Primary Studies On The Population Genetic Structure Of Dosidicus Gigas In The High Seas Of Eastern Pacific Ocean

The jumbo squid (Dosidicus gigas) is the membership of family Ommastrephidaeand the subfamily Ommastrephinae and is the largest and one of the most abundant ofthe nektonic squid. D.gigas are widely distributed in the eastern central Pacific, rangingfrom California(30N) to Chile(30S) and up to the125W along the equator. It iscommercially important fishery species in eastern Pacific. The main fishery areas ofD.gigas are the sea off Chile of the Southern Hemisphere and the California gulf of theNorthern Hemisphere.The samples derived from the Chinese squid jigging vessel were collected from theeastern Pacific waters (81.9°-94.9°W,8.9°-7.7°N,10.2°-11.3°S) from July to October2009. By using724bp fragment of mitochondrial cytochrome b gene (cyt b) and768bpfragment of Cytochrome Oxidase subunitⅠ(COⅠ) we analyzed the sequencevariations and population genetic structures for about150samples collected from sevensites of Peru and three sites of Costa Rica for better understanding the species’spopulation genetic structure. And the assessment of population genetic diversity levelsof jumbo squid is fundamental to the conservation and management of this species.The genomic DNA was extracted by phenol-chloroform method. Based on thecomplete mtDNA sequences of D.gigas，two pairs of polymorphic primers weredesigned by using Premier Primer5.0to amplify fragments of mtDNA cytb and COⅠgenes. Then the PCR products were ligated into T-Vector, cloned and sequenced. Thesequences were aligned using ClustalX1.83. Base composition and sequencesdivergences between haplotypes were calculated by MEGA(Molecular EvolutionaryGenetics Analysis)4.0software package. Neighbor-joining (NJ) analysis tree based onKimura2-parameter distance model was used to assess the relationships among mtDNAhaplotypes of D. gigas. Two genetic parameters, Nucleotide diversity index (π) andHaplotype diversity index (h) were calculated by using the DnaSP5software. Neutral test (Tajima’s D and Fu’s Fs parameters) was used to indicate the historical stability orpopulation expansion. In order to examine the genetic differentiation among differentpopulations，analysis of molecular variance (AMOVA) was carried out by ARLEQUINsoftware package. Genetic differentiation index and corresponding P value were used toevaluate genetic differentiation levels among different populations.Analysis of mtDNA Cytb sequences of jumbo squids from the ten localities got724bp fragment of155individuals. In the research,16variable sites were acquired, andall of them were parsimony sites.43haplotypes were identified from155individuals．The result revealed that the mean Haplotype diversity index was0.873,while the mean Nucleotide diversity index was0.00369.6haplotypes were shared by allthe populations, while Peru population possessed of the highest haplotypes (n=20). TheAMOVA test of D. gigas revealed that82.70%of the genetic variation occurred withinpopulations. FSTanalysis suggested that significant genetic differentiations were foundbetween the partial Peru populations and the Costa Rica populations, and even betweenpartial Peru populations. However, no significant genetic differentiations were detectedbetween Costa Rica populations.Analysis of mtDNA COⅠsequences of jumbo squids from the ten localities got768bp fragment of147individuals(the losed number due to the failure of PCR). In theresearch,60variable sites were acquired, and18of them were parsimony sites.48haplotypes were identified from147individuals．The result revealed that the meanHaplotype diversity index was0.00246, while the mean Nucleotide diversity index was0.751.6haplotypes were shared by all the populations, while Peru population possessedof the highest haplotypes (n=25). The AMOVA test of D. gigas revealed that91.803%of the genetic variation occurred within populations. FSTanalysis suggested thatsignificant genetic differentiations were found between the partial Peru populations andthe Costa Rica populations, and even between partial Peru populations. Highlysignificant genetic differentiations were detected in among Costa Rica populations.Both the mtDNA Cytb and mtDNA COⅠresults indicated that: Nucleotidediversity index (π) and Haplotype diversity index (h) of Dosidicus gigas in the highseasof eastern Pacific ocean is pretty high. The distinct overlaps among the10populationswere detected in the phylogenetic NJ tree, which indicated that the haplotypes were notphylogeographically structured. The neutral test of Tajima’s D and Fu’s Fs analysisrevealed that Dosidicus gigas’s populations of the highseas of eastern Pacific ocean had experienced a population-expanding phase in the history.Therefore, a combination of mitochondrial DNA analysis and microsatellitesmarkers can be used in the farther study of population structure identifications ofD.gigas and there is a urgent need for our final solution of the issue that the actualgenetic diversity level and population genetic structure of D.gigas. Moreover, We mustget the data from equator and non-equator area and records of the age and growth ofD.gigas.