Molecular Studies of Cospeciation in a Host-Parasite Assemblage

共种化理论认为，当两种生物体作为寄主和寄生虫复杂地联系在一起时，导致其中一个成员（寄主）形成物种的事件也会导致另一个成员（寄生虫）形成物种。本研究的主要目的是验证一组啮齿动物宿主（口袋地鼠）及其体外寄生咀嚼虱的共种假说。这将通过研究人员根据核酸分子序列差异的数量来比较宿主和寄生虫的进化变化量来完成。到目前为止，研究人员已经利用独立收集的口袋地鼠和咀嚼虱子的基因数据，为口袋地鼠和它们的咀嚼虱子制作了一棵进化树。用统计方法对口袋地鼠和嚼虱树的分支结构进行比较，发现它们的分支结构非常相似。虽然这是证明共同物种形成的必要证据，但这还不够充分：还必须证明这些宿主和寄生虫的物种形成事件几乎同时发生。这可以通过比较共存的宿主和寄生虫自假设的共种事件以来的分子变化量来检验。如果分子变化的量不等，这个理论就会被证伪。等量的变化将构成支持这种宿主-寄生虫组合的共种理论的有力证据。

The theory of cospeciation proposes that when two organisms are intricately associated as hosts and parasites, events that cause speciation in one member of the pair (the host) will also cause speciation in the other member (the parasite). The main purpose of this research is to test the hypothesis of cospeciation in a group of rodent hosts (pocket gophers) and their ectoparasitic chewing lice. This will be accomplished by the researchers comparing the amounts of evolutionary change in hosts and parasites based on amounts of sequence difference in nucleic acid molecules. To date, the researchers have used genetic data, gathered independently for pocket gophers and chewing lice, to produce an evolutionary tree for pocket gophers, and one for their chewing lice. When the branching structure of the pocket gopher and chewing louse trees was compared by statistical methods, it was found to be remarkably similar. Although this is necessary evidence to document cospeciation, it is not sufficient evidence: it must also be demonstrated that speciation events in these hosts and parasites occurred at approximately the same time. This can be tested by comparing amounts of molecular change in coexisting hosts and parasites since hypothesized cospeciation events. The theory will be falsified if there are unequal amounts of molecular change. Equal amounts of change will constitute strong evidence in support of the cospeciation theory for this host-parasite assemblage.