The effects of milkweed induced defense on parasite resistance in monarch butterflies, Danaus plexippus

Many plants express induced defenses against herbivores through increasing the production of toxic secondary chemicals following damage. Phytochemical induction can directly or indirectly affect other organisms within the community. In tri-trophic systems, increased concentrations of plant toxins could be detrimental to plants if herbivores can sequester these toxins as protective chemicals for themselves. Thus, through trophic interactions, induction can lead to either positive or negative effects on plant fitness. We examined the effects of milkweed (Asclepias spp.) induced defenses on the resistance of monarch caterpillars (Danaus plexippus) to a protozoan parasite (Ophryocystis elektroscirrha). Milkweeds contain toxic secondary chemicals called cardenolides, higher concentrations of which are associated with reduced parasite growth. Previous work showed that declines in foliar cardenolides caused by aphid attack render monarch caterpillars more susceptible to infection. Here, we ask...

多数植物在遭受植食性昆虫损伤后，可通过提升有毒次生代谢物的合成量，表达针对植食者的诱导防御（induced defenses）。植物化学诱导可直接或间接影响群落内的其他生物。在三营养级系统中，若植食性昆虫能够将此类毒素储积为自身的保护性化学物质，则植物毒素浓度升高反而可能对植物自身产生不利影响。因此，通过营养级相互作用，诱导防御可对植物适合度产生正向或负向影响。本研究探究了马利筋属（Asclepias spp.）的诱导防御对黑脉金斑蝶幼虫（Danaus plexippus）抵御原生动物寄生虫（Ophryocystis elektroscirrha）的抗性的影响。马利筋含有被称为强心甾类化合物（cardenolides）的有毒次生代谢物，其浓度升高与寄生虫生长受抑制显著相关。已有研究表明，蚜虫取食导致的马利筋叶片强心甾类化合物含量下降，会使黑脉金斑蝶幼虫更易感染寄生虫。在此，我们提出...