Nansei Islands Research Articles

First records of the subgenus Eurhipidia from Japan, with two new species (Diptera, Limoniidae, Rhipidia )

Species of Rhipidia (Eurhipidia) Alexander, 1965 are found in Japan for the first time. Two new species, R. (E.) honshuensissp. nov. from Honshu (Palaearctic Region) and R. (E.) okinawensissp. nov. from Nansei Islands (Oriental Region) are described. The images of the habitus, wings, and terminalia, distribution maps, and a key to the species are provided.

Priority sites for coral aquaculture in Kume Island based on numerical simulation

Global and local stresses such as increased water temperature and terrestrial sediment runoff significantly affect coral reef ecosystems. Over the past three decades, the increase in the intensity and frequency of coral bleaching has been a significant problem in tropical and subtropical coastal seas, and maintaining healthy coral reef ecosystems has long been a challenge. Coral cover in Shimajiri Bay on Kume Island, located in the Nansei Islands (Okinawa Prefecture, southern Japan), has declined due to exposure to high water temperatures, an outbreak of coral predators, and sediment (red soil) inflow from the land. From such a background, coral aquaculture has been implemented at a few stations in the bay. Therefore, it is essential to conduct aquaculture in suitable locations for coral growth and survival. This study aimed to select suitable locations for coral culture with high spatial resolution in an enclosed bay that was greatly affected by red soil runoff, mainly from a sugarcane field. A freshwater and red soil runoff model for the watershed was merged with a coastal hydrodynamic, red soil dispersal, and accumulation model at a spatial resolution of 75 m for Shimajiri Bay. The simulation results were validated using in situ continuous and routine observations. Simulations were conducted over ten years. Locations not subjected to high water temperature in the bay or river loading were selected based on topography, simulated water temperature, salinity, and red soil content of sea sediment. This coupled model enables us to evaluate the growth and survival conditions of cultured corals with high spatiotemporal resolution and quantitatively consider the reduction target of red soil runoff to realize robust coral growth and survival.

A Data-Driven Approach to Sugarcane Breeding Programs with Agronomic Characteristics and Amino Acid Constituent Profiling.

Sugarcane (Saccharum spp. hybrids) and its processed products have supported local industries such as those in the Nansei Islands, Japan. To improve the sugarcane quality and productivity, breeders select better clones by evaluating agronomic characteristics, such as commercially recoverable sugar and cane yield. However, other constituents in sugarcane remain largely unutilized in sugarcane breeding programs. This study aims to establish a data-driven approach to analyze agronomic characteristics from breeding programs. This approach also determines a correlation between agronomic characteristics and free amino acid composition to make breeding programs more efficient. Sugarcane was sampled in clones in the later stage of breeding selection and cultivars from experimental fields on Tanegashima Island. Principal component analysis and hierarchical cluster analysis using agronomic characteristics revealed the diversity and variability of each sample, and the data-driven approach classified cultivars and clones into three groups based on yield type. A comparison of free amino acid constituents between these groups revealed significant differences in amino acids such as asparagine and glutamine. This approach dealing with a large volume of data on agronomic characteristics will be useful for assessing the characteristics of potential clones under selection and accelerating breeding programs.

A new subtropical species of goby of the genus Luciogobius (Gobiidae) from southwestern Japan.

