbiont-localized space is interconnected between neighboring oocytes, and therefore the symbiotic bacteria can move across oocytes within the same ovariole, suggesting the possibility that the symbiont-infected oocytes may serve as the source of symbiont supply to developing young oocytes upstream in the same ovariole. Based on these observations, we provide a hypothesis as to how the post-embryonic developmental dynamics of the bacteriocytes are integrated into the vertical symbiont transmission and functioning in the cockroach-Blattabacterium endosymbiosis.

A major challenge in treating neurological diseases is the transport of compounds across the blood-brain barrier. Herein, we report the synthesis and characterization of nitrogen-doped graphene quantum dots (GQDs) that exhibit high tolerance in zebrafish larvae at high concentrations. In contrast to classical semiconductor quantum dots, vascular microinjection of these fluorescent carbon-based nanomaterials results in rapid tissue distribution and efficient neuronal internalization within the brain, highlighting their potential as nanocarriers for central nervous system delivery. Vascular microinjections of these quantum dots conjugated with the high-affinity Dyrk1A kinase inhibitor Leucettinib-21 (LCTB21) at nanomolar concentrations rescued cell-autonomous dendrite deficiencies in cerebellar Purkinje cells overexpressing human Dyrk1a. LCTB21 concentrations were significantly lower than those of the inhibitor alone. Dyrk1A activity is responsible for neurological defects in Down syndrome and acts as a priming kinase for Alzheimer's disease-associated proteins Tau and APP. Thus, efficient nanodelivery of Dyrk1A inhibitors across the blood-brain barrier improves therapeutic options while minimizing the treatment dose and potential side effects.

Vertebrate chemoreceptor genes play a central role in detecting environmental chemical compounds through the olfactory organs and taste buds, enabling the perception of odors and tastants that are critical for survival. Through evolutionary processes, these genes have repeatedly undergone duplication, divergence, and pseudogenization, giving rise to lineage-specific gene repertoires that reflect ecological and behavioral adaptation. While the canonical functions of these chemoreceptors are confined to the nasal and oral cavities, accumulating evidence, particularly in mammals, indicates that some chemoreceptors are expressed and function in non-chemosensory (extra-nasal/oral) organs. However, such extra-nasal/oral expression has rarely been examined from a broad evolutionary perspective across vertebrate lineages. Here, we systematically investigated organ-wide expression patterns of chemoreceptor genes by conducting comprehensive bulk RNA-seq analysis across 13 organs in four representative species: mouse, Xenopus, Polypterus, and zebrafish. In all species, the majority (95–97%) of chemoreceptor genes were expressed in olfactory and gustatory organs, as expected. Remarkably, a subset (1–29%) showed expression in extra-nasal/oral organs, suggesting that such extra-nasal/oral expression may be a common phenomenon across vertebrates. In particular, the evolutionarily conserved OR-κ gene, with stable gene copy numbers, exhibited organ-independent expression across all analyzed species. Single-cell RNA-seq data further revealed that OR-κ is predominantly expressed in immune cells, implying potential function of chemoreception in immune systems. Furthermore, genomic context analysis showed that the OR-κ gene is isolated from canonical OR gene clusters, suggesting it may have distinct transcriptional regulatory mechanisms compared to typical olfactory receptors. Our findings expand the conventional view of chemoreceptors as sensory-specialized molecules, highlighting their unexpected functional diversity across vertebrate organs. Notably, the OR-κ gene appears to have an ancient evolutionary origin that likely traces back to the common ancestor of vertebrates. Taken together, this study provides us compelling evidence to reconsider the functions and evolutionary trajectories of chemoreceptor genes in vertebrates.

