Sponsor
Portland State University. Department of Biology
First Advisor
Luis A. Ruedas
Term of Graduation
Spring 2026
Date of Publication
8-12-2026
Document Type
Thesis
Degree Name
Master of Science (M.S.) in Biology
Department
Biology
Language
English
Subjects
Cranial Morphometrics, Cryptic Diversity, Ecological Niche Modeling, Integrative Taxonomy, Mazama Pocket Gopher (Thomomys mazama), Species Delimitation
Physical Description
1 online resource (vii, 140 pages)
Abstract
The population genetic structure and geographic distribution of the pocket gopher genus Thomomys Wied-Neuwied, 1839, lends itself to speciation events. Conserved morphology, ecological specialization, and high rates of molecular evolution may increase the probability of allopatric speciation, thereby contributing to the presence of morphologically cryptic taxa. In light of these patterns of evolution, we assessed genetic divergence and phylogenetic relationships, cranial morphometric differentiation, and ecological divergence among taxa in the Thomomys mazama species complex to test the hypothesis that T. mazama is a single species. Species delimitation analysis using Bayesian Poisson Tree Processes (bPTP) and data from the mitochondrial cytochrome b gene suggested the presence of multiple candidate lineages within T. mazama. Multivariate cranial morphometric analyses indicated statistically significant yet modest differentiation among taxa, with the clearest interpretable signal involving rostral palatal proportions, cranial depth, and mandibular dimensions, although substantial overlap in multivariate morphospace persisted. Ecological niche modeling was undertaken to test for ecological discontinuities and geographic and environmental differentiation congruent with the lineage structure recovered in the genetic data. Results indicate broad differentiation in habitat distribution and environmental space, with generally low overlap among modeled taxa. Taxonomic designations directly inform the conservation and management status of species under the U.S. Endangered Species Act, highlighting the need for taxonomic revision where suitable, including subsequent recognition of species. While formerly widespread, the distribution of T. mazama has diminished substantially in area due to anthropogenic impacts. Although T. mazama currently is classified as a single species, the results of our phylogenetic, morphometric, and ecological analyses indicate the presence of multiple geographically structured lineages within T. mazama.
Rights
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Persistent Identifier
https://archives.pdx.edu/ds/psu/45140
Recommended Citation
St. Michael, Jessica Kate, "Integrative Evidence for Cryptic Diversity in the Thomomys mazama Species Complex: Phylogenetics, Cranial Morphometrics, and Ecological Niche Modeling" (2026). Dissertations and Theses. Paper 7206.