Luciogobius griseus n. sp., belonging to the Luciogobius platycephalus complex, is described on the basis of 40 specimens from the Nansei Islands, southwestern Japan (subtropical area). The new species is generally found in intertidal gravel sediments subjected to freshwater runoff from springs on coastal lines or river mouths and is characterized by the following combination of characters: total second dorsal-fin rays 912 (modally 11); total anal-fin rays usually 1214 (modally 13); pectoral-fin rays 1215 (modally 13); vertebrae 17 or 18 + 23 or 24 = 4042 (18 + 23 = 41); uppermost 24 (23) rays on pectoral fin free; 812 pectoral-fin rays branched (uppermost free rays and sometimes lowermost ray unbranched); pectoral-fin membrane not strongly concave anteriorly (except for free rays); pelvic fins united, forming a disk; head relatively short, 13.920.8% of standard length (SL); relatively short pre-pelvic fin, length 14.422.1% of SL; relatively long pre-dorsal fin, length 68.972.9% of SL; relatively long pre-anal fin, length 63.567.7% of SL; relatively short pelvic fin, length 2.84.7% of SL; distance between posterior end of pelvic fin and anus relatively long, 32.036.4% of SL (aforementioned morphometrics each distinguishing L. griseus n. sp. from other species in the L. platycephalus complex); and fresh specimens with greenish dark brown or gray body. A key to the L. platycephalus complex is provided, together with limited descriptions and remarks on the other two members of the complex.

Characteristics of the Blitzortung.org Lightning Location Catalog in Japan

We evaluated the detection efficiency and location accuracy of lightning discharges in Japan using Blitzortung.org, a volunteer-based network for locating lightning discharges from sferics measured by very low frequency (VLF) electromagnetic receivers that have been deployed worldwide in recent years. A comparison of the flash rate (the detected lightning rate per area and period) from Blitzortung.org with that from the satellite-based OTD/LIS and the ground-based World Wide Lightning Location Network (WWLLN) observations showed that Blitzortung.org clearly observed intense lightning activity in and around the Kanto area, including Tokyo, in summer, which is typical of Japanese lightning activity. However, it did not clearly observe lightning activity in and around the Nansei Islands, including Okinawa. Conversely, Blitzortung.org observed winter lightning activity in the Hokuriku area and off the Kanto. In addition, event studies have compared the detection efficiency and location accuracy of Blitzortung.org with those of the Japanese Lightning Location Network (JLDN) to infer their absolute values. The latest detection efficiency of Blitzortung.org in the Kanto area was estimated at roughly 90%. The mean location accuracy was estimated at up to 5.6 km.

Revision of goblin spiders (Araneae: Oonopidae) in the Nansei Islands, Southwest Japan, with description of a new species.

We revised the fauna of goblin spiders (Oonopidae) in the Nansei Islands, southwest Japan, and recognized 12 species of seven genera. Eleven of them were described species, namely, Gamasomorpha cataphracta Karsch, 1881, Heteroonops spinimanus (Simon, 1892), Ischnothyreus narutomii (Nakatsudi, 1942), Ischnothyreus peltifer (Simon, 1891), Ischnothyreus velox Jackson, 1908, Opopaea cornuta Yin & Wang, 1984, Opopaea deserticola Simon, 1892, Opopaea syarakui (Komatsu, 1967), Orchestina flava Ono, 2005, Xestaspis parmata (Thorell, 1890), and Xyphinus karschi (Bsenberg & Strand, 1906). A new species is described under the name of Ischnothyreus ogatai sp. nov. This paper provides photographs of each oonopid species, notes on habitat and distribution, and keys to the species. A detailed description of I. ogatai sp. nov. (for both sexes), morphological data regarding three species newly added to the Japanese fauna (X. parmata, I. velox, and O. cornata), and additional data on the genital morphology of G. cataphracta are also presented.

Revisiting the spawning fraction of Pacific bluefin tuna (Thunnus orientalis) caught in the Sea of Japan based on diurnal changes in spawning markers

The spawning fraction (SF) is an important reproductive trait used to assess the reproductive potential of indeterminate spawning fishes. To estimate the SF more accurately, the durations of spawning markers in ovaries need to be determined. The SF of the Pacific bluefin tuna Thunnus orientalis (PBF) in the Sea of Japan (SOJ) is higher than the SFs in its other main spawning grounds. The present study aimed to revisit the SF of the PBF in the SOJ by focusing on diurnal changes in spawning markers and estimating the duration of spawning markers in PBF ovaries. According to diurnal changes in the postovulatory follicle (POF) degeneration process and final maturation process of oocytes, POFs were observed in ovaries up to 38.5 h after ovulation. The revisited total SF throughout the spawning season was 0.34–0.43 in Area 1 and 0.50–0.64 in Area 2; these values are smaller than the SF previously estimated in the SOJ. The estimated SF of the PBF in the present study was equal to or slightly higher than that in the water between the Nansei Islands, Japan, and the northeast of the Philippines and higher than that in the Kuroshio-Oyashio transition area.

