Coevolutionary history of ecological replicates: comparing phylogenies of wing and body lice to Columbiform hosts

Phylogenies depict the history of speciation for groups of organisms. Comparing the phylogenies of interacting groups can reveal instances of tandem speciation, or "cospeciation" (Brooks and McLennan, 1991; Hoberg et al., 1997; Paterson and Gray, 1997). Understanding the conditions under which cospeciation takes place is a challenging task. In the case of hosts and their parasites, cospeciation occurs when isolation of host populations also isolates the parasites on those hosts. Patterns of cospeciation can break down owing to dispersal of parasites among host populations, sympatric speciation of parasites on a single host population, or extinction of parasites on a host population (Page and Charleston, 1998). All else being equal, ecologically similar parasites living on the same host should respond to isolation of host populations in the same way, yielding similar coevolutionary histories. In this chapter we compare cospeciation events in two such "replicate" groups of lice living on the same hosts. If forces promoting speciation, such as host speciation, act on these parasites in similar ways, then we would expect cospeciation events to be correlated between these parasite groups. On the other hand, if the parasites respond to isolation differently, then cospeciation events should be independent in the two groups.