Daito Islands Research Articles

Descriptions of two Cypridopsinae (Ostracoda, Crustacea) species from the Nansei Islands, Japan, with the first records of non-marine ostracods from the Daito Islands.

A new species, Potamocypris kusuokai sp. nov., is described based on males and females collected from Kitadaitojima, the northern-most of the Daito Islands, part of the Nansei Island archipelago in southwestern Japan. In addition, four other non-marine ostracod species found during sampling of the Daito Islands are reported, and these, together with the new species, are the first non-marine ostracods to be recorded from these remote Pacific islands. Potamocypris sudzukii Okubo, 1992, described from female specimens collected from Okinawa and Kuroshima, also part of the Nansei Islands, is redescribed based on a paratype specimen. This species is transferred to the genus Siamopsis Savatenalinton, 2017, which previously was only known from Thailand, extending the known distribution of the genus eastwards by about 2500 km. Plesiocypridopsis arsenia (Tressler, 1937), from the Philippines, is also transferred to Siamopsis, based on its original description. An overview of the current state of knowledge of non-marine ostracods of the Nansei Islands is provided.

Synergistic effect of secondary metabolites isolated from Pestalotiopsis sp. FKR-0115 in overcoming β-lactam resistance in MRSA.

Six aromatic secondary metabolites, pestalone (1), emodin (2), phomopsilactone (3), pestalachlorides B (4), C (5), and D (6), were isolated from Pestalotiopsis sp. FKR-0115, a filamentous fungus collected from white moulds growing on dead branches in Minami Daito Island. The efficacy of these secondary metabolites against methicillin-resistant Staphylococcus aureus (MRSA) with and without meropenem (β-lactam antibiotic) was evaluated using the paper disc method and broth microdilution method. The chemical structures of the isolated compounds (1-6) were characterised using spectroscopic methods, including nuclear magnetic resonance and mass spectrometry. All six isolated compounds exhibited synergistic activity with meropenem against MRSA. Among the six secondary metabolites, pestalone (1) overcame bacterial resistance in MRSA to the greatest extent.

The oceanographic isolation of the Ogasawara Islands and genetic divergence in a reef‐building coral

AbstractAimDue to their spatial isolation, oceanic islands are natural systems to study evolutionary divergence. The Ogasawara Islands belong to the most isolated archipelagos on Earth and are well‐known for their high terrestrial endemicity; however, less is known about the marine realm. Here, we analyse the degree of oceanographic isolation of the archipelago based on genetic data of a reef‐building coral and a biophysical dispersal model.LocationNorth‐Western Pacific (Ogasawara, Ryukyu, Daito Islands, Guam).TaxonGalaxea fascicularis L.MethodThree to 15 specimens were sampled at several sites in Ogasawara and its closest potential migration sources in southern Japan and the Mariana Islands (Guam) and RAD‐sequenced. 108 specimens from the common Pacific lineages ‘L’ (Ryukyu‐ and Daito Islands, Guam) and ‘Ogasawara’ (Ogasawara) were analysed with population genetics and demographic modelling. Oceanographic dispersal was investigated by inverse particle tracking using a Lagrangian particle advection simulation based on ROMS and applying biological dispersal parameters of G. fascicularis.ResultsThe G. fascicularis population in Ogasawara is genetically highly differentiated from the next closest reefs in the region and has diverged from the Ryukyu Islands under very little, asymmetric, eastward migration. Inverse particle tracking confirmed the oceanographic isolation of Ogasawara and showed that the islands are rarely but most likely reached by settlers from the Ryukyu Islands by long‐distance‐dispersal of exceptionally long‐lived larvae (>44 days), with no dispersal vice versa.Main conclusionsOgasawara is a dispersal sink location and the high degree of genetic differentiation in Galaxea has resulted from strong oceanographic isolation. This research highlights how oceanographic features impact species‐level genetic differentiation even in well‐dispersed taxa such as broadcast‐spawning corals, and they are likely even more pronounced in less vagile organisms. These findings suggest the Ogasawaran Archipelago should be considered an important priority for marine conservation, alongside its high importance for terrestrial conservation.