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.

Morphological and genetic analyses of Simulium (Gomphostilbia) okinawense Takaoka and S. (G.) tokarense Takaoka (Diptera: Simuliidae) from the Nansei Islands, Japan: redescription and transfer from the S. ceylonicum species-group to the S. asakoae species-group.

Simulium (Gomphostilbia) okinawense Takaoka and S. (G.) tokarense Takaoka, both from the Nansei Islands, Japan, were morphologically reexamined and genetically analysed by using the COI gene sequences. The female, male, pupa and mature larva of the two species are redescribed. Morphological reexamination shows that both species are more similar to species in the S. asakoae species-group than to those in the S. ceylonicum species-group, by having a medium-long female sensory vesicle, yellow tuft hairs (S. (G.) okinawense) or yellow tuft hairs mixed with a few to several dark hairs (S. (G.) tokarense) at the base of the radial vein in the female and male, and medium-long larval postgenal cleft. However, the body of the male ventral plate (viewed ventrally) is parallel-sided (S. (G.) okinawense) or parallelsided or slightly narrowed (S. (G.) tokarense) and not emarginated basally, differing from those of most species in the S. asakoae species-group. Our genetic analysis shows that S. (G.) tokarense is in the S. asakoae species-group, and S. (G.) okinawense formed a separate sister clade with other members of the S. asakoae species-group with high bootstrap support. From the results of morphological and genetic analysis combined, S. (G.) okinawense and S. (G.) tokarense are transferred from the S. ceylonicum species-group to the S. asakoae species-group.

Descriptions of two new Celticecis species (Diptera: Cecidomyiidae) that induce leaf galls on Celtis boninensis (Cannabaceae) in Japan

Two new species Celticecis insulicola Sato and Yukawa and Celticecis gracilicornis Sato and Yukawa (Diptera: Cecidomyiidae) are described from Japan based on morphological comparison with other congeners in the world. The definition of the genus Celticecis is broadened to include the two new species. Molecular phylogenetic analysis supported the results of identification. C. insulicola induces bullet-shaped galls, and C. gracilicornis induces slender conical galls on the leaves of Celtis boninensis Koidzumi (Cannabaceae), a plant of the southern part of Japan, mainly on the Nansei Islands in Kagoshima and Okinawa Prefectures. Both species are univoltine, mature larvae overwintering in the galls on the ground and adults emerging in early spring. C. insulicola was found on Amami, Uke and Okinoerabu Islands, Kagoshima Prefecture, and Okinawa Island, Okinawa Prefecture. C. gracilicornis was found on Amami and Okinawa Islands.

Characteristics of topographical location and spatial composition on villages on Kikaijima Island, Nansei Islands: Reconstructing spatial composition of villages immediately before and after World War II

AbstractThe purpose of this study was to reconstruct the spatial characteristics of the villages on Kikaijima Island immediately before and after World War II to examine the characteristics of these spatial characteristics within the context of the topographical situation of the villages. In this study, we clarified the commonalities and differences of the location and spatial composition of the villages by analyzing aerial photographs of all of the villages on Kikaijima Island by the US military immediately before and after World War II.

Has long‐distance flight ability been maintained by pigeons in highly insular habitats?

