Izu Islands Research Articles

Diurnal variations of different types of cloud over the Baiu–Meiyu frontal zone using retrieved cloud properties: Implication for the rainfall process

The diurnal variations of clouds and their relationships with the rainfall associated with the Baiu–Meiyu front in Eastern China and over the ocean in the south of Japan in June 2016–2019 are investigated with the cloud product retrieved from the infrared brightness temperature of the Himawari-8 satellite. Clouds are classified into three types: low (<3 km), middle (3–10 km), and high clouds (>10 km); high clouds are further divided into thin (0.1–1), moderately-thick (1–6), and thick (>6) clouds based on their cloud optical thickness. Prominent diurnal variations of high clouds were observed to have an evening-to-midnight maximum in Eastern China, an early-afternoon-to-evening maximum around the Ryukyu Islands, and an evening maximum around the Izu Islands. In Eastern China and around the Ryukyu Islands, there was a clear diurnal amplitude maximum of the thick cloud and the moderately-thick cloud. And the diurnal peak time of the thick cloud was 1–2 h later than the peak time of rainfall. Around the Izu Islands, a diurnal amplitude maximum of moderately-thick cloud was found. While for the thick cloud, its peak occurrence was found to be 4–6 h later than that of the rainfall. Our results suggest that the convective activity is highly related to the primary mode of the diurnal variation of rainfall and cloud in Eastern China and around the Ryukyu Islands. Meanwhile, it is less related to the diurnal variation of rainfall and cloud around the Izu Islands.

Specimen-based records of Kyphosus ocyurus (Perciformes: Kyphosidae) from the Miura Peninsula and Hachijo-jima Island, Izu Islands, Japan

Specimen-based records of Kyphosus ocyurus (Perciformes: Kyphosidae) from the Miura Peninsula and Hachijo-jima Island, Izu Islands, Japan

伊豆諸島北部，利島における更新世末期の流紋岩質テフラの層序

伊豆諸島北部，利島における更新世末期の流紋岩質テフラの層序

伊豆大島から得られた北半球初記録のゴンベ科魚類Cirrhitichthys guichenotiキリンゴンベ（新称）の記載と日本における生息状況

伊豆大島から得られた北半球初記録のゴンベ科魚類Cirrhitichthys guichenotiキリンゴンベ（新称）の記載と日本における生息状況

Taxonomic placement of &lt;i&gt;Phytophthora&lt;/i&gt; species isolated from &lt;i&gt;Angelica keiskei&lt;/i&gt; in the Izu Islands during the cool season

Taxonomic placement of &lt;i&gt;Phytophthora&lt;/i&gt; species isolated from &lt;i&gt;Angelica keiskei&lt;/i&gt; in the Izu Islands during the cool season

A new species of Nogunius Jaoszyski in Japan (Coleoptera: Staphylinidae: Scydmaeninae).

The genus Nogunius Jaoszyski was proposed to accommodate four species distributed exclusively in Japan: N. sokani Jaoszyski (Okinawa Island), N. aogashimanus Jaoszyski (Aogashima, Izu Islands), N. kerri Jaoszyski (Ishigaki Island), and N. fukuuzanus Jaoszyski (Okinawa Island). A female of an undescribed species collected in mainland Japan, on Shikoku, was also recorded. In the present paper we provide evidence that this interesting and apparently very rare genus occurs also on Kyushu. Nogunius sagaensis sp. n. is described, based on a single male collected in Saga Prefecture, NW Kyushu. Diagnostic characters of all nominal species are compared, and a distribution of Nogunius is summarized.

