Soft coral Sarcophyton (Cnidaria: Anthozoa: Octocorallia) species diversity and chemotypes

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.

Figure 1. Phylogenetic analyses of Sarcophyton species and relationship with chemotypes.

Phylogentetic tree of an alignment of utilizing mitochondrial protein-coding genes MutS homolog msh1 sequences for Sarcophyton specimens constructed by the maximum likelihood (ML) method. Values at branches represent ML, neighbor-joining (NJ) and maximum parsimony (MP) method bootstrap values, respectively. Monophylies with more than 95% Bayesian posterior probabilities are shown by thick branches. Sequences in bold without GenBank accession numbers are msh1 sequences newly obtained in this study. Color dots indicate different chemotypes as described in this study. For chemotype information see Figure 2 and for specimen information see Table 1.

Figure 2. Structures of cembranes from Sarcophyton species identified in this study.

Colored dots next to each cembrane are the same as in other figures.

Figure 3. In situ photographs of colonies of Sarcophyton.

A. Sarcophyton trocheliophorm, Sunabe 12. B. Sarcophyton glaucum clade B, Sunabe 13. C. Sarcophyton glaucum clade C, Mizugama 7. D. Sarcophyton glaucum clade D, Sunabe 17. E. Sarcophyton glaucum clade F, Zanpa 3. F. Sarcophyton ehrenbergi mixed clade, Sunabe 1.

Figure 4. Sclerites of Sarcophyton glaucum clades B, D and F, and their averages length and width.

All sclerites shown are surface sclerites; Clade B obtained from specimens Sunabe 6 and Sunabe 13; Clade D from Sunabe 2, Sunabe 19; Clade F from Zanpa 3, Mizugama 5, Mizugama 9. Images were taken using a scanning electron microscope.

Figure 5. Scatter plot and regression line of length and width of sclerites of each Sarcophyton glaucum clade.

Horizontal axis: width of sclerites, vertical axis: length of sclerites.

Figure 6. Map of collection sites of specimens examined in this study.

Okinawa Island is located in southern Japan.