Publications
A ‘fish finder’ for birds? Route-dependent foraging behavior of the brown booby ( Sula leucogaster ) following a passenger ferry in the Ogasawara Islands, Japan
Brown boobies (Sula leucogaster) exhibit route-dependent foraging behavior around passenger ferries, suggesting that these vessels may act as 'fish finders' by disturbing surface-associated prey like flying fish. Research conducted in the Ogasawara Islands, Japan—home to one of the largest breeding colonies—revealed a directional asymmetry: significantly higher numbers of boobies accompanied ferries departing from the main colony island (Hahajima) compared to southbound trips. The behavior peaked during the chick-rearing period in August, with birds following the ferry immediately upon departure but only appearing mid-route when traveling toward the colony. This pattern hints at cognitive abilities such as spatial memory and associative learning. The study highlights the potential of low-cost observational methods from public transport for behavioral research, offering a scalable approach for citizen science.
Coinvasional disruptions to island pollinator networks
Biological invasions can disrupt pollinator networks, but most studies focus on single invasive species. This study reveals that multiple co-occurring invaders—green anoles (a predator), western honey bees (a floral competitor), and invasive plants—synergistically reduce pollinator diversity and plant resource use in the Ogasawara Islands. Using structural equation models, researchers found that anole abundance had the strongest negative impact on pollinators, triggering cascading effects, while honey bee abundance directly reduced plant specialization. The degree of invasion influenced whether honey bees compensated for lost functions or exacerbated invasional meltdown. These findings underscore the need to evaluate invasions in a multistressor context to develop effective conservation strategies for vulnerable island ecosystems.
Ctenochaetus striatus
Ctenochaetus striatus, commonly known as the striated surgeonfish, exhibits a broad distribution across the Red Sea and Indo-West Pacific regions, including notable occurrences in the Ogasawara Islands. This species has been documented in various locations such as the Gulf of Suez, Gulf of Aqaba, and the main basin of the Red Sea, with historical records spanning from 1825 to recent observations. The study highlights its presence in diverse marine environments, ranging from East Africa to central Japan, underscoring its adaptability and ecological significance. Despite its widespread distribution, Ctenochaetus striatus is currently classified as Least Concern by the IUCN (2012), indicating a stable population status without immediate conservation concerns.
Forecasting the Risk of Reinvasion by the Giant African Snail in Ogasawara, Japan
A study on the Ogasawara Islands, Japan, identifies high-risk areas for potential reinvasion by the giant African snail (Achatina fulica), despite its declining population since the 1990s. Researchers developed species distribution models (SDMs) using MaxEnt, leveraging data from Chichijima and Hahajima in Ogasawara, as well as Hualien County, Taiwan—both sites with high-density populations. The model trained on Hahajima data proved most accurate for predicting conditions on Chichijima due to similar environmental factors, pinpointing previously unsurveyed but vulnerable zones. This approach demonstrates the effectiveness of transferring SDMs across regions to improve risk assessment in data-limited scenarios, offering a proactive strategy for invasive species management and early intervention.
New records of five polydesmidan millipedes (Diplopoda, Polydesmida) from the Ogasawara Islands, Japan, with notes on the postembryonic development of Prosopodesmus spp. (Haplodesmidae)
Researchers have uncovered five previously undocumented species of polydesmidan millipedes from the Ogasawara Islands, Japan, including Prosopodesmus jacobsoni, P. panporus, Cryptocorypha ornata, Dyskolonius uniramus, and Solaenaulus butteli. These findings double the known millipede diversity in the archipelago, with all species representing new records for Japan. Notably, specimens previously misidentified as Prosopodesmus sinuatus were corrected to Cryptocorypha ornata, while Solaenaulus butteli was confirmed from Chichi-jima Island. The study also examined postembryonic development in Prosopodesmus species, suggesting potential heterochronic shifts in sexual maturation. This research advances understanding of terrestrial invertebrate biodiversity in remote oceanic islands and highlights the importance of systematic surveys.
