Ecophysiology of chemical defense evolution in poison frogs

许多生物体，包括人类，暴露在饮食中的各种化合物中，可能会导致毒性。在自然界中，一些动物有特殊的生理学，使它们能够摄取毒素而不受伤害。一些中美洲和南美洲的毒蛙可以在它们的食物中隔离神经毒素，并将这些毒素重新用于化学防御，使其免受捕食。这些青蛙将生物碱从肠道通过血液输送到皮肤，在那里毒素储存在腺体中。这个项目调查了这些青蛙是如何应对摄取神经毒素的，结果可能提供更完整的口腔药物分布、新陈代谢和毒素抵抗的新方法的图景，因为许多毒素与人类使用的药物相似。这项研究将为美国和厄瓜多尔的所有年龄段提供学习经验，厄瓜多尔对毒蛙进行了研究和实地考察。高中生物教师将参与暑期研究，并将他们的研究成果纳入他们的科学课程。该奖项还将为当地社区大学的学生提供研究实习机会，这项研究的一部分将在斯坦福大学的本科实验室课程中进行。在厄瓜多尔，研究成果将通过在基多两栖动物研究和保护中心的教育展示向公众传播。毒蛙从节肢动物的食物中获得基于生物碱的化学防御，尽管这些亲脂性生物碱如何在没有自我毒性的情况下通过器官转移尚不清楚。本研究的目的是通过三个目的来了解毒蛙毒素隔离和自身抵抗的生理机制和趋同进化：(1)检验化学防御的独立进化起源与其产物参与小分子运输和代谢的基因的表达变化有关的假说。生物碱谱和几个组织中的基因表达将在代表化学防御进化的独立起源的毒蛙物种中进行量化。(2)验证这样一种假设，即生物碱的隔离是通过选择转运蛋白来进行隔离或排泄而进化的。在实验室饲养的有毒和无毒毒蛙中，跨器官的基因表达谱将被用来识别富含在隔离生物碱的组织中的膜转运蛋白。候选载体将在基于细胞的检测中进行功能测试。(3)研究小组最近在毒蛙体内发现了一种可以结合一系列生物碱的蛇针蛋白。我们将研究这种毒素海绵与各种生物碱的结合情况。这种毒素海绵是否对生物碱的隔离是必要的，将通过基因敲除研究来测试。总而言之，这项工作将检验毒蛙的化学防御通过多种机制进化的假设，每一种机制都发生在不同的有机体组织水平上。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Many organisms, including humans, are exposed to a variety of compounds in the diet that may result in toxicity. In nature, some animals have specialized physiology that allow them to ingest toxins without being harmed. Some Central and South American poison frogs can sequester neurotoxins in their diet and repurpose those toxins as a chemical defense from predation. These frogs move the alkaloids from the intestines, through the bloodstream and to the skin where toxins are stored in glands. This project investigates how these frogs cope with ingesting neurotoxins and the results may provide a more complete picture of oral drug distribution, metabolism, and new methods of toxin resistance, because many of the toxins are similar to pharmaceutical drugs used in humans. This research will provide learning experiences to all age groups in both the United States and Ecuador, where research and fieldwork on poison frogs is conducted. High school biology teachers will be involved in summer research and will incorporate their research findings into their science curriculum. This award will also provide research internships for local community college students, and a portion of this research will be conducted in an undergraduate laboratory course at Stanford University. In Ecuador, research will be communicated to the public through educational displays at the Centro Jambatu of Amphibian Research and Conservation in Quito. Poison frogs acquire alkaloid-based chemical defenses from dietary arthropods, although how these lipophilic alkaloids are moved across organs without self-toxicity is unclear. The goal of the proposed research is to understand the physiological mechanisms and convergent evolution of toxin sequestration and autoresistence in poison frogs through three aims: (1) Test the hypothesis that independent evolutionary origins of chemical defense is associated with expression changes of genes whose products are involved in small molecule transport and metabolism. Alkaloid profiles and gene expression in several tissues will be quantified across poison frog species that represent independent origins of chemical defense evolution. (2) Test the hypothesis that alkaloid sequestration evolved by co-opting transporter proteins for either sequestration or excretion. Gene expression profiling across organs in toxic and non-toxic lab-reared poison frogs will be used to identify membrane transporters enriched in tissues that sequester alkaloids. Candidate carriers will be functionally tested in cell-based assays. (3) A serpin protein in poison frogs that can bind a range of alkaloids was recently discovered by the research team. The binding profile of this toxin sponge for various alkaloids will be examined. Whether this toxin sponge is necessary for alkaloid sequestration will be tested through gene knockdown studies. Together, this work will test the hypothesis that chemical defense in poison frogs evolved via multiple mechanisms, each of which occur at a distinct level of organismal organization.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.