Islands as a crossroad of evolutionary lineages: A case study of <i>Centaurea</i> sect. <i>Centaurea</i> (Compositae) from Sardinia (Mediterranean Basin)

The Mediterranean Basin is a biodiversity hotspot, where islands play a key role because of their high biological diversity, degree of endemicity and human pressure. One of these islands, Sardinia, is a good evolutionary laboratory, especially for the study of complex genera, such as Centaurea. In particular, endemic species of Centaurea sect. Centaurea from Sardinia provides an interesting case study of plant evolution on continental islands. We attempted to clarify the processes leading to the diversification of Centaurea species on Sardinia using bi-parentally inherited nuclear markers and maternally inherited plastid markers. Our plastid results revealed the presence of five lineages of sect. Centaurea on the island. Three of them were defined as three species: C. ferulacea, C. filiformis and C. horrida. The other two lineages highlighted the complex evolutionary history of the two polyploids C. corensis and C. magistrorum. Multiple colonization events from the mainland involving the C. deusta and C. paniculata lineages among others, have led to the diversity of sect. Centaurea on Sardinia. One colonization event likely followed a southern path via the land connection between the mainland, the Calabrian Plate and Sardinia. A second pathway likely followed a northern connection, probably through the Tuscan Archipelago. Implications of these findings on conservation efforts for Centaurea endemics on Sardinia are also discussed.地中海盆地（Mediterranean Basin）是全球生物多样性热点区域，岛屿凭借其极高的生物多样性、特有性水平与人类活动压力，在此生态系统中发挥关键作用。撒丁岛（Sardinia）作为其中一座岛屿，是优质的进化研究实验室，尤其适合开展复杂类群的研究，例如矢车菊属（Centaurea）。具体而言，撒丁岛矢车菊组（sect. Centaurea）的特有物种为大陆岛屿的植物进化研究提供了极具价值的案例。 本研究借助双亲遗传核标记与母系遗传质体标记（plastid markers），尝试阐明驱动撒丁岛矢车菊属物种分化的演化进程。质体标记分析结果显示，该岛上的矢车菊组存在5个演化支系。其中3个支系对应3个物种：C. ferulacea、C. filiformis与C. horrida。剩余两个支系则揭示了多倍体物种C. corensis与C. magistrorum复杂的演化历史。 来自大陆的多次殖民事件（涉及C. deusta、C. paniculata等支系）共同促成了撒丁岛矢车菊组的物种多样性。其中一次殖民事件大概率经由南部路径，通过大陆、卡拉布里亚板块（Calabrian Plate）与撒丁岛之间的陆桥完成。第二条殖民路径则可能依托北部通道，大概率经由托斯卡纳群岛（Tuscan Archipelago）实现。 此外，本文还探讨了本研究结果对撒丁岛矢车菊特有物种保护工作的启示。