New Species and New Distributional Records of the Genus Microvelia Westwood (Hemiptera: Heteroptera: Veliidae) from the Japanese Ogasawara Islands, with an Illustrated Key to Ogasawaran Species
A new species of water treaders, Microvelia (Pacificovelia) amphitrite, has been identified from the Ogasawara Islands, along with a correction to previous misidentifications involving M. douglasi and the confirmation of M. yoshitomii's presence across nine islands in the archipelago. Field surveys revealed that these species prey on arthropods, including alien species, highlighting their ecological role. The study provides an illustrated key to Ogasawaran Microveliinae species, aiding future taxonomic research.
Fromia eusticha Fisher 1913
A new species of sea star, Fromia eusticha, has been described with distinct morphological traits, including a strongly stellate body, elongate arms, and unique plate arrangements. The species exhibits a high ratio of arm length to disc radius (R/r=4.4–4.8), acute interradial arcs, and a convex abactinal surface covered by granules. Actinal pedicellariae are most abundant around the oral region, with 1 to 8 bivalve types present. The study highlights morphological similarities between Fromia eusticha and another species, Fromia baruna sp. nov., emphasizing the importance of pedicellariae distribution in taxonomy. Distribution records confirm its occurrence across the Ogasawara Islands (Japan), Sulu Archipelago (Philippines), Bikini Atoll (Indonesia), and intertidal zones at depths ranging from 44 to 149 meters.
Genetic purging in an island-endemic pigeon recovering from the brink of extinction
A critically endangered pigeon, the red-headed wood pigeon, endemic to Japan's Ogasawara Islands, has defied expectations by recovering rapidly after predator removal despite extreme genetic inbreeding. Genomic analysis reveals that over 80% of its genome is homozygous, yet it harbors fewer highly deleterious mutations than widespread conspecifics—a phenomenon attributed to historical demographic shifts. Linkage disequilibrium suggests the population shrank from several thousand to under a hundred by the early 20th century due to human impacts, with gradual inbreeding likely purging harmful mutations over centuries. This study underscores how historical demography can mitigate mutation load in bottlenecked populations, offering critical insights for conservation strategies.
High Spatiotemporal Diversity of Sand Temperatures and Estimated Hatchling Sex Ratios of Green Turtle in an Important North Pacific Rookery
A new study on the Ogasawara Islands reveals significant spatiotemporal diversity in sand temperatures, leading to varying hatchling sex ratios of green turtles (Chelonia mydas) across seven key nesting beaches. The research, conducted from 2018 to 2019, found that these variations—ranging from male-biased to female-biased ratios—are likely influenced by environmental factors such as shading, vegetation cover, and sand color, rather than nest depth. This diversity underscores the need for continuous monitoring of nesting environments to inform effective conservation strategies for this critical North Pacific rookery.
Inter-sexual phenotypic divergence is correlated with habitat structure in an invasive lizard
Research on the Ogasawara Islands reveals that sexual dimorphism in invasive green anoles (Anolis carolinensis) is shaped by habitat structure, with male limb length adapting more dynamically than females. This divergence suggests exploitation of niche space, where males adjust to local conditions independently of females, potentially influencing intra-specific competition and invasive success. The study analyzed phenotypic traits across islands, providing evidence that ecological drivers, rather than sexual selection alone, play a significant role in shaping dimorphism. These findings parallel broader patterns observed in anole communities and underscore the importance of habitat structure in driving adaptive divergence.
Molecular and morphological evidence reveals a new lepidopteran genus, Micrometasia (Crambidae, Spilomelinae, Steniini), with implications for insular speciation of endemic moths in Japan
Researchers have uncovered a new genus of moth, Micrometasia, endemic to Japan, shedding light on the evolutionary and biogeographic patterns of insular speciation. This discovery, based on molecular and morphological evidence, includes two previously undescribed species: M. ryukyuensis from the Ryukyu Islands and M. melanatella from the Ogasawara Islands, along with a redescription of the female of M. bilineatella. Phylogenetic analysis using mitochondrial and nuclear genes places Micrometasia within the detritivorous tribe Steniini, hinting at potential undescribed diversity and multiple colonization routes into Japan's archipelago. The study also highlights small-scale radiation and morphological divergence on oceanic islands, offering new insights into the biodiversity of Japanese moths.
