J Plant Ecol ›› 2024, Vol. 17 ›› Issue (1): rtad036.DOI: 10.1093/jpe/rtad036

• Research Article •    

The conspicuously large bracts influence reproductive success in Thunia alba (Orchidaceae)

Shi-Mao Wu, Jiang-Yun Gao*   

  1. Institute of Biodiversity, School of Ecology and Environmental Science, Yunnan University, Kunming, Yunnan 650500, China
  • Received:2023-08-25 Revised:2023-10-20 Accepted:2023-11-04 Online:2023-11-09 Published:2024-02-01
  • Contact: * E-mail: jiangyun.gao@ynu.edu.cn


Abstract: In angiosperms, diverse floral traits are adaptations to various selective pressures and ecological functions. So far, studies on floral traits in orchids have focused primarily on the labellum but never on bracts. A bumblebee-pollinated and rewarding terrestrial or epiphytic herb, Thunia alba (Lindley) H. G. Reichenbach (Orchidaceae), has conspicuously large and curly bracts that enclose the spur and pedicel of flowers. We hypothesized that these large bracts could protect spurs against nectar robbers. To confirm this hypothesis, we experimentally removed the bracts to record the changes in visiting behavior of mutualistic pollinators and antagonistic nectar robbers and evaluated their effects on reproduction success. Our result revealed that Bombus breviceps, the only pollinator of T. alba, shifted to nectar robbery when the bracts were removed, and the proportion of robbed flowers also significantly increased. Thunia alba was found to be pollinator limited regardless of whether in intact treatment or removed bract treatment. Removal of bracts had no effect on the visiting frequency of B. breviceps, but it reduced male and female reproductive success. These findings indicate that, under complex environmental pressures with limited pollination, large bracts can protect against nectar robbers and enhance the fitness of T. alba.

Key words: bract, pollinator, nectar robbery, reproductive success, Thunia alba, Bombus breviceps

在被子植物中,多样的花部特征是为了适应各种选择压力和生态功能。到目前为止,对兰科植物花部特征的生态功能研究主要集中在唇瓣,而从未有对苞片的研究。本研究以一种熊蜂授粉并且提供花蜜报酬的地生或附生兰科植物笋兰(Thunia alba)为研究材料,其大而显著形似舟状的苞片包裹着花蜜距和花梗。我们猜想显著的大苞片能够保护蜜距,抵御盗蜜者。为了验证这一假设,我们通过实验去除苞片,记录传粉者和盗蜜者访花行为的变化,并评估了它们对笋兰繁殖成功的影响。研究结果表明,当苞片被去除后,唯一的传粉者短头熊蜂(Bombus breviceps)转变为盗蜜者,并且被盗蜜的花的比例也显著增加。无论是花苞片被去除的处理组还是未处理的对照组,笋兰都是受传粉者限制的。去除苞片对传粉者的访花频率并没有影响,但是显著降低了笋兰雄性和雌性的繁殖成功率。本研究表明,在复杂的授粉限制的环境压力下,大而显著的苞片可以防止花被盗蜜者盗蜜从而提高笋兰的整体适合度。

关键词: 苞片, 传粉者, 盗蜜, 繁殖成功, 笋兰(Thunia alba), 短头熊蜂(Bombus breviceps)