问答题 {{U}}Traditionally, pollination by wind has been viewed as a reproductive process marked by random events in which the vagaries of the wind are compensated for by the generation of vast quantities of pollen, so that the ultimate production of new seeds is assured at the expense of producing much more pollen than is actually used.{{/U}} Because the potential hazards pollen grains are subject to as they are transported over long distances are enormous, wind-pollinated plants have, in the view above, compensated for the ensuing loss of pollen through happenstance by virtue of producing an amount of pollen that is one to three orders of magnitude greater than the amount produced by species pollinated by insects. {{U}}However, a number of features that are characteristic of wind-pollinated plants reduce pollen waste.{{/U}} For example, many wind-pollinated species fail to release pollen when wind speeds are low or when humid conditions prevail. Recent studies suggest another way in which species compensate for the inefficiency of wind pollination. These studies suggest that species frequently take advantage of the physics of pollen motion by generating specific aerodynamic environments within the immediate vicinity of their female reproductive organs. {{U}}It is the morphology of these organs that dictates the pattern of airflow disturbances through which pollen must travel.{{/U}} The speed and direction of the airflow disturbances can combine with the physical properties of a species' pollen to produce a species-specific pattern of pollen collision on the surfaces of female reproductive organs. Provided that these surfaces are strategically located, the consequences of this combination can significantly increase the pollen-capture efficiency of a female reproductive organ. {{U}}A critical question that remains to be answered is whether the morphological attributes of the female reproductive organs of wind-pollinated species are evolutionary adaptations to wind pollination{{/U}} or are merely fortuitous. A complete resolution of the question is as yet impossible since adaptation must be evaluated for each species within its own unique functional context. {{U}}However, it must be said that, while evidence of such evolutionary adaptations does exist in some species, one must be careful about attributing morphology to adaptation.{{/U}} For example, the spiral arrangement of scale-bract complexes on ovule-bearing pine cones, where the female reproductive organs of conifers are located, is important to the production of airflow patterns that spiral over the cone's surfaces, thereby passing airborne pollen from one scale to the next. However, these patterns cannot be viewed as an adaptation to wind pollination because the spiral arrangement occurs in a number of non-wind-pollinated plant lineages and is regarded as a characteristic of vascular plants, of which conifers are only one kind, as a whole. Therefore, the spiral arrangement is not likely to be the result of a direct adaptation to wind pollination.
【正确答案】传统上,风媒被认为是一种带有随机色彩的繁衍过程,在这些过程中,植物通过产生大量的花粉来补偿风的变幻莫测,以至于最终新种子的产生所需的花粉比实际使用量要多得多。因为花粉颗粒传播较长距离时,它们遇到的潜在危险是很大的,因此根据上述观点,风媒植物为了弥补由偶发事件带来的花粉损失,要产生大量的花粉,这些花粉的数量是虫媒植物产生数量的一至三个数量级那么多。 但是,许多风媒植物的特征减小了花粉的损失浪费。例如,当风速较低或环境潮湿时,许多风媒植物就停止释放花粉。近来的研究提出了弥补风媒效率低下的另一种办法。这些研究指出,植物经常通过在紧靠它们雌性器官的附近区域产生一个特殊的空气动力环境,来利用花粉运动的物理原理。正是这些器官形态支配着花粉传播所必须经由的气流扰动的形式。这些气流扰动的速度和方向可以与植物花粉的物理特征结合起来,在雌性生殖器官表面产生一种植物种类所特有的花粉碰撞的形式。如果这些表面经过了战略性的布置,这种结合最终将会显著提高雌性生殖器官捕获花粉的效率。 还有一个关键性的问题需要回答:即风媒植物的雌性生殖器官的形态上的特征是适应风媒进化而来的,还是仅仅是一种偶然呢?这个问题的完全解决迄今还是不大可能的,因为适应对于每种植物都应该在其独特的功能背景下来评价。但是,必须指出的是:虽然在某些植物中的确存在着进化适应的证据,但把形态归因于进化还是需要小心谨慎的。举个例子来说,松柏目植物的雌性生殖器官位于带有胚珠的松球上,在其上螺旋状分布着鳞苞综合体,这对气体在松球表面螺旋向上流动形成气体流动形式是十分重要的,因此经过空中飞行的花粉就从一个鳞苞传播到另一个鳞苞。但是,这些形式不能看作是对风媒的适应,因为这种螺旋分布在许多非风媒植物的家系中也出现,并被视为是维管植物的一个特征,而松柏目植物就整个看来仅仅是其中一种。因此,螺旋分布不大可能是对风媒直接适应的结果。
【答案解析】