Amami-Oshima Island Research Articles

Facultative amphidromy involving estuaries in an annual amphidromous fish from a subtropical marginal range.

Variation in the life cycle of diadromous fishes can be explained by differential food availability between marine and freshwater habitats, since migration is often interpreted as a mechanism for exploiting food resources. Theoretically, a migration pattern of mainly remaining in freshwater occurs in tropical and subtropical habitats where fluvial productivity possibly exceeds marine productivity. However, in Yakugachi River, Amami-Oshima Island, southern Japan, low nutrient concentrations in the river suggest that food availability is limited for the subtropical Ryukyu-ayu Plecoglossus altivelis ryukyuensis. Since Ryukyu-ayu is an amphidromous fish that mainly grows in rivers after spending 2 months in the sea, limited food availability in rivers would force this species to migrate to other habitats with better food availability. Otolith increment and Sr:Ca analyses of 48 adult Ryukyu-ayu collected from the Yakugachi River revealed that all individuals visited estuaries more than three times after moving upstream. Although the specific growth rates of this species in the river had no correlation with the salinity profile in the fluvial period, this movement may be an adaptive choice because the salinity profile significantly affected the body size at maturity. Our results highlighted individual-based variations in amphidromous migration for utilizing estuaries, which could be explained by relatively higher productivity in estuarine than in freshwater and marine habitats.

「奄美・沖縄」の世界自然遺産登録と持続可能な観光への提言

「奄美・沖縄」の世界自然遺産登録と持続可能な観光への提言

徳之島と奄美大島に生息するコウモリ類の生態学的研究，特にリュウキュウテングコウモリMurina ryukyuanaについて

徳之島と奄美大島に生息するコウモリ類の生態学的研究，特にリュウキュウテングコウモリMurina ryukyuanaについて

Interspecific interference competition between two field cricket species

AbstractSpecies interactions, such as interspecific competition, determine population dynamics and community structure. In a park of Amami Oshima Island, Japan, two field cricket species Teleogryllus occipitalis (Audinet‐Serville) (Gryllidae) and Loxoblemmus equestris Saussure (Gryllidae) are dominant species. We examined the interference competition at the nymph and adult stages in the two crickets under controlled laboratory conditions. Survival and emergence rates of T. occipitalis were not affected by the density of L. equestris, whereas survival and emergence rates of L. equestris decreased as the density of T. occipitalis increased. These results showed that T. occipitalis was competitively superior over L. equestris in species interactions. We discuss inconsistency between the results and coexistence of these two species under field conditions.

Inferred Adult Foraging Grounds of Two Marine Turtle Species Nesting at Amami-Oshima, Japan

Abstract During late June and July in 2015, we tracked the postnesting migrations of 5 loggerhead turtles (Caretta caretta) and 5 green turtles (Chelonia mydas) from a beach on Amami-Oshima Island ...

Lecanorchis moritae (Orchidaceae, Vanilloideae), a new mycoheterotrophic species from Amami-Oshima Island, Japan, based on morphological and molecular data

A new species of the mycoheterotrophic genus Lecanorchis Blume (Orchidaceae), L. moritae, is described from Amami-Oshima Island, Japan. It is most similar to L. suginoana but differs in having a transversely elliptic (slightly contracted at base) midlobe (vs. semiorbicular, not contracted at base), more triangular with almost entire margins (vs. relatively rounded, denticulate margins) and reddish apices (vs. somewhat whitish apices) and a lip with white and purple hairs (vs. white and lemon yellow hairs) and sparse unicellular papillae scattered on the disc (vs. dense unicellular papillae). An illustration and nuclear ribosomal internal transcribed spacer (nrITS) sequence (i.e., DNA barcode) of the new species are also provided.

Notes on the feeding habits of the Okinawan fishing spider, Dolomedes orion (Araneae: Pisauridae), in the southwestern islands of Japan

Fishing spiders, Dolomedes Latreille, 1804 (Pisauridae), are thought to be important predators in semi-aquatic ecosystems, but relatively few studies have investigated feeding ecology of Asian species. Here, we report on the diet of the Okinawan fishing spider, Dolomedes orion Tanikawa, 2003, the largest cursorial spider in Japan, based upon field observations on Amami Oshima Island in Kagoshima Prefecture and a literature review. A total of 13 predation events were observed in field surveys and 10 records were found in the literature. Together, these indicate the consumption of a broad range of food items from arthropods to vertebrates, e.g., insects, harvestman, conspecific spiders, crustaceans (freshwater crab and prawn), two species of endemic frogs (Rana ulma, Odorrana narina), and an Okinawa tree lizard (Japalura polygonata polygonata). Because this species has substantial energy demands for growth, large prey items such as crustaceans and vertebrates seem to be its primary food resources with 10 of 23 prey items [= 43%] belonging to these two large-sized prey groups.

Hesitant Heritage: U.S. Bases on Okinawa and Japan's Flawed Bid for Yambaru Forest World Heritage Status

On February 1, 2019, the Japanese Ministry of the Environment submitted to UNESCO and the International Union for Conservation of Nature (IUCN) its nomination of four areas in the Ryukyu archipelago for UNESCO World Natural Heritage status. The areas are Amami-Oshima Island, Tokuno-Shima Island, the Northern Part of Okinawa Island, and Iriomote Island (see the Nomination Document and the Nomination Annexes).

