青藏高原东缘同域分布的2种橐吾属杂草的合子前生殖隔离

生殖隔离是阻止种间杂交、保持物种完整性和独立性的关键,对生物多样性的产生和维持有重要意义.不同物种间的生殖隔离形成阶段、方式和强度不完全相同,因而对物种间隔离机制的研究有助于揭示物种形成和维持机制.对青藏高原东缘同域分布的2种橐吾属杂草黄帚橐吾和箭叶橐吾的花期物候观察、访花昆虫观察及花粉-柱头亲和性进行研究,分析了2种橐吾多种合子前生殖隔离机制的特点及其在生殖隔离中的作用.结果表明: 黄帚橐吾种群花期比箭叶橐吾早20 d左右,虽然盛花期存在差异,但是2种群花期存在10 d左右的重叠期,并且在重叠期内2种橐吾花粉和柱头均具有活性.2种橐吾共享传粉昆虫,为泛化传粉模式,并且传粉者对2种植物的访花行为相似,存在2种植物间交叉访问.尽管2种橐吾花期不存在完全的时间隔离,也不存在完全的传粉者隔离,但2种橐吾柱头对异源花粉的亲和性差,表现为柱头对异源花粉有明显的排斥反应,异源花粉管在柱头上的生长过程明显受阻.这种花粉-柱头排异形式很有可能是2种橐吾属植物重要的合子前隔离机制,从而避免了种间的自然杂交,更好地维持了自然种群的多样性和遗传结构的稳定性.

Prezygotic reproductive isolation of two sympatric species of Ligularia weeds in eastern Qinghai-Tibet Plateau,China

Reproductive isolation, the key process to prevent interspecific hybridization and keep the completeness and independence of species, is crucial to the formation and maintenance of biodiversity. The forming steps, methods and intensities of reproductive isolation between different species are not completely the same. Literatures on reproductive isolation between species provide valuable evidence for speciation and its maintenance. Flowering phenology, flowering-visiting insects, and pollen-stigma compatibility were observed for Ligularia virgaurea and L. sagitta, two species of weeds sympatrically distributed in eastern Qinghai-Tibet Plateau. The characteristics of reproductive isolation mechanism of both species and its role in reproductive isolation were also studied. The results showed that the flowering period of L. virgaurea was 20 d earlier than that of L. sagitta. Although the full-blooming period separated, there was a roughly 10 d overlap between the two species. Meanwhile, the pollens and stigmas of the two species were both viability in the overlapped 10 d. L. virgaurea and L. sagitta shared the same types of pollinating insects, which was a generalized pollination type. Besides, the flower-visiting behavior towards the two species from the pollinators was similar, along with the interleaved access between the two species. There was no complete time isolation and no complete pollinator isolation between the two species, but the stigma had poor compatibility towards heterogenic pollen. The germination of pollen on stigma and growth of the pollen tube was hampered. Furthermore, the rejection of pollen-stigma was likely to be an important prezygotic reproductive isolation between L. virgaurea and L. sagitta, thus avoiding the natural hybridization and maintaining the diversity and genetic stability of the two species.