First record of Neoporphyra haitanensis (T.J.Chang &amp; B.F.Zheng) J.Brodie &amp; L.‐E.Yang (Bangiales, Rhodophyta) from Shikinejima Island and Hachijojima Island of the Izu Islands, southern central Japan

SUMMARYWe conducted a morphological observation and molecular phylogenetic analyses on bladed Bangiales collected from natural populations on Shikinejima Island and Hachijojima Island of the Izu Islands, southern central Japan. The morphological features of the gametophytic blades such as the blade shape, blade margin and reproductive cell divisions were extremely similar to those parameters of Neoporphyra haitanensis, a species cultivated in southern China, and Neoporphyra dentata. However, the blades collected from the two islands were thicker than the blades of N. dentata; this feature was the same as that of N. haitanensis. The chloroplast RUBISCO spacer sequences of present samples were identical to the sequences of N. haitanensis from China. Moreover, phylogenetic positions of three conchocelis strains isolated from the blades on the two islands were examined based on concatenated sequences of the chloroplast rbcL gene and nuclear 18S rRNA. The results showed that the strains were resolved in a clade including N. haitanensis; however, the strains were separated from N. haitanensis in China. Therefore, the bladed Bangiales from the two islands were identified as N. haitanensis. The present study is the first record of N. haitanensis in natural populations in Japan.

Tephrostratigraphy and Eruption History of Kozushima Volcano, Izu Islands, Central Japan during the Last 30,000 Years

Kozushima is a volcanic island, located in the northern part of the Izu Islands, approximately 170 km SSW of central Tokyo. The volcanism of Kozushima Volcano started at 80-60 ka and formed monogenetic volcanoes. The latest eruption occurred in AD 838, and was associated with the formation of the lava dome and pyroclastic cone of Tenjo-san. In order to contribute to the long-term forecasting of volcanic eruptions on the Izu Islands off Tokyo, the tephrostratigraphy and eruption history of Kozushima Volcano during the last 30,000 years is reconstructed. According to the geological surveys, the widespread Kikai-Akahoya (K-Ah; 7.3 cal ka) and Aira-Tanzawa (AT; 30.0 cal ka) tephras from southern Kyushu, and Niijima-Mukaiyama (Nj-My; AD 886), Niijima-Shikinejima (Nj-Sk; 8 cal ka) and Niijima-Miyatsukayama (Nj-Mt; 12.8 cal ka) tephras from the Niijima Volcano 20 km NNE of Kozushima are recognized. Tephras that also erupted from Kozushima Volcano are Kozushima-Tenjosan (Kz-Tj; AD 838), Kozushima-Ananoyama (Kz-An; 7-9 c), Kozushima-Chichibuyama-A′ (Kz-CbA′; 14-12.8 cal ka), Kozushima-Chichibuyama-A (Kz-CbA; 30-22 cal ka), and Kozushima-Chichibuyama-B (Kz-CbB; ca. 30 ka). Kz-An is formed by the activity of the northern volcanic chains (Kobe-yama–Anano-yama–Hanatate) just before the Tenjo-san eruption. Kz-CbA′ is distributed in southern Kozushima. Source vent and distribution of Kz-CbA′ have not yet been identified. The eruption history of Kozushima volcano over the last 30,000 years is as follows. At ca. 30 ka, Kz-CbB erupted in the central Kozushima, and the Nachi-san dome and Takodo-yama dome formed. At 30-22 ka, the Kz-CbA eruption in the southern Kozushima and the formation of the southern volcanic chain occurred. After the eruption of Kz-CbA′, the formation of the northern volcanic chain was followed by the eruption of Tenjo-san volcano. In addition, the eruption rate of Kozushima volcano is estimated during the last 30,000 years to be approximately 0.06 km3/1000 y in DRE.

Development of microsatellite markers for Meliosma arnottiana (Sabiaceae) disjunctively distributed in the Japanese archipelago

ABSTRACT Sixteen polymorphic nuclear microsatellite markers were developed for Meliosma arnottiana (Wright) Walp. (Sabiaceae), a deciduous or half-evergreen tree. In Japan, the species is disjunctively distributed in the Izu Islands and the southern part of the Japanese archipelago, and the Izu population (var. hachijoensis) is regarded as a threatened species. Variations in the 16 markers were compared between the two populations on the Izu and Ryukyu Islands. The mean number of alleles was 3.00 and 5.31, and the mean expected heterozygosity was 0.233 and 0.513, respectively, on the Izu and Ryukyu Islands, and the genetic differentiation between the two populations was statistically significant. Of the 16 primer sets, five were amplified in all three congeneric species M. myriantha, M. rigida and M. tenuis, and eight or nine were amplified in each species. These newly developed microsatellite markers will be used to evaluate genetic diversity and genetic differentiation in M. arnottiana populations and are potentially useful for population genetic studies on congeneric species.

