Biodiversity Science ›› 2007, Vol. 15 ›› Issue (6): 618-625.doi: 10.1360/biodiv.070181

Special Issue: Studies on Plant–Pollinator Interaction

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Floral advertisement and rewards in bumblebee-pollinated Aconitum kusnezoffii (Ranunculaceae)

Wanjin Liao*, Zhengmei Wang, Lina Xie, Wen Xiao, Yue Sun   

  1. Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering & Institute of Ecology, Bei-jing Normal University, Beijing 100875
  • Online:2007-11-20

Interaction between animal-pollinated plants and their pollinators is thought to be an important selecting force shaping the evolution of flowers. Successful pollination of a plant relies on its attractiveness to pollinators and the ability of the pollinators to deposit enough compatible pollen on the flower’s stigma. To assess the attractiveness, we manipulated the flower of Aconitum kusnezoffii by removing the sepals and pet-als, respectively. We then evaluated the mating system based on pollinator behavior and flower biology of A. kusnezoffii. The bumblebee, Bombus ignites, was the effective pollinator of A. kusnezoffii. Bumblebee be-havior differed on the manipulated flowers. The visiting frequency was significantly reduced by se-pal-removal treatment, but remained unchanged by nectar-removal treatment. Bumblebees were attracted by the flower exterior morphology formed by five sepals, not by the nectary formed by the two petals. The two lower sepals provided a landing platform, and the uppermost sepal functioned as a nectar guide, ensuring bumblebee find the nectar precisely and rapidly. The two lateral sepals restricted the direction in which a bumblebee can enter the flower, ensuring pollination efficiency in zygomorphic flowers. Nectar was the main reward for bumblebees, with a sugar concentration of 39.23% and histidine concentration of 0.25 μg/μL. The flower of A. kusnezoffii was large, protandrous and herkogamous, suggesting an outcrossing mating system based on the outcrossing index. In Aconitum inflorescences the oldest flowers were functionally female at the bottom of acropetal racemes, while younger flowers were functionally male at the upper positions. Bombus ignites generally flew from a younger functionally male flower near the top of an A. kusnezoffii inflorescence to an older functionally female flower near the bottom of another inflorescence, and then moved progres-sively upward. This behavior promoted the outcrossing of A. kusnezoffii. Aconitum kusnezoffii flowers were strongly protandrous, with the male phase lasting 2–4 days, during which the anthers gradually dehisced. Aconitum packaged pollen within each flower as individual anthers dehisced over a protracted period. Such pollen packaging necessarily limited pollen removal during single visits and increased male fitness by pro-moting pollen dispersal.

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