AbstractAimA reduction in dispersal ability has been thought to be a general trend for island land birds. However, recent studies have indicated that long‐distance dispersal among island habitats may be maintained in island pigeon populations. Here, we investigated whether pigeons could maintain their long‐distance dispersal ability to move among islands within the archipelago, even in highly insular conditions, by comparing two subspecies of Japanese wood pigeon distributed on islands with different levels of insularity.LocationThe Ogasawara, Izu and Nansei Islands in the north‐western Pacific Ocean.TaxonJapanese wood pigeon (Columba janthina).MethodsWe compared the hand‐wing index related to dispersal potential between the two subspecies: C. j. janthina and C. j. nitens. We performed phylogenetic analyses with likelihood and Bayesian frameworks and estimated population genetic structure using the principal component analyses and individual admixture analyses based on the genotype likelihood of MIG‐seq SNPs. We calculated divergence times of the two subspecies using Bayesian and PSMC models for MIG‐seq SNPs and whole genome data, respectively.ResultsC. j. nitens had a wing shape that was better suited for long‐distance flight than that of C. j. janthina. Both subspecies maintained sufficient gene flow among the islands within their habitat archipelagos, with no evidence of isolation by distance. The divergence time of the two subspecies was 0.67 (95%CI: 0.33–0.97) million years ago, which was sufficient to reduce dispersiveness compared to other cases of island land birds.Main ConclusionLong‐distance flight can be maintained under highly insular conditions despite long‐term isolation from the ancestral populations. This indicates that the strategy of maintaining dispersal ability may also be possible in island systems, where organisms have repeatedly and globally shown reduced dispersal ability. Although further studies are required to reveal its evolutionary processes, our study provides an exceptional case for island birds' biogeography.

Secondary contact of two cryptic Hokou gecko groups in the Izu Islands, Japan

We analyzed the mitochondrial DNA of Gekko hokouensis collected from the Izu Islands (maybe an introduced population) and the Nansei Islands (native population), both in Japan. A molecular phylogenetic analysis suggested that G. hokouensis of Japan belongs to a cryptic monophyletic group different from that of the currently discovered sample of China. Furthermore, the Japanese clade of G. hokouensis is differentiated into two subclades (Clade 1 and Clade 2 in this article). In the Nansei Islands, these two subclades form a complicated nested-distribution pattern and do not coexist on any of the islands, whereas both clades appear to coexist in the Izu Islands. The two clades exhibit high genetic diversity in the Nansei islands, which are the source population. Surprisingly, it has been revealed that high genetic diversity has also been maintained in the Izu Islands, which are the introduced population, in each clade. AMOVA has also revealed that the genetic differentiation between the populations in the Izu Islands and the Nansei Islands was not significant in each clade. These results suggest that the population of the Izu Islands is now in secondary contact between two clades by multiple migrations from various regions of the Nansei Islands.

Genomic analysis of a reef-building coral, Acropora digitifera, reveals complex population structure and a migration network in the Nansei Islands, Japan.

Understanding the structure and connectivity of coral populations is fundamental for developing marine conservation policies, especially in patchy environments such as archipelagos. The Nansei Islands, extending more than 1000 km in southwestern Japan, are characterized by high levels of biodiversity and endemism, supported by coral reefs, which make this region ideal for assessing genetic attributes of coral populations. In this study, we conducted population genomic analyses based on genome-wide, single-nucleotide polymorphisms (SNPs) of Acropora digitifera, a common species in the Nansei Islands. By merging newly obtained genome resequencing data with previously published data, we identified more than 4 million genome-wide SNPs in 303 colonies collected at 22 locations, with sequencing coverage ranging from 3.91× to 27.41×. While population structure analyses revealed genetic similarities between the southernmost and northernmost locations, separated by >1000 km, several subpopulations in intermediate locations suggested limited genetic admixture, indicating conflicting migration tendencies in the Nansei Islands. Although migration networks revealed a general tendency of northward migration along the Kuroshio Current, a substantial amount of southward migration was also detected, indicating important contributions of minor ocean currents to coral larval dispersal. Moreover, heterogeneity in the transition of effective population sizes among locations suggests different histories for individual subpopulations. The unexpected complexity of both past and present population dynamics in the Nansei Islands implies that heterogeneity of ocean currents and local environments, past and present, have influenced the population structure of this species, and similar unexpected population complexities may be expected for other marine species with similar reproductive modes.

