Tagane Shuichiro, Hiramatsu Michikazu, Okubo Hiroshi
Laboratory of Horticultural Science, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-858, Japan.
J Plant Res. 2008 Jul;121(4):387-95. doi: 10.1007/s10265-008-0167-7. Epub 2008 May 17.
We examined natural hybridization between two morphologically and ecologically divergent species on Yakushima Island-the light-purple flowered Rhododendron eriocarpum native to seaside habitats and the red flowered R. indicum native to riverside habitats. By investigation of morphological traits and amplified fragment length polymorphisms (AFLP) we found that hybrid individuals morphologically and genetically intermediate between the two species grow mainly in the seaside areas of the island. The degree of morphological and genetic variation was different among the seaside hybrid populations. Although most pollinator species were exclusive to one of the two flower color groups, the halictine bees of Lasioglossum were observed in both the color types. The crucial interspecific incompatibility after pollination has not been previously described. Geographic distance between the populations is likely to be an important primary factor in bringing about natural hybridization and determining the degree of introgression between R. eriocarpum and R. indicum. The fact that hybrids occur mostly in the seaside area on Yakushima Island indicates that asymmetrical introgression occurs from R. indicum to R. eriocarpum. Alternatively, strong habitat-mediated selection from recurrent floods may prevent the hybrids from colonizing riverside habitats.
我们研究了屋久岛上两个在形态和生态上存在差异的物种之间的自然杂交现象，即原产于海滨栖息地的浅紫色花朵的毛果杜鹃和原产于河边栖息地的红色花朵的皋月杜鹃。通过对形态特征和扩增片段长度多态性（AFLP）的研究，我们发现，在形态和遗传上介于这两个物种之间的杂交个体主要生长在该岛的海滨地区。海滨杂交种群之间的形态和遗传变异程度各不相同。尽管大多数传粉者物种只专一访问两种花色组中的一种，但在两种花色类型中均观察到了隧蜂属的隧蜂。此前尚未描述授粉后关键的种间不亲和性。种群之间的地理距离可能是导致自然杂交以及决定毛果杜鹃和皋月杜鹃之间渐渗程度的一个重要首要因素。杂交种大多出现在屋久岛的海滨地区这一事实表明，存在从皋月杜鹃到毛果杜鹃的不对称渐渗。或者，周期性洪水带来的强烈生境介导选择可能会阻止杂交种在河边栖息地定殖。