BACKGROUND: The transition from fins to limbs in vertebrates required a novel organization of spinal motor neurons to coordinate limb muscle activation. In amniotes, Hoxc9 represses lateral motor column (LMC) identity at thoracic levels, restricting limb-innervating Foxp1+ motor neurons to brachial and lumbar levels. In elasmobranchs, however, the genomic organization of HoxC genes has undergone extensive modifications, and Foxp1+ LMC-like neurons have been identified at paired-fin levels in some elasmobranch species lacking Hoxc9. These observations suggest that alternative mechanisms regulate motor neuron fate in chondrichthyans, particularly in sharks, although the responsible factors remain unclear. RESULTS: To identify the mechanism underlying this suppression, we examined Foxp1 and Hox gene expression in chicken and cloudy catshark (Scyliorhinus torazame) embryos. In chickens, Foxp1+ LMC neurons initially appeared at all rostrocaudal levels but became restricted to paired-limb levels through Hoxc9-mediated repression. In contrast, in cloudy catsharks, which lack Hoxc9, Foxp1 was downregulated at inter-fin levels where Hoxa9 is expressed. Sequence analysis revealed that the Foxp1 modulatory domain (MD), associated with LMC repression, is highly conserved in Hoxa9 across all examined chondrichthyan species. Hoxc9 genes are absent in most sharks but retained in rays and holocephalans, and these retained copies preserved the Foxp1 MD. Functional analysis in chicken embryos demonstrated that cloudy catshark Hoxa9 represses LMC identity and promotes preganglionic column (PGC) fate, similar to Hoxc9 in amniotes. CONCLUSIONS: These findings suggest that conserved Hox9-dependent mechanisms restrict Foxp1+ motor neurons at thoracic levels in sharks. In the absence of Hoxc9, cloudy catshark Hoxa9 retains the ability to repress Foxp1 and promote PGC fate, thereby contributing to the organization of motor innervation at paired-fin levels.

The orangutan (Pongo pygmaeus [Bornean] and Pongo abelii [Sumatran], Linnaeus, 1760) is the most endangered of the great apes, classified as Critically Endangered. Sperm cryopreservation is a valuable tool for banking genetic resources and solving the complexities of relocating animals; however, cryopreservation protocols remain suboptimal for this species. Due to their phylogenetic closeness, this study aimed to explore the applicability of a chimpanzee (Pan troglodytes, Blumenbach, 1775) sperm cryopreservation protocol to orangutans. To guide further modifications to the protocol, we revealed, for the first time, the comprehensive lipidomic and proteomic characterizations of orangutan ejaculates with parallel comparisons to chimpanzee ejaculates. Functional analyses of oxidative and osmotic stress responses were also conducted to provide valuable evidence of the physiological changes and defense mechanisms associated with sperm cryodamage. The cross-species multi-omic analyses revealed that, compared to the chimpanzee, the orangutan sperm lipid profile exhibited significant alterations after the freezing-thawing process, notably characterized by a substantial loss of cholesterol. While interspecies differences in antioxidant enzyme composition and activity were observed, there was insufficient evidence to support a heightened susceptibility of orangutans to oxidative stress. Conversely, orangutan sperm exhibited low tolerance to hypoosmotic conditions. To prevent cryodamage, a modified thawing protocol that implemented a serial dilution approach significantly minimized hypoosmotic shock and improved post-thaw motility to 19%. In conclusion, this study presents the first complete proteome and lipidome analyses of chimpanzee and orangutan ejaculates, providing valuable insights into the physiological changes and defense mechanisms associated with sperm cryopreservation. This knowledge enabled a science-based approach to improving cryopreservation protocols, moving beyond empirical trial-and-error.

The aim of this study was to determine the influence of static magnetic fields with intensities of 1 mT, 3 mT, and 5 mT on the embryonic and postembryonic development of the rainbow cichlid (Herotilapia multispinosa). The experiments were conducted using eggs obtained from sexually mature, actively spawning pairs of this species. Analysis of the results showed that the applied magnetic fields significantly affected the rate of embryogenesis, which, depending on the intensity, could be either accelerated or slowed down. In particular, exposure to a 5 mT field accelerated development and produced larger hatchlings with smaller yolk sacs but lower subsequent growth, whereas exposure to a 3 mT field prolonged embryogenesis, resulting in smaller hatchlings with relatively larger yolk sacs and faster posthatching growth. The findings suggest that appropriately selected magnetic field parameters may positively influence the development of eggs and larvae of the rainbow cichlid, indicating the potential application of this method in ornamental fish aquaculture to reduce breeding losses.

Sleep is a widespread phenomenon among animals, yet its evolutionary traits and core functions remain largely enigmatic. To elucidate the fundamental characteristics of behavioral sleep in fish, we conducted quantitative assessments of behavioral and physiological properties, including body movement, eye movement, yawning, and ventilation, during sleep in the cleaner wrasse Labroides dimidiatus under laboratory conditions. The sleep states of the cleaner wrasse were characterized by a decreased ventilation rate, occasional distinctive waving movements, rapid eye movement (REM) episodes, and an increasing trend in both ventilation rate and REM episodes toward the end of the night period. Waving movements, temporal decreases in ventilation rate, and REM episodes showed distinct relationships. The patterns of behavioral and physiological features observed in the cleaner wrasse closely resemble those documented in mammals, leading us to propose that the structure of behavioral sleep is conserved across vertebrate species. Our findings further support the notion that the alternation of two  sleep states, Non-REM/slow-wave sleep and REM/paradoxical sleep, constitutes a shared sleep structure of sleep across a wide range of vertebrate species.

