Genetic Analysis Of Common Venomous Jellyfishes In Thai Waters Based On Mitochondrial And Nuclear Genesequences

In recent years, because of human activities and climatic environment changes, the incidents of jellyfish blooming occured frequently. It not only changed the local marine ecosystem structure and function, but also had a serious impact on people’s health and safety, marine fishery resources and production. Therefore, it has an important significance to identify the jellyfish species and master their population dynamics. Traditional morphological identification method has many limitations, and DNA barcoding, as an emerging molecular biology technology is a short DNA sequences as a marker gene for species identification. It can effectively solve the difficulties faced by traditional identification methods. The combination of two methods can be adopted to abtain more accurate identification of species.The genetic diversity of common venomous Cubozoa, Scyphozoa and Hydrozoa jellyfish in the coastal waters of Thailand was investigated using the nuclear 18 S and mitochondrial 16 S rDNA, COI genes. It was also compared about the capability of these three molecular markers to discriminate those common jellyfish species. There were 13 genetically distinctive species among the 71 samples collected from Thai waters, including 6 Cubozoa species, 5 Scyphozoans and 2 Hydrozoan. However, it needs further information on the morphology and life cycle to determine the true taxonomic status of most species in this research. The K2P(Kimura 2-parameter) genetic distance was evaluated within and among the species based on the sequences of these three genes. The results showed much higher genetic divergence based on 16 S gene(0-0.062, 0.150-0.412 and 0.368-0.685 for intra-, inter-species and inter-classes genetic distances, respectively), COI gene(0-0.151, 0.164-0.299 and 0.271-0.385 for intra-, inter-species and inter-classes genetic distances, respectively) compared with those using18 S gene(0-0.002, 0.011-0.101 and 0.081-0.232 for intra-, inter-species and inter-classes genetic distances, respectively). At the same time, the A and T nucleotide composition of 16 S and COI gene was obviously higher than 18 S gene. And significant variation of nucleotide composition was detected between Cubozoa andScyphozoa,Cubozoa and Hydrozoa respectively using 16 S and COI gene. These results further indicated the relatively higher mutation rate of 16 S and COI gene, which could be applied for the genetic diversity studies among jellyfish species with close genetic relationship and the intra-species genetic population studies. Compared with the COI gene, the 16 S gene sequences are highly conserved within species, and their genetic difference is less than COI, which is more suitable for the classification of higher taxonomic category of the jellyfish. Compared with 16 S and COI sequences, 18 S sequences are also more suitable for the classification of species with higher taxonomic category.