Studies On Genetic Diversity Of Bluefin Tuna Thunnus Thynnus And Yellowfin Tuna Thunnus Albacares In Western Pacific And Molecular Phylogenetics In Scombridae

Genetic diversity of the bluefin tuna Thunnus thynnus and the yellowfin tuna Thunnus albacares in western Pacific was investigated by using the molecular marking like Microsatellites and Random Amplified polymorphic DNA(RAPD) analysis.The molecular phylogenetic evolution of 31 species in Scombridae was estimated from cytochrome b(Cyt b) in mitochondriai DNA and internal transcribed spacer 1(ITS1) sequences.The main results were shown as follows:1.The genetic diversity of T.thynnus was investigated by Microsatellites and RAPD.Of the Microsatellites primers screened,I0 produced highly reproducible Microsatellites bands.The percentage of polymorphic,Shannon's index and the average heterozygosity were 100%,1.1622 and 0.6486 respectively.The polymorphic information content(PIC) of polymorphic loci varied from 0.3571～0.8187,and the average PIC was 0.5462.It seemed that genetic diversity of the western Pacific bulefin tuna was at a high level.96 RAPD bands ranging from 250～2000 bp were recorded from 18 random primers.The mean percentages of polymorphic loci(P) were 33.3%and the Shannon's information index was 0.2430,both of these two values were lower than those of Microsatellites analysis,indicating that,compared to RAPD,the higher sensitive genetic marker Microsatellites will better reveal population genetic diversity.2.The genetic diversity of T.albacares was obtained by Microsatellites.54 loci were detected from 10 sets of microsatellite primers,mean number of alleles per locus was 5.40.The percentage of polymorphic and the average heterozygosity were 100% and 0.6486,respectively.The polymorphic information content(PIC) of polymorphic loci varied between 0.3080～0.8720,and the average PIC was 0.5637,indicating that genetic diversity of yellowfin tuna population was at a high level.3.A fragment with 311 bp of cytochrome b gene in mitochondrial DNA was amplified from 12 Genus 31 in Scombridae.Neighbour-joining(NJ),maximum-parsimony(MP) and maximum-likelihood methods were used to reconstruct the phylogenetic trees.It was affirmed that genus Thunnus locates at the top of the phylogenetic tree,it is the most recently diverged species and the most flourishing genus in Scombridae nowadays.The phylogenetic case of genus Sarda and Acanthocybium was not the same in different trees.The result exhibited very close relationship among Katsuwonus,Euthynnus,Auxis and Thunnus,which was consistent with traditional opinion,suggesting that they belonged to tribe Thunnini.In the analysis of phylogenetic relationship of Thunnini species,the result of ITS1 was basically consistent with that of Cyt b,with dissimilarity of the phylogenetic relationship within Thunnus species,which was supported by former research.