A Statistical Test for Host–Parasite Coevolution

Abstract.—A new method, ParaFit, has been developed to test the signicance of a global hypothesis of coevolution between parasites and their hosts. Individual host–parasite association links can also be tested. The test statistics are functions of the host and parasite phylogenetic trees and of the set of host–parasite association links. Numerical simulations are used to show that the method has correct rate of type I error and good power except under extreme error conditions. An application to real data (pocket gophers and chewing lice) is presented. [Coevolution; fourth-corner statistic; host-parasite; permutation test; phylogenetic analysis; power analysis; simulations; statistical test.] Parasites generally form tight ecological associations with their hosts. Biologists have long assumed that the evolution of para-sites is highly dependent on that of their hosts (Barrett, 1986; Klassen, 1992). This has led to the establishment of several “rules,” such as Farenholz’s Rule (1913)—“parasite phylogeny mirrors host phylogeny”—an