Species Diversity and Distribution of Non-fumigatus Aspergillus Species in Ogasawara Islands, Japan
A study on the Ogasawara Islands reveals that soil environments significantly influence the distribution of non-fumigatus Aspergillus species, including sections Flavi, Nigri, and Terrei. Researchers isolated 172 strains from 18 sites across three islands—Mukojima, Hahajima, and Chichijima—and identified seven section Flavi, five section Nigri, and three section Terrei species using calmodulin gene sequencing. Notably, Aspergillus tamarii, A. nomiae, A. niger, and A. tubingensis were dominant in forests (>60% frequency), while A. floccosus prevailed in bare land and grassland (>40%). A. pseudonomiae exhibited high occurrence across landscapes. The findings mirror previous observations for section Fumigati, suggesting environmental factors shape the dominance of these pathogenic fungi.
Warm season escape to deep: habitat range and seasonal movement of sand tiger shark Carcharias taurus in Ogasawara Archipelago, Japan
Sand tiger sharks (Carcharias taurus) in the Ogasawara Archipelago exhibit a unique vertical migration strategy, avoiding warm-season surface temperatures by diving to depths of up to 206 meters. Unlike their counterparts in Australia or the USA, which undertake long-distance horizontal migrations, these sharks exploit temperature stratification in the water column, remaining year-round residents of the region's continental shelf (30–200 m). Acoustic tracking and archival tagging revealed significantly higher detections in cooler months, with deeper habitat use during warmer periods. This study highlights an adaptive behavioral strategy tailored to the insular oceanic conditions of the Ogasawara Islands.
A new Hibiscus-feeding species of Bucculatrix (Bucculatricidae) from the Ogasawara Islands, Japan
Researchers have identified Bucculatrix flavimaculata, a new species of leaf-mining moth (Bucculatricidae) from the Ogasawara Islands, Japan, which feeds exclusively on Hibiscus. The discovery was supported by detailed morphological analysis of adult genitalia and larval biology, alongside phylogenetic reconstruction using COI-5P DNA barcoding. This study not only expands the known diversity of Bucculatrix species but also provides insights into their host plant relationships and evolutionary dynamics within this group. The findings contribute to our understanding of moth biodiversity in UNESCO-listed Ogasawara Islands, a global hotspot for conservation.
Conservation units and the origin of planted individuals of an endangered endemic species Lobelia boninensis in the Ogasawara Islands
Research on the endangered endemic plant species Lobelia boninensis in the Ogasawara Islands reveals two distinct genetic clusters, indicating significant differentiation between northern and southern populations. The study also identifies hybridization at an isolated site on Chichijima and traces the origin of transplanted individuals to a population in Hahajima. These findings suggest the presence of two conservation units, with current translocation practices posing a risk of genetic contamination. The research utilized genetic population structure and phylogenetic analyses across all known habitats of the species to inform conservation strategies.
Fish and coral assemblages of a highly isolated oceanic island: The first e DNA survey of the Ogasawara Islands
A pioneering environmental DNA (eDNA) survey of the Ogasawara Islands, a remote Pacific archipelago renowned for its unique marine biodiversity, has uncovered a rich diversity of 124 fish taxa and 38 scleractinian coral species. This study marks the first application of eDNA metabarcoding to assess marine reef ecosystems in this region, demonstrating its efficiency in rapidly capturing multi-taxa data from seawater samples without requiring on-site taxonomic expertise. The findings underscore the Ogasawara Islands' significance as a biodiversity hotspot and highlight the potential of eDNA for large-scale biomonitoring, offering insights into species distributions, invasive species, and conservation priorities in oceanic archipelagos.
