Amami-Oshima Island Research Articles

The complete mitogenome of an unidentified Oikopleura species

Appendicularians are planktonic tunicates abundant all over the world. Currently, only two complete annotated mitochondrial genome assemblies are available for appendicularians, both for cryptic species of Oikopleura dioica. This underrepresentation of available appendicularian mitochondrial genomes limits environmental DNA sequencing (eDNA) studies that rely on mitochondrial markers as a taxonomic barcode. We report the complete mitochondrial genome assembly and annotation of an unknown appendicularian species isolated from the Amami Oshima island, Kagoshima prefecture, Japan, that has significant sequence difference with other currently available assemblies and will serve as a useful resource for ecological studies and further mitochondrial studies of appendicularians.

An Attempt at Age Estimation of the Ryukyu Long-Furred Rat (Diplothrix legata) Using Tooth Wear Analysis: First Report on the Difference in Molar Wear Patterns between Rats in Okinawajima and Amami-Oshima Islands

An Attempt at Age Estimation of the Ryukyu Long-Furred Rat (Diplothrix legata) Using Tooth Wear Analysis: First Report on the Difference in Molar Wear Patterns between Rats in Okinawajima and Amami-Oshima Islands

Simulation of island ecotourism development based on SD and DPSIRM models: a case study of Amami-Oshima Island

Abstract Island ecotourism development seeks to balance environmental protection with socioeconomic growth, promoting sustainable practices that benefit both local ecosystems and communities, which is a priority in ecologically sensitive regions such as Amami-Oshima Island. This study identified key factors in ecotourism using an optimized Driver-Pressures-State-Impact-Response-Management (DPSIRM) framework and integrated a System Dynamics (SD) model to develop a simulation system for island ecotourism development. The model was used to analyze the dynamic changes in ecotourism under various scenarios between 2010 and 2035. The results indicated that the Coordinated Development Model, which simultaneously enhanced tourism benefits and conserved natural resources, was the optimal strategy for achieving a win-win outcome. In contrast, the Socioeconomically Driven and Ecological Protection models revealed limitations in resource allocation: the former prioritized transportation infrastructure, resulting in insufficient tourism service provision, while the latter strictly limited development, thereby suppressing tourism and economic activity. This research deepens our understanding of complex dynamics in island ecotourism and reveals the effect of certain management outcomes through scenario simulations, offering policymakers effective support for informed decision-making.

The complete mitogenome of an unidentified Oikopleura species.

Appendicularians are planktonic tunicates abundant all over the world. Currently, only two complete annotated mitochondrial genome assemblies are available for appendicularians, both for cryptic species of Oikopleura dioica. This underrepresentation of available appendicularian mitochondrial genomes limits environmental DNA sequencing (eDNA) studies that rely on mitochondrial markers as a taxonomic barcode. We report the complete mitochondrial genome assembly and annotation of an unknown appendicularian species isolated from the Amami Oshima island, Kagoshima prefecture, Japan, that has significant sequence difference with other currently available assemblies and will serve as a useful resource for ecological studies and further mitochondrial studies of appendicularians.

Survival and Movement of the Endangered Amami Woodcock Scolopax mira Revealed Through Banding on Amami-Oshima Island

Survival and Movement of the Endangered Amami Woodcock Scolopax mira Revealed Through Banding on Amami-Oshima Island

Role of an Eco-tour Guide Certification System in SustainableEcotourism on Amami-Oshima Island, Japan

Role of an Eco-tour Guide Certification System in SustainableEcotourism on Amami-Oshima Island, Japan

Genetic homogeneity in soldier crab Mictyris guinotae populations across their geographic distribution in the Ryukyu Islands, Japan

