Cophylogenetic studies of hosts and permanent ectoparasites provide a unique opportunity to reconstruct the history and environmental context in which the processes of diversification and speciation occur. Permanent ectoparasites share a common evolutionary history with their hosts, and one can reconstruct this macroevolutionary history by superimposing a parasite’s phylogeny onto the host’s phylogeny. Analyses of both mitochondrial and nuclear DNA sequences from Ramphastos toucans and their ectoparasitic Austrophilopterus chewing lice show little or no cospeciation in their cophylogenetic history. Secondly, monophyletic louse lineages are not necessarily restricted to monophyletic host lineages. Instead, closely related Austrophilopterus lice are found on more distantly related but sympatric toucan hosts and geography has significant phylogenetic signal on the louse phylogeny. A number of features of the host (e.g., hole nesting) and parasite (e.g., phoresis) life histories might promote these patterns of host-switching or dispersal between syntopic host species. In this talk, we will examine patterns of population genetic structure, phylogeographic structure, and gene flow in Austrophilopterus chewing lice to understand the underlying microevolutionary forces shaping the associations and cophylogenetic history with their toucan hosts. The addition of a microevolutionary approach can broaden our perspective on these events, because population genetic structure and processes such as dispersal are important factors underlying coevolutionary history. Thus, our understanding of macroevolutionary events such as host-switching will be illuminated by data on microevolutionary processes.