The needle nematode genus Longidorus comprises approximately 194 species of polyphagous plant ectoparasites distributed worldwide, some of which serve as vectors for plant viruses. However, the high species diversity and conserved morphology of these nematodes pose significant challenges for accurate identification of species. To address this issue, we conducted an integrative taxonomic study across 264 sites in major olive-growing regions (Greece, Morocco, Italy, Portugal, and Spain) of the Mediterranean Basin, including nearby patches of natural vegetation. Herein, we describe two new species, Longidorus olearum sp. nov. and Longidorus morocciensis sp. nov., and report Longidorus oakgracilis in Portugal for the first time. We performed a comprehensive study that integrates morphological and morphometric traits with molecular data from nuclear ribosomal RNA (rRNA) genes (D2-D3 expansion segments of 28 S, ITS1, and partial 18 S) and a mitochondrial DNA (mtDNA) marker, specifically the Cytochrome c oxidase subunit I (COI). The results of our phylogenetic analyses provided robust support for the delimitation of the newly described species, L. olearum sp. nov. and L. morocciensis sp. nov., and further clarified of three previously recognized species within the genus: L. magnus, L. oakgracilis, and L. vineacola. Phylogenetic relationships inferred from ribosomal and mitochondrial markers revealed that the majority of Longidorus species from the Mediterranean Basin clustered within subclades of Clade I. The phylogenetic placement of these species demonstrated strong congruence across lineages, corroborating previous studies on the genus. These findings contribute to a broader understanding of Longidorus biodiversity in the Mediterranean region and highlight the need for further intensive and wide-ranging nematological surveys.

Rhizocephalans (Thecostraca: Cirripedia) are parasitic crustaceans that infect a wide range of decapod hosts, including hermit crabs, crabs, and shrimps. These parasites exert profound effects on their hosts, inducing parasitic castration, suppressing the development of secondary sexual characteristics, feminizing male crabs, and altering male behavior to resemble that of females. In the present study, we examined the secondary sexual characteristics of two hermit crab species- Pagurus lanuginosus from Asari (Hokkaido, Japan) on the Sea of Japan coast and Pagurus filholi from Chikura (Chiba, Japan) on the Pacific coast-parasitized by Peltogasterella gracilis and Peltogaster sp., respectively. Specifically, we assessed the presence of secondary pleopods and the length of the right large cheliped. Our findings demonstrate that male P. lanuginosus and P. filholi parasitized by P. gracilis and Peltogaster sp. exhibit morphological changes and characteristics of females, confirming morphological feminization. The magnitude of parasitic effects on morphological feminization varies between the two host species depending on the rhizocephalan genus. Thus, the extent of feminization varies depending on the parasite genus. Notably, different parasite genera induced varying degrees of host modification, even within the same host species. Similarly, the level of feminization caused by a single parasite genus differed between host species. These results highlight the importance of understanding the characteristics of both the hermit crab host and rhizocephalan parasite in developing insights into parasitically induced morphological feminization.

In vertebrates, skeletal muscle comprises fast and slow fibers. Slow and fast muscle cells in fish are spatially segregated; slow muscle cells are located only in a superficial region, and comprise a small fraction of the total muscle cell mass. Slow muscles support low-speed, low-force movements, while fast muscles are responsible for high-speed, high-force movements. However, speed and strength of movement are not binary states, but rather fall on a continuum. This raises the question of whether any recruitment patterns exist within fast muscles, which constitute the majority of muscle cell mass. In the present study, we investigated activation patterns of trunk fast muscles during movements of varying speeds and strengths using larval zebrafish. We employed two complementary methods: calcium imaging and electrophysiology. The results obtained from both methods supported the conclusion that there are spatially-ordered recruitment patterns in fast muscle cells. During weaker/slower movements, only the lateral portion of fast muscle cells is recruited. As the speed or strength of the movements increases, more fast muscle cells are recruited in a spatially-ordered manner, progressively from lateral to medial. We also conducted anatomical studies to examine muscle fiber size. The results of those experiments indicated that muscle fiber size increases systematically from lateral to medial. Therefore, the spatially ordered recruitment of fast muscle fibers, progressing from lateral to medial, correlates with an increase in fiber size. These findings provide significant insights into the organization and function of fast muscles in larval zebrafish, illustrating how spatial recruitment and fiber size interact to optimize movement performance.

