{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T21:56:44Z","timestamp":1791237404087,"version":"4.1.0"},"reference-count":48,"publisher":"Zoological Society of Japan","issue":"3","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Zoological Science"],"published-print":{"date-parts":[[2026,3,11]]},"abstract":"<jats:p>Two types of Cladonema pacificum (Cnidaria, Hydrozoa) can be distinguished based on whether their medusae spawn after a dark-light transition (\u201clight type\u201d) or a light-dark transition (\u201cdark type\u201d). To clarify how these two types are related, we characterized C. pacificum from different sites in the Tohoku region of Japan. Essentially, only dark-type medusae were captured in the Pacific Ocean side, whereas light- and dark-type medusae were found sympatrically at some sampling points in Mutsu Bay and in the Sea of Japan side. We observed that the spawning times of the sympatric light and dark types differed in the field, suggesting that the gametes of the two types rarely encounter each other. A comparison of the DNA sequences of mitochondrial COI and nuclear ITS1 of the analyzed individuals suggests that the two types belong to separate clades. In crossbreeding experiments, offspring of the light and dark types (F1 hybrids) developed into planula larvae and metamorphosed into polyps, which then produced medusae with normal morphology. The F1 hybrid medusae had characteristics that were intermediate between the two types in terms of their spawning in response to both dark-light and light-dark cues, but with less sensitivity than the parent medusae. When F1 hybrids were used as one or both parents, planula larvae failed to metamorphose into normal polyps. These results indicate that the light and dark types of C. pacificum exhibit both prezygotic and postzygotic isolation, accompanied by distinct DNA sequences; thus, they can be considered as undergoing speciation or as already distinct species.<\/jats:p>","DOI":"10.2108\/zs250033","type":"journal-article","created":{"date-parts":[[2026,3,12]],"date-time":"2026-03-12T04:34:58Z","timestamp":1773290098000},"page":"236-249","source":"Crossref","is-referenced-by-count":0,"title":["Light and Dark Types of Cladonema pacificum (Cnidaria, Hydrozoa): Reproductive Isolation between the Two Types Leading to Speciation"],"prefix":"10.2108","volume":"43","author":[{"given":"Noriyo","family":"Takeda","sequence":"first","affiliation":[{"name":"Graduate School of Integrated Sciences for Life, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Takahito","family":"Hoshi","sequence":"additional","affiliation":[{"name":"Laboratory of Chronobiology, Graduate School of Bioscience, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Kanagawa 226-8501, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Fumiya","family":"Satoh","sequence":"additional","affiliation":[{"name":"Department of Biology, Miyagi University of Education, Aramaki-aza-Aoba 149, Aoba-ku, Sendai, Miyagi 980-0845, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Keita","family":"Nishizumi","sequence":"additional","affiliation":[{"name":"Laboratory of Chronobiology, Graduate School of Bioscience, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Kanagawa 226-8501, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nahomi","family":"Hongo-Yamakawa","sequence":"additional","affiliation":[{"name":"Department of Biology, Miyagi University of Education, Aramaki-aza-Aoba 149, Aoba-ku, Sendai, Miyagi 980-0845, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Saki","family":"Ishimori","sequence":"additional","affiliation":[{"name":"Department of Biology, Miyagi University of Education, Aramaki-aza-Aoba 149, Aoba-ku, Sendai, Miyagi 980-0845, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Haruka","family":"Satoh-Sugawara","sequence":"additional","affiliation":[{"name":"Department of Biology, Miyagi University of Education, Aramaki-aza-Aoba 149, Aoba-ku, Sendai, Miyagi 980-0845, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hiroshi","family":"Namikawa","sequence":"additional","affiliation":[{"name":"Department of Zoology, National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba, Ibaraki 305-0005, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kazunori","family":"Tachibana","sequence":"additional","affiliation":[{"name":"Laboratory of Chronobiology, Graduate School of Bioscience, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Kanagawa 226-8501, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ryusaku","family":"Deguchi","sequence":"additional","affiliation":[{"name":"Department of Biology, Miyagi University of Education, Aramaki-aza-Aoba 149, Aoba-ku, Sendai, Miyagi 980-0845, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"848","reference":[{"key":"8","doi-asserted-by":"crossref","unstructured":"S Fujita, E Kuranaga, Y Nakajima,  \"PeerJ.\"  7, \"Cell proliferation controls body size growth, tentacle morphogenesis, and regeneration in hydrozoan jellyfish Cladonema pacificum.\" e7579 (2019)","DOI":"10.7717\/peerj.7579"},{"key":"33","doi-asserted-by":"crossref","unstructured":"P Schuchert,  \"Rev Suisse Zool.\"  113, \"The European athecate hydroids and their medusae (Hydrozoa, Cnidaria): Capitata Part 1.\" 325 (2006)","DOI":"10.5962\/bhl.part.80356"},{"key":"48","doi-asserted-by":"crossref","unstructured":"K Zhou, Y Gu, L Wang, et al.  \"Acta Oceanol Sin.\"  41, \"Discovery of Cladonema multiramosum sp. nov. 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cytoplasmic incompatibility in parasitoid wasps.\" 10694 (2019)","DOI":"10.1002\/ece3.5588"}],"container-title":["Zoological Science"],"original-title":[],"deposited":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T21:13:43Z","timestamp":1791234823000},"score":1,"resource":{"primary":{"URL":"https:\/\/bioone.org\/journals\/zoological-science\/volume-43\/issue-3\/zs250033\/Light-and-Dark-Types-of-Cladonema-pacificum-Cnidaria-Hydrozoa\/10.2108\/zs250033.full"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,3,11]]},"references-count":48,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2026,6,1]]}},"URL":"https:\/\/doi.org\/10.2108\/zs250033","relation":{},"ISSN":["0289-0003","2212-3830"],"issn-type":[{"value":"0289-0003","type":"print"},{"value":"2212-3830","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,3,11]]}}}