探讨种间传粉在杜鹃花属自然杂交物种形成中的作用

The potential roles of interspecific pollination in natural hybridization of Rhododendron species in Yunnan,China

自然杂交是物种形成的一个途径,在植物进化中起着重要的作用。自然杂交主要通过种间的基因交流,花粉传递则是基因交流的主要途径。马缨花(Rhododendron delavayi)、大白花杜鹃(R.decorum)、迷人杜鹃(R.agastum)和露珠杜鹃(R.irroratum)是在云南广泛分布的杜鹃花种类,马缨花与大白花杜鹃形态上区别明显,而它们的可能杂交种迷人杜鹃和露珠杜鹃在形态上基本介于二者之间。本文对这4种杜鹃花的开花物候和访花昆虫的种类进行了观察,并进行了其繁育系统和种子萌发的实验。我们发现马缨花的花期从3月初至5月底,迷人杜鹃与露珠杜鹃花期基本一致,为3月初至4月初,二者同大白花杜鹃基本不存在花期重叠,大白花杜鹃的花期为4月中旬至5月底。4种杜鹃花的开花期不同年份稍有变化,其单花开花周期都在一周以上。4种杜鹃花的传粉昆虫虽然种类和数量上有所不同,但都以膜翅目和双翅目昆虫为主,中华蜜蜂(Apis cerana cerana)是其共有的传粉昆虫。繁育系统研究发现,除露珠杜鹃外,其余3种自花不育,而种间杂交不存在任何生殖障碍,可以产生萌发率很高的种子。通过分析4种杜鹃花开花物候重叠、共有传粉昆虫及种间杂交可育等现象,探讨了传粉昆虫和异花授粉的机制在自然杂交物种形成中的作用及杂交种的适应能力。

Natural hybridization mediated by pollen flow has been considered as an important factor to drive speciation in Rhododendron, one of the largest genera within alpine plants. The diversity of Rhododendron species is centered in southwestern China, yet the potential role of interspecific pollination in natural hybridization has not been empirically examined in this area. Here we investigated the flowering period and floral visitors, and conducted a series of pollination experiments to examine breeding systems and hybrid compatibility within four Rhododendron which are frequently sympatric in Yunnan Province. Rhododendron delavayi and R. decorum are clearly distinct by their morphological traits, but the putative hybrids R. agasturn and R. irroratum are morphologically between the other two species. We observed that R. delavayi flowered from the beginning of March to the end of May, R. agastum and R. irroratum flowered from the beginning of March to the beginning of April, and after their flowering periods ended, R. decorum began to flower until the end of May. The anthesis of single flowers of the four Rhododendron species was almost one week. The floral visitors belong to the Hymenoptera and Diptera Orders, and Apis cerana cerana visited all of the four Rhododendron species. We found that R. delavayi, R. agastum and R. decorum are self-incompatible, but not R. irroratum. No breeding barrier between any of the four species was detected by artificial pollination,and the hybrid seeds were fertile. The hybrids between four species showed equivalent fitness to their parents. We suggest that the role of potential interspecific pollination is essential to hybrid speciation and evolution of Rhododendron species.