Phylogeography of Schivereckia podolica (Brassicaceae) and the evolutionary history of the European steppe. Phylogeography of Schivereckia podolica

The genus Schivereckia (Brassicaceae) -now included in the genus Draba- comprises two species, S. podolica and S. doerfleri. Schivereckia podolica is an eastern European species of disjunct distribution in Russia, in the Ukraine, and Podolian-Galician outpost. Schivereckia doerfleri is reported from alpine fields of the Balkan Peninsula and from mountain chains in northern Anatolia, Turkey. Schivereckia podolica shares its ecological and biogeographic characteristics with a number of other steppe plants. These associations of “mysterious elements” give the impression of mountain and even alpine or arctic elements and attracted botanists since more than 100 years. The ‘relic hypothesis’ interprets the present locations of Schivereckia and its associates as relics of a formerly continuous distribution belt of a cool periglacial steppe vegetation. On the other side, it is hypothesised that Schivereckia podolica is indeed an ancient but not a relict species and is of Mediterranean origin. Thus, Schivereckia remains “one of the most mysterious species in florogenetic aspects”. We employed molecular markers such as nuclear ITS and chloroplast trnL-F sequencing, and DNA fingerprinting (RAPD) to elucidate the evolutionary history and historical biogeography of Schivereckia. RAPD data argue that this disjunction is the result of fragmentation of a formerly continuous distribution belt. Phylogenetic analyses revealed that the genus Schivereckia is monophyletic and nested within a highly supported clade of central Asian and Caucasian Draba species. No relations to Mediterranean Draba species could be detected. This supports the interpretation of Schivereckia as a glacial relic rather than a Mediterranean post-glacial immigrant. Our results argue for continuous persistence of certain steppe species since the Pleistocene, and support the view that the modern steppes of Europe are derived from Pleistocene glacial steppes.

原隶属于十字花科（Brassicaceae）的须弥芥属（Schivereckia），现并入葶苈属（Draba），该属共包含两个物种：S. podolica与S. doerfleri。其中，S. podolica为东欧物种，呈间断分布格局，见于俄罗斯、乌克兰及波多利亚-加利西亚孤立分布区；S. doerfleri则被报道分布于巴尔干半岛的高山原野，以及土耳其安纳托利亚北部的山脉链地带。S. podolica的生态与生物地理特征与诸多其他草原植物高度相似，这些被称为“神秘组分”的类群组合，呈现出山地乃至高山、北极类群的典型特征，百余年来始终备受植物学家关注。“残遗假说”将须弥芥属及其近缘类群的现存分布区，诠释为曾经连续分布的寒冷冰缘草原植被带的残遗遗存。与之相对的另一假说则认为，S. podolica实为起源于地中海区域的古老物种，而非残遗物种。因此，须弥芥属至今仍是“植物区系演化研究中最具神秘感的类群之一”。本研究采用核ITS序列、叶绿体trnL-F测序以及随机扩增多态性DNA（RAPD）指纹技术等分子标记手段，解析须弥芥属的演化历史与历史生物地理格局。RAPD数据分析表明，该类群的间断分布格局源于曾经连续的分布带发生片段化。系统发育分析结果显示，须弥芥属为单系类群，且嵌套于一支支持度极高的中亚与高加索葶苈属物种演化支中，未检测出其与地中海葶苈属物种存在亲缘关系。这一结果支持将须弥芥属视为冰期残遗类群，而非来自地中海区域的冰后迁入物种。本研究结果证实，部分草原物种自更新世以来便持续存续，同时也支持“欧洲现代草原源自更新世冰期草原”的学术观点。