Historic deforestation and non‐native plant invasions determine vegetation trajectories across an oceanic archipelago
A 77-year study of the Ogasawara Islands reveals that the recovery of subtropical oceanic island ecosystems is heavily influenced by historic deforestation and invasions of non-native plants, rather than simply time alone. The research found that islands with higher remaining proportions of native forest showed greater recoverability, while those with significant invasive species introductions exhibited altered vegetation trajectories. By comparing vegetation maps from 1935, 1979, and 2012, the study highlights the critical role of anthropogenic disturbances in shaping ecological restoration needs on these globally significant islands.
Integrative taxonomy of an East Asian songbird indicates rapid dwarfism after island colonization
A new study on the Japanese and Manchurian Bush Warbler (Horornis diphone–canturians) species complex reveals rapid evolutionary changes, including dwarfism and vocal divergence, following colonization of the remote Ogasawara Islands approximately 200,000 years ago. Using multi-locus phylogeographic and acoustic analyses, researchers confirmed that two continental subspecies (borealis and canturians) belong to H. canturians, contrary to recent proposals. While the endemic subspecies H. d. diphone shows distinct phenotypic traits, its lack of reciprocal monophyly and recent divergence time suggest retaining its current subspecies status. The study also highlights reduced genetic diversity in H. d. diphone, emphasizing the need for conservation efforts in the Ogasawara Islands to protect this unique subspecies.
Phylogenetic origin of dioecious Callicarpa (Lamiaceae) species endemic to the Ogasawara Islands revealed by chloroplast and nuclear whole genome analyses
A comprehensive phylogenomic analysis of three dioecious Callicarpa species endemic to the Ogasawara Islands reveals their evolutionary origins and colonization timeline. Using chloroplast genomes and 86 nuclear single-copy genes, researchers determined that these species diverged from East Asian continental relatives approximately three million years ago, likely through long-distance dispersal during the late Pliocene. The study highlights adaptive radiation and shifts in dioecious sex expression as key evolutionary trends on oceanic islands. Phylogenetic trees based on over 10,000 nuclear genes placed the insular species within an East Asian clade, though discrepancies with chloroplast tree topologies suggest incomplete lineage sorting or hybridization events.
Two remarkable new species of Glaucocharis (Lepidoptera, Crambidae, Crambinae) from the Ogasawara Islands, Japan
Researchers have identified two distinct new species of Glaucocharis moths, G. triochellaris and G. plumbofascialis, from the Ogasawara Islands, Japan. These species exhibit unique morphological traits that set them apart from other members of their genus. The study employed molecular phylogenetic analysis to confirm the evolutionary relationship between these new species and the broader Glaucocharis group, revealing a sister relationship and supporting the monophyly of the genus. High-resolution images of adult moths and genitalia were provided to aid in species identification.
Did Captain Beechey see a living Mandarina luhuana, an extinct land snail species?
A new study challenges the long-held belief that the land snail species Mandarina luhuana, first collected from the Ogasawara Islands in 1827, was already extinct by the time of human arrival. Using accelerator mass spectrometry dating on subfossil samples, researchers found evidence suggesting M. luhuana survived until at least the early 19th century—well after humans began inhabiting the islands in the 17th century. This contradicts the traditional view that the species was fossilized and extinct pre-human contact. The findings imply that human activity likely accelerated its extinction, highlighting the need for further research to understand the broader impact of early human colonization on island ecosystems.
Twenty-year changes in the composition of a mixed stock of foraging green turtles in the Yaeyama Islands of Japan
A recent study reveals a significant increase in the proportion of Japanese green turtles (Chelonia mydas) within the foraging aggregation around the Yaeyama Islands, Japan, over the past two decades. This shift is linked to an observed trend of increasing mean straight carapace length (SCL), suggesting reduced juvenile mortality due to declining sea turtle fisheries. Researchers compared natal origin compositions from 1997-1999 and 2016-2018, using single nucleotide polymorphisms to analyze size categories (<55 cm and >55 cm SCL). The findings indicate a stable proportion of Japanese turtles across size classes in recent years, while populations from lower latitudes showed substantial declines. This study provides detailed insights into the composition of the Yaeyama foraging aggregation, including size distributions and sex ratios, offering valuable data for conservation efforts.
