背景回顾：It is increasingly evident that plants interact with their outside world through the production of volatile organic compounds, but whether the volatiles have evolved to serve in plant defense is still a topic of considerable debate. 

研究基础：Unharmed leaves constitutively release small amounts of volatiles, but when the leaves are damaged by herbivorous arthropods, they emit substantially more volatiles. These herbivore-induced plant volatiles (HIPVs) attract parasitoids and predators that kill insect herbivores, and this can benefit the plants. 

提出问题：As yet, however, there is no tangible evolutionary evidence that this tritrophic interplay contributes to the selection forces that have shaped the volatile emissions of plants.

主要研究：With this in mind, we investigated the evolutionary changes in volatile emissions in invasive common ragwort and the respective defensive roles of its constitutive and inducible volatiles.

植物背景：This Eurasian plant has invaded other continents, where it evolved for many generations in the absence of specialized herbivores and their natural enemies.

结果：We found that, compared to native ragworts, invasive plants release higher levels of constitutive volatiles but considerably lower levels of herbivore-induced volatiles. As a consequence, invasive ragwort is more attractive to a specialist moth but avoided by an unadapted generalist moth. Importantly, conforming to the indirect defense hypothesis, a specialist parasitoid was much more attracted to caterpillar-damaged native ragwort, which was reflected in higher parasitism rates in a field trial. 

结论：The evolution of foliar volatile emissions appears to be indeed driven by their direct and indirect roles in defenses against insects.

 摘 要 

越来越多的证据表明，植物通过产生挥发性的有机化合物来与外界进行相互作用，但这些挥发物是否演化成为植物的防御手段，这仍是一个争论性的话题。未受损的叶片会组成型释放少量的挥发物，但当叶片被草食节肢动物损坏时，其释放的挥发性物质会大幅度增加。这些草食动物诱导的植物挥发物（HIPVs）会吸引那些捕食草食昆虫的寄生性和捕食性动物，从而间接保护了植物。然而，目前还没有明显的演化证据表明，这种三方之间的相互作用可以作为改变植物释放挥发性物质的选择力发挥作用。为此，作者在本文中研究了入侵植物臭千里光草挥发性物质释放的演化变化及其组成型和诱导型挥发物的各自防御作用。这种欧亚植物入侵了其他大陆，在那里没有该植物的专性食草动物及天敌的情况下，在这种情况下演化了很多代。作者发现，与原分布区的臭千里光草相比，入侵植物释放的组成型挥发物含量较高，但食草动物诱导的挥发物含量却明显降低。因此，入侵的臭千里光草对专性蛾更具吸引力，但对非适应的泛型蛾不具吸引力。重要的是，根据间接防御假说，专性寄生生物会更容易被发生蛾幼虫虫害的原分布区臭千里光草所吸引，这在田间试验中反应在原分布区臭千里光草的寄生率更高。叶挥发性物质释放的演化似乎确实是由其在抵御昆虫方面的直接和间接作用所驱动的。

 通讯作者 

** Ted C.J. Turlings **