The transparent jellyfish body is often difficult to see underwater, as its refractive index is similar to that of seawater, resulting in a low light reflectance on the body surface. Nevertheless, the outlines of jellyfish can be recognized by the slight reflection of light from their body surfaces. In some jellyfish species, the epidermis covering the body surface has an array of microvilli, nanostructures that can potentially reduce light reflection. However, the anti-reflective effect is minimal in water, as the difference in the refractive indices of tissue and seawater is so small that reflectance is low, even on flat surfaces. In jellyfish that have pneumatophores, structures used in floating and drifting on the sea surface, light reflection on the surface is expected to be large and noticeable owing to the large differences in refractive indices between the pneumatophore exposed above the water surface and air. In the current study, we examined the epidermal ultrastructure and refractive index of the pneumatophores of a Portuguese man o' war (Physalia physalis) and a by-the-wind sailor (Velella velella). The refractive index of P. physalis pneumatophores measured with an Abbe refractometer was approximately 1.344. Microvillar arrays were found in epidermal cells of both P. physalis and V. velella. Based on the length, thickness, and pitch of the microvilli, we constructed simplified structural models for the simulation of light reflection using rigorous coupled wave analysis (RCWA). Our simulations showed that reflectance on the microvillar models could be greater or less than that on the flat surface, depending on light conditions (wavelength and angle of incidence), but with an overall effect of reduced reflection. Reflection reduction in microvillar models was particularly significant at large incident angles, where reflectance was extremely high on the flat surface. Microvillar arrays found on the epidermis potentially reduce surface reflections of the pneumatophore and contribute to the reduction in visibility of the pleustonic hydrozoans above the sea surface. Moreover, less reflection at the pneumatophore surface indicates greater transmission of light through transparent bodies, potentially providing a counter-illumination effect that obscures the shadow of the hydrozoan bodies, depending on the intensity of ambient light.

Day length, also known as photoperiod, is an important reproductive regulatory factor in most seasonal breeders. Brandt's vole, a long-day breeder, exhibits significant differentces in reproductive development depending on the photoperiod of the season of birth, as is seen in other rodent seasonal breeders. However, there is a lack of comprehensive studies on the effects of photoperiod across different seasons. In the present study, we investigated the impact of long (LP) and short photoperiod (SP) on postnatal development in male voles. We measured somatic and testicular parameters from weaning at three postnatal weeks (PNW3) to PNW19, weighed testis mass from birth, and confirmed the status of testicular development by observing the histological features of the seminiferous epithelium. The results showed no difference in testis mass between LP and SP males up to PNW3, with normal initiation of intratubular meiosis and the presence of leptotene/zygotene spermatocytes in both groups. From PNW4 to PNW10, SP males displayed slower growth in both somatic and testicular parameters and showed suppressed development of primary spermatocytes and Leydig cells compared to LP males. After PNW10, both groups experienced photo-refractoriness, characterized by a reversal of gonadal activity. During this stage, SP voles spontaneously initiated gonadal development and resumed the meiotic process, while LP males showed testicular degeneration accompanied by a progressive loss of germ cells ranging from spermatids to primary spermatocytes. Until PNW19, both groups reached similar testis size and mass. Interestingly, this refractoriness was observed in only half of the males in each group, suggesting a bet-hedging survival strategy that allows populations to cope with unpredictable environmental changes, such as fluctuations in temperature and food. These findings highlight the importance of photoperiod as a key environmental factor in influencing sexual maturation in young Brandt's voles, and indicate that the impact of photoperiod in adult voles can be flexible in vole adulthood, varying according to their natural life cycle. This suggests a bet-hedging survival strategy of photo-refractoriness with complex interactions between environmental cues and life history traits.