ABSTRACT The Japanese Archipelago comprises a chain of islands; therefore, gaps between islands can represent potential dispersal barriers for coastal species, especially those inhabiting tidal flats. This study investigates the population genetic structure of the soldier crab Mictyris guinotae (Brachyura: Thoracotremata: Mictyridae) using mitochondrial COI gene sequences. Specimens were collected from Tanegashima Island and five Ryukyu Islands, covering the species’ known geographic distribution. Although the Mantel test identified a moderate trend (r2 = 0.41, P < 0.01) for isolation by distance, all populations exhibited high haplotype and nucleotide diversities, with neither analysis of molecular variance nor ΦST detecting genetic differences among populations. Notably, the northernmost population (Tanegashima Island), approximately 260 km from the nearest known geographic distribution on Amami-Oshima Island, shared haplotypes with other populations, although the number of specimens from Tanegashima Island is only four due to its small population size. This absence of genetic differences among populations of M. guinotae differs from other intertidal organisms in the region examined in previous studies. Mismatch distributions suggest contrasting demographic history in M. guinotae and the sand bubbler crab Scopimera ryukyuensis, which has been revealed to show population genetic structuring despite its similar geographic distribution to M. guinotae. The present study provides another case of genetic diversity among intertidal organisms in the Ryukyu Islands.

The complete mitogenome of an unidentified Oikopleura species

Appendicularians are planktonic tunicates abundant all over the world. Currently, only two complete annotated mitochondrial genome assemblies are available for appendicularians, both for cryptic species of Oikopleura dioica. This underrepresentation of available appendicularian mitochondrial genomes limits environmental DNA sequencing (eDNA) studies that rely on mitochondrial markers as a taxonomic barcode. We report the complete mitochondrial genome assembly and annotation of an unknown appendicularian species isolated from the Amami Oshima island, Kagoshima prefecture, Japan, that has significant sequence difference with other currently available assemblies and will serve as a useful resource for ecological studies and further mitochondrial studies of appendicularians.

Deformation mechanisms and fluid conditions of mélange shear zones associated with seamount subduction

Lithologic heterogeneity and the presence of fluids have been linked to seamount subduction and collocated with slow earthquakes. However, the deformation mechanisms and fluid conditions associated with seamount subduction remain poorly understood. The exhumed Chichibu accretionary complex on Amami-Oshima Island preserves mélange shear zones composed of mudstone-dominated mélange and basalt–limestone mélange deformed under sub-greenschist facies metamorphism. The mudstone-dominated mélange contains sandstone, siliceous mudstone, and basalt lenses in an illitic matrix. The basalt–limestone mélange contains micritic limestone and basalt lenses in a chloritic matrix derived from the mixing of limestone and basalt at the foot of a seamount. The basalt–limestone mélange overlies the mudstone-dominated mélange, possibly representing a submarine landslide from the seamount onto trench-fill terrigenous sediments. The asymmetric S–C fabrics in both mélanges show top-to-SE shear consistent with megathrust-related shear. Quartz-filled shear and extension veins in the mudstone-dominated mélange indicate brittle failure at near-lithostatic fluid pressure and low differential stress. Microstructural observations show that deformation in the mudstone-dominated mélange was accommodated by dislocation creep of quartz and combined quartz pressure solution with frictional sliding of illite, whereas the basalt-limestone mélange was accommodated by frictional sliding of chlorite and dislocation creep of coarse-grained calcite, with possible pressure solution creep and diffusion creep of fine-grained calcite. The mélange shear zones formed in association with seamount subduction record temporal changes in deformation mechanisms, fluid pressure, and stress state during megathrust shear with brittle failure under elevated fluid pressure, potentially linking tremor generation near subducting seamounts.

Coordinated development of island ecotourism: A comprehensive evaluation of Amami-Oshima Island

Coordinated development of island ecotourism: A comprehensive evaluation of Amami-Oshima Island

Analysis of the occurrence of the fall armyworm, Spodoptera frugiperda, in the winter season on the southwestern islands of Japan using the insect's strontium radiogenic isotope ratio (87Sr/86Sr)

