Comes Hans Peter, Tribsch Andreas, Bittkau Christiane
Fachbereich für Organismische Biologie, Paris-Lodron-Universität Salzburg, 5020 Salzburg, Austria.
Philos Trans R Soc Lond B Biol Sci. 2008 Sep 27;363(1506):3083-96. doi: 10.1098/rstb.2008.0063.
Continental shelf island systems, created by rising sea levels, provide a premier setting for studying the effects of geographical isolation on non-adaptive radiation and allopatric speciation brought about by genetic drift. The Aegean Archipelago forms a highly fragmented complex of mostly continental shelf islands that have become disconnected from each other and the mainland in relatively recent geological times (ca <5.2 Ma). These ecologically fairly homogenous islands thus provide a suitable biogeographic context for assessing the relative influences of past range fragmentation, colonization, gene flow and drift on taxon diversification. Indeed, recent molecular biogeographic studies on the Aegean Nigella arvensis complex, combining phylogenetic, phylogeographic and population level approaches, exemplify the importance of allopatry and genetic drift coupled with restricted gene flow in driving plant speciation in this continental archipelago at different temporal and spatial scales. While the recent (Late Pleistocene) radiation of Aegean Nigella, as well as possible instances of incipient speciation (in the Cyclades), is shown to be strongly conditioned by (palaeo)geographic factors (including changes in sea level), shifts in breeding system (selfing) and associated isolating mechanisms have also contributed to this radiation. By contrast, founder event speciation has probably played only a minor role, perhaps reflecting a migratory situation typical for continental archipelagos characterized by niche pre-emption because of a long established resident flora. Overall, surveys of neutral molecular markers in Aegean Nigella have so far revealed population genetic processes that conform remarkably well to predictions raised by genetic drift theory. The challenge is now to gain more direct insights into the relative importance of the role of genetic drift, as opposed to natural selection, in the phenotypic and reproductive divergence among these Aegean plant species.
由海平面上升形成的大陆架岛屿系统，为研究地理隔离对由遗传漂变导致的非适应性辐射和异域物种形成的影响提供了一个绝佳的环境。爱琴海群岛形成了一个高度破碎的复合体，主要由大陆架岛屿组成，这些岛屿在相对较近的地质时期（约<520万年）彼此以及与大陆断开了连接。因此，这些生态上相当同质的岛屿为评估过去的分布范围破碎化、殖民化、基因流动和漂变对分类群多样化的相对影响提供了一个合适的生物地理背景。事实上，最近对爱琴海野芝麻复合体进行的分子生物地理学研究，结合了系统发育、谱系地理学和种群水平的方法，例证了异域性和遗传漂变以及有限的基因流动在驱动这个大陆群岛不同时空尺度上的植物物种形成中的重要性。虽然爱琴海野芝麻最近（晚更新世）的辐射以及可能的初始物种形成实例（在基克拉泽斯群岛）被证明受到（古）地理因素（包括海平面变化）的强烈影响，但繁殖系统（自交）的转变和相关的隔离机制也促成了这种辐射。相比之下，奠基者事件物种形成可能只起到了次要作用，这或许反映了大陆群岛典型的迁徙情况，由于长期存在的本地植物群导致生态位被抢占。总体而言，迄今为止对爱琴海野芝麻中性分子标记的调查揭示了种群遗传过程，这些过程与遗传漂变理论提出的预测非常吻合。现在的挑战是更直接地了解遗传漂变相对于自然选择在这些爱琴海植物物种的表型和生殖分化中所起作用的相对重要性。