Evolution of short tails and breakdown of honest signaling system during a severe winter in the Pacific swallow Hirundo tahitica

In dynamic selection regimes, an honest signal that indicates high quality in favorable environments might be negatively related to quality in unfavorable environments, though empirical evidence is scarce. Here, we studied the relationship between plumage ornaments and physiological state in the Pacific swallow Hirundo tahitica on Amami Oshima Island in 2 years with contrasting weather conditions: a once-in-a-century severe winter and a mild winter in the following year. Previous studies have shown that, during the severe winter, many Pacific swallows, particularly those with long tails, died whereas no carcasses were found in the next year, indicating relaxed selection during mild years. Here we showed that after the severe winter, the offspring generation had shorter tails than the parental generation, which could not be explained by age or yearly difference in tail length, indicating the evolution of short tails. Moreover, the relationship between tail length and body condition differed between years: longer-tailed swallows had a better body condition in the mild winter, whereas the reverse tendency was found in the severe winter. A similar relationship was found between plasma corticosterone level, an indicator of physiological stress, and tail length (i.e., swallows with longer tails tended to have lower corticosterone levels during the mild winter while the reverse pattern was found during the severe winter). In contrast, another plumage ornament, pheomelanin pigmentation, was positively linked to body condition during the two study years and had no detectable relationship with the plasma corticosterone levels. Differences in the relationship between specific plumage traits and physiology may help to explain the diversity of tail length and plumage coloration in hirundines.

Breeding season and life history of <i>Lingula anatina</i> after settlement in Amami-Oshima Island, Kagoshima, Japan

Breeding season and life history of <i>Lingula anatina</i> after settlement in Amami-Oshima Island, Kagoshima, Japan

Possible domestic dispersal of Bactrocera dorsalis during 2015 occurrence on the small islands of south‐western Japan

AbstractAlthough Japan has maintained the state of eradication of the oriental fruit fly, Bactrocera dorsalis Hendel complex (Diptera: Tephritidae) since 1986, B. dorsalis complex are occasionally trapped within a limited area and short time period on Japan's small south‐western islands. Trapping events occurred on Amamioshima Island, Kagoshima Prefecture, in 2015, and male adults were also caught in surveillance traps on neighbouring Tokunoshima (south of Amamioshima) and Yakushima (north of Amamioshima) islands as well as on several islands in Okinawa Prefecture (south of Amamioshima). To investigate possible domestic dispersal of the pest from Amamioshima Island, a trajectory analysis was performed to reveal the timing and flight distance of possible dispersal. Surveillance data indicated that the first trappings on Tokunoshima and Yakushima islands occurred in November, which was after the number of trapped male adults on Amamioshima Island peaked in late October. Backward trajectories from Tokunoshima Island beginning 14 days prior to the first trapping passed over Amamioshima Island, which suggested possible dispersal between the islands. Several backward trajectories from the islands in Okinawa Prefecture also passed Amamioshima Island. Moreover, forward trajectories from Amamioshima Island beginning during peak occurrence, from mid‐October to early November, arrived over Tokunoshima, Iheya and Okinawa islands where the flies were caught. Such circumstantial evidence suggests that domestic dispersal of B. dorsalis complex occurred on Amamioshima Island. A situation similar to that on Tokunoshima Island also occurred on Yakushima Island. However, since the number of traps has been limited until the first capture, it was not clear when and from where the immigrants arrived on the island.

Taxonomic review of the mirine plant bug genus Stenotus Jakovlev in Japan and adjacent regions in Asia (Hemiptera: Heteroptera: Miridae: Mirinae)

The mirine plant bug fauna of the genus Stenotus Jakovlev in Japan, Korea, East China, and Russian Far East is reviewed. Seven species are recognized in the study area; of these, two new species are herein described, namely S. hasegawai sp.n., restricted to cool-temperate climate zones in Japan and Sakhalin, Russia and S. takaii sp.n. assumed to be endemic to Amami-Oshima Island of the Japanese Ryukyus. The Taiwanese species, S. insularis Poppius, is reported from the Ryukyus for the first time and redescribed; the other taxon, S. viridis (Shiraki), is regarded as a nomen dubium, lacking any type series. An additional new species from Nepal, S. ramduwalae sp.n., is described. A checklist of East Asia and Oriental species and a key to all known East Asian species are provided. Stenotus longiceps Poppius is transferred to Zalmunna Distant. The zoogeography of these East Asian Stenotus species is discussed.

