点地梅属的分子系统学、生物地理学和垫状形态的趋同进化

Molecular phylogeny and biogeography of Androsace (Primulaceae) and the convergent evolution of cushion morphology

报道了青藏高原地区的点地梅属AndrosaceL .及羽叶点地梅属PomatosaceMaxim .共 1 4种 2 9个居群的ITS与trnL_FDNA序列各 2 7与 2 5条 ;并结合已报道相关种类的有关序列 ,构建了“点地梅群”的分子系统发育树。研究发现“点地梅群”的 4个属为一单系类群 ,含有两个稳定的分支 :一支全部由点地梅属的种类组成 ,另一支分别由羽叶点地梅属、DouglasiaLindley、VitalianaSesler和 9种点地梅属植物组成 ;点地梅属裂叶组sect.SamueliaSchlechtd .的 3个种与点地梅组sect.Androsace的 2个种在 3套序列分析中位于不同的系统位置。各分支基部的种都分布在中国东南部及青藏高原东部 ,分子地理标记的结果支持形态学提出该地区为“点地梅群”植物起源地的假设。从青藏高原东部地区向欧洲及其他北半球地区存在不同时期内多个进化支的多次扩散。粗略的时间估算表明该群植物可能是在第三纪的中新世以来才开始发生的。垫状种类分别在青藏高原和欧洲独立起源 ,而在青藏高原地区的分化要早于在欧洲的分化 ,在前一地区可能与青藏高原自中新世开始发生的造山运动、形成高海拔的山地有关 ,而在后一地区则是与第三纪末至第四纪的冰期气候反复波动有关。垫状植物在青藏高原上的大规模分布则可能较晚 ,与冰期结束后全新世晚期气?

Androsace L. consists of more than 100 species distributed mainly in northern temperate areas. This genus, typically characterized by having small flowers with a constricted corolla throat, was subdivided into six sections: sect. Samuelia Schlechtd., sect. Mirabiles (Hand. -Mazz.) Yang & Huang, sect. Androsace, sect. Chamaejasme Koch., sect. Aizoidium Hand. -Mazz., and sect. Orthocaulon Hand. -Mazz. In this genus, the species with cushion-like growth belong to sect. Chamaejasme occurring in alpine habitats. There are other three small genera in the tribe Androsaceae. Pomatosace Maxim., with only one species, P. filicula Maxim., endemic to Qinghai-Tibetan Plateau, is traditionally placed in the subtribe Soldanellinae because of its circumscissile capsules, but other morphological characters and the recently reported evidence from cytology indicate that its affinity is closer with Androsace. Douglasia Lindley has eight homogeneous species in Northern American mountains. Vitaliana Sesler, with only one species in the European Alps, is usually considered a congener of Douglasia. These four genera, morphologically similar in having small flowers with a constricted corolla throat and 'Androsace pollen', referred here as 'Androsace group', am disjunctly distributed from the Qinghai-Tibetan Plateau, to Central- and Northern-Asia, Europe and North America. It is an ideal group to elucidate the origin and dispersal patterns of the Northern Hemisphere flora, which has a distribution center in the eastern Qinghai-Tibetan Plateau and the Hengduan Mountains. In addition, the habits of this group range from annuals to rosette perennials and cushion-like perennials. The cushion-like species are disjunctly distributed in the central Qinghai-Tibetan Plateau and European Alps mountains. Further studies are needed to determine whether they are closely related to each other or it is only the result of convergent evolution under the habitat pressure selection in separate sites. We firstly reported cpDNA trnL-F, nrDNA ITS sequences respectively or both for 29 populations of 14 species in Androsace and Pomatosace mainly from the central Qinghai-Tibetan Plateau. A phylogeny was further constructed for these species, and those distributed in Europe and North America in 'Androsace group' and related genera in Primulaceae based on newly reported sequences and those downloaded from GenBank. Phylogenetic inferences indicated that the four genera in 'Androsace group' form a well-supported monophyletic clade. Two main clades were discovered in the 'Androsace group': a wholly Androsace clade, and the other comprising Pomatosace, Douglasia, Vitaliana and nine Androsace species in all analyses. The grouping and position of three species of sect. Samelia and two species of sect. Androsace varied according to the analyses of the different datasets, trnL-F, ITS or a combination of them. The biogeographical mapping of species distribution revealed that the basal species of each clade sited in southeastern China and the eastern Qinghai-Tibetan Plateau, which obviously supports the origin area hypotheses for 'Androsace group' based on morphological studies. From the eastern Qinghai-Tibetan Plateau multiple lineages spread to and colonized Europe in different ages. The crude timing based on ITS sequence differentiation indicated a recent diversification of 'Androsace group' within Miocene of the Tertiary. The cushion-like species evolved independently in Asia and Europe. The origin and diversification of cushion-like species in the Qinghai-Tibetan Plateau might be earlier than those in Europe. Their occurrence in the Qinghai-Tibetan Plateau area might be correlated with the large-scale uprising of the plateau and the mountains building since Miocene. But the appearance of the cushion-like species in Europe might result from the fast habitat isolation due to the climate oscillation and the cycles of developing and retreating of the ice sheet in the Northern Hemisphere during the Quaternary. The large-scale colonization of cushion-like Androsace species in the Qinghai-Tibetan Plateau probably occurred in the late Holocene when the global climate re-cooled after the end of glacial cycles. The intraspecific genetic differentiation in some species might partly reflect their retreat and re-colonization in the Qinghai-Tibetan Plateau area during the climate oscillation.