Graduation Date
Spring 2026
Document Type
Thesis
Program
Master of Science degree with a major in Biology
Committee Chair Name
Oscar Vargas
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
Erik Jules
Second Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Third Committee Member Name
Rachael Wade
Third Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Fourth Committee Member Name
Ho Yi Wan
Fourth Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Sixth Committee Member Affiliation
Community Member or Outside Professional
Keywords
Erysimum, Erysimum menziesii, Erysimum concinnum, Evolution, Systematics, California Floristic Province, Microevolution, Budding speciation, Convergent evolution, Genetics, Phylogenetics, Ecological speciation, Cryptic species, Dunes
Abstract
Morphological similarity among geographically isolated populations can obscure deep evolutionary divergence, especially when convergent evolution under similar environmental conditions yields comparable phenotypes across independent lineages. Such cryptic diversity is likely underestimated in hotspots like the California Floristic Province (CFP), a global biodiversity hotspot, defined by its Mediterranean-like climate and encompassing most of California, southwestern Oregon, and northwest Baja California. The CFP is home to a disproportionate number of narrow endemics whose origins and evolutionary relationships remain poorly understood. Here, I investigate the evolutionary origins of Erysimum menziesii (Brassicaceae), a federally endangered California coastal dune endemic whose fragmented distribution has led to its assumed paleoendemic status, despite limited phylogenetic investigation. Its close morphological similarity and overlapping distribution with Erysimum concinnum have blurred the species boundaries between the two taxa, with both hypothesized to be derived from Erysimum capitatum. Using ddRADseq across 182 individuals spanning 31 populations from Del Norte County to Monterey County, I assessed the phylogenetic position of E. menziesii relative to E. concinnum and E. capitatum, evaluated the speciation mechanism, and assessed genetic differentiation within and among species using STRUCTURE, principal component analysis, and pairwise Fst. I found that both E. menziesii and E. concinnum form a cryptic species complex, with each species comprising four independent lineages that have repeatedly colonized similar coastal environments, with E. menziesii occupying coastal dunes and E. concinnum occupying coastal bluffs. High pairwise differentiation among E. menziesii lineages (Fst = 0.205-0.602), combined with their morphological similarity, reflects convergent evolution driven by similar selective pressure found in dune system, supporting multiple independent neoendemic origins. In Mendocino and Monterey Counties, phylogenetic and genetic evidence support budding speciation from proximal coastal progenitors rather than the suspected E. capitatum. Current species boundaries in both taxa fail to reflect the underlying evolutionary diversity, with each lineage warranting recognition as a distinct taxonomic unit and independent management for conservation.
Citation Style
Chicago-style
Recommended Citation
Jones, Cameron M., "Species boundaries of the rare Menzies’ wallflower (Brassicaceae: Erysimum menziesii), an endemic of the northern California coast" (2026). Cal Poly Humboldt theses and projects. 2571.
https://digitalcommons.humboldt.edu/etd/2571
Included in
Bioinformatics Commons, Botany Commons, Integrative Biology Commons