Evolutionary effects of geographic and climatic isolation between Rhododendron tsusiophyllum populations on the Izu Islands and mainland Honshu of Japan.

Geographic and environmental isolations of islands and the mainland offer excellent opportunity to investigate colonization and survival dynamics of island populations. We inferred and compared evolutionary processes and the demographic history of Rhododendron tsusiophyllum, in the Izu Islands and the much larger island Honshu, treated here as the mainland, using thousands of nuclear SNPs obtained by ddRAD-seq from eight populations of R. tsusiophyllum and three populations of R. tschonoskii as an outgroup. Phylogenetic relationships and their habitats suggest that R. tsusiophyllum had evolved and migrated from cold north to warm south regions. We detected clear genetic divergence among populations in three regions of Honshu and the Izu Islands, suggesting restricted migration between them due to isolated habitats on mountains even in the mainland. The three regions have different changes in effective population size, especially, genetic diversity and population size of the Izu Islands are small compared to the others. Further, habitats of populations in the Izu Islands are warmer than those in Honshu, suggesting that they have undergone adaptive evolution. Our study provides evidences of montane rather than insular isolation on genetic divergence, survival of populations and significance of adaptive evolution for island populations with small population size and low genetic diversity, despite close proximity to mainland populations.

Refugia during the last glacial period and the origin of the disjunct distribution of an insular plant

AbstractAimAlthough many phylogeographic studies have focused on continental refugia, the roles of islands as refugia have long been overlooked. In this study, we conducted phylogeographic studies of a plant with insular distribution, Microtropis japonica, to elucidate the potential roles of islands as refugia during recent glacial periods. Specifically, we test the hypothesis that two remote groups of Japanese islands (the Izu and Ryukyu Islands) were refugia for M japonica.LocationThe Izu and Ryukyu Islands of Japan and their adjacent areas including the Japanese mainland and Taiwan.TaxonMicrotropis japonica (Celastraceae).MethodsA total of 363 individuals were sampled from 44 populations of M japonica. To elucidate population genetic differentiation and demographic change in M japonica, we performed molecular variance and mismatch distribution analyses based on chloroplast DNA (cpDNA) sequence variations and Bayesian clustering and gene flow estimates based on nuclear single‐nucleotide polymorphism (SNP) data. In addition, to examine distribution changes, ecological niche modelling using the maximum entropy method was used to determine suitable habitats existing currently or during the last glacial maximum, using occurrence data and six bioclimatic variables.ResultsBoth cpDNA and nuclear SNP data showed genetic differentiation between two disjunct regions. However, cpDNA data indicated genetic differentiation within the Ryukyu Islands but not within the Izu Islands, while nuclear SNP data indicated genetic differentiation within both island groups. Ecological niche modelling showed that both the Izu and Ryukyu archipelagos had contained some islands with a climate compatible with modern M japonica climate envelopes despite climate oscillations.Main conclusionsIslands within both the Izu and Ryukyu archipelagos may have supported M japonica populations throughout historical climate oscillations. The current disjunct distribution of M japonica strongly reflects its refugial locations during the last glacial period and the subsequent range expansion. Islands were important refuges, contributing to the modern disjunct distribution of M japonica.

