Convergently evolved toxic secondary metabolites in plants drive the parallel molecular evolution of insect resistance

Natural selection imposed by natural toxins has led to striking levels of convergent evolution at the molecular level. Cardiac glycosides represent a group of plant toxins that block the Na,K-ATPase, a vital membrane protein in animals. Several herbivorous insects have convergently evolved resistant Na,K-ATPases, and in some species, convergent gene duplications have also arisen, likely to cope with pleiotropic costs of resistance. To understand the genetic basis and predictability of these adaptations, we studied five independent lineages of leaf-mining flies (Diptera: Agromyzidae). These flies have colonized host plants in four botanical families that convergently evolved cardiac glycosides of two structural types: cardenolides and bufadienolides. We compared each of six fly species feeding on such plants to a phylogenetically related but nonadapted species. Irrespective of the type of cardiac glycoside in the host plant, five out of six exposed species displayed substitutions in the ...

天然毒素介导的自然选择，使得生物在分子水平上呈现出极高程度的趋同演化。强心苷（cardiac glycosides）是一类能够阻断钠钾ATP酶（Na,K-ATPase）的植物毒素，而钠钾ATP酶是动物体内一种关键的膜蛋白。多种植食性昆虫已趋同演化出具有抗性的钠钾ATP酶；在部分物种中，还出现了趋同基因重复现象，这大概率是为了应对抗性所带来的多效性代价。为阐明这类适应性演化的遗传基础并预测其可重复性，我们对5个独立起源的潜蝇（Diptera: Agromyzidae）谱系展开了研究。这类潜蝇已定殖于四个植物科的寄主植物，而这些寄主植物分别趋同演化出两种结构类型的强心苷：强心甾烯（cardenolides）与蟾毒配基（bufadienolides）。我们将6种以这类植物为食的蝇类，各与一个系统发育亲缘关系相近但未发生适应性演化的物种进行对比分析。无论寄主植物所含强心苷的类型如何，6个受试物种中有5个在……中显示出氨基酸替换。