Synergistic effects of direct and indirect defences on herbivore egg survival in a wild crucifer

Evolutionary theory of plant defences against herbivores predicts a trade-off between direct (anti-herbivore traits) and indirect defences (attraction of carnivores) when carnivore fitness is reduced. Such a trade-off is expected in plant species that kill herbivore eggs by exhibiting a hypersensitive response (HR)-like necrosis, which should then negatively affect carnivores. We used the black mustard (Brassica nigra) to investigate how this potentially lethal direct trait affects preferences and/or performances of specialist cabbage white butterflies (Pieris spp.), and their natural enemies, tiny egg parasitoid wasps (Trichogramma spp.). Both within and between black mustard populations, we observed variation in the expression of Pieris egg-induced HR. Butterfly eggs on plants with HR-like necrosis suffered lower hatching rates and higher parasitism than eggs that did not induce the trait. In addition, Trichogramma wasps were attracted to volatiles of egg-induced plants that also expr...植食动物防御的进化理论预测：当食肉动物适合度（fitness）下降时，植物的直接防御（抗植食动物性状）与间接防御（吸引食肉动物）之间存在权衡（trade-off）。通过表现出超敏反应（hypersensitive response, HR）样坏死来杀死植食动物卵的植物类群，便存在这类权衡，且该过程会对食肉动物产生负面影响。本研究以黑芥（Brassica nigra）为实验材料，探究这一潜在致死的直接防御性状如何影响专性寄主菜粉蝶（Pieris spp.）的寄主选择偏好与/或适合度表现，以及它们的天敌——小型卵寄生蜂（Trichogramma spp.，赤眼蜂属）。在黑芥种群内部及种群之间，我们均观察到菜粉蝶卵诱导的超敏反应表达存在差异。与未诱导该性状的卵相比，表现出超敏反应样坏死的植株上的菜粉蝶卵，其孵化率更低、寄生率更高。此外，赤眼蜂会被卵诱导植株释放的挥发物所吸引，而该植株同时也表达...