Characterization of polymorphic microsatellite markers for the Japanese endangered land snail Mandarina
Researchers have developed 23 polymorphic microsatellite markers for the endangered land snail genus Mandarina, found exclusively in the Ogasawara Islands. These markers enable non-lethal genetic analysis of three species: M. mandarina, M. chichijimana, and M. suenoae, with varying degrees of usability (15, 12, and 9 markers respectively) for multiplex PCR. The study addresses critical knowledge gaps in the genetic diversity and population structure of Mandarina, which is nearly extinct in the wild due to invasive predators. By providing robust genetic tools, this work supports ex situ conservation efforts initiated in 2010, offering a foundation for targeted breeding programs and monitoring strategies to preserve these vulnerable species.
Diversity and Distribution of Aspergillus fumigatus and Its Related Species in Izu and Ogasawara Islands, Japan
A comprehensive analysis of Aspergillus section Fumigati, a group of fungi known to cause aspergillosis, reveals distinct distribution patterns across the Izu and Ogasawara Islands, Japan. The study found that Aspergillus fumigatus, a significant pathogen, was predominantly present in forest sites on islands from Izu-oshima to Hachijojima but absent entirely in the Ogasawara Islands. Conversely, other species like Aspergillus felis, A. pseudoviridinutans, and A. udagawae showed higher occurrence in bare land and grassland sites, with notable regional variations. Seasonal sampling indicated that A. pseudoviridinutans maintained a high frequency year-round in grasslands, while A. fumigatus exhibited significant seasonal variability in forest sites. These findings underscore the influence of both island location and landscape on fungal distribution, providing critical insights for understanding environmental factors shaping pathogen diversity.
Examination of color preferences of invasive green anoles in the Ogasawara Islands
Invasive green anoles (Anolis carolinensis) in the Ogasawara Islands show a strong aversion to blue, making it an effective color for fencing to restrict their movement. Behavioral experiments revealed that green anoles preferred brown over other colors, while native snake-eyed skinks (Cryptoblepharus nigropunctatus) favored red. These findings suggest that using blue Teflon™-sheet fences could reduce the transborder crossing rate of invasive anoles, while changing adhesive trap colors from red to brown may lower bycatch of native skinks. The study employed choice experiments with colored papers to assess color preferences in both species, providing actionable insights for improving eradication efforts without harming local fauna.
Has long‐distance flight ability been maintained by pigeons in highly insular habitats?
A unique study challenges the notion that island land birds universally lose their long-distance dispersal ability, demonstrating that pigeons can maintain this capability even under highly insular conditions. Researchers compared two subspecies of Japanese wood pigeon (Columba janthina) across different archipelagos in the north-western Pacific Ocean, finding that one subspecies exhibited wing morphology better suited for long-distance flight than the other. Genetic analyses revealed sufficient gene flow among islands within each subspecies' habitat, with no isolation by distance, and estimated their divergence time at approximately 0.67 million years ago. This exceptional case suggests that maintaining dispersal ability may be a viable strategy in island systems, contrary to the global trend of reduced dispersiveness in island birds.
ICESat-2 Applications for Investigating Emerging Volcanoes
A groundbreaking application of NASA’s ICESat-2 satellite laser altimeter, combined with visible imagery, reveals unprecedented insights into the rapid formation and erosion of newly emerged volcanic islands. Focusing on Niijima Fukutoku-Okanoba (NFO) in Japan’s Ogasawara Islands, this study demonstrates how high-resolution satellite datasets can quantify elevation profiles and surface structures of short-lived volcanic features, previously inaccessible to traditional monitoring methods. The integration of ICESat-2 altimetry with Landsat-8 and Planet imagery provides a novel framework for understanding the dynamic evolution of these islands, advancing our comprehension of submarine volcanism in remote, shallow-water settings.
