Preliminary Studies On The Population Genetic Structure Of Prionace Glauca In The Global Ocean

The blue shark (Prionace glauca) is the main by-catch species in tuna long linefishery，which is one of the most abundunt species in the world. The blue shark isconsidered a keystone predator in the ecosystem. Investigations on blue sharkpopulation genetic structure could make a contribution to maintaining the sustainabledevelopment of the blue shark resources. In this study，we used blue shark specimenssampled by commercial fisheries near equator region from September2010toFebruary2012as the research object, evaluated their population structure and geneticdiversity by using the sequence data of the control region（D-loop）and COI gene ofthe mitochondrial. The main results are shown as follows:（1）In this study,165individuals were sampled By using694bp fragment of themitochondrial DNA D-loop region, we analyzed the sequence variations andpopulation genetic structures for165samples collected from Pacific，Atlantic andIndian Ocean sea areas. A total of145mtDNA haplotypes and110variable sites weredetected in the694bp segment of the mitochondrial control region. The nucleotidecompositions were A：33.46%，T：36.40%，C：18.61%，G：11.53%，respectively.The haplotype diversities were high and the mean haplotype diversity was0.9973±0.0014, while the nucleotide diversity was0.01510±0.00091. The AMOVAtest of Prionace glauca revealed that99.28%of the genetic variation occurred withinpopulations and0.72%of the genetic variation occurred among populations. Theneighbor-joining tree revealed no significant genetic differentiation between fivesampling locations. Low Fstvalues and high Nmvalues from this investigationindicated no significant genetic differentiation because the high rates of gene flowbetween the Prionace glauca populations.（2）By using721bp fragment of mitochondrial cytochrome c oxidase subunit I (COI), we analyzed the sequence variations and population genetic structures for242samples collected from8locations. In total，22variable sites were acquired, and all ofthem were parsimony sites.21haplotypes were identified from242individuals. Thelength of this region (COI) contained721bp nucleotides and the T，C，A and Gcontents were36.42%,20.72%,26.91%and15.95%respectively. The analysis ofmtDNA COI sequences of blue shark in all sampling localities revealed that the meanhaplotypic diversity was0.644, while the nucleotide diversity was0.00123. TheAMOVA test of Prionace glauca reveales that96.07%of the genetic variationoccurred within populations，and3.93%of the genetic variation occurred amongpopulations. Both the neighbor-joining tree and the haplotype network revealed nosignificant genetic differentiation between eight sampling locations. Low Fstvaluesand high Nmvalues from this investigation indicated no significant geneticdifferentiation and high rates of gene flow between the three oceans of the blue sharkpopulations. Nucleotide mismatch distributions for all populations were unimodalsuggesting that blue shark has experienced a population expansion，Tajima’s D andFu’s Fs neutrality test showed significant deviation from neutral molecular evolution.（3）There were some differences between the results based on the D-loopfragment sequence data and the COI gene sequence data. Both these two analysesshowed the Three Ocean consisted of a single panmictic population of blue shark，high rates of gene flow between these sampling locations and that the geneticdiversities were lower than before. Compared to the results based on the D-loopfragment sequence data, the results based on the COI gene sequence data betterrevealed differences of population genetic structure，providing evidence of the blueshark resource management and protection. In this case, the study had a certaintheoretical and practical significance. Provide the necessary reference for the rationaldevelopment and utilization of resources in blue shark populations, as well as theestablishment of relevant fisheries protection zone.