DISSERTATION RESEARCH: Experimental Selection for Cheating in a Mutualistic Symbiont

本研究通过实验研究了倒立水母与其共生藻类之间的共生关系。这种共生关系，连同共生体的传染性传播，代表了一类共生体的合作仍然无法解释。一项选择实验解决了维持共生合作的两种相反假设：伙伴忠诚（Partner fidelity），即合作伙伴之间的重复互动倾向于合作伙伴而不是欺骗者；伙伴选择（Partner choice），即宿主可以不同地奖励合作的共生体和/或惩罚欺骗者。宿主之间的共生体传播被实验操纵；一种方法是在不相关的宿主之间（欺骗选择）进行传染，另一种方法是在父母和后代之间（合作选择）进行垂直传播。对实验进化的寄主和共生体的适应度分析将解决伴侣选择或伴侣忠诚是否稳定了这种共生关系中的合作，以及自然界中是否存在欺骗共生体。共生关系与共生体的传染传播是生物学中尚未解决的问题。理论指出，虽然共生生物的垂直传播有利于合作，但传染传播有利于寄生。尽管如此，自然界充满了共生关系，共生体是水平获得的。此外，水母和相关珊瑚的白化代表了生态上重要的，但人们对这种共生关系的破坏知之甚少。这项研究有望帮助解开这些鲜为人知的共生关系的进化维持。

This study experimentally examines the symbiosis between the upside-down jellyfish and its algal symbiont. This mutualism, with infectious transmission of symbionts, represents a class of symbioses for which symbiont cooperation remains unexplained. A selection experiment addresses two opposing hypotheses for the maintenance of symbiont cooperation: Partner fidelity, in which repeated interactions between partners favors cooperators over cheaters and partner choice, in which hosts can differentially reward cooperating symbionts and/or punish cheaters. Symbiont transmission between hosts is experimentally manipulated; one treatment enforces infectious transmission- between unrelated hosts (selection for cheating ) and the other vertical transmission- between parent and offspring (selection for cooperation). Fitness assays on experimentally evolved hosts and symbionts will resolve whether partner choice or partner fidelity stabilizes cooperation in this symbiosis and whether cheater symbionts exist in nature.Mutualisms with infectious transmission of symbionts are an unsolved problem in biology. Theory states that while vertical transmission of symbionts favors cooperation, infectious transmission favors parasitism. Nonetheless, nature abounds with mutualisms in which the symbionts are horizontally acquired. Furthermore, bleaching in jellyfish and related corals represents an ecologically important, yet poorly understood breakdown of this mutualism. This study promises to help unravel the evolutionary maintenance of these poorly understood symbioses.