Joly Simon, Heenan Peter B, Lockhart Peter J
Allan Wilson Centre for Molecular Ecology and Evolution, Massey University, New Zealand.
Mol Phylogenet Evol. 2009 May;51(2):365-72. doi: 10.1016/j.ympev.2009.02.015. Epub 2009 Feb 28.
The Southern Alps in New Zealand contain many herbaceous plant groups that have radiated during the Plicoene-Pleistocene. The species in these genera tend to be polyploid relative to their overseas close relatives, an observation of much interest given that hybridization and allopolyploidy have recently been suggested as a possible stimulus for adaptive radiation. We were interested to determine whether or not allopollyploidy was a feature of Pachycladon, a genus which is hypothesised to have adaptively diversified onto different geological substrates in the mountains of the South Island of New Zealand. Phylogenetic analyses of five single-copy nuclear genes show that Pachycladon species have two copies of each gene representing two highly diverged evolutionary lineages from the Brassicaceae. Molecular clock analyses of all loci suggest that the two genome copies in Pachycladon diverged 8 million years ago, and that the allopolyploid origin of the genus occurred during the Pleistocene between 1.6 and 0.8 million years ago. This hybridization event at the origin of the Pachycladon radiation is perhaps the most extreme example yet reported of successful hybridization between distantly related parents.
新西兰的南阿尔卑斯山脉包含许多在上新世-更新世期间辐射演化的草本植物群。相对于其在海外的近缘亲属，这些属中的物种往往是多倍体，鉴于杂交和异源多倍体最近被认为可能是适应性辐射的一种刺激因素，这一观察结果备受关注。我们感兴趣的是确定异源多倍体是否是厚叶荠属（Pachycladon）的一个特征，该属被假设已在新西兰南岛山区的不同地质基质上适应性地多样化。对五个单拷贝核基因的系统发育分析表明，厚叶荠属物种的每个基因都有两个拷贝，代表十字花科的两个高度分化的进化谱系。对所有基因座的分子钟分析表明，厚叶荠属的两个基因组拷贝在800万年前发生了分化，该属的异源多倍体起源发生在更新世期间的160万至80万年前。厚叶荠属辐射起源时的这种杂交事件可能是迄今报道的远缘亲本之间成功杂交的最极端例子。
