Doctor of Philosophy (PhD)


Biological Sciences

Document Type



Historically, comparisons of host and parasite phylogenies have concentrated on cospeciation. However, many of these comparisons have demonstrated that the phylogenies of hosts and parasites are seldom completely congruent, suggesting that phenomena other than cospeciation play an important role in the evolution of host-parasite assemblages. Other coevolutionary phenomena, such as host switching, parasite duplication (speciation on the host), sorting (extinction), and failure to speciate can also influence host-parasite assemblages. In this dissertation I explore several aspects of the evolutionary history of Ramphastos toucans and their ectoparasitic chewing lice using molecular phylogenetic and cophylogenetic reconstructions. First, using mitochondrial DNA sequences, I reconstructed the phylogeny of the Ramphastos toucans. I used this phylogeny to assess whether the striking similarity in plumage and bare-part coloration of sympatric Ramphastos is due to convergence or shared ancestry. Ancestral character state reconstructions indicate that that at least half of the instances of similarity in plumage and bare-part coloration between sympatric Ramphastos are due to homoplasy. Second, using mitochondrial and nuclear protein-coding DNA sequences, I reconstructed the phylogeny of ectoparasitic toucan chewing lice in the Austrophilopterus cancellosus subspecies complex, and compared this phylogeny to the phylogeny of the hosts to reconstruct the history of coevolutionary events in this host-parasite assemblage. Three salient findings emerged. (1) reconstructions of host and louse phylogenies indicate that they do not branch in parallel and that their cophylogenetic history shows little or no significant cospeciation. (2) members of monophyletic Austrophilopterus toucan louse lineages are not necessarily restricted to monophyletic host lineages. Often, closely related lice are found on more distantly related, but sympatric, toucan hosts. (3) the geographic distribution of the hosts apparently plays a role in the speciation of these lice. These results suggest that for some louse lineages, biogeography may be more important than host associations in structuring louse populations and species. This is particularly true in cases where host life history (e.g. hole-nesting) or parasite life history (e.g. phoresis) might promote frequent host switching events between syntopic host species. These findings highlight the importance of integrating biogeographic information into cophylogenetic studies.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Frederick H. Sheldon