Understanding the role of Pleistocene climatic oscillations for evolution.A palaeogenomic case study of the European crow hybrid zone

物种形成在空间和时间上展开。不同种群之间的生殖隔离最容易在地理隔离期间演变，并在二次接触时受到考验。在随后的基因交换的影响下，除了经历分歧选择的突变外，整个基因组范围内累积的分歧预计将被侵蚀。据推测，第四纪期间的气候振荡助长了这种时空种群动态：在不利的环境条件下，种群陷入截然不同的避难所，一旦条件改善，种群的活动范围就会扩大。这一流行的生物地理学模型通过基于剩余种群样本的遗传签名的种群重建获得了支持。很少使用直接的遗传证据对其进行测试。古老的遗传物质可以填补这一空白，因为它允许观察种群在空间和时间上的动态。作为一个模型，我们在这里使用了欧洲灰色帽鸦和全黑腐肉乌鸦之间经过充分研究的接触区，假设是在冰川-间冰期循环期间反复发生的孤立和再殖民事件所塑造的。将来自约50个古代样本(70,000-500个碱基)的全基因组信息与先前从118个现存个体测序的基因组相结合，将允许(1)重建欧洲乌鸦在空间和时间上的人口学历史，(2)追踪受性选择影响的基因的等位基因动力学，这些基因对预合子分离有已知的影响。这项研究计划允许对生物多样性的主流生物地理模型进行直接审查，并提供对物种形成动态的基本见解。

Speciation unfolds in space and time. Reproductive isolation between diverging populations most easily evolves during periods of geographic isolation and is put to the test upon secondary contact. Under the influence of ensuing gene exchange, the accumulated genome-wide divergence is expected to erode except around mutations experiencing divergent selection. Climatic oscillations during the Quaternary have presumably fueled such spatio-temporal population dynamics: during unfavorable environmental conditions populations contracted into disparate refugia, expanding their range as soon as conditions improved. This popular biogeographic model has gained support by population reconstruction based on genetic signatures of remnant population samples. It has rarely been tested using direct genetic evidence. Ancient genetic material can fill this gap as it allows observation of population dynamics through space and time. As a model, we here use the well-studied contact zone between grey-coated hooded and all-black carrion crows in Europe, hypothesized to be shaped by repeated events of isolation and recolonization during glacial-interglacial cycles. Combining genome-wide information from ~50 ancient samples (70,000 - 500 BP) with previously sequenced genomes from 118 extant individuals will allow (1) reconstructing the demographic history of European crows in space and time and (2) track the allelic dynamics of genes subject to sexual selection with known effects on prezygotic isolation. This research program allows direct scrutiny of the prevailing biogeographic model of biodiversity and provides fundamental insight to the dynamics of speciation.