Award Date


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Biological Science

First Committee Member

Brett R. Riddle

Number of Pages



Evidence of deep geographic structure in many taxonomic lineages throughout the arid regions of western North America suggests potential for recovering episodes of vicariant isolation and divergence through comparative biogeographic approaches. Vicariance biogeography predicts that suites of co-occurring taxa should demonstrate similar geographic patterns of genetic divergence resulting from simultaneous isolation of formerly contiguous regional populations. Previous molecular phylogeographic work on small, non-volant desert taxa tended to focus on one or two species, often with limited distributions. Different methods of sampling and analyses confound general statements about the presence of regional endemic biotas. Assessment of general biogeographic patterns in biotas therefore requires sampling co-occurring species across the same genetic markers; This dissertation addresses the historical biogeography and molecular population structure of four widespread desert lizards (Crotaphytidae: Crotaphytus bicinctores, C. collaris, Gambelia wislizeni and Phrynosomatidae: Sceloporus magister). Each species manifests evidence of a complex hierarchical phylogeographic structure of recent distributional fluctuations nested within deep phylogeographic disjunctions correlated with physiographic features postulated to have generated vicariant events. Comparison of interspecific patterns of isolation and divergence across taxa suggests four regions of endemism: EASTERN (roughly congruent with the Chihuahuan desert and parts of the Great Plains), CENTRAL (primarily the Sonoran Desert, but also containing parts of the eastern Colorado Plateau), WESTERN (Mojave and Great Basin deserts, and also including the Owens Valley and parts of the western Colorado Plateau) and PENINSULAR (Peninsular Desert of Baja, California) that are consistent with models of late Pliocene/early Pleistocene vicariant isolation of arid dwelling species; For Crotaphytus collaris, limited genetic divergence and diversity in the northern parts of its range contrasts with high diversity in the southern parts of the range, suggesting recent Pleistocene colonization of the Great Plains and Colorado Plateau. Large divergences across the EASTERN and CENTRAL regions, however, suggest that northward colonization consisted of two independent events from spatially isolated regional populations. Gambelia wislizeni also exhibits a pattern of recent northward expansion, with the eastern and western Great Basin apparently reflecting independent colonization events from a common source population within the Mojave desert. This pattern of recent northward expansion within the WESTERN region is also suggested by C. bicinctores and Sceloporus magister. These patterns are consistent with previous models of Pleistocene habitat fluctuations along with other published simulations of effective female population size and gene flow during the Pleistocene; While the observed levels of divergence among all four species were consistent with a late Pliocene/early Pleistocene vicariant scenario, the model of regional endemism presented herein is independent of temporal considerations. Standardized datasets obtained from co-occurring taxa collected from the same localities and sampled across the same gene regions generated testable hypotheses about the generalities of biogeographic responses of desert reptiles of western North America to the geological and climatic events of the last ten million years.


American; Bicinctores; Biogeography Collaris; Comparative; Crotaphytidae; Crotaphytus; Crotaphytus Collaris; Deserts; Four; Gambelia; Lizards; Magister; North; Phrynosomatidae; Sceloporus; Species; Western; Wislizeni

Controlled Subject

Zoology; Ecology

File Format


File Size

6635.52 KB

Degree Grantor

University of Nevada, Las Vegas




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