兔耳兰食源性欺骗传粉的研究

Food-deceptive pollination in Cymbidium lancifolium (Orchidaceae) in Guangxi,China

兰科植物具有精巧、多样化的花部结构以及高度多样的吸引传粉者方式。作者对广西雅长兰科植物自治区级保护区内的一个兔耳兰(Cymbidium lancifolium)居群进行了连续2年的观察和研究。观察发现兔耳兰唯一的传粉者为膜翅目蜜蜂科的中华蜜蜂(Apis cerana cerana)。中华蜜蜂一般直接落在唇瓣外弯的中裂片上,然后调整身体的方向,进入花中,当发现花中无蜜液等回报时,借助于后足的蹬力退出花朵。在退出的过程中,花粉块连同药帽会通过粘盘粘附在中华蜜蜂的胸部。中华蜜蜂在花内的停留时间为8-71s,平均18.3s(N=11)。根据观察我们推测兔耳兰可能是通过其唇瓣上无规则的紫栗色小斑点(假蜜导)来吸引中华蜜蜂为其传粉,属于食源性欺骗方式。在传粉过程中兔耳兰的药帽与花粉团和粘盘一起粘在中华蜜蜂背部。药帽的存在能够阻止下一朵被拜访的花实现雌性功能。兔耳兰药帽高度(0.154±0.032cm)(N=10)加上传粉昆虫胸高(2005年为0.37±0.03cm(N=10),2006年0.35±0.04cm(N=7))大于传粉通道入口的高度(0.29±0.04cm)(N=21),支持兔耳兰可能通过药帽来减少同株异花授粉现象的推测。2005和2006年该兔耳兰居群的自然繁殖成功率分别为21.13%和21.28%。繁育系统实验证明兔耳兰是高度自交亲和物种,自交和异交的繁殖成功率没有显著性差异,表明该种在结实过程中未显示近交衰退。兔耳兰不存在无融合生殖和自花授粉的现象,其结实依赖传粉者。TTC法检测结果显示兔耳兰种子活力达85.78%(N=11),可见种子活力不是制约兔耳兰种子萌发的主要原因。因此传粉者的密度和访问频率可能是影响兔耳兰结实的重要因素,并最终影响兔耳兰种群的维持和扩张。

The orchid family is renowned for its enormous diversity of pollination mechanisms and unusually high occurrence of non-rewarding flowers compared to other plant families. We investigated the pollination biology of Cymbidium lancifolium during 2005 and 2006 in the Yachang Nature Reserve, Guangxi Province, SW China. Our observations showed that Apis cerana cerana （Hymenopterous, Apidae） was the only pollinator. The bee directly landed on the mid-lobe, then adjusted its direction and entered into the flower. When it found no rewards in the flower, it would exit from the flower with the hind legs forcibly grasping the mid-lobe. The pollinaria together with the anther cap adhered to the thorax by the viscidium during the retreating process of the bees. The pollinator stayed for 8-71 s in the flower with an average of 18.3 s （N= 11）. It is likely that C. lancifolium attracted the bee by the purplish chestnut spots on the labellum （false nectarguides） exploiting the foraging preference of bees. The anther cap that remained on the back of the pollinator blocked the pollinaria from being received by the subsequently visited flower. The height of the anther cap （0.154 ± 0.032 cm） （N= 10） together with thorax of the pollinator （2005：0.37 ± 0.03 cm （N= 10）, 2006：0.35 ± 0.04 cm （N= 7）） was higher than the entrance of the flower （0.29 ± 0.04 cm） （N = 21）, suggesting a possibility of anther cap retention for geitonogamy. The reproductive success in the population was respectively 21.13% and 21.28% in 2005 and 2006. Breeding experiments showed that C. lancifolium was self-compatible and there was no significant difference in reproductive success between self-pollination and cross-pollination. There was neither apomixes nor spontaneous autogamy. The pollination success of this species was dependent on pollinators. The viability of seed by TTC was estimated as 85.78% （N = 11）, and it was not considered to be the key limiting factor for seed germination. Therefore, it is suggested that other factors, such as the density of the pollinators and their pollination frequency, influence the fruit set and maintenance of the population of C. lancifolium.