山莨菪(茄科)的传粉生物学

Pollination biology of Anisodus tanguticus (Solanaceae)

茄科的多数种类具有自交不亲和的特点,主要通过异花传粉结实;但是,一些物种或者物种内的部分种群或者个体却高度自交亲合,转变为自交的繁育系统。该科植物山莨菪(Anisodus tanguticus)主要分布在青藏高原,开花较早,比其他晚开花的植物种类更加缺少有效的异花传粉昆虫。我们选择了位于不同海拔高度的2个种群进行比较研究,主要目的是检验该物种的繁育系统是否在极端环境下由于传粉者的缺乏而发生了部分改变。研究发现,山莨菪的花不完全雌性先熟,柱头和花药间的平均距离随着花开放时间的延长而不断缩小,但两者在多数花的单花花期结束时并没有发生接触。因此,山莨菪花主要表现为适应异花传粉的雌雄异位特征。然而,少数花(4.9%)的柱头和花药发生接触,为"自动自交"的传粉解除了空间隔离。2个种群的多数个体存在自交不亲和机制,应具有异花传粉的繁育系统;但是部分个体具有明显的自交亲和能力,为自交提供了生理基础。高海拔种群的传粉昆虫主要是厕蝇(Fannia sp.),它们在不同植株间的活动能够保证异花传粉结实;同时该种群的部分个体存在"自动自交"。低海拔种群的主要访花昆虫是蚂蚁,它们在花内的活动导致花粉在同一朵花内传递,而引起"协助自交";而异花传粉昆虫厕蝇的访花频率则较高海拔种群低。两个种群的结实均由于异花传粉者不足而受到传粉限制。因此两种不同类型的自交机制为该早期开花植物异花访花昆虫的不足提供了一定程度上的繁殖补偿。

Self-incompatibility occurs widely in the Solanaceae, but a few species in this family, or a few intraspecific populations or a few individuals within the populations are highly self-compatible and their breeding systems have evolved from outcrossing to selfing. We studied pollination biology of Anisodus tanguticus from this family, a perennial endemic to the Qinghai-Tibetan Plateau. This species flowers in the early summer and probably suffers from the serious limitations of the outcrossing pollinator. We aimed to test whether the breeding systems of a few individuals in this species have shifted from outcrossing to selfing. Our experiments and observations were conducted in two populations with different altitudes. Most flowers of this species were incompletely protogynous, and the mean distance between the stigma and anthers decreased gradually with floral longevity. Both stigma and anthers did not come into touch when the corolla wilted in most of the monitored flowers and such herkogamy favours outcrossing. However, the complete contact of stigma and anthers in 4.9% of the measured flowers suggested potential occurrence of ＂autonomous selfing＂ in these flowers. Most of the examined individuals in both populations are self-incompatible and have to depend on insects for pollination. However, a few of them were found to be self-compatible. Flies were the effective outcrossing pollinators in the high altitude population and ＂autonomous selfing＂ was detected in a few individuals of this population. In contrast, the effective outcrossing pollinators were rarely observed in the low altitude population and the dominant visitors or pollinators, ants in this population, transferred pollen within the single flower, which finally resulted in ＂facilitated selfing＂. Pollination limitations were obvious in both populations due to the lack of enough outcrossing pollinators. Two different selfing mechanisms, uncovered here, may provide a partial compensation for the natural reproduction of this alpine species in the arid alpine habitats when flowering at the early summer.