Records of seven mugilid species from the Daito (Borodino) Islands, southern Japan

Records of seven mugilid species from the Daito (Borodino) Islands, southern Japan

Phylogenetic analysis ofDioscorea(Dioscoreaceae) from Japan and adjacent regions based on plastid and nuclear DNA sequences, with special reference to the taxonomic status of selected taxa

AbstractTo clarify phylogenetic relationships among Japanese Dioscorea taxa and to re-examine taxonomy based on these relationships, we conducted molecular phylogenetic analyses of four plastid regions [trnK (including matK), rbcL, atpB and trnL-F] and two nuclear regions (PHYC and 18S rDNA) for all Dioscorea taxa from Japan and selected taxa from adjacent regions. Although species are often sympatric and variation in leaf shape is relatively wide within species and not clearly demarcated between species, our results suggest that Japanese Dioscorea spp. do not hybridize. Our results also resolve several taxonomic issues surrounding Japanese species. We confirm that D. japonica, D. polystachya, D. pseudojaponica and D. tabatae, which are morphologically similar, are distinct species. Further, plants from the Daito Islands identified as D. luzonensis, which have never been observed to flower to our knowledge, are attributable to D. pseudojaponica. Dioscorea zentaroana, often treated as a synonym of D. asclepiadea, was found to be distinct from the latter. Dioscorea izuensis should be treated as D. collettii var. izuensis. In conclusion, 16 species and three varieties of native Dioscorea should be recognized in Japan.

A new subspecies of the mantis Hierodula patellifera (Mantodea: Mantidae) from the Daito Islands, the Ryukyus, Japan

A new subspecies of the Asian mantis Hierodula patellifera (Audinet-Serville, 1839), Hierodula patellifera daitoanassp. nov., is described based on specimens collected from the Daito Islands, the Ryukyus, Japan. This new subspecies is distinguished from the nominotypical subspecies H. patellifera patellifera in adulthood by the relatively larger body size, the larger number of antennal segments, the presence of a white marking along the dorsal-inner surface on the procoxa, and marginal spines of the procoxa comprising two large and several small tooth-like projections.

Validity and redescription of the poorly known Japanese blenny Alticus orientalis Tomiyama 1955 (Perciformes: Blenniidae)

The poorly known blenny Alticus orientalis Tomiyama 1955 is considered a valid species and redescribed on the basis of 73 specimens (36 males and 37 females), 20.5–83.5 mm in standard length (SL). The species is characterized by the following combination of characters: dorsal-fin spines 14 (rarely 13); pectoral-fin rays 15 (very rarely 14 or 16); pelvic-fin rays I, 4; caudal-fin rays 12 (very rarely 11); supraorbital cirrus finely branched (except in specimens < ca. 20 mm SL); canine-like teeth absent on lower jaw; 1–9 small conical teeth on vomer (rarely secondarily lost); 3 (very rarely 2) pores in mandibular series; pre-anal-fin length 37.6–43.2 (mean 40.4) % SL in males, 39.9–46.9 (43.0) % SL in females; caudal-fin length 19.0–24.2 (21.8) % SL in males, 19.7–25.2 (22.4) % SL in females; pre-anal-fin length / caudal-fin length 1.6–2.2 (1.9) in males, 1.8–2.2 (1.9) in females; cheek without black spots; and head and pectoral fin without small black dots. Although A. orientalis is most similar to Alticus montanoi (Sauvage 1880) [all Japanese specimens previously identified as Alticus saliens (Lacepede 1800) are actually this species], it can be distinguished from the latter by the presence of teeth on the vomer, a greater number of pores in the mandibular series, greater pre-anal-fin length, and slightly shorter caudal-fin length. In addition, genetic analysis supports the divergence of A. orientalis from available sequences from other species of Alticus. In Japanese waters, A. orientalis is distributed around (and probably endemic to) the Izu and Ogasawara islands, whereas A. montanoi is distributed in the Ryukyu and Daito islands.

