Evolutionary significance of phytochemical diversity:Cardenolides as a model system

植物产生各种各样的有毒化合物，作为对食草昆虫的防御。一组经典的研究毒素是硬核内酯（又名心脏糖苷），它结合并特异性抑制无处不在的动物阳离子泵Na+K+- atp酶，这参与了基本的生理过程。由于在过去的50年里，香心石是许多化学生态学研究的主题，它们为了解食草昆虫对宿主植物毒素的进化适应提供了一个很好的模型。一种昆虫适应胡桃木脂的一个主要例子是帝王蝶（Danaus plexippus）。该物种的毛虫不仅能够耐受寄主植物天麻属（夹竹桃科）中所含的桃香内酯，而且还能储存这些化合物用于自身的防御（封存）。植物通常拥有属于同一化学类别的结构不同的毒素光谱。例如，某些种类的石竹属植物可以产生多达30种不同的石竹烯。然而，尚不清楚这种品种是否具有生态或进化意义。因此，我想测试一下植物化学多样性是否会对专业食草动物产生负面影响。为此，我将使用君主及其寄主植物（Asclepias spp.）作为模型系统。此外，本构生产植物在受到昆虫攻击（诱导）时也会产生更高水平的心髓内酯。因此，我还将测试植物诱导后的毛虫体内是否有更高的果核内酯浓度，以及植物在诱导后是否会产生特异性的果核内酯，这种果核内酯对丛田鼠的毒性特别强。此外，我将研究在君主中选择性地隔离特定的桃香内酯是否是一种避免自毒性的优化方法。为了回答这些问题，我将采用一种结合生态、生化和化学分析技术的综合方法。

Plants produce a variety of toxic compounds which function as a defense against herbivorous insects. One classically studied group of toxins are the cardenolides (aka cardiac glycosides) which bind to and specifically inhibit the ubiquitous animal cation pump Na+K+-ATPase which is involved in essential physiological processes.Since cardenolides were subject of many chemoecological studies during the last five decades, they provide an excellent model to understand evolutionary adaptations of herbivorous insects to host plant toxins. A prime example for the adaptation of an insect to cardenolides is the monarch butterfly (Danaus plexippus). The caterpillars of this species are not only able to tolerate cardenolides contained in their host plant Asclepias (Apocynaceae) but also store these compounds for their own defense (sequestration).Plants often possess a spectrum of structurally different toxins belonging to the same chemical class. Some species of Asclepias, for example, produce up to 30 different cardenolides. However, it is unknown whether such a variety is of ecological or evolutionary significance.I therefore want to test whether phytochemical diversity has a negative impact on a specialist herbivore. For this I will use the monarch and its host plants (Asclepias spp.) as a model system. Besides constitutive production plants also produce higher levels of cardenolides upon insect attack (induction). Hence, I will also test whether caterpillars after plant induction possess higher cardenolide concentrations in their body and whether plants, upon induction, produce specific cardenolides which are especially toxic for D. plexippus. Moreover, I will investigate whether selective sequestration of particular cardenolides in the monarch is an optimization to avoid autotoxicity.To answer these questions I will perform an integrative approach combining ecological, biochemical and chemical-analytical techniques.