Cloning And Sequencing Of Dugongs And Other Key Species Of Seagrass Ecosystems In South China Sea

Hainan Island, with rich marine plant and animal resources, is located in the subtropical areas. In this paper, two key species of seagrass ecosystems in South China Sea:Syringodium isoetifolium (Aschers.) Dandy and Dugong dugon were studied for gene cloning and sequencing. We sequencing the internal transcribed spacer(ITS) and18S ribosomal RNA(rRNA) genes in ribosomes of Syringodium isoetifolium and Dugong dugon, as well as ITS2and mitochondrion cytochrome b (Cytb) genes of Dugong dugon. The sequences were analyzed and aligned with other species using DNA stars and BLASTn in GenBank. MEGA5.1was used to stuty the nucleotide composition percentages, interspecific genetic distances and sequence differences between different species based on Kimuar2-parameter model. Molecular phylogenetic trees of seagrass and mammals were constructed using MEGA5.1based on neighbor-joining (NJ) method. Bootstrap confidence for phylogenetic trees was1000replicates. Phylogenetic relationships of8species of seagrass and9species of mammals were showed in the phylogenetic trees. This paper is divided into the following four sections:1:Literature review. Systematically summarize about the materials of Syringodium isoetifolium and Dugong dugon in South China Sea by reading quantities of related references and documents.2:Phylogenetic analysis of Syringodium isoetifolium and other main species based on ITS regions and18SrDNA sequences. Cloning and sequencing of ITS and18SrDNA sequences of Syringodium isoetifolium were conducted and phylogenetic tree was constructed for research and discussion.3:Phylogenetic analysis of Dugong dugon and other main species based on ITS regions,18SrDNA sequences and Cytb sequences. Cloning and sequencing of ITS,18SrDNA and Cytb sequences of Dugong dugon were conducted and phylogenetic tree was constructed for research and discussion.4:Summary and expectation. From the results of Syringodium isoetifolium and Dugong dugon experiments, it is concluded that:the sequences we amplificated showed a high level of confidence. The results of interspecific genetic distances are similar with molecular phylogenetic trees:(1) Belonged to Cymodoceaceae, Syringodium isoetifolium has a closer genetic relationship with Cymodocea rotundata. Phyllospadix iwatensis and Zostera Marina (Zosteraceae) clustered together, and Posidonia australis (Posidoniaceae) was in a separate branch. Enhalus acoroides and Halophila ovalis (Hydrocharitaceae) clustered together, then Cymodoceaceae, Zosteraceae, and Posidoniaceae clustered in a big branch. The overall genetic relationship is roughly the same as the classifications in seagrass.(2) Dugong dugon (Sirenia) and Monotremata are much more original in mammal evolution, which results in a closer genetic relationship in the phylogenetic tree. Artiodactyla, Carnivora, and Cetacea clustered in a big branch means a higher evolutionary status in mammals.