Foster Susan A, McKinnon Gay E, Steane Dorothy A, Potts Brad M, Vaillancourt René E
School of Plant Science and Cooperative Research Centre for Forestry, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia.
New Phytol. 2007;175(2):370-380. doi: 10.1111/j.1469-8137.2007.02077.x.
Three small populations of a dwarf ecotype of the forest tree Eucalyptus globulus are found on exposed granite headlands in south-eastern Australia. These populations are separated by at least 100 km. Here, we used 12 nuclear microsatellites and a chloroplast DNA marker to investigate the genetic affinities of the dwarf populations to one another and to their nearest populations of tall E. globulus. Cape Tourville was studied in greater detail to assess the processes enabling the maintenance of distinct ecotypes in close geographical proximity. The three dwarf populations were not related to one another and were more closely related to adjacent tall trees than to one another. At Cape Tourville the dwarf and tall ecotypes were significantly differentiated in microsatellites and in chloroplast DNA. The dwarf and tall populations differed in flowering time and no evidence of pollen dispersal from the more extensive tall to the dwarf population was found. The three dwarf populations have evolved in parallel from the local tall ecotypes. This study shows that small marginal populations of eucalypts are capable of developing reproductive isolation from nearby larger populations through differences in flowering time and/or minor spatial separation, making parapatric speciation possible.
在澳大利亚东南部暴露的花岗岩岬角上发现了三个小叶桉矮化生态型的小种群。这些种群相隔至少100公里。在此，我们使用12个核微卫星和一个叶绿体DNA标记来研究矮化种群之间以及它们与最近的高大叶桉种群之间的遗传亲缘关系。对图维尔角进行了更详细的研究，以评估在地理上相近的情况下维持不同生态型的过程。这三个矮化种群彼此之间没有亲缘关系，与相邻的高大树木的关系比它们彼此之间的关系更密切。在图维尔角，矮化和高大生态型在微卫星和叶绿体DNA方面有显著差异。矮化和高大种群在开花时间上不同，未发现有花粉从分布更广的高大种群传播到矮化种群的证据。这三个矮化种群是从当地的高大生态型平行进化而来的。这项研究表明，桉属植物的小边缘种群能够通过开花时间的差异和/或微小的空间隔离，从附近较大的种群中发展出生殖隔离，从而使邻域物种形成成为可能。
