McKinnon Gay E, Vaillancourt René E, Steane Dorothy A, Potts Brad M
School of Plant Science and Cooperative Research Centre for Sustainable Production Forestry, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia.
Mol Ecol. 2004 Dec;13(12):3751-62. doi: 10.1111/j.1365-294X.2004.02364.x.
The process of genetic assimilation of rare species by hybridizing congeners has been documented in a number of plant genera. This raises the possibility that some of the genetic diversity found in phylogeographical studies of widespread species has been acquired through hybridization with species that are now rare or extinct. In this fine-scale phylogeographical analysis, we show that a rare eucalypt species is leaving its trace in the chloroplast genome of a more abundant congener. The heart-leafed silver gum, Eucalyptus cordata, is a rare endemic of south-eastern Tasmania. Its populations are scattered amidst populations of more abundant related species, including the Tasmanian blue gum, Eucalyptus globulus. Using 339 samples from across the full range of both species, we compared chloroplast (cp) DNA haplotype phylogeography in E. globulus and E. cordata. The genealogy and distribution of chloroplast haplotypes suggest that E. globulus has acquired cpDNA from E. cordata in at least four different mixed populations. Shared haplotypes are highest in E. globulus sampled within 2 km of known E. cordata populations and drop to zero at a distance of 25 km from the nearest known E. cordata population. Localized haplotype sharing occurs in the absence of obvious hybrid zones or locally shared nuclear ribosomal DNA sequences. Given that the future loss of E. cordata from some mixed populations is likely, these findings indicate that phylogeographical analyses of organellar DNA should consider the possibility of introgression, even from species that have been eliminated from the sites of interest.
通过杂交同属物种对稀有物种进行基因同化的过程，已在许多植物属中得到记载。这就引发了一种可能性，即在对广泛分布物种的系统地理学研究中发现的一些遗传多样性，是通过与现已稀有或灭绝的物种杂交而获得的。在这项精细尺度的系统地理学分析中，我们表明一种稀有桉树物种正在其更常见的同属物种的叶绿体基因组中留下痕迹。心叶银桉（Eucalyptus cordata）是塔斯马尼亚东南部的一种稀有特有物种。其种群散布在包括塔斯马尼亚蓝桉（Eucalyptus globulus）在内的更常见近缘物种的种群之中。我们使用了来自这两个物种整个分布范围的339个样本，比较了蓝桉和心叶银桉的叶绿体（cp）DNA单倍型系统地理学。叶绿体单倍型的谱系和分布表明，蓝桉至少在四个不同的混合种群中从心叶银桉那里获得了cpDNA。在距离已知心叶银桉种群2公里范围内采集的蓝桉样本中，共享单倍型比例最高，而在距离最近已知心叶银桉种群25公里处，共享单倍型比例降至零。在没有明显杂交带或局部共享核糖体DNA序列的情况下，出现了局部单倍型共享现象。鉴于心叶银桉在一些混合种群中未来可能消失，这些发现表明，对细胞器DNA的系统地理学分析应考虑基因渗入的可能性，即使是来自已从相关地点消失的物种。
