Doctor of Philosophy (PhD)


Biological Sciences

Document Type



Studies of cophylogeny greatly increase understanding of associations between hosts and their parasites. This study uses molecular data to test the hypothesis that members of two rodent families (Geomyidae and Heteromyidae) and their associated lice (Geomydoecus and Fahrenholzia, respectively) show a statistically significant pattern of cophylogeny. Both host groups are generally solitary organisms and both louse groups are obligate ectoparasites, often exhibiting extreme degrees of host specificity. This intimate and potentially long-term association likely has resulted in coevolutionary adaptations and counter adaptations on the part of both symbiotic partners. Phylogenetic analysis of chewing lice (Geomydoecus) reveals two major clades corresponding to the G. coronadoi and G. mexicanus species complexes. These louse complexes are reciprocally monophyletic, and each clade within each complex parasitizes a different species of pocket gopher. Both louse species complexes exhibit a significant pattern of cophylogeny when compared to their hosts. The mitochondrial COI gene of lice of the G. coronadoi complex is evolving approximately 2 -3 times faster than the COI gene of their hosts, whereas the COI gene of lice of the G. mexicanus complex is evolving at roughly the same rate as the same gene of their hosts. Future analyses are necessary to determine why evolutionary rates in these two parasite lineages differ. The phylogenetic analysis of sucking lice (Fahrenholzia) resolves relationships among 11 of the 12 currently recognized species and identifies several possible cryptic species. Although there is conflict among the basal nodes of the host and parasite phylogenies, cophylogenetic analysis reveals significant topological congruence between these lice and their heteromyid hosts. The mitochondrial COI gene of Fahrenholzia lice is evolving roughly 1.6 times faster than the COI gene of their hosts, but additional comparisons of molecular rates are necessary to determine if this rate difference is shared by other groups of sucking lice and their hosts. Results of this study indicate that a combination of tree-based, distance-based, and data-based methods should be used in cophylogeny analyses. The final chapter of this dissertation presents a compilation of mammal-louse associations reveals and offers a preliminary assessment of sucking louse prevalence and abundance on heteromyid rodents.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Mark S. Hafner