Interchanges and movements of humpback whales in Japanese waters: Okinawa, Ogasawara, Amami, and Hokkaido, using an automated matching system
Humpback whales in the western North Pacific exhibit distinct interchange patterns among Japanese regions, suggesting the existence of multiple subgroups within the population. Using an automated matching system with 80.9% accuracy, researchers analyzed 3,532 fluke photo IDs from Hokkaido, Ogasawara, Amami, and Okinawa. The study found higher interchange indices among Japanese areas compared to previous studies linking Ogasawara/Okinawa to Hawaii or Mexico, indicating shared use of these regions by the same population. High within-region return indices suggest site fidelity, while Hokkaido may serve as a migration corridor between northern feeding and southern breeding grounds. These findings imply at least two geographic groups: one utilizing Ogasawara and the Mariana Archipelago, and another using Amami, Okinawa, and the Philippines, migrating along the Ryukyu and Philippine Trench.
Records of four mantis shrimp species (Crustacea: Stomatopoda) from the Ryukyu and Ogasawara islands, Japan
A recent study documents the first specimen-based record of the mantis shrimp species Gonodactylaceus ternatensis and expands the distributional records of three other species—Lysiosquilloides siamensis, Alimopsoides tuberculatus, and Busquilla plantei—in Japanese waters. Notably, this marks the first occurrence of Lysiosquilloides in Japan and the northern hemisphere for Alimopsoides. The research provides taxonomic diagnoses, ecological insights, and standard Japanese names for these species, contributing significantly to the understanding of mantis shrimp diversity in the Ryukyu and Ogasawara islands. This study enhances our knowledge of crustacean biodiversity in these remote and ecologically significant regions.
The oceanographic isolation of the Ogasawara Islands and genetic divergence in a reef‐building coral
The Ogasawara Islands exhibit significant oceanographic isolation, leading to substantial genetic divergence in the reef-building coral Galaxea fascicularis. This study reveals that the coral population in Ogasawara is highly differentiated from its nearest neighbors, primarily due to limited and asymmetric eastward migration from the Ryukyu Islands. Using a combination of population genetics, demographic modeling, and inverse particle tracking based on oceanographic data, researchers confirmed that long-distance larval dispersal—exceeding 44 days—is the only plausible mechanism for gene flow into Ogasawara, with no reciprocal dispersal. These findings underscore the archipelago's role as a dispersal sink and highlight its importance for marine conservation, alongside its recognized terrestrial significance.
DNA-based diversity assessment reveals a new coral barnacle, Cantellius alveoporae sp. nov. (Balanomorpha: Pyrgomatidae) exclusively associated with the high latitude coral Alveopora japonica in the waters of southern Korea
A new coral barnacle species, Cantellius alveoporae sp. nov., has been discovered exclusively associated with the high-latitude coral Alveopora japonica in southern Korea. This specialist species was identified through DNA-based diversity assessment, including COI and 12S DNA sequencing, revealing it as distinct from previously described Cantellius euspinulosum and other cryptic species. The study also confirmed that C. euspinulosum, a generalist barnacle found across the Indo-Pacific, is morphologically and genetically distinct from its Korean counterpart. Additionally, the research identified at least five cryptic species within the C. euspinulosum complex, some of which are also specialists on specific coral genera. The findings highlight the importance of molecular studies in unraveling hidden biodiversity, particularly in marine ecosystems like the Ogasawara Islands.
History and the Bonin (Ogasawara) Islands
A novel perspective on the historical development of Japanese nationality and identity emerges from the study of the Ogasawara Islands, revealing how legal status and debates over Japanese identity evolved during critical periods. This research highlights the often-overlooked translingual and transcultural diversity among Japanese nationals in these Pacific islands, offering unique insights into the emergence of notions of nation, empire, and citizenship in Japan. By focusing on the lives of individuals who lived through formative times, the study bridges gaps in understanding race and ethnicity in Asia and its connections to the Pacific.
