Yokosuka City Museum

Yokosuka, Japan

Yokosuka City Museum

Yokosuka, Japan
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Sunobe T.,Tokyo University of Marine Science and Technology | Sado T.,Natural History Museum and Institute | Hagiwara K.,Yokosuka City Museum | Manabe H.,Kagoshima University | And 8 more authors.
Die Naturwissenschaften | Year: 2017

Size-advantage and low-density models have been used to explain how mating systems favor hermaphroditism or gonochorism. However, these models do not indicate historical transitions in sexuality. Here, we investigate the evolution of bidirectional sex change and gonochorism by phylogenetic analysis using the mitochondrial gene of the gobiids Trimma (31 species), Priolepis (eight species), and Trimmatom (two species). Trimma and Priolepis formed a clade within the sister group Trimmatom. Gonadal histology and rearing experiments revealed that Trimma marinae, Trimma nasa, and Trimmatom spp. were gonochoric, whereas all other Trimma and Priolepis spp. were bidirectional sex changers or inferred ones. A maximum-likelihood reconstruction analysis demonstrated that the common ancestor of the three genera was gonochoristic. Bidirectional sex change probably evolved from gonochorism in a common ancestor of Trimma and Priolepis. As the gonads of bidirectional sex changers simultaneously contain mature ovarian and immature testicular components or vice versa, individuals are always potentially capable of functioning as females or males, respectively. Monogamy under low-density conditions may have been the ecological condition for the evolution of bidirectional sex change in a common ancestor. As T. marinae and T. nasa are a monophyletic group, gonochorism should have evolved from bidirectional sex change in a common ancestor.

Matsukawa M.,Tokyo Gakugei University | Shibata K.,Yokosuka City Museum | Sato K.,Tokyo Gakugei University | Xing X.,CAS Institute of Vertebrate Paleontology and Paleoanthropology | Lockley M.G.,University of Colorado at Denver
Biological Journal of the Linnean Society | Year: 2014

The ancient terrestrial ecosystems of the Lower Cretaceous Yixian Formation and the Jiufotang Formation, consecutive components of the Jehol Group in Northeast China were reconstructed using an energy-flow and food-web model. This model can be used to quantitatively estimate population densities for ancient terrestrial vertebrates based on food webs, net primary productivity, and three categories of energy-transfer efficiency. The results indicate that densities reached 866 individuals km-2 and 4122 individuals km-2 in two ecosystems, respectively. The main component of the vertebrate fauna of the Yixian Formation consisted of large herbivorous dinosaurs, while much smaller avians dominated the Jiufotang fauna. The model also indicates a temporal transition in the dinosaur fauna from the Yixian fauna to the Jiufotang fauna in which theropods decreased and ceratopsids became more abundant. We then compared these estimates of biodiversity with the Early Cretaceous Choyr fauna of Mongolia, and Tetori fauna of Japan using Simpson's diversity indices. Those indices, based on biomass, indicate that the biodiversities of the Jehol fauna lay between those of the Choyr and Tetori faunas. This range in biodiversity seems attributable to fundamental differences in vegetation and the environment. © 2014 The Linnean Society of London.

Matsukawa M.,Tokyo Gakugei University | Shibata K.,Yokosuka City Museum
Ichnos:an International Journal of Plant and Animal | Year: 2015

One hundred and seventy three Cenozoic vertebrate track sites from Miocene to 1600 A.D have been reported in Japan. Three ichnofaunas can be recognized: a perissodactyl and artiodactyl ichnofauna in the Miocene, an artiodactyl and proboscidean ichnofauna in the Plio-Pleistocene, and human ichnofauna from about 900–800 B.C. to about 1400–1600 A.D. Track data indicate that a predominance of large vertebrates in fluvio-lacustrine environment in lowland changed from perissodactyls to proboscidean through Miocene to Plio-Pleistocene, and ancient people then occupied lowlands instead of large animals. Pes length of proboscidean tracks revealed temporal variation, and the relationship between proboscidean body sizes and tracks was observed. The Cenozoic Japanese proboscidean trackways can be distinguished on the basis of trackway width, as narrow- and wide-gauge, but the difference between of those narrow- and wide-gauge trackways probably indicates generic level differences. The Cenozoic Japanese bird tracks can be identified as four types: ?crane (Family Gruidae?), ?heron (Family Ardeidae?), ?stork (Family Ciconiidae?), and ?shorebird tracks. © 2015, Copyright © Taylor & Francis Group, LLC.

