入侵植物在入侵地逃逸了與其協(xié)同進化的專食性昆蟲但是又面臨新的廣食性昆蟲的取食,，所以入侵植物的防御策略在入侵地會發(fā)生改變。由于入侵植物在入侵地面臨的昆蟲取食壓力較小,，所以將用于防御的資源轉移到生長繁殖,，從而競爭能力增強（EICA競爭力增強進化假說）。很多研究已經報道了入侵植物防御與生長之間的權衡,，發(fā)現有些入侵植物的防御能力下降,，但是也有很多研究得出相反的結論。關于這些爭論的主要原因是沒有對不同類型的防御能力進行深入研究,。因為植物防御不同食性昆蟲的化學防御物質是不同的,，數量防御物質主要防御專食性昆蟲而質量防御物質主要防御廣食性昆蟲。目前沒有研究報道入侵植物不同類型防御物質是如何演化的,。
中科院武漢植物園入侵生物學課題組博士生王毅在丁建清研究員和院外籍研究員,、美國萊斯大學Evan Siemann教授指導下，比較了烏桕入侵地種群（美國）和原產地種群（中國）的兩大類化學防御物質（5種類黃酮和4種單寧）的差異,，以及入侵種群化學防御變化對不同食性昆蟲發(fā)育的影響,。研究成果3月23日在線發(fā)表于國際生態(tài)學期刊Journal of Ecology。
結果顯示,，烏桕入侵地種群的類黃酮含量升高而單寧含量下降,，不同類型的化學防御物質之間存在權衡。這些化學防御物質的變化導致了專食性昆蟲在入侵地種群上發(fā)育更好,，而廣食性昆蟲則不然,。由于這些次生代謝物質的生物合成成本可能存在差異，入侵植物因此獲得了更多的資源用于生長和繁殖,。
本研究發(fā)現了入侵植物應對天敵昆蟲群落變化而發(fā)生的防御策略的轉化,，從植物抗性次生代謝產物演化的角度揭示了入侵機制。在國際上第一次報道了入侵植物不同類型抗性化學物質的演化,，并發(fā)現了這些化學物質的變化影響了不同食性昆蟲的發(fā)育,，為進一步揭示植物入侵機制提供了新的依據。（生物谷 bioon.com）
doi:10.1111/j.1365-2745.2012.01980.x
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Genetic variation in anti-herbivore chemical defences in an invasive plant
Yi Wang, Evan Siemann, Gregory S. Wheeler, Lin Zhu, Xue Gu, Jianqing Ding
Plants produce a variety of secondary metabolites such as flavonoids or tannins that vary in effectiveness against different herbivores. Because invasive plants experience different herbivore interactions in their introduced versus native ranges, they may vary in defence chemical profiles. We subjected tallow tree (Triadica sebifera) seedlings from native (China) and introduced (US) populations to induction by leaf clipping or one of three Chinese caterpillars (two generalists and one specialist). We measured the concentrations of five flavonoids and four tannins in leaves produced before or after damage. We measured growth of caterpillars fed these leaves from plants of each induction treatment or undamaged controls. Plants from introduced populations had higher flavonoids and lower tannins than plants from native populations, especially in new leaves following induction. Caterpillar responses to changing chemical concentrations varied in direction and strength, so overall performance varied from significantly lower (generalist Grammodes geometrica), unchanged (generalist Cnidocampa flavescens), to significantly higher (specialist Gadirtha inexacta) on introduced populations. Synthesis. Together, such a trade-off in secondary metabolism in invasive plants and the effect on herbivores suggest divergent selection may favour different chemical defences in the introduced range where co-evolved natural enemies, especially specialists, are absent.
