STATISTICAL TESTS OF HOST-PARASITE COSPECIATION

A history of cospeciation (synchronous speciation) among ecologically associated, but otherwise distantly related, species is often revealed by a strong correspondence of their phylogenies. in this paper, we pr esent several tests of cospeciation that use maximum-likelihood and Ba yesian methods of phylogenetic estimation. The hypotheses tested inclu de: (1) topological agreement of phylogenies fur coevolving groups; (2 ) identical speciation times of associated species; and (3) identical evolutionary rates in genes of associated species. These tests are app lied to examine a possible instance of host-parasite coevolution among pocket gophers and lice using mitochondrial COI DNA sequences. The ob served differences between gopher and louse trees cannot be explained by sampling error and are consistent with a rate of host switching abo ut one-third the host speciation rare. A subset af the gopher-louse da ta is consistent with a common history of evolution (i.e., the topolog ies and speciation limes are identical). However, the relative rate of nucleotide substitution is two tu four times higher in the lice than in the gophers.