Department of Ecology and Evolutionary Biology, and Department of Entomology, Cornell University, Ithaca, NY 14853, USA.
Biozentrum Grindel, Molekulare Evolutionsbiologie, Martin-Luther-King Platz 3, 20146 Hamburg, Germany.
New Phytol. 2012 Apr;194(1):28-45. doi: 10.1111/j.1469-8137.2011.04049.x. Epub 2012 Jan 31.
Cardenolides are remarkable steroidal toxins that have become model systems, critical in the development of theories for chemical ecology and coevolution. Because cardenolides inhibit the ubiquitous and essential animal enzyme Na⁺/K⁺-ATPase, most insects that feed on cardenolide-containing plants are highly specialized. With a huge diversity of chemical forms, these secondary metabolites are sporadically distributed across 12 botanical families, but dominate the Apocynaceae where they are found in > 30 genera. Studies over the past decade have demonstrated patterns in the distribution of cardenolides among plant organs, including all tissue types, and across broad geographic gradients within and across species. Cardenolide production has a genetic basis and is subject to natural selection by herbivores. In addition, there is strong evidence for phenotypic plasticity, with the biotic and abiotic environment predictably impacting cardenolide production. Mounting evidence indicates a high degree of specificity in herbivore-induced cardenolides in Asclepias. While herbivores of cardenolide-containing plants often sequester the toxins, are aposematic, and possess several physiological adaptations (including target site insensitivity), there is strong evidence that these specialists are nonetheless negatively impacted by cardenolides. While reviewing both the mechanisms and evolutionary ecology of cardenolide-mediated interactions, we advance novel hypotheses and suggest directions for future work.
卡烯内酯是一种显著的甾体毒素，已成为模型系统，对化学生态学和共同进化理论的发展至关重要。由于卡烯内酯抑制普遍存在且必不可少的动物酶 Na⁺/K⁺-ATPase，因此大多数以含有卡烯内酯的植物为食的昆虫都是高度特化的。这些次生代谢物具有巨大的化学形式多样性，零星分布在 12 个植物科中，但在夹竹桃科中占主导地位，在那里它们存在于> 30 个属中。过去十年的研究表明，卡烯内酯在植物器官中的分布模式，包括所有组织类型，以及在物种内和跨物种的广泛地理梯度上存在模式。卡烯内酯的产生具有遗传基础，并受到草食动物的自然选择。此外，还有强有力的证据表明存在表型可塑性，生物和非生物环境可预测地影响卡烯内酯的产生。越来越多的证据表明，Asclepias 中诱导产生的卡烯内酯具有高度特异性。虽然含有卡烯内酯的植物的草食动物经常隔离毒素，具有警戒色，并具有几种生理适应性（包括靶位不敏感性），但有强有力的证据表明，这些专食者仍然受到卡烯内酯的负面影响。在回顾卡烯内酯介导的相互作用的机制和进化生态学的同时，我们提出了新的假设，并为未来的工作指明了方向。
