Soft Coral Sarcophyton (Cnidaria: Anthozoa: Octocorallia) Species Diversity and Chemotypes

Research on the soft coral genus Sarcophyton extends over a wide range of fields, including marine natural products and the isolation of a number of cembranoid diterpenes. However, it is still unknown how soft corals produce this diverse array of metabolites, and the relationship between soft coral diversity and cembranoid diterpene production is not clear. In order to understand this relationship, we examined Sarcophyton specimens from Okinawa, Japan, by utilizing three methods: morphological examination of sclerites, chemotype identification, and phylogenetic examination of both Sarcophyton (utilizing mitochondrial protein-coding genes MutS homolog: msh1) and their endosymbiotic Symbiodinium spp. (utilizing nuclear internal transcribed spacer of ribosomal DNA: ITS- rDNA). Chemotypes, molecular phylogenetic clades, and sclerites of Sarcophyton trocheliophorum specimens formed a clear and distinct group, but the relationships between chemotypes, molecular phylogenetic clade types and sclerites of the most common species, Sarcophyton glaucum, was not clear. S. glaucum was divided into four clades. A characteristic chemotype was observed within one phylogenetic clade of S. glaucum. Identities of symbiotic algae Symbiodinium spp. had no apparent relation to chemotypes of Sarcophyton spp. This study demonstrates that the complex results observed for S. glaucum are due to the incomplete and complex taxonomy of this species group. Our novel method of identification should help contribute to classification and taxonomic reassessment of this diverse soft coral genus.

关于肉质软珊瑚属（Sarcophyton）的研究涵盖海洋天然产物、多种西松烷型二萜（cemburanoid diterpenes）分离等多个研究领域。然而，目前学界仍未明确软珊瑚如何合成种类如此丰富的代谢产物，且软珊瑚多样性与西松烷型二萜合成之间的关联尚不清晰。为阐明二者间的内在联系，本研究针对日本冲绳海域采集的肉质软珊瑚属标本开展了系统分析，采用三种研究方法：对骨针（sclerites）进行形态学检查、化学型（chemotype）鉴定，以及分别基于线粒体蛋白编码基因MutS同源基因（msh1）对肉质软珊瑚属、基于核糖体DNA核内转录间隔区（ITS-rDNA）对其共生虫黄藻属（Symbiodinium spp.）开展系统发育分析。柱形肉质软珊瑚（Sarcophyton trocheliophorum）标本的化学型、分子系统发育分支与骨针构成了清晰独立的类群，但最为常见的灰肉质软珊瑚（Sarcophyton glaucum）的化学型、分子系统发育分支类型与骨针之间的关联仍不明确。灰肉质软珊瑚被划分为4个系统发育分支，其中一个系统发育分支的灰肉质软珊瑚呈现出特征性化学型。共生藻类虫黄藻属（Symbiodinium spp.）的种类与肉质软珊瑚属物种的化学型无明显关联。本研究表明，针对灰肉质软珊瑚所观察到的复杂实验结果，源于该物种类群不完善且复杂的分类学现状。本研究提出的新型鉴定方法，将有助于为这类多样性丰富的软珊瑚属开展分类学研究与分类学重新评估（taxonomic reassessment）提供有力支撑。