大東諸島固有陸産貝類の保全へ向けた，外来種が与える影響の解明と飼育技術の確立 ―大東諸島陸産貝類保全グループ―

大東諸島固有陸産貝類の保全へ向けた，外来種が与える影響の解明と飼育技術の確立 ―大東諸島陸産貝類保全グループ―

Molecular discrimination and phylogeographic patterns of clones of the parthenogenetic gecko Lepidodactylus lugubris in the Japanese Archipelago

AbstractVertebrates usually reproduce sexually in which males and females contribute their offspring genome and produce genetically diverse offspring. However, some of them are asexual without genetic contribution from males. The nocturnal gecko, Lepidodactylus lugubris, is all females and reproduces parthenogenetically. This gecko is known to consist of diploid and triploid clones in the tropical and subtropical regions, which can be identified by their dorsal marking patterns, ploidy, and protein polymorphism. This gecko is also distributed in the southern parts of Japan, and several clones have been reported. In this study, we investigated the origins and genetic diversity of Japanese L. lugubris by clonal discrimination using microsatellite and mitochondrial DNA analyses. A total of 748 individuals were collected from 21 islands of five island groups (Ogasawara, Okinawa, Miyako, Yaeyama and Daito Islands) and 17 clones were distinguished genetically. Mitochondrial cyt b sequences of these clones suggested that they were all closely related and differentiated recently. Clonal diversity was much higher (14 clones) in the Daito Islands than in the other island groups in which only one or two clones coexisted. Judging from the dorsal marking patterns and ploidy known so far, six clones were cosmopolitan and may be colonized from the outside of Japan. However, other 11 clones were endemic to the Daito Islands and explained by possible hybridization between the one female diploid clone and one male diploid clone because other 9 clones were triploid and all had the combinations of polymorphic microsatellite alleles of these female and male diploid clones. Although the males have never been recorded in the Daito Islands, males might appear in the past. These findings contribute to understanding of clonal diversity and dynamics of asexually reproducing animals. If diploid parthenogenetic geckos can produce triploid clones by mating with the diploid males, clonal diversity would increase rapidly in a small island, and such newly produced triploid clones would expand widely.

Long‐Range Radiation and Interference Pattern of Multisource M2 Internal Tides in the Philippine Sea

AbstractLong‐range radiation and interference of M2 internal tides from multiple sources in the Philippine Sea are examined by driving a high‐resolution numerical model. The M2 internal tides are effectively generated around the boundary area, which includes the Luzon Strait, Ryukyu Island chain, Bonin Ridge, Mariana Arc, and Izu Ridge, favoring the occurrence of complex interference patterns. The local sources (mainly Daito Islands and Palau Ridge) inside the basin contribute to a small portion (~5%) of total energy but enhance the geographical inhomogeneity of the baroclinic field. The mode‐1 and mode‐2 M2 tidal beams from boundary sources radiate a long distance into the basin but exhibit different interference‐modulated geography variations. A 2‐D line source model characterizing interference can reproduce the general baroclinic field. Two notable interference cases are investigated: (1) the superposition of internal tides from Luzon Strait and Miyako Strait bifurcates into several southeastward beams, consistent with previous numerical simulations and altimeter measurements, and (2) the interference between Tokara Strait and Bonin Ridge exhibits a multiscale spatial pattern, which is modulated by the local generated energy and bathymetry features. Energetic dissipation occurs both near the boundary sources and in the basin. A locally dissipated fraction q of ~0.4 is estimated at the Luzon Strait and Bonin Ridge with continuous bathymetry features, while q of ~0.6 is estimated at the Ryukyu Island chain and Mariana Arc with discrete topographic variability. A lower locally dissipated fraction indicates a stronger energy flux radiating into the basin, where enhanced dissipation coincides closely with the interference‐modulated flux field.

Holocene relative sea level history from phreatic overgrowths on speleothems (POS) on Minami Daito Island, Northern Philippine Sea

This research aims to elucidate the Holocene sea level (SL) variability on Minami Daito Island, Japan, where no previous such research has been done due to the apparent absence of any SL indicators. Here we use phreatic overgrowths on speleothems (POS) in a cave as an alternative SL indicator. The relationship between the highest modern groundwater fluctuation level (GWFL) and the highest POS level was studied, and the oldest POS calcite was dated using the radiocarbon method considering the dead carbon proportion (the “reservoir effect”). The results show that SL reached its Holocene maximum between ca. 5.1 and 4.6 ka cal BP, after which it remained more or less stable till the present day, with a possible minor sea-level drawdown of ca. 30–35 cm. Although the timing of the maximum Holocene SL coincides with mid-Holocene SL highstand observed across the tropical and subtropical Indo-Pacific, the relative stability of the SL after reaching its peak is not expected in the given subtropical setting. The SL on Minami Daito did not have a distinct highstand in the Holocene and instead followed closely the eustatic sea-level change. These findings are important in better understanding the mechanisms that control local relative SL variability and show the high value of POS as precise SL indicator.

