南海鸢乌贼的遗传差异:种群分化还是种间分化

Genetic differentiation of the purpleback flying squid, Sthenoteuthis oualaniensis, in the South China Sea: population or species divergence

利用线粒体ND2、COI和16SrDNA序列,对2012年9月至2015年9月采自南海的鸢乌贼(Sthenoteuthis oualaniensis)样本进行了种群遗传结构的分析。系统发育关系显示鸢乌贼中型群和微型群各自形成了单系群分支,而分支内没有形成与地理群体或季节群体对应的支系。分子方差分析同样表明,地理群体或季节群体之间不存在明显的遗传分化,而中型群和微型群之间具有极显著的遗传分化(F_(ST)=0.94092～0.9899, P<0.0001)。遗传多样性分析显示,鸢乌贼中型群和微型群均呈现出较高的单倍型多样性(0.9465和0.8545)和较低的核苷酸多样性(0.0051和0.0021),中型群的遗传多样性指数要高于微型群。基于ND2、COI和16SrDNA序列计算的中型群和微型群之间的遗传距离分别达到了14.0%、9.6%和8.8%,远大于类群内的遗传分化(平均<1%)。研究结果表明,南海鸢乌贼存在分布高度重合且有显著遗传分化的两个种群,即中型群和微型群。中型群和微型群之间的遗传差异达到了种间分化的水平,提示体型较大、具有背部发光器的中型群鸢乌贼(典型鸢乌贼)与体型较小、背部发光器缺失的微型群鸢乌贼可能是两个相互独立的种类。

In the present study,the population differentiation of the purpleback flying squid (Sthenoteuthis oualaniensis) in the South China Sea was examined based on mitochondrial ND2,COI,and 16S rDNA sequences,using samples collected between September 2012 and September 2015.Phylogenetic analysis revealed two significantly divergent monophyletic groups corresponding to the “medium form” and the “dwarf form,” but no geographical lineages corresponding to the sampling localities or seasonal groups were found.The Analysis of Molecular Variance also revealed significant genetic differentiation between the “medium form” and the “dwarf form”(FST=0.94092-0.9899,P<0.0001),while no genetic variance between either geographic populations or seasonal groups was found.The genetic diversity analysis showed that both the “medium form” and the “dwarf form” of S.oualaniensis in the South China Sea were characterized by high haplotype diversity (0.9465 and 0.8545) and low nucleotide diversity (0.0051 and 0.0021).The genetic distance between the ‘medium form’ and the “dwarf form” based on ND2,COI,and 16S sequences were 14.0%,9.6%,and 8.8%,respectively.The genetic distances between the two forms were considerably larger than the genetic distances within each of the two forms (<1%).It was demonstrated that two divergent populations of S.oualaniensis were sympatrically distributed in the South China Sea,i.e.the “medium form” and the “dwarf form.” The genetic differentiation between these two populations was similar to that among separate species within Ommastrephidae,which indicated that the two morphologically distinct forms of the purpleback flying squid,namely the “medium form”(middle sized,with a photophore) and the “dwarf form”(small sized,without a photophore),are two distinct species.