Gehrke Berit, Kandziora Martha, Pirie Michael D
Institut für Spezielle Botanik und Botanischer Garten, Johannes Gutenberg Universität, Mainz, Germany and
Institut für Spezielle Botanik und Botanischer Garten, Johannes Gutenberg Universität, Mainz, Germany and.
Ann Bot. 2016 Jan;117(1):121-31. doi: 10.1093/aob/mcv159. Epub 2015 Oct 31.
Alpine and arctic environments worldwide, including high mountains, are dominated by short-stature woody plants (dwarf shrubs). This conspicuous life form asserts considerable influence on local environmental conditions above the treeline, creating its own microhabitat. This study reconstructs the evolution of dwarf shrubs in Alchemilla in the African tropical alpine environment, where they represent one of the largest clades and are among the most common and abundant plants.
Different phylogenetic inference methods were used with plastid and nuclear DNA sequence markers, molecular dating (BEAST and RelTime), analyses of diversification rate shifts (MEDUSA and BAMM) and ancestral character and area reconstructions (Mesquite).
It is inferred that African Alchemilla species originated following long-distance dispersal to tropical East Africa, but that the evolution of dwarf shrubs occurred in Ethiopia and in tropical East Africa independently. Establishing a timeframe is challenging given inconsistencies in age estimates, but it seems likely that they originated in the Pleistocene, or at the earliest in the late Miocene. The adaptation to alpine-like environments in the form of dwarf shrubs has apparently not led to enhanced diversification rates. Ancestral reconstructions indicate reversals in Alchemilla from plants with a woody base to entirely herbaceous forms, a transition that is rarely reported in angiosperms.
Alchemilla is a clear example of in situ tropical alpine speciation. The dwarf shrub life form typical of African Alchemilla has evolved twice independently, further indicating its selective advantage in these harsh environments. However, it has not influenced diversification, which, although recent, was not rapid.
包括高山在内的全球高山和北极环境中，矮小的木本植物（矮灌木）占主导地位。这种显著的生活型对树线以上的当地环境条件产生了相当大的影响，创造了自身的微生境。本研究重建了非洲热带高山环境中羽衣草属矮灌木的演化过程，在该环境中它们是最大的分支之一，也是最常见且数量最多的植物之一。
使用了不同的系统发育推断方法，结合质体和核DNA序列标记、分子年代测定（BEAST和RelTime）、多样化速率变化分析（MEDUSA和BAMM）以及祖先性状和分布区重建（Mesquite）。
据推断，非洲羽衣草属物种起源于向热带东非的远距离扩散，但矮灌木的演化是在埃塞俄比亚和热带东非独立发生的。鉴于年龄估计存在不一致，确定一个时间框架具有挑战性，但它们似乎起源于更新世，最早可能在中新世晚期。以矮灌木形式对高山样环境的适应显然并未导致多样化速率提高。祖先重建表明，羽衣草属植物从具有木质基部的植物转变为完全草本形式，这种转变在被子植物中很少有报道。
羽衣草属是热带高山原地物种形成的一个明显例子。非洲羽衣草属典型的矮灌木生活型已经独立演化了两次，进一步表明其在这些恶劣环境中的选择优势。然而，它并未影响多样化，尽管多样化是近期发生的，但并不迅速。
