DNA Barcoding And Molecular Phylogeny Of The Scleractinia

Scleractinia belongs to Scleractinia, Hexacorallia, Anthozoa, Cnidaria. It was reported that there were174species of Scleractinia in China, subordinated to54genera of14families. Highly similarity of phenotypic characters among Scleractinia species result into too much difficulty in coral species identification and classification, which can be truly solved with DNA sequence analysis. Up to date, there are just several reports on molecular phylogenic study of Scleractinia. Here, we expect to discover intra-specific and inter-specific genetic distances, and molecular phylogenic relationships among tens of Scleractinia individuals collected from Hainan Island by analyzing DNA sequences of both ribosomal internal transcribed spacer (ITS) and mitochondrial cytochrome c oxidase Ⅲ(COⅢ) Besides, the potential possibility for ITS and COⅢ sequences using as DNA barcode in Scleractinia was also discussed. The main results in this study were as following:1. There are three fragments for ITS sequences, including ITS1,5.8S and ITS2. Among65individuals of Scleractinia, the length of ITS1range from185bp to250bp with the content of GC ranging from40.1%to63.1%, while the length of ITS2range from188bp to238bp with the content of GC ranging from43.7%to74.4%. The length of5.8S also changed among Scleractinia species with a range from153bp to195bp. These results were the same as other reported on study of Scleractinia. Variable sites and information site are much more than conserved sites in ITS sequences. There are more Transversion nucleotides (108) than transition nucleotides (89), namely a ratio of0.82.2. Phylogenetic trees were constructed based on ITS sequences of Scleractinia. It was show that:(1) For Pavona, a genus of the family of Agariciidae, three species of P. varians, P. decussate and P. minuta were clustered into a branch as expected;(2) For Porites, a genus of the family of Poritidae, most of P. lutea individuals were also clustered into a branch as expected;(3) For Platygyra, a genus of the family of Faviidae, the whole individuals of P. crosslandi and P. sinensis were also clustered together, in line with traditional taxonomy;(4) Most individuals whose cluster results were obviously different from phenotype characters are belong to several genera in Faviidae, especially three genera of Plesiastrea, Echinophyllia, Echinopora and Favites.3. For COⅢ sequences of Scleractinia, the average content of A, T, C and G are41.1%,21.0%,21.8%and16.1%respectively. The content of A+T is significant higher than that of C+G, and these four fundamental bases are uniform distributed in every individual. There are341conserved sites,176variable sites,118information sites, and16singleton sites in COⅢ DNA sequences of Scleractinia. Furthermore, the number of Haplotype is29, with a Haplotype diversity index of0.898and a nucleotide diversity index of0.12833. Therefore, the genetic diversity of Scleractinia was quite abundant. As concerned from triplet codon, the base substitution frequency of third nucleotide (0.95) was much higher than that of the other two bases.4. Phylogenetic trees were constructed based on COⅢ DNA sequences of Scleractinia. Results showed that:(1) phylogenetic relationship among intra-specific individuals is consistent with the traditional taxonomy, except that individuals from two different genera, Leptastrea and Plesiastrea of Faviidae, were clustered into a branch;(2) phylogenetic relationship among species within genus was also consistent with the traditional taxonomy.(3) However, phylogenetic relationship among genera within family was quite disorder, obviously inconsistent with results of traditional taxonomy. Platygyra crosslandi (belonging to Platygyra, a genus of Faviidae) was clustered into a branch with Leptastrea purpurea (belonging to Leptastrea, another genus of Faviidae) firstly, but then they were clustered into a branch with Echinophyllia aspera, belonging to Echinophyllia, a genus from another family of Pectiniidae. Subsequently, they were clustered together with Hydnophora exesa (belonging to Hydnophora, a genus from a different family of Merulinidae), and finally clustered into a branch with Plesiastrea and Leptastrea, two genera from the same family of Faviidae.5. Phylogenetic branch tree of Scleractinia based on ITS DNA sequences and COⅢ sequences showed that ITS and COⅢ sequence is not suitable for phylogeny mark of high taxonomic category, but can be effective as molecular markers in intraspecific.