Muloko-Ntoutoume N, Petit R J, White L, Abernethy K
Unité de Génétique Moléculaire des Ecosystèmes Tropicaux, CIRMF, BP 769, Franceville, Gabon,Laboratoire de Génétique et d'Amélioration des arbres forestiers, INRA, Pierroton, BP 45, F-33611 Gazinet cedex, France.
Mol Ecol. 2000 Mar;9(3):359-63. doi: 10.1046/j.1365-294x.2000.00859.x.
One of the dominant savannah colonists in Gabon is Aucoumea klaineana or Okoumé (Burseraceae), an endemic species which belongs to a monotypic genus. Chloroplast DNA (cpDNA) variation was studied in this species by means of PCR amplification of 40 kb of cpDNA sequences, followed by restriction analysis of the resulting fragments. No insertion/deletion events were noted, and a single point mutation was found. The level of differentiation among the 19 populations studied was relatively low (GST = 0.54) compared to other plant species (mean of 0.76), in agreement with the pioneer status of the species. However, cpDNA diversity was geographically structured, with the less frequent haplotype occurring only in populations from southern Gabon. This distribution might suggest either that there were two ancient source populations of Okoumé, one in the north and the other in the south, from which the colonizing process of the savannah began after the last ice age, or alternatively that there was one polymorphic source in the south. The low level of cpDNA diversity could indicate that Okoumé populations in these refugia were quite small.
加蓬热带稀树草原的主要定居植物之一是奥古曼（Aucoumea klaineana）或奥古梅（Okoumé，橄榄科），这是一种属于单型属的特有物种。通过对40 kb叶绿体DNA（cpDNA）序列进行PCR扩增，随后对所得片段进行限制性分析，研究了该物种的叶绿体DNA变异。未发现插入/缺失事件，仅发现一个单点突变。与其他植物物种（平均值为0.76）相比，所研究的19个种群之间的分化水平相对较低（GST = 0.54），这与该物种的先锋地位相符。然而，cpDNA多样性具有地理结构，频率较低的单倍型仅出现在加蓬南部的种群中。这种分布可能表明，奥古梅有两个古老的源种群，一个在北部，另一个在南部，自上一个冰河时代后，热带稀树草原的殖民化进程就从这两个种群开始；或者，也可能表明南部存在一个多态性源种群。cpDNA多样性水平较低可能表明这些避难所中的奥古梅种群规模相当小。