Factors limiting organic matter decomposition and the nutrient supply of soils on the Daito Islands

Factors limiting organic matter decomposition and the nutrient supply of soils on the Daito Islands

Habitat Selection by the Bull-Headed ShrikeLanius bucephaluson the Daito Islands at the Southwestern Limit of Its Breeding Range

Abstract Since the 1970s the Bull-headed Shrike Lanius bucephalus has established a breeding population on the Daito Islands. The islands represent the southwestern limit of the species' breeding range. We investigated the habitat selection of this isolated population during the 2003 breeding season in the agricultural landscape of Minami-daito Island. A comparison of habitat types around shrike nests and randomly selected points, showed that shrikes largely foraged in sugarcane fields and utilized fences and utility wires as suitable perch sites. Our results suggest that it is the open, cultivated areas (sugarcane has been grown on the island since 1900) that have provided suitable habitat for the Bull-headed Shrike allowing it to establish a breeding population on the Daito Islands.

沖縄県北大東島のサトウキビの中・小型収穫機と搬出機の連携作業に着目した作業能率分析

機械による効率的な農作業を進めるためには，圃場毎の作業実態に応じて作業機を最適な方法で利用する計画を策定する必要がある．最適な作業計画のためには，作業機の作業面積，作業内容および作業時間などの作業履歴を記録し，データを詳細に分析し，その結果から最適な作業方法を明らかにする必要がある．サトウキビ機械収穫作業において収穫機と搬出機の両方に市販の安価なGPSを取り付け，両者の軌跡を分析することで，数パーセントの誤差で，収穫機と搬出機の作業実態を分析することができた．有効作業効率は小型収穫機は0.29（一方向刈）および0.37（往復刈），中型収穫機では0.27（一方向刈）および0.38（往復刈）であった．圃場作業量および有効作業量は中型収穫機は小型収穫機のほぼ二倍であった．収穫機と搬出機の相互の挙動を解析することで，作業の非効率な部分を明らかにし，効率の改善の可能性を示すことができた．そのことにより，小型収穫機については搬出機との連携作業を最適化することで，現在より能率向上できる可能性があることがわかった．また，降雨量と機械稼働の関係から小型収穫機は中型収穫機より稼働率が6%程度高い可能性があることがわかった．

戦前期の沖縄における製糖工場とその建設が地域に与えた影響

The sugar industry was the most important industry in Okinawa Prefecture before World War II. The purpose of this paper is to examine the influence of sugar refinery factories' construction on area development in Okinawa Prefecture. This study focuses on the Nishihara (old/new), Takamine (old/new), Kadena, Tomigusuku and Ginowan sugar refinery factories located on the Okinawa Main Island, the Miyako sugar refinery factory located on the Miyako Island, and the Daito sugar refinery factory located on the South Daito Island, constructed before World War II. 1) Many old newspaper articles published in Okinawa Prefecture before World War II and other materials allowed us to reorganize their factory's construction processes and to examine the reasons to select each factory's location. These 7 factories' construction periods were divided into two phases; old Nishihara, old Takamine and Kadena factories were constructed around 1910, and other 6 factories were constructed around 1917. It is inferred that the former factory's constructions were caused by "Sugar Industry Development 10-year Plan" released at 1901 and the latter by "Okinawa Prefecture's Industry Development 10-year Plan" released at 1915. In addition, the water sources to cool their machines, the transportation of their sugar refinery machines to each factory site and the transportation of their sugar products from each site affected the selection of each factory's location. 2) Some aerial photos taken by the U.S. forces, in addition to some documents and other materials, were used to restore the former layouts for new Nishihara, new Takamine, Kadena, Miyako and Daito factories. However, Tomigusuku and Ginowan factories' former layouts were impossible to restore because of a lack of documents and materials since these two factories had operated for only a short time. New Takamine, Miyako and Daito factories were constructed later, divided their sites into their factory area and company-house area by using their geographical features. Three factories located on the Okinawa Main Island had a smaller company-house area than Daito factory located on the South Daito island, an isolated island, since their workers commuted from their surrounding villages at the former 3 factories. 3) Various materials and documents allowed us to examine the influence of these sugar refinery factories' construction in Okinawa Prefecture before World War II. Three factories; new Nishihara, new Takamine and Kadena, located on the Okinawa Main Island caused their surrounding area development by cooperating with light railways for transporting their sugar products to Naha, capital of Okinawa Prefecture. The Miyako factory caused the whole Miyako Island's industrial development since Miyako Island had few industries at that time and sugar industry was one of the main industries. The Daito factory caused the cultivation of South Daito Island itself since the pioneers for this island had started to cultivate sugar cane. In subsequent research, the comparison with the sugar industry in Okinawa Prefecture after World War II and the comparison with the sugar refinery factory and their company houses constructed in Taiwan, Hokkaido and other areas continue.

