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.