Natal origin of Pacific bluefin tuna Thunnus orientalis determined by SIMS oxygen isotope analysis of otoliths.

Accurate understanding of changing population dynamics associated with climate change is critical for managing highly migratory fish species. However, long-term data on population dynamics and the resulting recruitment variability is still lacking for many species, making it difficult to predict and integrate the effects of ocean warming into management schemes. In this study, high-resolution stable oxygen isotope (δ18O) analysis was performed on the otoliths of adult Pacific bluefin tuna Thunnus orientalis using secondary ion mass spectrometry (SIMS) to determine the natal origin of an individual fish. The core δ18Ootolith corresponding to the larval stage greatly varied among the individuals, indicating that the larvae experienced a wide range of thermal environments. The non-hierarchical cluster analysis performed on the core δ18Ootolith grouped fish into those with higher δ18Ootolith (lower temperature) and those with lower δ18Ootolith (higher temperature), most likely representing relative temperature difference experienced between fish born in the Sea of Japan and in the Nansei Islands area. The Nansei Islands area cluster showed more variability in the early otolith growth indicating a longer spawning season, which is consistent with the observed longer spawning duration in this area. The absolute temperature estimates based on the SIMS-measured core δ18Ootolith were significantly higher than those expected from sea surface temperature data, suggesting the effects of matrix-related bias on the temperature offsets. The relative temperature difference, however, matched well with the known spawning temperature range of the two spawning grounds. The recruitment contribution from each spawning ground (all year-classes pooled, n = 51) was 45% in the Sea of Japan and 55% in the Nansei Islands area. Overall, this study demonstrated the effectiveness of SIMS δ18Ootolith analysis for investigating the natal origin of fish and its potential application in fish population dynamics studies.

Moths and butterflies on alien shores: Global biogeography of non‐native Lepidoptera

AbstractAimLepidoptera is a highly diverse, predominantly herbivorous insect order, with species transported to outside their native range largely facilitated by the global trade of plants and plant‐based goods. Analogous to island disharmony, we examine invasion disharmony, where species filtering during invasions increases systematic compositional differences between native and non‐native species assemblages, and test whether some families are more successful at establishing in non‐native regions than others.LocationHawaii, North America, Galapagos, Europe, South Africa, South Korea, Japan, Nansei Islands, Ogasawara Islands, Australia, New Zealand.TaxonLepidoptera.MethodsWe compared numbers of non‐native, unintentionally introduced Lepidoptera species with the land area of 11 regions worldwide. Differences among native and non‐native assemblages in the distribution of species among families were investigated using ordination analysis. We tested whether invasion disharmony is explained by propagule pressure (proxied by species richness in border interceptions) and if families were associated with specific trade commodities.ResultsIn total, 741 non‐native Lepidoptera species, accounting for 0.47% of the global diversity of lepidopterans, are established in at least one of the 11 regions. Crambidae, Pyralidae, Tineidae and Gracillariidae were particularly successful invaders, whereas the two most species‐rich families, Erebidae and Geometridae, were under‐represented among non‐native Lepidoptera. Much of the variation in species numbers in the native, and less so in the non‐native assemblages could be attributed to land area. Although native assemblages were similar among nearby regions, non‐native assemblages were not, suggesting geography had little effect on invasion disharmony. Comparison of established with intercepted species revealed that macromoth families were generally under‐represented in establishments, whereas several micromoth families were under‐represented in interceptions. This discrepancy may relate to greater detectability of larger species or high propagule pressure via associations with specific invasion pathways.Main conclusionsInvasion disharmony in Lepidoptera appears to be driven by processes unrelated to the success of native assemblages. While native assemblages developed through long‐term evolutionary radiation, the composition of non‐native assemblages is driven by differential invasion pathways and traits affecting the establishment of founder populations that vary among families.

Active Expression of Genes for Protein Modification Enzymes in Habu Venom Glands.

