Data from: 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 expressed HR, and this attraction depended on the Trichogramma strain used. Consequently, HR did not have a negative effect on egg parasitoid survival. We conclude that even within a system where plants deploy lethal direct defences, such defences may still act with indirect defences in a synergistic manner to reduce herbivore pressure.

植食性动物防御进化理论预测，当食肉动物适合度下降时，植物的直接防御（抗植食性性状）与间接防御（吸引食肉动物）之间存在权衡。在通过类过敏反应（hypersensitive response, HR）样坏死杀死植食性动物卵的植物物种中，这类权衡本应存在，且该过敏反应会对食肉动物产生负面影响。本研究以黑芥（Brassica nigra）为材料，探究这种具有潜在致死性的直接防御性状，如何影响专性菜粉蝶属（Pieris spp.）蝴蝶的寄主选择与/或生长表现，以及它们的天敌——小型卵寄生蜂（Trichogramma spp.）的相关情况。在黑芥种群内部以及种群之间，我们均观察到菜粉蝶卵诱导的过敏反应表达存在差异。与未诱导该性状的卵相比，在表现出类HR坏死的植株上的粉蝶卵，孵化率更低且寄生率更高。此外，卵诱导植株的挥发物可吸引寄生蜂，且这类植株同时表达HR，该吸引效应取决于所用的寄生蜂品系。因此，过敏反应并未对卵寄生蜂的存活率产生负面影响。本研究结论表明，即便在植物部署致死性直接防御的系统中，这类防御仍可与间接防御协同作用，从而降低植食性动物的危害压力。