Species status of Incisitermes spp. (Isoptera: Kalotermitidae) in Japan

AbstractThe species status of Japanese populations of Incisitermes immigrans from Iwo and Minami Daito Islands was examined using mitochondrial 16S molecular barcode sequences. The molecular sequences of these two populations were compared to those of other Incisitermes spp. deposited in the GenBank database using a maximum likelihood phylogenetic analysis. This analysis suggested that the Minami Daito population is indeed I. schwarzi, as suspected previously, while the sequence of the Iwo Island population was identical to that of authentic I. immigrans. In addition to I. minor, which is recorded from middle and southern Japan, the presence of three Incisitermes species in Japan was confirmed.

Environments of limestone caves and the machanism of groundwater percolation beneath different vegetation in Minami- Daito Island, Okinawa Prefecrture, southwest Japan.

Environments of limestone caves and the machanism of groundwater percolation beneath different vegetation in Minami- Daito Island, Okinawa Prefecrture, southwest Japan.

Analysis of discharge consistency and performance of a sugarcane billet planter with side-conveyer concept

Sugarcane is an important economic crop of Okinawa Prefecture. The sugarcane billet planter has been widely used in Okinawa due to high labor costs and planting time limits. Most of them were powered by hydraulic systems to avoid ground wheel drive problems when working under high moisture heavy clay conditions. This study aimed to evaluate the performance and discharge consistency of the sugarcane billet planter, YABIKU B600, operated in Minami Daito Island, Okinawa Prefecture. The Ni28 cultivar seed cane was harvested and chopped to an average length of 21.8 cm by Austoft TM2008 harvester. The field experiment was done with 3 replications. A video camera with GPS logger was positioned over the hopper of the planter during the tests to examine the performance and planting consistency of the planter. The numbers of discharged billets at each frame were recorded to calculate the discharge index or planting rate. Moreover, the speed, GPS position and time of each activity were collected to obtain the field capacity and field efficiency of the planter. The results showed that the average traveling speed of the planter was 0.97 m/s. The field capacity was 0.24 ha/hr with a field efficiency of 45.66%. The average discharge index was 7.2 billet/m. Considering a discharge index range of 8-10 billet/m, the precision index averaged 24.63%.

Differences of the growth process of stalagmite and the machanism of groundwater percolation beneath different vegetation in Minami- Daito Island, Okinawa Prefecrture, southwest Japan.

Differences of the growth process of stalagmite and the machanism of groundwater percolation beneath different vegetation in Minami- Daito Island, Okinawa Prefecrture, southwest Japan.

First Japanese Specimen-based Record of Liopropoma tonstrinum (Teleostei: Serranidae), from Minami-daito Island, Daito Islands, southern Japan

A single specimen (25.8 mm standard length) of a serranid fish, Liopropoma tonstrinum Randall and Taylor, 1988, was collected from Minami-daito Island in the Daito Islands, southern Japan. This species was previously known based on specimens from Christmas Island in the eastern Indian Ocean, and various islands in the Pacific Ocean, including the Society Islands, American Samoa, Fiji, New Caledonia, Indonesia, Palau, Micronesia, the Marshall Islands, and Wake Island, as well as from underwater photographs taken in the Mariana Islands and southern Japan. Thus, the present specimen represents the first record from Japan based on a voucher specimen, as well as the northernmost specimen-based record of this species up to now.