Zoological Science

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ISSN / EISSN : 0289-0003 / 2212-3830
Current Publisher: Zoological Society of Japan (10.2108)
Total articles ≅ 3,416
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, Reina Senokuchi, Hidetaka Nomaki, Tomo Kitahashi, Daisuke Uyeno, Motohiro Shimanaga
Zoological Science, Volume 38; doi:10.2108/zs200153

Abstract:
Copepods in the family Dirivultidae are one of the most successful meiofauna in deep-sea hydrothermal vent fields and are abundant near venting fluid. Although vents are spatially limited ocean habitats, they are distributed widely in the Atlantic, Pacific, and Indian Oceans. However, knowledge of dirivultid biogeography and phylogeography remains limited, especially in the northwestern Pacific. Here, we obtained partial mitochondrial COI gene sequences of three dirivultids from the northwestern Pacific—Stygiopontius senokuchiae and an unidentified Chasmatopontius species from vent fields in the Izu–Bonin Arc and Stygiopontius senckenbergi associated with the squat lobster Shinkaia crosnieri in the Okinawa Trough—and analyzed them in comparison with existing data. The among-species sequence diversity exceeded 80 out of 560 bp (14% or 0.166 in Kimura 2-parameter distance), whereas the within-species diversity was less than 10 bp (2% or 0.018 in Kimura 2-parameter distance), with no genetic saturation. Each species formed a monophyletic clade and the genetic region targeted is deemed reliable for identifying species and populations for these copepods. Among the three genera targeted, only Chasmatopontius formed a monophyletic cluster, while Aphotopontius and Stygiopontius did not. Species delimitation analyses suggested the existence of cryptic species in Chasmatopontius. Subdivision among local populations was observed in Aphotopontius, but not in Stygiopontius in the same distribution, implying potential differences in dispersal ability among different genera of dirivultids. Further sampling is required, to fill the spatial gaps to elucidate the biogeography and evolution of dirivultids in the global deep ocean.
Keiichi Kakui, Yasunori Kano
Zoological Science, Volume 38; doi:10.2108/zs200167

Michio Hori, Jyun-Ichi Kitamura, Masayoshi Maehata, Satoshi Takahashi,
Zoological Science, Volume 38; doi:10.2108/zs200155

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Siyu Zhang, Yongshi Shi, Zicheng Zeng, Fan Xin, Li Deng, Antai Wang
Zoological Science, Volume 38; doi:10.2108/zs200121

Haruka Yamaguchi, Masato Hirose, Mayuko Nakamura, Sumio Udagawa, Kohei Oguchi, Junpei Shinji, Hisanori Kohtsuka, Toru Miura
Published: 25 February 2021
Zoological Science, Volume 38; doi:10.2108/zs200143

Takanori Nishino, Takahiro Hosokawa, Xian-Ying Meng, Ryuichi Koga, Minoru Moriyama,
Published: 25 February 2021
Zoological Science, Volume 38; doi:10.2108/zs200163

Abstract:
Many plant-sucking stinkbugs possess a specialized symbiotic organ with numerous crypts in a posterior region of the midgut. In stinkbugs of the superfamily Pentatomoidea, specific γ-proteobacteria are hosted in the crypt cavities, which are vertically transmitted through host generations and essential for normal growth and survival of the host insects. Here we report the discovery of an exceptional gut symbiotic association in the saw-toothed stinkbug, Megymenum gracilicorne (Hemiptera: Pentatomoidea: Dinidoridae), in which specific γ-proteobacterial symbionts are not transmitted vertically but acquired environmentally. Histological inspection identified a very thin and long midgut symbiotic organ with two rows of tiny crypts whose cavities harbor rod-shaped bacterial cells. Molecular phylogenetic analyses of bacterial 16S rRNA gene sequences from the symbiotic organs of field-collected insects revealed that (i) M. gracilicorne is stably associated with Pantoea-allied γ-proteobacteria within the midgut crypts, (ii) the symbiotic bacteria exhibit a considerable level of diversity across host individuals and populations, (iii) the major symbiotic bacteria represent an environmental bacterial lineage that was reported to be capable of symbiosis with the stinkbug Plautia stali, and (iv) the minor symbiotic bacteria also represent several bacterial lineages that were reported as cultivable symbionts of P. stali and other stinkbugs. The symbiotic bacteria were shown to be generally cultivable. Microbial inspection of ovipositing adult females and their eggs and nymphs uncovered the absence of stable vertical transmission of the symbiotic bacteria. Rearing experiments showed that symbiont-supplemented newborn nymphs exhibit improved survival, suggesting the beneficial nature of the symbiotic association.
Kenichi Kobayashi, Kazutoshi Yamamoto, Sakae Kikuyama, Yukinobu Tanaami, Takeo Machida, Tetsuya Kobayashi
Published: 25 February 2021
Zoological Science, Volume 38; doi:10.2108/zs200063

Taku Okamoto, Seita Tsukamoto, Masaki Kuro-O, Takeo Kuriyama, Masaharu Motokawa
Published: 25 February 2021
Zoological Science, Volume 38, pp 148-161; doi:10.2108/zs200051

Abstract:
We investigated the geographic diversification of Plestiodon finitimus, which occurs in the central to northern parts of the Japanese Islands, based on a time-calibrated mitochondrial DNA (mtDNA) phylogeny and external morphological characters. The mtDNA phylogeny suggests that P. finitimus diverged from its sister species Plestiodon japonicus in western Japan 2.82-4.63 million years ago (MYA), which can be explained by geographic isolation due to the spread of sedimentary basins in the Pliocene. The primary intraspecific divergence was that between P. finitimus lineages in central and northeastern Japan 1.58-2.76 MYA, which could have been caused by the upliftings of major mountain ranges. In the northeastern lineage, mtDNA and morphological characters suggest a geographic differentiation between sub-lineages of the northwestern Tohoku District (α) and other areas (β). Although the sub-lineage β occurs in a disjunct geographic range, consisting of Hokkaido and the central to south of Tohoku, these areas are bridged by populations with intermediate characteristics along the Pacific side of northern Tohoku. Overall, the geographic variation in P. finitimus in northern Japan can be explained by an initial allopatric divergence of the sub-lineages α and β at 0.71-1.39 MYA, a recent northward expansion of the sub-lineage β, and subsequent secondary introgressive hybridization between the sub-lineages.
Kanae Igawa-Ueda, , Akihiro Tame, Katsushi Yamaguchi, Shuji Shigenobu, Yuki Hongo, Yoshihiro Takaki, Katsunori Fujikura, Tadashi Maruyama, Takao Yoshida
Published: 25 February 2021
Zoological Science, Volume 38, pp 140-147; doi:10.2108/zs200129

Abstract:
Symbiotic associations with beneficial microorganisms endow a variety of host animals with adaptability to the environment. Stable transmission of symbionts across host generations is a key event in the maintenance of symbiotic associations through evolutionary time. However, our understanding of the mechanisms of symbiont transmission remains fragmentary. The deep-sea clam Phreagena okutanii harbors chemoautotrophic intracellular symbiotic bacteria in gill epithelial cells, and depends on these symbionts for nutrition. In this study, we focused on the association of these maternally transmitted symbionts with ovarian germ cells in juvenile female clams. First, we established a sex identification method for small P. okutanii individuals, and morphologically classified female germ cells observed in the ovary. Then, we investigated the association of the endosymbiotic bacteria with germ cells. We found that the symbionts were localized on the outer surface of the cell membrane of primary oocytes and not within the cluster of oogonia. Based on our findings, we discuss the processes and mechanisms of symbiont vertical transmission in P. okutanii.
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