AbstractSpodoptera frugiperda, an invasive pest insect that targets maize and other crops, first arrived in Japan in the summer of 2019. This species occurs year‐round in East Asian subtropical regions such as southern mainland China and the island of Taiwan, where the mean air temperature in the coldest month is above 10°C. Adults are similarly found throughout the year on the southwestern islands of Japan. Trap monitoring there showed continuous or intermittent S. frugiperda catches in the three winter seasons since 2019. However, it was difficult to distinguish between immigrants arriving from these neighbouring areas and local individuals occurring on each Japanese island. In this study, the possible natal origin of captured insects on five small islands (Yonagunijima, Taramajima, Okinawajima, Amamioshima and Tanegashima) was determined by investigating the strontium radiogenic isotope ratios (87Sr/86Sr) and comparing them with those of reference hosts and insects. Since trapping data and the 87Sr/86Sr values of trapped insects didn't support S. frugiperda's winter breeding on the northernmost island, Tanegashima, further analysis was limited to the four southern islands. The 87Sr/86Sr values of reference host plants and reared insects on the four islands ranged from 0.70929 to 0.71009, while those of catch insects ranged from 0.70885 to 0.71090. The 87Sr/86Sr values of the catch insects and the reference on the four islands did not differ significantly. In addition, the monthly averages of daily mean air temperature in January and February 2020–2022 were above 10°C, and the wind direction at the surface was mostly from the northeast or northwest. These pieces of evidence, together with winter host availability, suggested that S. frugiperda occurs year‐round on the islands. In other words, the year‐round occurrence area of S. frugiperda in East Asia extends to the Japanese southwestern islands below Amamioshima Island.

Fertilizer Management, Soil Chemical Properties, Leaf Mineral Contents, and Fruit Quality in Passion Fruit Orchards on Amami-Oshima Island

Fertilizer Management, Soil Chemical Properties, Leaf Mineral Contents, and Fruit Quality in Passion Fruit Orchards on Amami-Oshima Island

Observation of air-exposure behaviour in the reef hermit crab, Calcinus elegans (H. Milne Edwards, 1836) (Decapoda, Diogenidae)

Abstract Many species of hermit crabs, such as Calcinus and Clibanarius spp., live on the rocky shores of tropical and warm temperate regions. During low tides, some of these species climb out of the tidal pools onto rock surfaces exposed to the air. In the genus Calcinus, however, such ‘Air-exposure (AE) behaviour’ was only known previously from Calcinus laevimanus. During a field study of the hermit crab fauna on Amami Oshima Island, Kagoshima, Japan, the AE behaviour of Calcinus elegans (Decapoda, Diogenidae) was observed on rocky shores. Moreover, the repeatability of the AE behaviour was confirmed. Therefore, we documented the AE behaviour of C. elegans as a second record of AE behaviour among Calcinus species by providing videographic evidence. The findings indicate that the AE behaviour has evolved in a broader range of Calcinus species than was previously assumed.

Occurrence of Selenothrips rubrocinctus (Giard) on sweet gum in Kyoto Prefecture, Japan

The red-banded thrips Selenothrips rubrocinctus (Giard) was originally distributed throughout northern South America. This thrips attacks tropical fruits such as mango, cocoa, and guava in North America, Asia, and Central and South Africa. In Japan, it has been observed on mango and guava in Okinawa Prefecture, Amami-Oshima Island in Kagoshima Prefecture, the Ogasawara Islands in Tokyo Metropolis, and Kochi Prefecture; on Actinidia rufa in Miyazaki Prefecture; and on maple trees in Kyoto Prefecture. In late September 2022, damage caused by S. rubrocinctus was observed in sweet gum in Kyoto Prefecture, with gray or dark brown leaves. This is the first record of S. rubrocinctus occurring on sweet gum in Japan. The degree of damage to the leaves and the occurrence of adults and larvae of the thrips were investigated in sweet gum lining streets and road facilities in Kyoto Prefecture. Damage caused by the thrips to sweet gum was observed in areas south of Kameoka, and adults and larvae were detected in areas south of Nantan, Kyoto Prefecture.

The effect of temperature and irradiance on the photosynthesis of a seagrass, Halodule uninervis, from Amami-Oshima Island, Kagoshima

分布北限に近い奄美大島産海草ウミジグサの光合成における光と温度の影響を明らかにした。15℃と24℃における光合成光曲線は，最大純光合成速度が15℃で顕著に抑制された。総光合成速度と最大量子収率による光合成温度曲線（8–40℃）は，それぞれ30.5℃と23.9℃で最大となった。15℃と24℃，光量300と1000 μmol photons m－2 s－1の組み合わせによる光と温度の複合応答では，低温·強光条件で量子収率が顕著に低下し，その後の暗馴致でも回復しなかったことから，低温光阻害が示唆された。

