花柱卷曲性异交机制及其进化生态学意义

FLEXISTYLY AND ITS EVOLUTIONARY ECOLOGICAL SIGNIFICANCE

有花植物具有纷繁复杂的繁育系统 ,以避免或促进自交或异交。花柱卷曲性异交机制 (Flexistyly)是最近在热带山姜属 (Alpinia)植物中发现的一种促进异交的行为机制。具有这一机制的种类其自然种群中的个体根据开花行为的不同分为两种表型 :一种上午散发花粉而其柱头向上反卷 ,远离昆虫拜访的通道 ;另一种其柱头上午垂向唇瓣 ,能够接受拜访昆虫的传粉 ,但自身的花药却不打开。到中午时分 ,两种表型花通过互为相反的柱头卷曲运动转换性别———前者柱头向下卷曲 ,后者柱头向上卷曲且花药打开。每朵花的花期为 12h ,两种表型在自然种群中的比例为 1:1。这一独特的机制还具有显著的进化生态学适应性 ,为雌雄异株的起源和进化提供了一种可能的途径。

There are divers breeding systems in the flowering plants, and different breeding systems have different ways of avoiding or promoting inbreeding or outbreeding. Flexistyly is a new behavioral outbreeding mechanism recently found in Alpinia ginger plants. The flexistyly mechanism has two flower phenotypes within a natural population. One releases its pollen in the morning, and holds its stigma out of the way of any visiting insects. The other type holds back its pollen, but its stigma is downward_curved and receptive to pollen_laden insects. Around midday, the two flower types swap sexual roles through reciprocal, synchronous, active stigma flexing movement. Plants that release their pollen in the morning most likely donate pollen only to those that release pollen in the afternoon, and vice versa. A flower lasts only one day, and the ratio of the two phenotypes in natural populations is 1:1. With this outcrossing mechanism, the plants not only prevent self_pollination within the same flower (autogamy), but also prevent the transfer of pollen between flowers on the same plant (geitonogamy), and even between the plants of the same phenotype. Flexistyly has significant implications in evolutionary ecology - encouraging outcrossing and avoiding inbreeding depression, as well as reducing interference between the presentation of pollen and stigmas. This intriguing mechanism adds to the diversity of breeding systems that have contributed to the evolutionary success of flowering plants. With two 'temporal dioecious' morphs in which the stigmas behave synchronously and reciprocally, flexistyly probably could be easily converted into a dioecious condition, and may be a possible pathway by which dioecy evolved.