Exploring the trends of adaptation and evolution of sclerites with regards to habitat depth in sea pens
Yuka Kushida,
Yukimitsu Imahara,
Hin Boo Wee,
Iria Fernandez-Silva,
Jane Fromont,
Oliver Gomez,
Nerida Wilson,
Taeko Kimura,
Shinji Tsuchida,
Yoshihiro Fujiwara,
Takuo Higashiji,
Hiroaki Nakano,
Hisanori Kohtsuka,
Akira Iguchi,
James Davis Reimer
Affiliations
Yuka Kushida
Faculty of Geo-Environmental Science, Rissho University, Kumagaya, Saitama, Japan
Yukimitsu Imahara
Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
Hin Boo Wee
Institut Perubahan Iklim, Universiti Kebangsaan Malaysia, Selangor Darul Ehsan, Malaysia
Iria Fernandez-Silva
Department of Biochemistry, Genetics and Immunology, Campus Universitario, University of Vigo, Vigo, Spain
Jane Fromont
Collections & Research, Western Australian Museum, Welshpool, Western Australia, Australia
Oliver Gomez
Collections & Research, Western Australian Museum, Welshpool, Western Australia, Australia
Nerida Wilson
Collections & Research, Western Australian Museum, Welshpool, Western Australia, Australia
Taeko Kimura
Department of Life Sciences, Graduate School of Bioresources, Mie University, Tsu, Mie, Japan
Shinji Tsuchida
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Kanagawa, Japan
Yoshihiro Fujiwara
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Kanagawa, Japan
Takuo Higashiji
Okinawa Churaumi Aquarium, Okinawa Churashima Foundation, Motobu, Okinawa, Japan
Hiroaki Nakano
Shimoda Marine Research Center, University of Tsukuba, Shimoda, Shizuoka, Japan
Hisanori Kohtsuka
Misaki Marine Biological Station, Graduate School of Science, University of Tokyo, Miura, Kanagawa, Japan
Akira Iguchi
Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
James Davis Reimer
Molecular Invertebrate Systematics and Ecology Laboratory, Graduate School of Engineering and Science, University of the Ryukyus, Nishihara, Okinawa, Japan
Octocorals possess sclerites, small elements comprised of calcium carbonate (CaCO3) that are important diagnostic characters in octocoral taxonomy. Among octocorals, sea pens comprise a unique order (Pennatulacea) that live in a wide range of depths. Habitat depth is considered to be important in the diversification of octocoral species, but a lack of information on sea pens has limited studies on their adaptation and evolution across depth. Here, we aimed to reveal trends of adaptation and evolution of sclerite shapes in sea pens with regards to habitat depth via phylogenetic analyses and ancestral reconstruction analyses. Colony form of sea pens is suggested to have undergone convergent evolution and the loss of axis has occurred independently across the evolution of sea pens. Divergences of sea pen taxa and of sclerite forms are suggested to depend on habitat depths. In addition, their sclerite forms may be related to evolutionary history of the sclerite and the surrounding chemical environment as well as water temperature. Three-flanged sclerites may possess the tolerance towards the environment of the deep sea, while plate sclerites are suggested to be adapted towards shallower waters, and have evolved independently multiple times. The common ancestor form of sea pens was predicted to be deep-sea and similar to family Pseudumbellulidae in form, possessing sclerites intermediate in form to those of alcyonaceans and modern sea pens such as spindles, rods with spines, and three-flanged sclerites with serrated edges sclerites, as well as having an axis and bilateral traits.
