入侵植物在入侵地逃逸了与其协同进化的专食性昆虫但是又面临新的广食性昆虫的取食，所以入侵植物的防御策略在入侵地会发生改变。由于入侵植物在入侵地面临的昆虫取食压力较小，所以将用于防御的资源转移到生长繁殖，从而竞争能力增强（EICA竞争力增强进化假说）。很多研究已经报道了入侵植物防御与生长之间的权衡，发现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结论。关于这些争论的主要原因是没有对不同类型的防御能力进行深入研究。因为植物防御不同食性昆虫的化学防御物质是不同的，数量防御物质主要防御专食性昆虫而质量防御物质主要防御广食性昆虫。目前没有研究报道入侵植物不同类型防御物质是如何演化的。
中科院武汉植物园入侵生物学课题组博士生王毅在丁建清研究员和院外籍研究员、美国莱斯大学Evan Siemann教授指导下，比较了乌桕入侵地种群（美国）和原产地种群（中国）的两大类化学防御物质（5种类黄酮和4种单宁）的差异，以及入侵种群化学防御变化对不同食性昆虫发育的影响。研究成果3月23日在线发表于国际生态学期刊Journal of Ecology。
结果显示，乌桕入侵地种群的类黄酮含量升高而单宁含量下降，不同类型的化学防御物质之间存在权衡。这些化学防御物质的变化导致了专食性昆虫在入侵地种群上发育更好，而广食性昆虫则不然。由于这些次生代谢物质的生物合成成本可能存在差异，入侵植物因此获得了更多的资源用于生长和繁殖。
本研究发现了入侵植物应对天敌昆虫群落变化而发生的防御策略的转化，从植物抗性次生代谢产物演化的角度揭示了入侵机制。在国际上第一次报道了入侵植物不同类型抗性化学物质的演化，并发现了这些化学物质的变化影响了不同食性昆虫的发育，为进一步揭示植物入侵机制提供了新的依据。（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.
