Cospeciation in Host-Parasite Assemblages: Comparative Analysis of Rates of Evolution and Timing of Cospeciation Events

Abstract

Documentation of widespread cospeciation in a host-parasite assemblage requires statistical evidence that the congruence observed between the host and parasite phylogenies exceeds that expected by chance. Although the validity of this test rests on the assumption of independence of the host and parasite phylogenies, this critical assumption may be violated in many tests of cospeciation. Herein, we emphasize the need for rigorous tests of cospeciation in host-parasite assemblages, and we show how estimates of genetic distance can be used to investigate relative rates of evolution and timing of phylogenesis in the hosts and parasites once widespread cospeciation has been documented for the assemblage. The method involves a nonparametric test of association between genetic-distance matrices for the hosts and their parasites. If the association is statistically significant, the relationship is examined in greater detail using bivariate analysis. We use an example from our studies of pocket gophers and chewing lice to illustrate how genetic distances can be used to explore relative rates of genetic change in the two groups and to investigate relative timing of cospeciation events in the assemblage.