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中展开。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，累积的全基因组差异预计将被削弱，除了经历分歧选择的突变。第四纪期间的气候波动可能助长了这种时空种群动态：在不利的环境条件下，种群收缩成不同的避难所，一旦条件改善，它们就会扩大范围。这一流行的生物地理模型得到了基于残余种群样本遗传特征的种群重建的支持。它很少使用直接的遗传证据进行测试。古老的遗传物质可以填补这一空白，因为它允许通过空间和时间观察种群动态。作为一个模型，我们在这里使用了一个被充分研究过的接触区，在欧洲，灰冠乌鸦和全黑腐肉乌鸦之间的接触区，假设是由冰期-间冰期循环期间反复的隔离和再定居事件形成的。将来自约50个古代样本（70,000 - 500 BP）的全基因组信息与来自118个现存个体的先前测序的基因组相结合，将允许(1)在空间和时间上重建欧洲乌鸦的人口历史；(2)追踪受性选择影响的基因的等位基因动力学，并已知其对前合子分离的影响。这个研究项目允许对生物多样性的主流生物地理模型进行直接审查，并为物种形成的动态提供基本的见解。

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.