Shibata K.,Yokosuka City Museum | Ito M.,Chiba University | Nemoto N.,Kumamachi Elementary School | O'Hara S.,Teikyo Heisei University
Island Arc | Year: 2010

This paper examined sequence-stratigraphic features of a gravelly fluvial system of the Iwaki Formation, which developed in a forearc-basin setting in Northeast Japan during the Eocene through Oligocene. On the basis of three-dimensional architectural element analysis, we discriminated three major cycles of channel complexes, which contain ten component channel deposits in total in the fluvial succession. Component channel deposits in the uppermost part of each cycle are sandier and associated with overbank muddy deposits and coal beds as compared with those in the lower part of the cycle. Mean clast-size also decreases upsection in the entire gravelly fluvial deposits. The fluvial succession is interpreted to have been deposited in response to an overall rise in relative sea level that was superimposed by three short-term relative sea-level rises on the basis of vertical stacking patterns and component lithofacies features of channel deposits, and of correlation of the fluvial succession with an age-equivalent marine succession in an area about 50 km offshore. However, geometry and stacking patterns of the channel complexes do not exhibit any distinct temporal variation and amalgamated channel and bar deposits are dominant throughout the transgressive fluvial succession. On the other hand, an overall fining-upward pattern of the entire Iwaki Formation fluvial deposits in association with three component fining-upward patterns is distinct, and is interpreted to be consistent with the tenet of the standard fluvial sequence-stratigraphic models. This indicates that the present example represents one type of variation in the standard fluvial sequence-stratigraphic models, possibly reflecting the forearc-basin setting, which is generally represented by higher valley slope, higher shedding of coarse-grained sediments, and shorter longitudinal profiles to the coastal area as compared with a passive-continental-margin setting. © 2010 Blackwell Publishing Asia Pty Ltd.

Kato S.,University of Tokyo | Kato S.,University of Tsukuba | Sakayama H.,Kobe University | Morishima H.,Funabashi Kowagama High School | And 7 more authors.
Cytologia | Year: 2010

Chara altaica A. Braun (Charales, Charophyceae), a monoecious species of the section Desvauxia, was newly found in Japan and studied by light and scanning electron microscopy (SEM) as well as gene sequence analysis of the large subunit of Rubisco (rbcL). Our first SEM observations of C. altaica oospores revealed that small papillae were scattered on the fossa wall, an SEM oospore wall ornamentation that is essentially different from that of the monoecious species C. (sect. Desvauxia) evoluta T. F. Allen. Phylogenetic analysis demonstrated that C. altaica and 10 European samples of the dioecious species C. (sect. Desvauxia) canescens Desvaux & LoiseleurDeslongchamps formed a robust monophyletic group, in which the rbcL gene sequence from C. altaica is identical to those from 4 parthenogenetic samples, but different from 6 other bisexual and parthenogenetic samples of C. canescens. © 2010 The Japan Mendel Society.

Shibata K.,Yokosuka City Museum | Ito M.,Chiba University
Geomorphology | Year: 2014

The relationships between the bankfull channel width and the mean, bankfull, and maximum discharges of Japanese rivers were examined using the hydrological and geomorphological data from 368 sites. The relationships between the bankfull channel width and the mean and bankfull discharges do not show any distinct regional variations. In contrast, the relationship between the maximum discharge and the bankfull channel width shows regional variations, and the lower and higher maximum discharges relative to bankfull channel widths are documented in the fluvial systems in Hokkaido and Southwest Japan, respectively. These variations are interpreted to reflect regional variations in precipitation intensity during the rainy season, and the magnitude and frequency of typhoon-related flooding. The relationship between the bankfull channel width and the bankfull discharge can be described by an empirical equation similar to that described from modern fluvial systems on the European and American continents. Consequently, this empirical equation may have wider applicability for the estimation of hydrological features of modern and ancient fluvial systems, not only in active margin settings influenced by mid-latitude temperate climates, but also in passive continental margins and continental interior basins. © 2014 Elsevier B.V.