Magnetization structure of Nishinoshima volcano, Ogasawara island arc, obtained from magnetic surveys using an unmanned aerial vehicle
Researchers uncovered the first three-dimensional magnetization structure of Nishinoshima volcano, part of the UNESCO-listed Ogasawara Islands, using unmanned aerial vehicle (UAV) magnetic surveys. The study revealed an average magnetization of 3.0 A/m across the island, along with two strongly magnetized bodies beneath the summit crater and northeastern flank, likely representing chilled magma reservoirs at depths of several hundred meters. Conducted in September 2018 and June 2019, the surveys demonstrated that UAV-based magnetic data collection—combined with advanced 3D inversion analysis—offers a safe, cost-effective method for studying remote volcanic systems. The findings suggest potential for future monitoring of volcanic activity through repeated surveys, which could track changes in magnetization linked to magmatic processes.
Phylogeography of cicadas on continental and oceanic islands in the northwestern Pacific region
A study on the phylogeography of cicadas in the northwestern Pacific region reveals that long-distance dispersal, possibly wind-borne, facilitated the colonization of oceanic islands like the Ogasawara Islands. The research, focusing on the genus Meimuna, shows that genetic divergence among species was larger on continental islands that disconnected from the mainland earlier, aligning with geological history. However, intraspecific genetic differentiation varied between species within the same island region, suggesting ecological characteristics also played a role. The study used phylogenetic analysis, divergence time estimation, and population genetics to uncover these patterns, providing insights into how cicada fauna evolved across different island types.
Redescription of the brackish water crab Ptychognathus glaber Stimpson, 1858 based on the topotypic material from the Ogasawara Islands and new record of P. lipkei N.K. Ng, 2010 from Japan (Decapoda: Brachyura: Varunidae)
A critical re-evaluation of the brackish water crab Ptychognathus glaber reveals its geographic distribution is likely limited to the Ogasawara Islands, Japan, while specimens previously identified as P. glaber from the Ryukyu Islands belong to a distinct species, P. lipkei, newly recorded in Japan. This study provides a detailed redescription of P. glaber and compares it with P. lipkei using morphological and genetic analyses, including mitochondrial 16S rRNA gene sequences. The findings clarify taxonomic confusion and suggest that P. glaber is genetically closer to P. ishii, prompting further morphological comparisons between these species. This research corrects historical misidentifications and advances the understanding of crab biodiversity in Japanese waters.
Effect of Diet and Water Availability on Rattus norvegicus (Rodentia: Muridae) Distribution
Norway rats (Rattus norvegicus) thrive across Japan's diverse climates, but their distribution is primarily constrained by diet and water availability, not temperature. A study across subarctic, temperate, and subtropical zones revealed that rats in Hokkaido’s uninhabited islands sustained populations year-round by scavenging carcasses, while those in Tokyo Bay faced seasonal recruitment peaks due to dehydration in winter. In Hahajima (Ogasawara Islands), chronic water scarcity forced rats to rely on plant matter, leading to weight loss. The research highlights that protein-rich diets and hydration are critical for rat survival, offering insights into their ecological adaptability.
Genetic diversity, structure, and demography of Pandanus boninensis (Pandanaceae) with sea drifted seeds, endemic to the Ogasawara Islands of Japan: Comparison between young and old islands
Population genetic analyses reveal that Pandanus boninensis, endemic to the Ogasawara Islands, exhibits significantly lower genetic diversity and distinct demographic patterns on younger volcanic islands compared to older ones. Clustering of EST-SSR markers shows strong divergence between populations on old Bonin and young Volcano Islands, with evidence suggesting population expansion in older islands and reduction in younger ones. Migration appears limited between island groups, with rare movement from south to north among older islands. These findings highlight the evolutionary significance of young island populations as models for early-stage colonization, characterized by small effective sizes and low genetic diversity.
