Studies On The Population Genetic Diversity Of Thunnus Albacares In The Centeral Pacific Ocean

Yellowfin tnua (Thunnus albacares) is a highly migration pelagic fishes, whichis widely distributed in tropical and subtropical waters through-out the Pacificocean, the Atlantic ocean and the Indian ocean. It has become a highlighted speciesby fishery for its commercial values, but the previous studies pointed out thatyellowfin tuna in the western and central Pacific ocean is overfished. In order toobtain a sustainable yellowfin tuna fisheries in the Pacific ocean and a reasonablefishery management, clearly understanding the genetic population structure in thecentral pacific ocean is need for proposing a reasonable strategy to ensure thesustainable tuna fishery. So, our study combined the mitochondria COⅠ, Cytb andD-Loop gene to obtain the population genetic diversity and genetic populationstructure in the central pacific ocean, there are results:1)Total203mitochondrial COⅠgene sequences form11locations released38variable sites, and61haplotypes were detected. The haplotypes diversity andnucleotide diversity is0.650and0.00364respectively. The AMOVA test ofyellowfin tuna revealed that94.13%of the genetic variation occurred withinpopulations and5.87%of the genetic variation occurred among populations.FSTanalysis released that there are significant differenstion between some samplinglocations, significant difference was found in stock of the southern hemisphere andnorthern hemisphere, as to the east and west stock. The negative values of Tajima ’sD and Fu’ s Fs suggests that stocks recently experienced expansion, expansionoccurred in about1.86million years ago. According to the haplotypes networkevolution,11stocks can be obviously divided into two categories, shows that theexistence of significant geographical population.2)A total of18mtDNA haplotypes and8variable sites were detected in the663bp segment of mtDNA cytb gene from197samples. The haplotype diversity is0.689±0.023and Nucleotide diversity is0.00163±0.00012, both the haplotype diversity and nucleotide diversity are low, suggested that a low genetic diversityamong the yellowfin tuna in central Pacific Ocean. The Tajima ’s D and Fu’ s Fs arenegative indicated that a recently population expansion may occurred, and theunimodal nucleotide mismatch distribution curve corroborate to the populationexpansion occurred, inferring the expansion happened about1.10million years ago.Based on the coalescent theory, from the haplotype evolution network, we can inferthat the haplotype1is the primitive haplotype, and haplotype2is a new haplotypeevolved from the haplotype1, but the high frequencies of haplotype2suggestedthat the yellowfin tuna genetic diversity became singleness. So it is a seriouschallenge for tunas fishery management, in order to maintain the sustainabledevelopment of yellowfin tuna fisheries, a reasonable management strategy canavoid the genetic diversity decline.3)The samples derived from the Chinese vessels were collected from7locations of centeral Pacific ocean waters （16°S~8°N;160°W~155°E） fromSeptember2009to January2012.By using585bp fragments of mtDNA D-Loopgene, we analyzed the sequence variations and population genetic structures of108samples collected from7locations.In total,23variable sites were acquired, and80haplotypes were identified. Analysis of mtDNA D-Loop gene sequences from7localities revealed that the mean haplotypic diversity and nucleotide diversitywas h=0.994±0.002andπ=0.00892±0.00038respectively. The AMOVA testsrevealed that98.18%of the genetic variation occurred within populations, FSTanalysis suggested that there were significant genetic differentiations were foundwithin the7localities. Neutrality test and the mismatch distribution indicated arecent population expansion that occurred about33,500,000–54,400,000years ago,suggested a frequency genetic exchange and a poor genetic structure. A singlepopulation and a low genetic diversity，calling for a responsible and effectivemanagement to ensure the sustainable development of yellowfin tuna.4)From the study we performed above, the mitochondrial DNA control D-Loop (mtDNA D-Loop) gene on the evolutionary rate is the fastest, the second ismitochondrial cytochrome c oxidase (CO Ⅰ) gene, and at last the mitochondrialcytochrome b gene (Cytb). However, the results of the three molecular markeranalysis, only CO Ⅰ and Cytb detected a significant genetic differencesbetween sampling locations, revealed a significant differentiation in central Pacific geographical population status. But D-Loop gene is a highly evolutionrates gene, while in testing the sensitivity of population genetic differentiation ispoorer, showed that CO Ⅰ and Cytb gene has better applicability in confirmedyellow fin tuna mitochondria marker identification on the geographical populationdifferentiation.Therefore, we can concluded that there are significantdifferentiation between south population and north population, so we will make afurther study about growth rate and reproduction, and so on, in order to put forwarda reasonable management advices for a substainable development.