乌桕抵御昆虫能力的适应性进化及其机制

Environmental changes are driving forces for plant adaptive evolution of defense to herbivory, affecting evolutionary interactions between plants and herbivores. The insect herbivores and their damage on plants in native ranges often differ with those in invasive ranges, thus selection may favor invasive plants to evolve novel defense against herbivores. Therefore, studies on the varying resistance to herbivores between conspecific plants from invasive and native populations that are genetically related and exploring the potential variations in gene level will provide new insights for understanding the mechanisms through which invasive plants rapidly adapt to new environments. Native to China, tallow is a perennial plant which has been introduced in the United States for more than 200 years. Our previous studies show that the origin of plants (invasive and native ranges) significantly affects the development of specialist insects that have coevolved with tallow in native ranges. However, we know little about the adaptive evolution of plant defense to herbivore and the mechanisms involved. To address these questions, we proposal to examine and compare the variations in plant resistance traits and specialist insect performance through analysis of secondary chemical compounds and field and laboratory experiments, using genetically related genotypes of invasive and native plant populations. We will also conduct molecular studies through transcriptome sequencing and bioinformatics analysis to unravel the mechanisms responsible for the observed intraspecific variation in chemical resistance to insects. The results will break new ground in our understanding of invasive plant adaptation to new environments in response to differing insect herbivores, as well as the mechanisms for such variations.

环境变化是植物防御能力适应性进化的驱动力,影响植物与昆虫的互作关系演化。与原产地相比，入侵植物在新环境下天敌昆虫种类和危害往往发生很多变化，因此，新的选择压力可能驱使植物抵御昆虫的能力发生变化。通过比较同种入侵植物原产和入侵地具有亲缘关系的不同种群抗虫能力变化及其在基因水平上的差异，有助于探索和揭示入侵植物迅速适应新环境的机制，具有重要的进化生态学意义。乌桕是原产我国的多年生植物，已入侵美国200多年，前期研究表明，专食性昆虫在乌桕入侵和原产地种群上发育状况不同，但乌桕抗虫适应性进化规律和机制仍不清楚。本项目以具有明确亲缘关系的乌桕原产和入侵地种群为对象，利用专食性昆虫开展野外和室内试验，比较不同种群抗虫特征和次生代谢的差异，揭示抗虫性变化规律；同时开展转录组学和生物信息学分析，比较关键抗虫次生代谢物质基因的变异。这些研究结果将阐明入侵植物在新环境下，为响应天敌变化而产生的适应性及机制。

环境变化是植物适应性进化的重要驱动力，特别是对植物与昆虫的互作关系产生重要影响。入侵植物是研究新环境下适应性进化的理想材料，因为环境变化会导致天敌昆虫种类和危害也发生很多变化。本研究以原产我国、现入侵美国的多年生植物乌桕为例，通过比较其原产地和入侵地不同种群抗虫能力变化及其代谢水平上的差异，探索和揭示入侵植物适应新环境的基本机制和规律。. （1）我们通过比较来自中国和美国的近20个乌桕种群，发现美国种群酚类物质含量要低于中国种群，美国种群饲养的专食性昆虫红胸律点跳甲成虫和幼虫成活率高于中国种群；成虫取食显著增加了幼虫的成活率，而降低了根中的缩合单宁、总单宁和总酚含量，而且这种效应在美国种群中更强；（2）幼叶转录组测序结果表明，与原产地种群相比，入侵地种群调控单宁合成通路的两个基因表达可能发生了变化；（3）食性测定结果表明，专食性昆虫偏好在入侵地种群上产卵，而广食性昆虫则偏好在原产地种群产卵；（4）入侵地种群的挥发性物质对于专食性昆虫有强烈的吸引作用，入侵和原产地种群挥发性物质的差异还影响寄生蜂的选择行为，表明了植物入侵可导致三级营养关系的演化；（5）为了揭示乌桕在大尺度上的入侵化学防御机制，我们分别对不同纬度梯度下乌桕原产地种群与入侵地种群的昆虫取食危害和防御物质的进行调查与采样分析，发现原产地乌桕的叶片危害率整体高于入侵地乌桕的叶片危害率，但入侵地和原产地乌桕叶片危害率均没有明显纬度变化趋势；原产地乌桕健康叶片总酚含量随着纬度增加而减少，入侵地乌桕健康叶片、危害叶片和原产地乌桕危害叶片的总酚含量没有明显的纬度变化趋势；（6）我们还发现不同纬度的气候因子和土壤养分对乌桕植株的生长和防御也有显著影响。这些结果对于揭示植物防御能力的进化具有重要意义，对于控制植物入侵也会产生指导作用。