智利酒莓這種植物總是面臨雙重困境：要么冒著被蟲子吃掉的風(fēng)險，沐浴在陽光中,；要么遠離陽光,，這樣雖然可以躲開蟲子，卻有可能因缺乏光合作用而枯萎,。最新研究發(fā)現(xiàn)，智利酒莓采取折中的辦法來化解它的困境：把葉子長得足夠大以獲取更多的陽光,，但又不能太大,，否則會成為蟲子們的美餐。
這種生長速度很快的植物生活在溫暖,、多雨的環(huán)境里,，它的葉子必須長得很大以獲得足夠多的陽光，但蛞蝓,、象鼻蟲以及其他食草動物同時也覬覦著它鮮嫩肥大的葉子,。
為了弄清楚智利酒莓如何處理這一現(xiàn)實的矛盾，研究人員把它的幼苗種植在不同的環(huán)境中：有的生活在充足的陽光里,，有的生活在陰影之中,，有的面臨食草昆蟲的騷擾，有的則沒有,。
研究結(jié)果顯示,，在沒有敵害的情況下，不同環(huán)境中的智利酒莓都擁有同樣大小和數(shù)量的葉子,，而在有蟲子的環(huán)境里,，它們的葉片則要小得多。
這一研究結(jié)果刊發(fā)在這個月的《美國博物學(xué)家》（The American Naturalist ）網(wǎng)絡(luò)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.
