DISSERTATION RESEARCH: Experimental Selection for Cheating in a Mutualistic Symbiont

这项研究通过实验研究了倒置的水母与其藻类共生体之间的共生关系。这种互惠共生，伴随着共生体的传染性传播，代表了一种共生体，共生体之间的合作仍未得到解释。选择实验解决了维持共生体合作的两个截然相反的假设：伙伴忠诚度，即伙伴之间的重复互动有利于合作者而不是作弊者；以及伙伴选择，其中主人可以不同地奖励合作共生体和/或惩罚作弊者。宿主之间的共生体传播是经过实验操纵的；一种治疗方法强制执行感染性传播--在不相关的宿主之间(选择作弊)，另一种是垂直传播--在父母和后代之间(选择合作)。对实验进化的宿主和共生体进行的适应度分析将决定在这种共生中，伴侣的选择或伴侣的忠诚度是否会稳定合作，以及自然界中是否存在作弊共生体。共生体的传染性传播是生物学中一个悬而未决的问题。理论认为，虽然共生体的垂直传播有利于合作，但传染性传播有利于寄生。尽管如此，自然界充斥着互惠共生，共生体是水平获得的。此外，水母和相关珊瑚的漂白代表了这种互惠关系在生态上的重要破裂，但人们对此知之甚少。这项研究承诺将有助于解开这些鲜为人知的共生体的进化维持。

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.