Phylogeography Of Sthenoteuthis Oualaniensis In The East Indian Ocean And West Pacific Based On MtDNA

The purpleback flying squid Sthenoteuthis oualaniensis is an economically important species widely distributed in the Indo-Pacific Ocean with abundant resources.Five morphological populations with different distributions of S.oualaniensis were observed in the Indian Ocean and the Pacific.However,the population genetic structure of S.oualaniensis has not been systematically compared and studied between the Pacific Ocean and Indian Ocean.In order to explore the genetic diversity,phylogenetic relationship and phylogeographic pattern of S.oualaniensis,samples from eight geographic populations in the East Indian Ocean-West Pacific were analyzed based on mitochondrial DNA cytochrome b(Cyt b)and cytochrome coxidase I(COI)genes.The results showed that the overall haplotype diversity and nucleotide diversity of S.oualaniensis in the East Indian Ocean-West Pacific were high.Four deeply divergent genetic lineages from different sea basins including the South China Sea,the Philippine Sea,the northern East Indian Ocean and the southern East Indian Ocean were observed,respectively.The level of genetic differentiation among 4 geographic groups is high,so S.oualaniensis can be divided into four geographic populations: the South China Sea population,the Philippine Sea population,the northern East Indian Ocean population,and the southern East Indian Ocean population.The lineages of the northern East Indian Ocean,southern East Indian Ocean and South China Sea experienced population expansions during the late Pleistocene.Climate change and sea level fluctuations during the Pleistocene could have led to population expansions of marine species.The South China Sea is separated from the Philippine Sea by the First Island Chain,and Kuroshio is the main current system in the Philippine Sea.The isolation of the First Island Chain and different current systems may have led to the genetic divergence of S.oualaniensis between the South China Sea and Philippine Sea.In addition,S.oualaniensis in the South China Sea likely migrated to the Philippine Sea through the intermediate water exchange in the Luzon Strait.Different surface circulation systems and oceanographic conditions including hypoxic zone in the Bay of Bengal,monsoon currents in the northern East Indian Ocean,and stable currents in the southern East Indian Ocean could be responsible for genetic divergence of S.oualaniensis between the northern and southern regions of East Indian Ocean.Thus the different lineages or populations between northern East Indian Ocean and southern East Indian Ocean should be helpful in the natural reserve design and fisheries management of S.oualaniensis.Gene flow between the northern and southern populations likely resulted from the current in the bay mouth of Bengal and thermohaline circulation in the East Indian Ocean.The monsoon current and Indonesian throughflow also likely caused limited gene flow between the East Indian Ocean and the Pacific.