Al-Rabab'ah Mohammad A, Williams Claire G
Department of Forest Science, Texas A & M University, College Station, Texas, USA.
Mol Ecol. 2004 May;13(5):1075-84. doi: 10.1111/j.1365-294X.2004.02142.x.
The retreating edge hypothesis for species responding to climate change predicts severe bottlenecks and eventual extinction. The disjunct Lost Pines population at the westernmost edge of the widespread Pinus taeda range is well suited for testing this prediction. The occurrence of one or more genetic bottlenecks in the Lost Pines population was tested using 34 nuclear microsatellite markers and a control sample from the larger, more continuous east Texas P. taeda forests. The Lost Pines population has undergone drastic contractions in effective population size between 3000 and 30 000 years bp. These results were supported by: (i) detection of transient heterozygosity excess, (ii) a mode-shift indicator of allele frequencies, and (iii) a ratio of allele number to allele size range. No bottleneck was detected for the east Texas control using any of the three methods. The distribution of allele frequencies was skewed for the Lost Pines population compared to the control, indicating a loss of rare alleles. However, allelic diversity was similar between the Lost Pines population and its east Texas control; the mean allele number per locus was 5.29 and 5.38, respectively. It is proposed that the Lost Pines population was the western refugium for P. taeda during Pleistocene glaciation and that East Texas P. taeda forests descended from the bottlenecked Lost Pines population.
物种对气候变化响应的退缩边缘假说预测会出现严重瓶颈并最终导致灭绝。广泛分布的火炬松分布范围最西端孤立的失落松林种群非常适合检验这一预测。使用34个核微卫星标记和来自更大、更连续的东德克萨斯火炬松森林的对照样本，对失落松林种群中一个或多个遗传瓶颈的发生情况进行了检测。失落松林种群在距今3000至30000年前有效种群大小经历了急剧收缩。这些结果得到了以下几点支持：（i）检测到瞬时杂合子过剩，（ii）等位基因频率的模式转移指标，以及（iii）等位基因数量与等位基因大小范围的比率。使用这三种方法中的任何一种，均未在东德克萨斯对照中检测到瓶颈。与对照相比，失落松林种群的等位基因频率分布存在偏差，表明稀有等位基因有所丢失。然而，失落松林种群与其东德克萨斯对照之间的等位基因多样性相似；每个位点的平均等位基因数分别为5.29和5.38。有人提出，失落松林种群是更新世冰川期火炬松的西部避难所，东德克萨斯火炬松森林则起源于经历瓶颈的失落松林种群。
