| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 96 === Because only a few studies of azooxanthellate scleractinians exist and results of 16S rDNA analyses of coral phylogeny are ambiguous, a mitochondrial genomics study can provide further understanding of scleractinian evolution. Both Euphyllia ancora and Polycyathus sp. which contain zooxanthellae belong to the suborder Caryophylliina and were previously separated into the robust subclade with family-level debates. The genera, Fungiacyathus and Madrepora, have also been the subject of taxonomic debate after radioimmunoassay and mitochondrial sequence analyses.
Four mitochondrial (mt) genomes, two from azooxanthallate corals, Fungiacyathus stephanus and Madrepora oculata, and two from zooxanthellate corals, Euphyllia ancora and Polycyathus sp., were sequenced in this study. Three major features were discovered in the azooxanthellate mt genomes. First, gene rearrangement of cytochrome oxidase subunit II (COII) and cytochrome oxidase subunit III (COIII) and a poly (T) variation in the nad4 protein-coding gene were found in the mt genome of M. oculata. These characters are discussed in the Scleractinia for the first time. Second, F. stephanus presented a loose genome (19,381 bp) with a group I intron in the cox1 gene. In contrast, the zooxanthellate coral, Polycyathus sp., had the most compact mt genome (15,356 bp) among all the scleractinians known to date. Euphyllia ancora presented an extremely long cox1 gene. Phylogenetic analyses also showed unique information of these four mt genomes in the evolutionary trees, and M. oculata formed a single lineage with robust clade corals, supporting the result of rearrangement of the COII and COIII genes. Fungiacyathus stephanus grouped with the Poritidae. The cox1 group I intron occurs in the Fungiacyathus-Poritidae lineage. The high sequence similarity of cox1 intron nucleotides between Fungicyathus and the Poritidae indicates that azooxanthellate and zooxanthellate corals have the same origin of cox1 group I intron. The two Caryophylliina corals, Polycyathus and Euphyllia, were respectively grouped with the robust and complex clades. This suggests that Caryophylliina corals are not monophyletic. In conclusion, based on a mitogenomic approach, this study provides some insights into the phylogenetic relationships and evolution of mitochondrial genomes among these taxonomically ambiguous taxa.
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