The Drepanosiphinae is a Holarctic subfamily of Aphididae comprising six genera: Drepanaphis, Drepanosiphoniella, Drepanosiphum, Megalosiphonaphis, Shenahweum, and Yamatocallis, all of which exhibit strict host plant associations, primarily with Acer species. Despite long-standing taxonomic attention, evolutionary relationships within the group remain poorly resolved, and some important aspects of their biology, such as their patterns of association with symbionts, have been unexplored despite evidence that species in the subfamily might be involved in atypical nutritional symbioses. Here, we present a molecular phylogenetic reconstruction of this subfamily and investigate the evolution of its endosymbiotic consortia. Phylogenetic analyses were conducted using multiple DNA markers, employing both Bayesian inference (BI) and maximum likelihood (ML) approaches. Endosymbionts were characterized using high-throughput sequencing of a fragment of the bacterial 16S rRNA gene. The resulting phylogenies are largely congruent across markers and methods and consistently support the monophyly of Drepanosiphinae. Drepanaphis and Drepanosiphum form a well-supported clade as sister to Drepanosiphoniella, while Yamatocallis and Megalosiphonaphis form a distinct, more distantly related clade. Within Drepanaphis, species group according to host plant use rather than traditional morphological groupings, revealing three host-associated clades: rubrum, saccharum, and grandidentatum. Endosymbiont characterization revealed that, in addition to the obligate symbiont Buchnera aphidicola, most Drepanosiphinae species also host a Sodalis-like bacterium, consistent with previous genomic evidence for a dual nutritional symbiosis with this bacterium. However, Sodalis was absent in most Yamatocallis species, indicating a complex and potentially dynamic evolutionary history of symbiotic relationships within the subfamily. Patterns of association with Wolbachia, Rickettsia, Fukatsuia, Serratia and Arsenophonus suggest a limited role in nutrition. By integrating phylogenetic reconstruction with symbiont profiling, this study provides the most comprehensive evolutionary framework to date for Drepanosiphinae and reinforces the view that nutritional symbioses in aphids are evolutionarily dynamics.

Latitudinal variation plays an important role in driving local adaptation and intraspecific polymorphism across a wide range of organisms. Among teleost fishes, populations from higher latitude tend to have more vertebrae than those from lower latitude, which is known as “Jordan’s rule”. Vertebral number is determined during embryogenesis by the number of somites formed, but the genetic mechanisms underlying this latitudinal variation remain largely unclear. The medaka (Oryzias latipes) species complex, including O. latipes, O. sakaizumii, O. sinensis and an undescribed species from East Korea, is a freshwater teleost species group distributed across a latitudinal range from 25° to 40°N. This wide geographical distribution makes medaka an ideal model system for studying latitudinal variation in morphological trait. In this study, we found a positive correlation between abdominal vertebral number and the latitude of original sampling sites of 90 wild-derived stocks of the O. latipes species complex. To further examine the environmental and genetic contributions to this trait, we reared 10 selected stocks originating from different latitudes at four incubation temperatures (22, 24, 26, 28 °C) until somite stage. Across all temperatures within each phylogenetic subgroup, stocks from higher latitudes consistently developed a greater number of abdominal vertebrae. Finally, we performed a genome-wide association study (GWAS) to identify genomic loci associated with vertebral number variation in these wild-derived stocks. This analysis revealed a single nucleotide polymorphism (SNP) on chromosome 10 that was significantly associated with total vertebral count. Taken together, our findings demonstrate that wild-derived stocks of the O. latipes species complex retain latitudinal variation in vertebral number. This system provides a powerful framework for investigating the evolutionary and genetic bases of geographic trait variation in teleost fishes.

Corals are known for their symbiotic relationships, yet there is limited evidence of chemoautotrophic associations. This is despite some corals occurring near cold seeps where chemosymbiotic fauna abound including mussels that host sulfur-oxidizing chemoautotrophs from the SUP05 cluster (family Ca. Thioglobaceae). We investigated whether corals near cold seeps associate with related bacteria and report here that these associations are widespread. We screened corals, water, and sediment for Thioglobaceae using 16S metabarcoding and found ASVs associated with corals at high relative abundance (10 - 91%). These ASVs were specific to coral hosts, absent in water samples, and rare or absent in sediment samples. Using metagenomics and transcriptomics, we assembled the genome of one phylotype associated with Paramuricea sp. B3 (ASV 4) which contained the genetic potential to oxidize sulfur and fix carbon, and confirmed that these pathways were transcriptionally active. Furthermore, its relative abundance was negatively correlated with the stable isotopic composition of its host coral's tissue suggesting some contribution of chemoautotrophy to the coral holobiont. We propose that some lineages of Thioglobaceae may facultatively supplement the diet of their host corals through chemoautotrophy at seeps or may provide essential amino acids or vitamins. This is the first documented association between chemoautotrophic symbionts and corals at seeps and suggests that the footprint of chemosynthetic environments is wider than currently understood.