Potts Bradley M, Reid James B
Botany Department, University of Tasmania, Hobart, Tasmania, 7001, AUSTRALIA.
Evolution. 1988 Nov;42(6):1245-1255. doi: 10.1111/j.1558-5646.1988.tb04184.x.
An example from the genus Eucalyptus is used to argue that hybridization may be of evolutionary significance as a means of gene dispersal where seed dispersal is limited. A previous study of regeneration of E. risdonii and E. amygdalina indicated that the current selective regime was favoring E. risaonii. However, the dispersal of E. risdonii by seeds is shown to be limited (s, = 4.6 m). By comparison, the flow of E. risdonii genes into the range of E. amygdalina by pollen dispersal and F hybridization is widespread (s = 82 m). While the actual level of hybridization is low, interspecific hybridization effectively doubles the dispersal of E. risdonii genes into the range of E. amygdalina. This pollen flow can have a significant genetic impact, since isolated hybrids or patches of abnormal phenotypes have been found 200-300 m from the species boundary. Based on lignotuber size, some of these patches appear to have been founded by F hybrids. The frequency of E. risdonii types in the patches appears to increase with patch size suggesting that there is selection for this phenotype in subsequent generations. E. risdonii-like individuals were recovered in the progeny from both intermediate and E. risdonii backcross phenotypes. These results suggest that E. risdonii may invade suitable habitat islands within the E. amygdalina forest, independently of seed migration, by long-distance pollen migration followed by selection for the gene combinations of the pollen parent.
以桉属的一个例子来论证，在种子传播受限的情况下，杂交作为一种基因传播方式可能具有进化意义。先前一项关于里斯登桉和杏仁桉再生的研究表明，当前的选择机制有利于里斯登桉。然而，研究显示里斯登桉通过种子传播的范围有限（s = 4.6米）。相比之下，里斯登桉的基因通过花粉传播和F杂交流入杏仁桉分布范围的情况则很普遍（s = 82米）。虽然实际的杂交水平较低，但种间杂交有效地使里斯登桉基因在杏仁桉分布范围内的传播距离增加了一倍。这种花粉流可能会产生重大的遗传影响，因为在距离物种边界200 - 300米处发现了孤立的杂种或异常表型斑块。基于木瘤大小，其中一些斑块似乎是由F杂种形成的。斑块中里斯登桉类型的频率似乎随着斑块大小的增加而增加，这表明在后代中对这种表型存在选择。在中间型和里斯登桉回交表型的后代中都发现了类似里斯登桉的个体。这些结果表明，里斯登桉可能通过远距离花粉迁移，随后对花粉亲本的基因组合进行选择，从而独立于种子迁移，侵入杏仁桉森林内适宜的栖息地岛屿。
