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In the hydrozoan jellyfish Clytia hemisphaerica, MIH neuropeptides induce oocyte maturation and gamete release directly after light stimulus. This study characterizes Clytia sp. IZ-D, which releases gametes in the evening, demonstrating a 14-hour delay after light under a 24-hour cycle and a 20-hour interval under constant light, with competence acquisition shaping the synchronized timing. The proposed atypical circadian mechanism may buffer light-cycle instability and maintain reproductive isolation from related Clytia species.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":40,"@type":76,"position":81},"https://docshare.wps.com/document/research-report/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/a-light-entrained-clock-mechanism-in-a-hydrozoan-jellyfish-synchronizes-evening-gamete-release/444996/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/a-light-entrained-clock-mechanism-in-a-hydrozoan-jellyfish-synchronizes-evening-gamete-release/444996.png","ImageObject",300,407,{"name":92,"@type":93},"kopisore","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-10-02","2026-09-29",true,{"@type":102,"interactionType":103,"userInteractionCount":14},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"What triggers gamete release in Clytia jellyfish according to the text?","Question",{"text":112,"@type":113},"Gamete release is induced by maturation-inducing hormone (MIH) neuropeptides released from opsin-expressing cells in the gonad, directly upon light stimulus.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"How does Clytia sp. IZ-D synchronize evening gamete release under different light conditions?",{"text":117,"@type":113},"Under a 24-hour light cycle, it spawns 14 hours after the light stimulus; under constant light, it shows autonomous and synchronized spawning cycles with a 20-hour interval.",{"name":119,"@type":110,"acceptedAnswer":120},"What mechanism is proposed to explain the evening spawning timing in this species?",{"text":121,"@type":113},"The timing is proposed to be controlled by an atypical circadian mechanism based on progressive development of gamete competence to MIH and modulation of the opsin-controlled MIH signaling pathway.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},444996,1790921365,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":133,"doc_module":4,"category_id":39,"category_name":40,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":14,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":139,"language":140,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":141,"faqs":142,"seo_title":143,"seo_description":67,"update_tm":144,"read_time":145},962090880963,"https://ap-avatar.wpscdn.com/davatar_6f874abed73319feea01a86fa6f0fab8","OPEN ACCESS  \nCitation: Kitsui R, Takeda N, Houliston E, Deguchi R, Momose T (2026) A light-entrained clock mechanism in a hydrozoan jellyfish synchronizes evening gamete release. PLoS Biol 24(1): e3003502. [https://doi.org/10.1371/](https://doi.org/10.1371/)[ ](https://doi.org/10.1371/)[journal.pbio.3003502](journal.pbio.3003502)  \nAcademic Editor: Mariana Federica Wolfner, Cornell University, UNITED STATES OF AMERICA  \nReceived: June 13, 2025  \nAccepted: October 31, 2025  \nPublished: January 6, 2026  \nPeer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: [https://doi.org/10.1371/journal](https://doi.org/10.1371/journal). pbio.3003502  \nCopyright: © 2026 Kitsui et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution,  \nRESEARCH ARTICLE  \nA light-entrained clock mechanism in a hydrozoan jellyfish synchronizes evening gamete release  \nRuka Kitsui1, Noriyo Takeda2, Evelyn Houliston3, Ryusaku Deguchi1*, Tsuyoshi Momose3*  \n1 Department of Biology, Miyagi University of Education, Sendai, Miyagi, Japan, 2 Graduate School of Integrated Sciences for Life, Hiroshima University, Hiroshima, Japan, 3 Laboratoire de Biologie du Développement (LBDV), Sorbonne Université, CNRS, UMR7009, Villefranche-sur-Mer, France  \n* [deguchi@staff.miyakyo-u.ac.jp](deguchi@staff.miyakyo-u.ac.jp) (RD); [tsuyoshi.momose@imev-mer.fr](tsuyoshi.momose@imev-mer.fr) (TM)  \nAbstract  \nFor marine species that reproduce by external fertilization, spawning is precisely coordinated within a local population to maximize the chances of producing offspring. Gamete release is often synchronized with respect to the diel light changes at dawn and dusk. In the hydrozoan jellyfish Clytia hemisphaerica, spawning occurs when oocyte maturation and gamete release are induced by maturation-inducing hormone (MIH) neuropeptides released from opsin-expressing cells in the gonad, directly upon light stimulus. Here, we characterize the distinct spawning cycle of a previously undescribed species Clytia sp. IZ-D, identified on the Pacific coast of Japan, which releases gametes in the evening. Clytia sp. IZ-D jellyfish spawn 14 hours after alight stimulus under a 24-hour light cycle and exhibit autonomous and synchronized spawning cycles with a 20-hour interval under constant light. We find that the female spawning cycle reflects the oocyte growth and their acquisition of competence for maturation, such that each day a new batch of growing oocytes becomes responsive to MIH at a time that correlates with the timing of actual spawning. We propose that the synchronized evening spawning in this species is controlled by an atypical circadian timing mechanism based on the progressive development of gamete competence to MIH and modulation of the opsin-controlled MIH signaling pathway. This mechanism may provide resilience to light cycle instability due to local climate variation and ensure reproductive isolation from other Clytia species by shifting the gamete release timing.  \nIntroduction  \nMarine organisms rely on various environmental cues to synchronize sexual behavior and gamete release, thereby maximizing the chances of successful sexual reproduction. Precise synchronization of spawning timing often depends on daily changes in  \nPLOS Biology | [https://doi.org/10.1371/journal.pbio.3003502](https://doi.org/10.1371/journal.pbio.3003502) January 6, 2026 1 / 22  \nand reproduction in any medium, provided the original author and source are credited.  \nData availability statement: The datasets for sea surface temperature, sunrise/sunset time, spawning timing, numbers of released oocytes, delay from MIH addition to GVBD, IPBF or IIPBF (Figs 1–7 , S1 and S3) are available a","cbCaivgYMxbvkRgK","https://ap.wps.com/l/cbCaivgYMxbvkRgK","pdf",2300759,22,"English","# Abstract\n# Introduction\n## Environmental cues and spawning synchronization\n## Molecular basis of light-controlled maturation in hydrozoans","[{\"question\":\"What triggers gamete release in Clytia jellyfish according to the text?\",\"answer\":\"Gamete release is induced by maturation-inducing hormone (MIH) neuropeptides released from opsin-expressing cells in the gonad, directly upon light stimulus.\"},{\"question\":\"How does Clytia sp. IZ-D synchronize evening gamete release under different light conditions?\",\"answer\":\"Under a 24-hour light cycle, it spawns 14 hours after the light stimulus; under constant light, it shows autonomous and synchronized spawning cycles with a 20-hour interval.\"},{\"question\":\"What mechanism is proposed to explain the evening spawning timing in this species?\",\"answer\":\"The timing is proposed to be controlled by an atypical circadian mechanism based on progressive development of gamete competence to MIH and modulation of the opsin-controlled MIH signaling pathway.\"}]","A light-entrained clock mechanism in a hydrozoan jellyfish synchronizes evening gamete release | PDF",1790710000,55]