Abstract
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.
Highlights
Soft corals (Cnidaria: Anthozoa: Octocorallia) often equal or exceed the total coverage of scleractinian corals in coral reef ecosystems [1,2,3,4], and as dominant space-occupiers, important structural components of coral reef communities, and contributors to coral reef biomass [4,5], have been the subjects of biological studies since the nineteenth century.The subclass Octocorallia includes soft corals, gorgonians, and sea pens
In order to more fully understand the relationship between secondary metabolites and Sarcophyton species, in this study we examined specimens from Okinawa, Japan utilizing three methods; 1) novel morphological examination of sclerites, 2) chemotype identification, and 3) phylogenetic examination of both Sarcophyton and their endosymbiotic Symbiodinium spp. (ITS-rDNA sequences)
Of the 31 ‘‘clear’’ Sarcophyton sequences, 13 sequences were identified as being from Sarcophyton trocheliophorum, 16 from Sarcophyton glaucum, one from Sarcophyton elegans, with the remaining one sequence not assignable to any previously reported species group
Summary
The subclass Octocorallia includes soft corals, gorgonians, and sea pens. Most soft corals belong to the order Alcyonacea, which is comprised of the families Xeniidae, Nephtheidae, and Alcyoniidae. The family Alcyoniidae contains the genera Sinularia, Lobophytum and Sarcophyton, and members of this group are among the dominant benthic organisms in the coral reefs in Okinawa and other Pacific Ocean areas [1,2,4,6]. Sarcophyton species are very hardy and are dominant in many coral reef areas. Sarcophyton species are characterized by a distinct sterile stalk, a broad, flared, smooth, mushroomshaped top called a capitulum, and by the shape of their sclerites, which are found in the interior coenenchymal tissue of the colony
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