Phylogenic Study Of Scleractinian Corals Based On Mitochondrial Genes

Scleractinian corals (Cnidaria: Anthozoa: Hexocorallia), the most importantreef-building organism, are primarily distribute the tropical and subtropical neriticareas. There are varieties of corals living in the shallow water in Xuwen, withimportant value in science researching and exploiting. Four mitochondrialmarkers(COⅠ,16S rRNA,12S rRNA and combined gene sequences) wereamplified in order to analyse the classification and phylogenetic relationship of127samples, which are belong to28species of13genera, collected from Xuwen,Guangdong province. The mainly results as followed:1. Partial sequences of COⅠgene from28species were487-533bp, theGenbank accession numbers were JQ920441-JQ920469, and the homology of COⅠsequences was between80.1%and99.8%; with large pecent of T(38.38%), the totalcontent of A+T was bigger than G+C; R stand for transition/transversion was2.53.Genetic distance of inter and intra genus and families appeared to be graduallyincreasing, the genetic distance inter Poritidae and even compared with other coralswere minimum, opposed to Faviidae. Regarded of analysis technique(Neighbor-joining, Maximum Parsimony and Maximum Likelihood) for constructingphylogenetic trees had similar topologies: the separated Faviidae as root clade Ⅰ,and clade Ⅱ was composed of Poritidae, Oculinidae, Acroporidae, Agariciidae andDendrophylliidae rank on the top, differences was mainly from branch length andnode ratings, suggested that mitochondrial genes in coral evolution are moreconservative. Well different genus polymerize also emerged, such as Gonioporaduofaciata classified to Porites, while Porites cylindrical polymerized withGoniopora.2. We obtained two different kinds of fragments in16S rRNA, sequences lengthbetween503-688bp, Genbank accession number were JQ347805-JQ347827,sequences of Faviidae were smaller than others. The sequences were rich in AT(61.63%), but differential between A and T was not obvious; transitions occurredmainly between A and G, while transversion mainly occurred between A and T, R(transition/transversion) was1.3. Genetic distance and system construction results were similar to COⅠ conclusion, but in clade Ⅱ Agariciidae and Merulinidaeaggregated as one group.3. The sequencing results showed that12S rRNA gene fragments length werebetween703bp-887bp, the Genbank accession numbers were JQ347805-JQ347849,in which the Faviidae fragments were smaller. Sequence base composition showedsignificant AT bias, transition/transversion was1.08. Compared with other corals inthis study, the genetic distance of outgroup was the largest, Faviidae followed.Phylogenetic tree construction and genetic distance results were similar to16S rRNAsequence results, expect that Agariciidae and Merulinidae polymerization, at thesame time as a sister group of Oculinidae.4. The base composition of three-gene combined sequences still reflected theAT bias characteristics. Except for C base, content of other base had little difference,variable sites accounted for about47%. Compared to single gene study results, theGenetic distance result had no significant changes, but by the construction of themolecular phylogenetic system, it clustered much more reasonable in clade Ⅱ,suggested that combined gene sequences could be an effective molecularclassification tool in higher order element of scleractinian corals.