背景回顾：Persian walnut, Juglans regia, occurs naturally from Greece to western China, while its closest relative, the iron walnut, Juglans sigillata, is endemic in southwest China; both species are cultivated for their nuts and wood. 

主要研究：Here, we infer their demographic histories and the time and direction of possible hybridization and introgression between them. We use whole-genome resequencing data, different population-genetic approaches (PSMC and GONE), and isolation-with-migration models (IMa3) on individuals from Europe, Iran, Kazakhstan, Pakistan, and China.

结果1-种间分化与基因流：IMa3 analyses indicate that the two species diverged from each other by 0.85 million years ago, with unidirectional gene flow from eastern J. regia and its ancestor into J. sigillata, including the shell-thickness gene. 

结果2-种内群体演化：Within J. regia, a western group, located from Europe to Iran, and an eastern group with individuals from northern China, experienced dramatically declining population sizes about 80 generations ago (roughly 2400 to 4000 years), followed by an expansion at about 40 generations, while J. sigillata had a constant population size from about 100 to 20 generations ago, followed by a rapid decline. Both J. regia and J. sigillata appear to have suffered sudden population declines during their domestication, suggesting that the bottleneck scenario of plant domestication may well apply in at least some perennial crop species. 

结果3-渐渗与驯化：Introgression from introduced J. regia appears to have played a role in the domestication of J. sigillata. 

 摘 要 

波斯核桃（Juglans regia）自然分布于希腊到中国西部，但其近缘物种铁核桃（Juglans sigillata）是中国西南特有的一个种；这两个核桃树种都因其坚果和木材而被广泛种植。本文中，作者推测了波斯核桃和铁核桃各自的群体演化历史，以及相互之间可能的杂交和渐渗时间和方向。作者通过全基因组重测序数据，不同的群体遗传学方法（PSMC和GONE），以及隔离迁移模型（IMa3）对来自欧洲、伊朗哈萨克斯坦、巴基斯坦和中国的核桃群体进行了分析。IMa3分析显示，波斯核桃和铁核桃大约在85万年前分化，并且存在从波斯核桃东部群体及其祖先种向铁核桃的单向基因流，其中就包括了果壳加厚基因。在波斯核桃种，位于欧洲到伊朗的西部群体和来自于中国南部的东部群体大概在80个世代，即2400到4000年前经历了急剧的群体衰减事件，随后在40个世代前经历了一次群体扩张事件；而铁核桃在过去100～20个世代间都保持着较为稳定的群体大小，但之后发生了群体的衰减。无论是波斯核桃，还是铁核桃，似乎在其驯化过程中群体都受到了突然的衰减，表明植物驯化导致的群体瓶颈可能至少适用于一些多年生的作物。来自于引种波斯核桃的基因渐渗在铁核桃的驯化过程中发挥了重要作用。

 白伟宁