The recent and rapid spread of Themeda triandra
The recent and rapid spread of Themeda triandra
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DOI：
10.1080/23818107.2017.1391120
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发表时间：
2017-01-01
期刊：
影响因子：
1.5
通讯作者：
Lehmann, Caroline E. R.
中科院分区：
文献类型：
--
作者：
Dunning, Luke T.;Liabot, Anne-Lise;Lehmann, Caroline E. R.
热带稀树草原覆盖了20%以上的陆地表面。它们维持着哺乳动物食草动物的高度多样性，并促进频繁的火灾，这两者都取决于底层的草成分。这些栖息地通常由相对较少的类群占主导地位，占主导地位的草种的进化起源在很大程度上是未知的。在这里，我们追溯属Themeda，其中包含了一些广泛的草种占主导地位的热带稀树草原的起源。完整的叶绿体基因组组装的7个样品，并补充了叶绿体和核ITS标记的71个样品代表18的27 Themeda物种。系统发育分析支持该属和广泛分布的优势T. triandra。这个物种出现类似于1.5 Ma，来自一个在亚洲热带稀树草原生活了数百万年的群体。它在大约1.3Ma的时间迁移到澳大利亚，在大约0.5Ma的时间迁移到非洲大陆，在那里它迅速在先前存在的热带稀树草原中传播，并取代了其他物种。Themeda quadrivalvis是分布第二广的Themeda种，它是T. triandra基于整个叶绿体基因组，并可能代表了一年生形式，否则几乎无法区分从T. triandra。对T. triandra强调了热带草地生物群落在千年时间尺度上的活力，这一点尚未得到重视，在最近的进化时期，物种优势发生了巨大的变化。随后的物种更替可能对整个热带稀树草原的火灾和草食动物制度产生了深远的影响。
Tropical savannas cover over 20% of land surface. They sustain a high diversity of mammalian herbivores and promote frequent fires, both of which are dependent on the underlying grass composition. These habitats are typically dominated by relatively few taxa, and the evolutionary origins of the dominant grass species are largely unknown. Here, we trace the origins of the genus Themeda, which contains a number of widespread grass species dominating tropical savannas. Complete chloroplast genomes were assembled for seven samples and supplemented with chloroplast and nuclear ITS markers for 71 samples representing 18 of the 27 Themeda species. Phylogenetic analysis supports a South Asian origin for both the genus and the widespread dominant T. triandra. This species emerged similar to 1.5 Ma from a group that had lived in the savannas of Asia for several million years. It migrated to Australia similar to 1.3 Ma and to mainland Africa similar to 0.5 Ma, where it rapidly spread in pre-existing savannas and displaced other species. Themeda quadrivalvis, the second most widespread Themeda species, is nested within T. triandra based on whole chloroplast genomes, and may represent a recent evolution of an annual growth form that is otherwise almost indistinguishable from T. triandra. The recent spread and modernday dominance of T. triandra highlight the dynamism of tropical grassy biomes over millennial time-scales that has not been appreciated, with dramatic shifts in species dominance in recent evolutionary times. The ensuing species replacements likely had profound effects on fire and herbivore regimes across tropical savannas.