Geographic Variation in Skull Morphology of the Japanese Crocodile Newt, Echinotriton andersoni (Amphibia: Urodela: Salamandridae), Inferred from Geometric Morphometrics

The Anderson's crocodile newt, Echinotriton andersoni, is an endangered species distributed in the islands of Central Ryukyus, Japan. This species is well known to show high intraspecific genetic variation among islands, but its morphological variation has not been explored. We examined the skull variation in this species including enigmatic specimens collected from Taiwan by using geometric morphometrics, and found sexual differences and geographic variation mainly between the Okinawa group (Okinawajima Island) and the Amami Group (Amamioshima and Tokunoshima Islands). We further found close resemblance between the Taiwanese specimens and the female specimens from Amamioshima Island.

An assessment of Ryukyu Archipelago's coral communities over a wide latitudinal range

An assessment of Ryukyu Archipelago's coral communities over a wide latitudinal range

Middle Miocene forearc alkaline magmatism in Amami-Oshima Island, central Ryukyu Arc: implications for paleoreconstruction of Shikoku Basin

During the middle Miocene, forearc alkaline magmatism occurred in the Outer Zone of Southwest Japan and the northern Ryukyu Arc, resulting in the formation of forearc alkaline basaltic rocks with ocean island basalt (OIB)-like chemical signatures. In contrast, subduction-related magmatism was present in the central Ryukyu Arc. However, the southwestern margin of the forearc alkaline magmatism was poorly constrained in the Ryukyu Arc. We examined two basaltic dikes in the Chichibu accretionary complex of Amami-Oshima Island, the central Ryukyu Arc. The dikes cut massive basalt, reddish chert, varicolored shale, and grey chert. The chemical compositions of basaltic dikes are characterized by the enrichment of incompatible trace elements, possibly representing a low degree of partial melting from a deep mantle source. 40Ar/39Ar dating analyses indicate that the basaltic dikes yield ages of 16.37 ± 0.14 Ma and 16.51 ± 0.10 Ma. The paleomagnetic analyses on stepwise thermal demagnetizations allowed extracting the direction of stable magnetizations with unblocking temperatures of 450–575 °C for the two dikes [(Dec, Inc) = (138.1°, − 13.3°), (124.0°, − 24.9°)]. The magnetization could be primary, acquired either as part of a secular variation or a geomagnetic excursion during reversed polarity chron/subchron. The 40Ar/39Ar ages and paleomagnetic directions within the error range imply that they intruded almost simultaneously during C5Cn.2r (16.532–16.434 Ma). The age and trace element patterns of the basaltic dikes are comparable to those of Miocene alkaline basaltic rocks, which resulted from forearc alkaline magmatism during the initial subduction of the young and warm Shikoku Basin. The discovery of alkaline basaltic dikes on Amami-Oshima Island suggests that the distribution of middle Miocene forearc alkaline magmatism may extend to the central Ryukyu Arc. Hence, the northern end of the Kyushu-Palau Ridge (i.e., southern end of Shikoku Basin) could have been located south of Amami-Oshima Island around 16.5–16.4 Ma, then moved eastward to the current location.Graphical

Estimation of the Origin of suspended fine particulate organic matter in the subtropical Amami-Oshima Island streams

Estimation of the Origin of suspended fine particulate organic matter in the subtropical Amami-Oshima Island streams

A New Record of Hypsugo pulveratus on Amami-Oshima Island, Japan and Comparison with H. alaschanicus

Three vespertilionid bats were captured from Amami-Oshima Island, and had an average forearm length of 35 mm and average body weight of 8 g. From the side of the bat skulls, the ridge of the crown was slightly curved at the base of the snout; the second upper premolar (P2) in the bats was relatively large; the male baculum was shaped like an elongated, 3-mm-long spear tip and was very similar in both shape and size to that of Hypsugo pulveratus. The phylogenetic tree inferred from the mitochondrial COI gene sequences revealed that these bats clustered with H. pulveratus. Therefore, the bats from Amami-Oshima Island were identified as H. pulveratus. The present paper lists and depicts the morphological differences between H. pulveratus and H. alaschanicus so far known from the territory of Japan. Finally, genetic analysis based on the barcoding gene sequences revealed that these species formed distinct clades.