Investigating the effects of nest shading on the green turtle ( Chelonia mydas ) hatchling phenotype in the Ogasawara islands using a field‐based split clutch experiment
Conservation practices such as nest shading can significantly alter the phenotype of green turtle (Chelonia mydas) hatchlings, potentially influencing their fitness. A study conducted on the Ogasawara Islands, an important rookery in the North Pacific, used a field-based split clutch experiment to investigate these effects. Researchers equally divided clutches and placed half under shaded conditions while the other half remained unshaded. Findings revealed that shading produced hatchlings with improved self-righting responses, larger carapace sizes, fewer nonmodal scute patterns, and smaller unabsorbed yolk sacs—indicating potential benefits to their survival. These results suggest that while shading may help mitigate the effects of global warming on sex ratios, its broader implications for hatchling fitness must be carefully considered.
Prevalence and antimicrobial-resistance profiles of Salmonella spp. isolated from green anoles (Anolis carolinensis) collected on the Haha-jima of the Ogasawara archipelago, Japan
A study on Haha-jima, part of Japan's Ogasawara Islands, reveals that 30.4% of green anoles (Anolis carolinensis), an invasive species, tested positive for Salmonella enterica in their large intestines. Notably, 37.5% of these Salmonella strains exhibited resistance to oxytetracycline, a commonly used antimicrobial agent. This suggests that green anoles may contribute to the transmission of Salmonella on the island, posing potential risks to both public and ecological health. The research analyzed samples collected between 2009 and 2010, assessing resistance against 12 antimicrobial agents.
Redescription of the specimen of Thrissina dussumieri (Teleostei: Clupeiformes: Engraulidae), collected from the Ogasawara Islands
A long-overlooked specimen of the fish species Thrissina dussumieri, collected from the Ogasawara Islands nearly 90 years ago, has been rediscovered and redescribed in detail. This confirms the presence of T. dussumieri in Japanese waters, contributing to the understanding of engraulid fish diversity in the region. The study provides a comprehensive morphological description and proposes a new standard Japanese name for the species, 'Tsurugi-katakuchi.'
Sphaerillo boninensis Nunomura, 1990 (Crustacea, Isopoda, Oniscidea) is a junior synonym of a pantropical species, Venezillo parvus (Budde-Lund, 1885)
A re-examination of the holotype and paratype of Sphaerillo boninensis from Chichijima Island, part of the UNESCO-listed Ogasawara Islands, reveals that this species is not distinct but rather a junior synonym of the pantropical Venezillo parvus. This finding clarifies taxonomic confusion in Isopoda (Crustacea) and updates the regional biodiversity record for this globally recognized World Heritage Site. The study employed morphological analysis to compare key traits, confirming the synonymy based on shared characteristics with Venezillo parvus described from other regions.
Taxonomic review of the lace bug genus Omoplax ( Hemiptera: Heteroptera: Tingidae ) endemic to “ Oriental Galapagos ” (the Ogasawara Islands, Japan ) with the description of its new allied genus and species
A taxonomic review of lace bugs (family Tingidae) from the Ogasawara Islands, Japan—nicknamed the 'Oriental Galapagos'—identifies three species belonging to two endemic genera: Acanthomoplax tomokunii gen. et sp. nov., Omoplax desecta, and O. majorcarinae. This study represents a significant contribution to the understanding of biodiversity in this isolated archipelago, providing a key for species identification. The research builds on prior work by Horváth (1912) and Guilbert (2001), expanding the taxonomic framework with a newly described genus and species. The Ogasawara Islands' unique ecological setting makes this study particularly valuable for conservation efforts and comparative studies in island biogeography.
Two independent signals detected by ocean bottom electromagnetometers during a non-eruptive volcanic event: Ogasawara Island arc volcano, Nishinoshima
Researchers detected two independent signals—magnetic field variations and volcanic slope tilt changes—during a non-eruptive event on Nishinoshima, an active oceanic island arc volcano near Tokyo. These signals occurred in mid-November 2016, between eruptions in 2015 and 2017, indicating complex volcanic activity without surface eruption. Using ocean bottom electromagnetometers deployed for the first time around the island, the study estimated sources of demagnetization and deflation beneath the northeast slope but found that simple models were insufficient to explain the observed data. The findings suggest that such instruments can effectively monitor volcanic activity when strategically placed, offering new insights into non-eruptive volcanic processes.
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