Molecular Studies of Cospeciation in a Host-Parasite Assemblage

协种作用理论认为，当两个生物作为宿主和寄生虫错综复杂地联系在一起时，导致其中一个成员(宿主)物种形成的事件也会导致另一个成员(寄生虫)物种形成。本研究的主要目的是检验一组啮齿动物宿主(袋鼠)及其体外寄生的咀嚼虱子之间的协同作用假说。这将通过研究人员根据核酸分子的序列差异量比较宿主和寄生虫的进化变化量来完成。到目前为止，研究人员已经使用为口袋地鼠和咀嚼虱子独立收集的遗传数据，创建了口袋地鼠的进化树和它们的咀嚼虱子的进化树。用统计方法比较袋鼠和食虱树的分枝结构时，发现它们的分枝结构非常相似。虽然这是证明共分类的必要证据，但这并不是充分的证据：还必须证明这些宿主和寄生虫中的物种形成事件几乎同时发生。这可以通过比较自假设的共种事件以来共存宿主和寄生虫中的分子变化量来检验。如果有不等量的分子变化，这个理论就会被证伪。等量的变化将构成强有力的证据，支持这种寄主-寄生虫组合的协种理论。

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.