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The first record of egg masses in tunicates deposited by the snubnose sculpin, Orthonopias triacis, from the Northeastern Pacific: evidence for convergent evolution of an unusual reproductive strategy.

  • Awata, Satoshi1
  • Ito, Takeshi1, 2
  • Crow, Karen D2
  • Koya, Yasunori3
  • Munehara, Hiroyuki4
  • 1 Laboratory of Animal Sociology, Graduate School of Science, Osaka City University, Osaka, Japan. , (Japan)
  • 2 Department of Biology, San Francisco State University, San Francisco, California, USA.
  • 3 Department of Biology, Faculty of Education, Gifu University, Gifu, Japan. , (Japan)
  • 4 Usujiri Fisheries Station, Field Science Center for Northern Biosphere, Hokkaido University, Hakodate, Japan. , (Japan)
Published Article
Journal of fish biology
Publication Date
Oct 07, 2021
DOI: 10.1111/jfb.14920
PMID: 34622452


In this study, the authors report the first record of egg masses deposited in solitary tunicates by the snubnose sculpin, Orthonopias triacis, from the Northeastern Pacific. Four egg masses were discovered in the tunicate Ascidia ceratodes that were genetically determined to be O. triacis. Female O. triacis had long ovipositors that allow deposition of their eggs inside the atrium of the tunicates. A comparison of host-tunicate size with ovipositor length of sculpins from the Northwestern Pacific, including the genera Furcina and Pseudoblennius, revealed that O. triacis had shorter ovipositors and spawned in the atrium of smaller species of tunicates. Ancestral state reconstruction of egg deposition in solitary tunicates using 1.86Mbp RNAseq data of 20 sculpin species from Northeastern and Northwestern Pacific revealed that this unusual spawning behaviour may have evolved convergently in different species occurring in the Northeastern vs. the Northwestern Pacific. © 2021 Fisheries Society of the British Isles.

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