Population Genetics Structure And Molecular Phylogeography Of Three Oceanic Ommastrephidae Species

Ommastrephes bartramii, Illex argentinus and Dosidicus gigas which areabundant squid species and widely distributed in the Pacific Ocean, theAtlantic Ocean and the Indian Ocean are major fishing objects for Chinapelagic squid fishing industry. Understanding and mastering the presentpopulation genetic diversity and genetic structure of three Ommastrephidaespecies is a foundation of assessing and managing these fishery resourcesscientifically and reasonablely, while carrying out the research of molecularphylogeography reveals formation mechanism of phylogeographic pattern andevolutionary process of three Ommastrephidae species. In this text, westudied population genetic structure of three Ommastrephidae species anddiscussed their formation mechanism of phylogeographic pattern bymitochondrial DNA (mtDNA) markers and microsatellite markers. The resultscan be summarized as follows:(1) Part of microsatellite-enhanced genomic library of O. bartramii wasconstructed by the method of streptavidin magnetic beads.68positive clones were detected and60of them comprised microsatellite sequences.40pairmicrosatellite primers were synthesized for polymerase chain reaction (PCR)trials using DNA and8polymorphic microsatellite loci (PIC=0.726–0.958)were screened.Pair-end genomic library of D. gigas was constructed by Illumina solexsequencing platform, and a total of12503microsatellite sequences wereisolated and5177loci could be designed primers.100pair microsatelliteprimers were synthesized randomly for PCR trials, and39polymorphicmicrosatellite loci were screened (PIC=0.487–0.945),13of which extremelysignificant deviated from HWE (P<0.01) after Bonferroni correction formultiple comparisons.Cross-amplification of microsatellite loci among three Ommastrephidaespecies was detected, and12polymorphic microsatellite loci(PIC=0.520–0.959) for D. gigas showed positive results in O. bartramii,4ofwhich deviated extremely significant from HWE (P<0.01) after Bonferronicorrection for multiple comparisons.(2) Molecular phylogeography of O. bartramii in the North Pacific Oceanwas investigated by sequence analysis of mitochondrial cytochrome c oxidasesubunit Ⅰ (CO Ⅰ) and cytochrome b (Cytb). Results showed that nosignificant distinct lineages were detected, and the relative frequency ofindividuals did not differ significantly among sample locations, which indicated that no significant genetic structure of O. bartramii was existed. Itwas supposed that O. bartramii might be experienced a recent populationexpantion during postglacial stage. As a result, the frequent gene flow mayoccur.13microsatellite loci were used for the analysis of genetic diversity andgenetic structure of six populations of O. bartramiiin the North Pcific Ocean.Results showed that all the6populations showed high genetic diversities andno significant genetic differentiations among populations were examinedwhich possibly due to characteristic of its life history as well as oceancurrents. The North Pacific O. bartramii should be considered as a singlestock in their assessment and management.(3) Molecular phylogeography of I. argentinus in the Southwest AtlanticOcean was investigated by sequence analysis of mitochondrial COⅠ andCytb genes. Results showed that no significant distinct lineages were detectedand no significant genetic differentiations were examined. It was supposedthat I. argentinus might be contracted only in one glacial refugia duringglacial periods of Pleistocenethe, and extensive gene flow occured without asignificant phylogeographic structure.7microsatellite loci were used for the analysis of genetic differentiationsbetween fall spawning cohort and winter spawning cohort of I. argentinus aswell as the impact of temporal variation on winter spawning cohort. Results showed that no phylogeographic structure between two spawning cohorts andthe temporal variation showed no significant effect on genetic diversity whichmay be caused by ocean currents and characteristic of its life history.(4) Molecular phylogeography of D. gigas in the East Pacific Ocean wasinvestigated by sequence analysis of mitochondrial COⅠ and Cytb genes.Results showed that a significant distinct lineages was detected and nosignificant genetic differentiations were examined between populations ofequatorial waters and off the coast of Peru. However, they all exhibitedsignificant genetic variation aginst population off the coast of Costa Rica.12microsatellite loci were used for the analysis of genetic variation ofpopulations of equatorial waters and off the coast of Peru. Results showedthat2geographical populations showed high genetic diversities and weak butsignificant genetic differentiation was found which indicated that the geneticstructure pattern of D. gigas was caused by ocean currents as well as historyfactor. The East Pacific D. gigas should be considered as at least three stocksin their assessment and management.(5) To evaluate the genetic variance and estimate divergence time of thethree Ommastrephidae species, partial sequence of the fragments of16SrRNA, Cytb and28S rDNA genes were amplified and sequenced. Resultsshowed that divergence time between O. bartramii and D. gigas was6.53–7.90million years ago, while it was7.65–9.25million years ago between O. bartramii and I. argentinus, which might had occurred in fromMicene to Pliocene. The phylogenetic relationships of Ommastrephidaespecies demonstrated that Illicinae and Todarodinae species clustered togetherfirst, and then clustered together with Ommastrephinae.