Defence by plant toxins in milkweed bugs (Heteroptera: Lygaeinae) through the evolution of a sophisticated storage compartment

摘要

Species of the heteropteran subfamily Lygaeinae possess special subcuticular compartments to store cardiac glycosides, plant-derived defensive compounds, which they release upon predator attack. In adults of the large milkweed bug, Oncopeltus fasciatus, these storage compartments have previously been described as a modified integument, forming a fluid-filled dorsolateral space. Here we use three-dimensional imaging of serial histological sections and synchrotron radiation-based micro-computed tomography data to reveal the morphology of these storage compartments and the mechanisms used for the release of a cardiac glycoside-rich fluid upon attack. Our comparative analysis revealed that the morphology and release mechanism vary among the species investigated. By reconstructing these traits on a recent molecular phylogeny of the Lygaeinae, we demonstrate that the adaptations for the storage and release of cardiac glycosides have evolved in a stepwise manner.