智利酒莓这种植物总是面临双重困境：要么冒着被虫子吃掉的风险，沐浴在阳光中；要么远离阳光，这样虽然可以躲开虫子，却有可能因缺乏光合作用而枯萎。最新研究发现，智利酒莓采取折中的办法来化解它的困境：把叶子长得足够大以获取更多的阳光，但又不能太大，否则会成为虫子们的美餐。
这种生长速度很快的植物生活在温暖、多雨的环境里，它的叶子必须长得很大以获得足够多的阳光，但蛞蝓、象鼻虫以及其他食草动物同时也觊觎着它鲜嫩肥大的叶子。
为了弄清楚智利酒莓如何处理这一现实的矛盾，研究人员把它的幼苗种植在不同的环境中：有的生活在充足的阳光里，有的生活在阴影之中，有的面临食草昆虫的骚扰，有的则没有。
研究结果显示，在没有敌害的情况下，不同环境中的智利酒莓都拥有同样大小和数量的叶子，而在有虫子的环境里，它们的叶片则要小得多。
这一研究结果刊发在这个月的《美国博物学家》（The American Naturalist ）网络版上。（生物谷Bioon.com）
doi:10.1086/666612
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Herbivores Modify Selection on Plant Functional Traits in a Temperate Rainforest Understory
Cristian Salgado-Luarte (Universidad de Concepción, Chile) and Ernesto Gianoli (Universidad de Concepción, Universidad de La Serena, Universidad Católica de Chile)
Trees in rainforests seem to live a quiet life, but in fact they are in constant struggle. On one hand, there is a struggle for light. Some species are more able to endure low light than others, and then shade-intolerant species are in dire straits when they are growing beneath a green ceiling (a close canopy). To prolong their chances of survival in the shaded understory, young trees from shade-intolerant species modify their attributes. For instance, they build larger and thinner leaves in order to maximize light capture. On the other hand, trees suffer the attacks of herbivores. But leaf consumption is rarely random: most herbivores are choosy. Not surprisingly, insects usually prefer thinner leaves that are easier to chew. Therefore, it is expected that the presence of herbivores would modify the fate of those saplings adapted to the dim understory of rainforests. This had not been evaluated earlier and it is what two Chilean researchers tested in the temperate rainforest of Southern South America, the Valdivian forest. Working with the light-demanding species Aristotelia chilensis, Cristian Salgado-Luarte and Ernesto Gianoli studied the patterns of natural selection on plant traits both in sun and shade environments, with and without herbivores (exclusion via insecticides). In the sun, plants survive better when their growth rate and photosynthesis are higher, and herbivore presence does not affect these patterns. In contrast, plant survival in the shade is associated with intermediate growth rate and increased specific leaf area (SLA, the leaf area displayed per unit dry mass), and herbivores do modify this pattern. In particular, as expected, herbivores reduce the strength of natural selection acting on SLA in shade. Thus, herbivory may modify the evolutionary trajectory of plant functional traits, preventing them from attaining the optimal level that enhances light capture in the shaded forest understory. This is crucial for light-demanding species, which may be already at their physiological limit of tolerance of light shortage before insects identify them as food. Research addressing the evolution of shade tolerance in forest ecosystems should incorporate the selective role of herbivores.
