1. The porbeagle shark Lamna nasus is a large highly migratory shark distributed in cold and temperate marine waters of the North Atlantic and Southern Hemisphere (SH). According to the International Union for Conservation of Nature, the porbeagle is assessed globally as Vulnerable and regionally as Critically Endangered in the North Atlantic and the Mediterranean Sea. This study explored, for the first time, the population genetics of L. nasus at a regional (south‐east Pacific Ocean) and global scale.
2. In this study, the null hypotheses of no genetic discontinuities among populations (i) within the SH, and (ii) between the SH and Northern Hemisphere (NH) were tested. Also, the demographic history of L. nasus in different ocean basins was assessed. Two mitochondrial markers (Control Region [CR] and cox1) well suited for population genetics inferences in sharks were used.
3. Spatial–genetic analyses suggested two genetic clusters co‐occurring in the south‐eastern Pacific Ocean. A two‐way ANOVA using the cox1 but not the CR mtDNA fragment detected an effect of genetic identity on shark body size. Phylogeographic analyses, haplotype networks, and analyses of molecular variance demonstrated genetic differences between populations from the NH and SH but not among populations in the SH.
4. Migration estimates indicated limited current maternal gene flow between the two hemispheres but high gene flow within hemispheres. Two well‐defined haplotype groups with star‐like shapes inhabited all ocean basins in the SH. These results could reflect a historical scenario of reproductive isolation and more recent mixture among previously isolated populations in the SH. A Bayesian skyline plot analysis indicated sudden population expansion in the SH occurring ~100–125 kya.
5. This study highlights the need for additional studies focusing on the population genomics (using nuclear markers, i.e. single nucleotide polymorphisms) and the general biology of L. nasus to explore the existence of genetically dissimilar populations in the SH. Such studies will help implementing efficient genetic monitoring programmes.

中文翻译：

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濒临灭绝的高度La游鲨Lamna nasus的区域种群遗传学和全球系统地理学：对渔业管理和保护的影响

1. 斑尾鲨Lamna nasus是一种高度迁徙的大型鲨鱼，分布在北大西洋和南半球（SH）的冷温带海洋水域中。根据国际自然保护联盟的资料，在北大西洋和地中海，全球范围内都将波格比格犬评为易受伤害的地区，并在区域内将其评为极度濒危。这项研究首次探索了区域（东南太平洋）和全球范围内纳豆菌的种群遗传学。
2. 在这项研究中，检验了人口不存在遗传不连续性的零假设（i）在南半球内部，以及（ii）在南半球和北半球（NH）之间。此外，还评估了不同海洋盆地中纳豆菌的人口历史。使用了两个非常适合鲨鱼种群遗传学推断的线粒体标记（控制区[CR]和cox1）。
3. 空间遗传分析表明，东南太平洋同时存在两个遗传簇。使用cox1而非CR mtDNA片段进行的双向方差分析检测到遗传同一性对鲨鱼体型的影响。系谱分析，单倍型网络和分子变异分析表明，NH和SH种群之间的遗传差异，而SH种群之间没有遗传差异。
4. 迁移估计表明，两个半球之间目前的母体基因流有限，但半球内的基因流较高。南海的所有海盆中都生活着两个形状清晰的单倍型群，它们呈星形。这些结果可能反映了生殖隔离的历史情景，以及南部隔离区以前隔离的人群之间的最新混合情况。贝叶斯天际线图分析表明，西南部的人口突然膨胀，发生在100-125 kya左右。
5. 这项研究强调需要针对人群基因组学（使用核标记，即单核苷酸多态性）和纳氏乳杆菌的一般生物学开展更多研究，以探索SH中遗传异种种群的存在。这些研究将有助于实施有效的遗传监测计划。