Jintsu Y.,University of Tsukuba | Uchifune T.,Yokosuka City Museum | Machida R.,University of Tsukuba
Arthropod Systematics and Phylogeny | Year: 2010

Structural features of the eggs of a basal phasmatodean, Timema monikensis Vickery & Sandoval, 1998 (Timematidae) were examined. The eggs of this species are soft and deposited coated with soil and/or other extraneous particles. The chorion, which is transparent and weakly sclerotized, is composed of an endochorion and an exochorion. The non-inclined operculum is located at the anterior pole of the egg. The chorion in the marginal region of the operculum is thinned to form an opercular collar together with the chorion of the egg body. An inverted triangular micropylar plate is on the ventral side of the egg attached to the opercular collar. The micropylar plate is without external differentiations but is specialized inside the chorion. A single micropyle, with a simple funnel-shaped chorionic opening, occurs on either side of the micropylar plate. The posterior mound, located at the posterior pole, is a thickened chorion rich in fi ne vertical striations, and the serosal cuticle beneath is thickened and highly specialized. The eggs of Timematidae were characterized and compared with those of Euphasmatodea and Embioptera. A phylogenetic discussion is presented, strongly supporting the assemblage of Timematodea, Euphasmatodea and Embioptera as monophyletic. © Museum für Tierkunde Dresden.

Sunobe T.,Tokyo University of Marine Science and Technology | Hagiwara K.,Yokosuka City Museum
Journal of Applied Ichthyology | Year: 2013

Summary: Intersexual gonads were detected in three clupeiform species, Sardinops melanostictus, Sardinella zunasi and Englaulis japonicus, collected in Tokyo Bay off Yokohama City, Japan, of which appearance rates were 18.2, 34.6 and 33.9 %, respectively. While spermatogenesis proceeded normally in these individuals, previtellogenic stage oocytes were detected outside of the testes in the hermaphrodites, appearing as a single cell or small clusters. The results suggest that these species are non-functional hermaphrodites. As intersexual gonads have been reported in other clupeiform species collected before significant pollution and/or at sites far from urban influences, such non-functional hermaphrodites may be common occurrence in the order. However, high rates of hermaphrodite appearance also suggest the possibility that the development of these oocytes were induced by environmental estrogens. © 2012 Blackwell Verlag GmbH.

Schoville S.D.,University of Tsukuba | Uchifune T.,Yokosuka City Museum | Machida R.,University of Tsukuba
Molecular Phylogenetics and Evolution | Year: 2013

Fragment islands, viewed from the paradigm of island biogeographic theory, depend on continual immigration from continental sources to maintain levels of species diversity, or otherwise undergo a period of relaxation where species diversity declines to a lower equilibrium. Japan is a recently derived fragment island with a rich endemic flora and fauna. These endemic species have been described as paleoendemics, and conversely as recently derived Pleistocene colonists. Geological events in the Miocene period, notably the fragmentation and collision of islands, and the subsequent uplift of mountains in central Japan, provided opportunities for genetic isolation. More recently, cyclical climatic change during the Pliocene and Pleistocene periods led to intermittent land bridge connections to continental Asia. Here we investigate the pattern and timing of diversification in a diverse endemic lineage in order to test whether ongoing migration has sustained species diversity, whether there is evidence of relaxation, and how geological and climatic events are associated with lineage diversification. Using multi-locus genetic data, we test these hypotheses in a poorly dispersing, cold-adapted terrestrial insect lineage (Grylloblattodea: Grylloblattidae) sampled from Japan, Korea, and Russia. In phylogenetic analyses of concatenated data and a species tree approach, we find evidence of three deeply divergent lineages of rock-crawlers in Japan consistent with the pattern of island fragmentation from continental Asia. Tests of lineage diversification rates suggest that relaxation has not occurred and instead endemism has increased in the Japanese Grylloblattidae following mountain-building events in the Miocene. Although the importance of climate change in generating species diversity is a commonly held paradigm in Japanese biogeography, our analyses, including analyses of demographic change and phylogeographic range shifts in putative species, suggests that Pleistocene climatic change has had a limited effect on the diversification of rock-crawlers. © 2012 Elsevier Inc.

Omori Y.,Yokosuka City Museum
Journal of Japanese Botany | Year: 2010

Chloranthus japonicus Siebold (Chloranthaceae) with green foliate projections instead of white filamentous stamens was found in Miura Peninsula, Kanagawa Pref., central Japan. These foliate projections, foliose stamens, had three lobes, which were narrowly ellipse in shape, 4-5 mm long and 1-2 mm wide. They looked like trilobate bracts enclosing gynoecia. About three months after anthesis, these stamens fell off from the inflorescence axis with sterile gynoecia. The foliose stamen is considered to be an example of phyllody.

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