Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level



Biological Sciences


Michael E. Douglas

Committee Member

Andrew J. Alverson

Second Committee Member

Thomas F. Turner

Third Committee Member

Marlis R. Douglas


Biological sciences, Catostomus, Colorado, Evolution, Hybridization, Introgression, Reticulate


Hybridization is neither simplistic nor phylogenetically constrained, and post hoc introgression can have profound evolutionary effects. Most studies have focused on tractable model systems, rather than organisms with complicated phylogenetic histories. Finescale Sucker (genus Catostomus) in western North America is recognized as a paradigm of fish hybridization. Yet, its extent of historic and contemporary introgression is largely unstudied, an aspect that impedes the resolution of its phylogeny as a baseline for conservation. To explore reticulation in this group, I assayed variation of 20 Catostomus species across temporal and geographic scales by analyzing hundreds of samples and employing a combination of molecular and bioinformatic approaches.

Chapter-1 examined hybridization among native suckers in an anthropogenically-fragmented environment using sequence analysis of mitochondrial and nuclear markers. Introgression was not detected, but hybridization with Utah Sucker likely lowers recruitment in the rarer Bluehead Sucker in the Bonneville Basin.

Chapter-2 tested discordant mitochondrial and morphological hypotheses by evaluating historical introgression in Catostomus using 14,007 ddRAD loci comprising 179,811 SNPs. A well-supported phylogeny offered insights into the effects of admixture on different phylogenetic methods, but tests for introgression allowed resolving previous taxonomic discords.

Chapter-3 dissected phylogenomic patterns and tested species-delimitations for taxa with admixed ancestry. Comparative population genetic and phylogenetic analyses supported taxonomic revisions in two species of conservation concern, and highlight that response to vicariant events is modulated by species-specific life history variation.

Chapter-4 assessed historic and contemporary admixture across 10 co-occurring endemic and invasive species using ~90k SNPs with hundreds of unlinked, fixed species-specific markers. This genomic approach allowed to discern complex hybridization patterns across an entire basin and revealed elevated reproductive isolation at greater phylogenetic distance.

In combination, these analyses examined evolutionary reticulation among freshwater fishes of conservation concern in a large, geographically diverse, but heavily altered watershed, the Colorado River Basin, and highlighted both the complexity and constraints of introgressive hybridization. Insights from this study will aid in conservation of aquatic ecosystems in the arid Southwest further jeopardized by anthropogenic threats and an uncertain climatic future.