Graduation Date

Spring 2024

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

Oscar Vargas

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Jeffrey White

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Erik Jules

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Eric LoPresti

Fourth Committee Member Affiliation

Community Member or Outside Professional


Abronia, Abronia villosa var. aurita, Evolution, Systematics, California Floristic Province, Microevolution, Budding speciation, Budding divergence, Biogeography, Genetics, Phylogenetics, Ecological speciation, Progenitor, Derivative

Subject Categories



Physical barriers to gene flow are the traditional evidence for species divergence. Conversely, there has been increasing acknowledgment of speciation in the face of gene flow as an evolutionary process. Budding speciation involves peripheral populations adapting to local ecological conditions, thereby budding off from a widespread progenitor species. Budding speciation is distinguished by ecological divergence and is generally evidenced by asymmetrical range size and nested phylogenetic relationships of sister species. The narrow endemic Abronia villosa var. aurita is adapted to montane sandy washes adjacent to its widespread sister variety, the desert dwelling var. villosa. Here, I tested the hypothesis that A. villosa var. aurita is derived from its sister variety via budding divergence. My investigation employed phylogenomic and genetic structure analyses of a clade comprised of A. villosa and its close allies, A.umbellata and A. gracilis. My results reveal that Abronia villosa var. aurita is a recently budded taxon, phylogenetically nested within its sister variety yet still showing unique genetic structure. Unexpectedly, I found evidence that var. aurita comprises two reciprocally monophyletic subclades, separated by an elevational gradient. I also confirmed Tillet’s 1967 hypothesis that A. villosa would hybridize with the coastal A. umbellata in the localities where they are sympatric. Ultimately, my study shows a recent but complex history of divergence and subsequent post-divergence processes, illustrating the importance of capturing nuanced snapshots of microevolutionary mechanisms as they occur.

Citation Style



Thesis/Project Location


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