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Abstract：
Cophylogenetic studies examine the congruence between host and parasite phylogenies. There are few studies that quantify the relative contribution of coevolutionary events, i.e. duplication, loss, failure-to-diverge, host-switching and spreading in trophically-transmitted parasites at the marine realm. We addressed this issue in the Brachycladiidae, a cosmopolitan digenean family specific to marine mammals. We used, for the first time, distance-based and event-based methods to explicitly test the coevolutionary events that have shaped the current brachycladiid-marine mammal associations. Parasite phylogeny was constructed using mtDNA ND3 sequences of nine brachycladiid species, and host phylogeny using cytochrome b sequences of 104 mammalian species. A total of 50 host-parasite links were identified. Distance-based methods supported the hypothesis of a global non-random association of host and parasite phylogenies. Significant individual links (i.e., 24 out of 50) were those related to Campula oblonga, Nasitrema delphini, N. globicephalae and Brachycladium atlanticum and their associated taxa from the Delphinoidea. Regarding event-based methods, we explored 54 schemes using different combinations of costs for each potential coevolutionary event. Three coevolutionary scenarios were identified across all schemes and in all cases the number of loss events (87-156) was the most numerous, followed by failure-to-diverge (40), duplication (3-6), host-switching (0-3) and cospeciation (0-2). We developed a framework to interpret the evolution of this host-parasite system and confirmed that failure-to-diverge and colonization with or without subsequent diversification could have been decisive in the establishment of the associations between brachycladiids and marine mammals.
摘要：
同系遗传学研究检查了宿主和寄生虫系统发育之间的一致性。很少有研究量化共同进化事件的相对贡献，即重复，损失,失败发散，寄主转换和在海洋领域滋养传播的寄生虫中传播。我们在Brachycladiidae中解决了这个问题，海洋哺乳动物特有的世界性双基因家族。我们使用,第一次,基于距离和基于事件的方法来明确测试共同进化事件，这些事件已经塑造了当前的Brachyclid-海洋哺乳动物协会。寄生虫系统发育是使用9种brachyclatiid物种的mtDNAND3序列构建的，使用104种哺乳动物的细胞色素b序列进行宿主系统发育。总共鉴定了50个宿主-寄生虫联系。基于距离的方法支持宿主和寄生虫系统发育的全球非随机关联的假设。重要的单个链接(即，50人中有24人）是与Campulaoblonga有关的人，Nasitremadelphini,来自Delphinoidea的球形轮藻和大西洋Brachyclum及其相关分类群。关于基于事件的方法，我们为每个潜在的协同进化事件使用不同的成本组合探索了54个方案.在所有方案中确定了三种共同进化方案，在所有情况下，损失事件的数量（87-156）是最多的，其次是失败发散(40)，重复(3-6)，宿主交换(0-3)和共种(0-2)。我们开发了一个框架来解释这种宿主-寄生虫系统的进化，并证实了在有或没有随后的多样化的情况下，未能发散和定殖可能是建立brachycladiids与海洋哺乳动物之间关联的决定性因素。