Calling-Site Preferences of Three Co-occurring Endangered Frog Species on Amami-Oshima Island

Abstract Hotspots of amphibian species diversity typically occur in limited geographical ranges, and critically endangered habitats often contain a large number of endemic amphibian species. In such regions, it is prudent to engage conservation strategies for multiple amphibian species simultaneously. To correctly identify suitable habitats for multiple species, species interactions should be considered in species distribution models. In this study, we adopted a joint species distribution model to determine the abiotic and biotic factors that affect calling-site choice in three endangered co-occurring frog species on Amami-Oshima Island, and examined whether they co-occur more than expected after considering the overlapping preferences in environmental variables. Occurrences of Babina subaspera, Odorrana splendida, and O. amamiensis were assessed by monitoring mating calls using automatic digital voice recorders at 67 sites in 12 streams and explained by 8 environmental variables: water flow volume, tempe...

Possible courtship behaviour of Devonian fish: Evidence from large radial trace fossils in northwestern China

Possible courtship behaviour of Devonian fish: Evidence from large radial trace fossils in northwestern China

Variation in growth performance of Ryukyu-ayu, Plecoglossus altivelis ryukyuensis, inferred from otolith analysis

Ryukyu-ayu (Plecoglossus altivelis ryukyuensis) is an amphidromous fish species that migrates between the sea and rivers over its one-year life span. Although growth performance during the early marine stage may affect growth in the later riverine stage of this species’ life cycle, no studies have specifically examined this relationship in P. a. ryukyuensis. In the present study, we reconstructed the growth trajectories of P. a. ryukyuensis individuals collected from the Yakugachi River, Amami-Oshima Island, Japan in 2016 (n = 47) throughout their growth period in both the sea and river by using otolith analysis. Using this, we determined the age and body size of individuals at the time of their upstream migration, as well as their growth rates during the marine and riverine stages. Results showed that body size at upstream migration significantly affected body size at the riverine stage, indicating that juveniles with larger body size in the sea had better growth performance in the river. Individuals with higher growth rates during the marine stage tended to enter the river younger and at larger body sizes than those with lower marine growth rates. Our results demonstrated the close linkage between the growth performance in the sea and in rivers of P. a. ryukyuensis. This information will contribute to better understanding variations in growth patterns of this endangered species and potentially aid in its conservation.

A new garden eel, Heteroconger fugax (Congridae: Heterocongrinae),from the northwestern Pacific Ocean.

Heteroconger fugax sp. nov. (Congridae: Heterocongrinae) is described from a single specimen collected from Amami-oshima island, Japan. The new species is most similar to Heteroconger tomberua Castle Randall 1999, known from Fiji and New Caledonia, in having a remarkably slender body with numerous small spots and a vertebral count close to 200. However, it can be distinguished from H. tomberua by the presence of a large distinct white blotch on the opercle; more numerous, dense spots over the entire head, including lips; ground color of body uniformly cream, without microscopic melanophores; numerous small conical cirri on the chin; and dorsal-fin origin located more posteriorly to appressed pectoral-fin tip. A survey of underwater photographs of Heteroconger on photographic database revealed H. fugax to be widely distributed in the northwestern Pacific Ocean, from the Ryukyu Archipelago to Borneo.

A colour variation of Clibanarius virescens (Krauss, 1843) (Decapoda, Anomura) collected from Amami Oshima Island and Okinawa, Japan

During our survey on the intertidal hermit crab fauna on Amami Oshima Island and Okinawa Island, southwestern Japan, we collected specimens identified asClibanariusspecies by their morphological features, but that had an unknown coloration for the genus: they have whitish ambulatory legs and a whitish shield. For species identification of these specimens, we observed their coloration and morphology and also performed phylogenetic analyses using the genes mitochondrial cytochrome c oxidase I (COI) and nuclear histone H3. The analysis has shown that these specimens are to be identified asClibanarius virescens(Krauss, 1843).

Molluscan death assemblages washed upon Ohama Beach, Amami-Oshima Island, southwestern Japan

Molluscan death assemblages washed upon Ohama Beach, Amami-Oshima Island, southwestern Japan

How to Maintain a Rural Settlement through Screening and Accepting I-Turn Migrants in Amami-oshima Island, Japan: Counterevidence to the “Marginal Settlement Discourse” by Examining the Case of Katetsu, Setouchi-cho

本論は，鹿児島県奄美大島の瀬戸内町嘉鉄において，Iターン者の価値観と集落の機能に注目し，Iターン者を取り入れた集落の維持形態を明らかにした．1990年代末以降，嘉鉄には大都市圏からの移住者が継続的に流入している．彼らは島内の都市的地域を避け，選択的に嘉鉄に居住する．Iターン者が嘉鉄に住居を確保するには，住宅所有者の社会的ネットワークに参加することが求められる．また移住前，住民は会合を開き，移住希望者に対し集落行事への参加を確認する．閉鎖的な住宅市場と集落行事に関する合意形成は，地域社会に適合する人材を選別する役割を果たす．移住後，集落行事は従前の住民がIターン者を受け入れる場所となる．非都市的生活を希求するIターン者と彼らを選別して受け入れる集落の機能が結びつき，嘉鉄ではIターン者を空間的・社会的に取り入れた集落維持が行われている．本論は，限界集落論を反証する事例として位置づけられる．

Evaluating the effectiveness of forest bird monitoring by sound recording on Amami-Oshima Island, Japan

Evaluating the effectiveness of forest bird monitoring by sound recording on Amami-Oshima Island, Japan