MOLECULAR PHYLOGENIES AND HOST-PARASITE COSPECIATION - GOPHERS AND LICE AS A MODEL SYSTEM

Recent methodological advances permit a rigorous comparison of phyloge netic trees for hosts and their parasites to determine the extent to w hich these groups have cospeciated through evolutionary time. In cases where significant levels of cospeciation are indicated, comparison of amounts of evolutionary change that have accumulated along analogous branches in the host and parasite trees provides a direct assessment o f relative rates of evolution in the two groups. Far such a comparison to be meaningful, the features compared in the hosts and parasites sh ould be genetically based, evolutionarily homologous, and should evolv e in a roughly time-dependent fashion within each group. Nucleotide se quences encoding homologous genes in hosts and parasites are an ideal source of data for comparative studies of evolutionary rates. Recent s tudies of pocket gophers and their lice are used to illustrate the var iety of questions that can be addressed through phylogenetic study of host-parasite systems.