Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level



Biological Sciences


Michael Douglas

Committee Member

Marlis Douglas

Second Committee Member

Andrew Alverson

Third Committee Member

David Philipp


Conservation Biology, Phylogenetics, Population Genetics


Evolution occurs at various spatial and temporal scales. For example, speciation may occur in historic time, whereas localized adaptation is more contemporary. Each is required to identify and manage biodiversity. However, the relative abundance of Speckled Dace (Rhinichthys osculus), a small cyprinid fish in western North America (WNA) and the study species for this dissertation, establishes it an atypical conservation target, particularly when contrasted with the profusion of narrowly endemic forms it displays. Yet, the juxtaposition of ubiquity versus endemism provides an ideal model against which to test hypotheses regarding the geomorphic evolution of WNA. More specifically, it also allows the evolutionary history of Speckled Dace to be contrasted at multiple spatial and temporal scales, and interpreted in the context of contemporary anthropogenic pressures and climatic uncertainty.

Chapter II dissects the broad distribution of Speckled Dace and quantifies how its evolution has been driven by hybridization/ introgression. Chapter III narrows the geographic focus by interpreting Speckled Dace distribution within two markedly different watersheds: The Colorado River and the Great Basin. The former is a broad riverine habitat whereas the latter is an endorheic basin. Two biogeographic models compare and contrast the tempo and mode of evolution within these geologically disparate habitats.

Chapter IV employs a molecular clock to determine origin of Speckled Dace lineages in Death Valley (CA/NV), and to contrast these against estimates for a second endemic species, Devil’s Hole Pupfish (Cyprinodon diabolis). While palaeohydrology served to diversify Rhinichthys, its among-population connectivity occurred contemporaneously. These data also provide guidance for assessing the origin of the Devil’s Hole Pupfish, a topic of considerable contention.

The final two chapters present bioinformatic software that facilitates the analysis of single-nucleotide-polymorphism (SNP) DNA data (used herein). Chapter V describes COMP-D, a program designed to assess introgression among lineages, whereas Chapter VI presents programmatic modifications to BAYESASS that allow migration to be quantified from SNP datasets.

These five studies provide an in-depth understanding of contemporary and historical processes that shape aquatic biodiversity in environments prone to anthropogenic disturbance. They also highlight the complexities of evolutionary mechanisms and their implications for conservation in a changing world.