蝶形花植物猪屎豆自花传粉机制研究

Autogamy mechanism of Crotalaria pallida(Fabaceae: Papilionoideae)

关键词:  猪屎豆, 蝶形花, 主动自交, 先锋植物, 快速扩张

Key words:  Crotalaria pallida, Papilionoideae, autogamouy, pioneer plant, rapidly spread

摘要:

猪屎豆(Crotalaria pallida)为典型的蝶形花植物,分布极广,是路边或遭破坏生境中最常见的先锋种之一,野外观察未发现其有营养生殖的现象,主要为种子繁殖。该研究通过对自然生境中猪屎豆开花物候、访花昆虫及繁育系统的研究,旨在从繁殖的角度阐述其快速扩张的能力。结果表明:尽管猪屎豆的主要访花昆虫是蜜蜂,但蜜蜂的访花频率极低 [(1.73±1.30)次/花序·h^-1],且在整个花期内花药和柱头均被龙骨瓣包裹,蜜蜂访花时未成功接触柱头和花粉,不能实现传粉,因此蜜蜂不是猪屎豆有效的传粉昆虫,这与假说“蝶形花普遍是对膜翅目昆虫,尤其是对蜜蜂传粉的适应”不一致。人工授粉结果显示,猪屎豆为自交亲和种,不存在无融合生殖现象,其繁殖主要通过主动自交生产种子来实现,且在自交过程中长短花药都参与主动自交。这种自交方式不同于其他蝶形花植物的主动自交仅由短花药实现。对猪屎豆而言,长短花药均参与自交能够增加柱头的授粉几率,保证其在不利的生境中成功结籽,是其成功扩张的关键因素之一。

Abstract:

Crotalaria pallida is a typical plant of Papilionoideae. Althought it has evolved various adaptations to establish and spread rapidly through prolific seed production and/or asexual propagules, self-fertilization is always an important aspect to decide its colonization ability. It is widely distributed and is the most common pioneer plant on the road sides or destroyed envioronment. In our observation, it lacks pollinators in nature and also lacks vegetative reproduction. How does this species survive in such unpredictable habitats? We focus on its floral morphology, reproductive biology and pollinator behavior to explain its reproductive success. We observed flower development, detected pollen viability and stigma receptivity, performed manual pollination and monitored the behavior of main pollinators in C. pallida. Papilionaceous flowers are reported to show adaptation for bees which are their pollinators. Few insects visited the flowers. Several bees were observed visiting flowers but visiting frequency was low(1.73 ± 1.30 visits·inflorescence^-1·h^-1). Because the stigma and stamens were enclosed in the petal of the keel in the flower development, the visitors were not contacting any reproductive organs, and they could be considered as visitors not effecting pollination. The results of pollination experiments showed that C. pallida was self-compatible and was capable of autonomous selfing. In our study, both long-and short-anthers' descended time and function in fruit set were different from those autogamous species in the genus. For C. pallida, both long-anthers and short-anthers participated into selfing and there was no difference in fruit sets between long-and short-anther selfing(t=1.786, P=0.060). While for other species in the genus, autogamy was realized by short anthers. For C. pallida, therefore, automatic self-pollination increases the chances of seed production and protect it against extinction. Compared with other species, only short-anthers participate into autogamous pollination, both long- and short-anthers providing pollen grains to the stigma increases the success of pollination and fruit set, which is an evolutionary mechanism for the spread of C. pallida. This results are consistent with the hypothesis that species proficient at autogamy are better adapted to establish new populations and thus can more readily expand their range.