Data from: Origins of the Greenland shark (Somniosus microcephalus): impacts of ice-olation and introgression

Herein, we use genetic data from 277 sleeper sharks to perform coalescent-based modeling to test the hypothesis of early Quaternary emergence of the Greenland shark (Somniosus microcephalus) from ancestral sleeper sharks in the Canadian Arctic-Subarctic region. Our results show that morphologically cryptic somniosids S. microcephalus and Somniosus pacificus can be genetically distinguished using combined mitochondrial and nuclear DNA markers. Our data confirm the presence of genetically admixed individuals in the Canadian Arctic and sub-Arctic, and temperate Eastern Atlantic regions, suggesting introgressive hybridization upon secondary contact following the initial species divergence. Conservative substitution rates fitted to an Isolation with Migration (IM) model indicate a likely species divergence time of 2.34 Ma, using the mitochondrial sequence DNA, which in conjunction with the geographic distribution of admixtures and Pacific signatures likely indicates speciation associated with processes other than the closing of the Isthmus of Panama. This time span coincides with further planetary cooling in the early Quaternary period followed by the onset of oscillating glacial-interglacial cycles. We propose that the initial S. microcephalus–S. pacificus split, and subsequent hybridization events, were likely associated with the onset of Pleistocene glacial oscillations, whereby fluctuating sea levels constrained connectivity among Arctic oceanic basins, Arctic marginal seas, and the North Atlantic Ocean. Our data demonstrates support for the evolutionary consequences of oscillatory vicariance via transient oceanic isolation with subsequent secondary contact associated with fluctuating sea levels throughout the Quaternary period—which may serve as a model for the origins of Arctic marine fauna on a broad taxonomic scale.

本研究利用277尾睡鲨的遗传数据，开展基于溯祖理论（coalescent theory）的建模分析，以验证“格陵兰睡鲨（Somniosus microcephalus）于第四纪早期在加拿大北极-亚北极区域由祖先睡鲨分化形成”这一假说。研究结果表明，形态上隐存的睡鲨科物种格陵兰睡鲨（S. microcephalus）与太平洋睡鲨（Somniosus pacificus），可通过联合使用线粒体与核DNA标记实现遗传区分。本研究数据证实，加拿大北极、亚北极以及东大西洋温带区域存在遗传混合个体，暗示物种初始分化后发生二次接触时伴随渐渗杂交（introgressive hybridization）。基于迁徙隔离（Isolation with Migration, IM）模型拟合的保守替换速率，基于线粒体序列计算得到的物种分化时间约为2.34百万年（Ma）；结合混合个体的地理分布与太平洋遗传信号，该结果表明物种形成过程并非由巴拿马地峡闭合所主导。该时间跨度与第四纪早期的全球进一步降温，以及周期性冰期-间冰期循环的起始时间相吻合。我们提出，格陵兰睡鲨与太平洋睡鲨的初始分化以及后续的杂交事件，可能与更新世冰期旋回的起始相关——海平面波动制约了北极大洋盆地、北极边缘海与北大西洋之间的连通性。本研究数据支持“第四纪时期以暂时性海洋隔离引发的周期性异域分化，伴随海平面波动带来的二次接触”这一进化过程的有效性，该过程可作为广分类尺度下北极海洋动物群起源的研究模型。