Genes encoding snake venom toxins have been studied extensively. However, genes involved in the modification and functioning of venom proteins are little known. Protobothrops is a genus of pit vipers, which are venomous and inhabit the Nansei (Southwest) islands of Japan, Taiwan China, Vietnam, Thailand, Myanmar, Nepal, Bhutan, and India. Our previous study decoded the genome of Protobothrops flavoviridis, a species endemic to the Nansei Islands, Japan, and revealed unique evolutionary processes of some venom genes. In this study, we analyzed genes that are highly expressed in venom glands to survey genes for candidate enzymes or chaperone proteins involved in toxin folding and modification. We found that, in addition to genes that encode venom proteins and ribosomal proteins, genes that encode protein disulfide isomerase (PDI) family members (orthologs of human P4HB and PDIA3), Selenoprotein M (SELENOM), and Calreticulin (CALR) are highly expressed in venom glands. Since these enzymes or chaperones are involved in protein modification and potentially possess protein folding functions, we propose that P4HB, SELENOM, CALR, and PDIA3 encode candidate enzymes or chaperones to confer toxic functions upon the venom transcriptome.

Reproductive dynamics of Pacific bluefin tuna (Thunnus orientalis) off the Nansei Islands, southern Japan

To describe seasonal changes in the reproductive traits of Pacific bluefin tuna (Thunnus orientalis), we examined the spawning season, spawning fraction (SF), spawning interval, batch fecundity (BF) and monthly changes in the horizontal distribution of spawning fish (SP) in the Nansei Islands and the waters off southwestern Honshu Island, Japan. SP were observed at sea surface temperatures (SSTs) between 19 and 29 °C, and the frequency of SP tended to increase with SST. SP were observed from early May to mid-July and most frequently in late June. The SP distribution in the Nansei Islands tended to expand northward with time. Mature female fish were widely distributed between the Nansei Islands and the waters off southwestern Honshu Island throughout the study period. The total SF during the spawning season was 0.24, which was equal to the 4.17-day spawning interval. The SF tended to increase with time. The number of days since the start of the fishing season (Days) positively affected the probability of the occurrence of specimens with postovulatory follicles among mature fish. The mean and relative BFs during the spawning season were 9.74 ± 6.72 (million oocytes) and 64.8 ± 38.4 (oocytes/g), respectively. The BF was positively affected by increases in the fork length (FL) and Days. These results suggest that the reproductive traits of Pacific bluefin tuna in the Nansei Islands are influenced by environmental and maternal conditions.

Association between fatty acid signature and growth rate of larval Pacific bluefin tuna in two major spawning grounds

Fatty acid composition and total fatty acids of field-caught Pacific bluefin tuna (PBF) Thunnus orientalis larvae were investigated to identify relationships between spawning ground, physiological condition, and growth rate. Multivariate statistical analyses revealed that both growth rate and environmental conditions at spawning grounds were substantially associated with variations in fatty acid compositions. Fast-growing larvae typically contained more α-linolenic acid and 22:5n-3, which are important as metabolic precursors of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Larval PBF fatty acid compositions differed by spawning ground; larvae caught around the Nansei Islands contained more 15:0, 17:0, 19:0, and 22:5n-6, and less EPA and arachidonic acid (ARA) than those from the Sea of Japan. Differences in larval odd-numbered fatty acid compositions might indicate different degrees of dependence on microbial loop energy supply between spawning grounds. Environments subject to sudden changes, such as those in water temperature and prey density in the Sea of Japan, might cause variability in fatty acid profiles, including extremely low %DHA. We suggest that continuous food intake and subsequent fatty acid catabolism for energy generation would be needed to facilitate fast growth.

The Japanese Seabass Lateolabrax japonicus (Lateolabracidae) from Tanega-shima island, Osumi Islands, Kagoshima Prefecture, Japan: first specimen-based record from the Nansei Islands

The Japanese Seabass <i>Lateolabrax japonicus</i> (Lateolabracidae) from Tanega-shima island, Osumi Islands, Kagoshima Prefecture, Japan: first specimen-based record from the Nansei Islands