Detection of Target and Suppression of Sea and Weather Clutter in Stormy Weather by Weibull/CFAR

AbstractIn stormy weather due to typhoon approaching the Izu Islands, I have observed sea and weather clutter containing a target (ship) using an S‐band radar with a frequency of 3.05 GHz, a beamwidth of 1.8°, a pulsewidth of 0.5 μs, and a pulse‐repetition frequency of 1600 Hz. To analyze such clutter amplitude statistics, I have used partial Q–Q plot, which is more rigorous fit of the distribution to the data than conventional Q–Q plot. It has been found that the sea and weather clutter amplitudes obey the Weibull distribution with the shape parameters of c = 6.23 for entire data and c = 5.83 to 8.78 for small data within the beamwidth of an antenna. I have applied Weibull/CFAR (constant false alarm rate) circuit configured by modifying cell‐averaging (CA) LOG/CFAR circuit to the observed data. It has been found that ship is detected, and sea and weather clutter is suppressed with improvement of 33.61 dB by Weibull/CFAR. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Identification of a new potyvirus isolated from Angelica keiskei

A potyvirus with the proposed name ashitaba mosaic virus was detected in ashitaba [Angelica keiskei (Miq.)] plants exhibiting mosaic and vein clearing in Japan. The host range of the virus includes species from three families, Apiaceae, Chenopodiaceae, and Solanaceae. The genome of the virus was determined to comprise 9,651 nucleotides, excluding the poly(A) tail. A phylogenetic analysis based on the polyprotein revealed the virus is closely related to carrot thin leaf virus and potyviruses isolated from Apiales and Apiaceae plant species. Sequence comparisons indicated the nucleotide and polyprotein amino acid identities between the isolated virus and related species are 53.4–60.5% and 49.7–58.7%, respectively. These results suggest this virus is a new species in the genus Potyvirus. Furthermore, the results of a field survey suggest the virus may be widespread on the Izu Islands, with isolates classified into two genotypes.

Iracundus signifer Jordan and Evermann, 1903 (Scorpaenidae) from northern Izu-oshima island, Izu Islands, Japan: first record from outside Iriomote-jima island in Japanese waters and the northernmost record for the species

<i>Iracundus signifer</i> Jordan and Evermann, 1903 (Scorpaenidae) from northern Izu-oshima island, Izu Islands, Japan: first record from outside Iriomote-jima island in Japanese waters and the northernmost record for the species

Simultaneous Multi-AUV Operation as Real Practice - High-efficiency and High-definition Bottom Survey in Izu Islands

Simultaneous Multi-AUV Operation as Real Practice - High-efficiency and High-definition Bottom Survey in Izu Islands

伊豆諸島南部地域の医療習俗:～八丈島・青ヶ島の巫俗を中心に～

伊豆諸島南部地域の医療習俗:～八丈島・青ヶ島の巫俗を中心に～

Motivations of citizen contributors for participating in an Izu Islands bird survey in which participants are given opportunities to communicate with managers

Motivations of citizen contributors for participating in an Izu Islands bird survey in which participants are given opportunities to communicate with managers

伊豆諸島，利島火山の新期活動の年代： 14 C年代値と地形判読を基に

伊豆諸島，利島火山の新期活動の年代： 14 C年代値と地形判読を基に

Field survey toward island ecosystem recovery after the extermination of goats on Hachijo-kojima Island ―Natural History Research Association of the Izu Islands―

Field survey toward island ecosystem recovery after the extermination of goats on Hachijo-kojima Island ―Natural History Research Association of the Izu Islands―

Active deformation of Sagami Bay triggered by approach of the Izu island arc

Sagami Bay in central Japan is known as the seismogenic and tsunamigenic zone of the 1703 and 1923 Kanto earthquakes that caused devastating damage in the Tokyo metropolitan area. However, the tsunamigenic structure within the frontal wedges of the subduction zone remains unresolved after the last disastrous events. In the present study, the detailed structural features of the shallowest structure of the Sagami Tectonic Line in Sagami Bay were revealed by seismic reflection, a deep-towed high-resolution sub-bottom profiler, and swath bathymetry data. Based on our data, the middle segments of the Sagami Tectonic Line, which is distributed along the southwestern rim of the Miura Knoll, are considered highly likely to be an active fault that has been a repeatedly active feature. The trough-fill sediments of the south Sagami Bay are currently thought to be actively deformed by the compressive stress accompanying northwestward subduction of the tip of Izu-Ogasawara (Bonin) Arc crust on the Philippine Sea plate.