Sponsor
Portland State University. Department of Biology
First Advisor
Susan E. Masta
Term of Graduation
Summer 2025
Date of Publication
9-12-2025
Document Type
Thesis
Degree Name
Master of Science (M.S.) in Biology
Department
Biology
Language
English
Subjects
Chelicerata, Cryptic species, Mundochthonius, Pacific Northwest, Phylogeography, Pseudoscorpion
Physical Description
1 online resource (vii, 87 pages)
Abstract
Understanding the processes that drive genetic divergence and species formation is central to evolutionary biology. Invertebrates with low dispersal ability, such as pseudoscorpions, are especially prone to cryptic diversification due to their occupancy of niche microhabitats and sensitivity to landscape barriers. Despite their ecological roles as predators and bioindicators, pseudoscorpions remain one of the least studied arachnid groups, with limited taxonomic resolution and few integrative studies. This research focuses on the genus Mundochthonius in the Pacific Northwest, particularly M. pacificus, a morphologically conserved species whose true diversity and distribution remain poorly understood.
Field surveys guided by a GIS-based habitat suitability model were conducted across Oregon, Washington, Idaho, and Montana. A total of 56 individuals were sequenced for mitochondrial COI and 25 for nuclear 28S, revealing eight geographically structured COI clades and an east–west split across the Cascade Range. Inland populations formed a distinct eastern clade (M. sp.), genetically divergent from M. pacificus and likely representing an undescribed species. The range of M. pacificus found in this study was limited to the west side of the Cascade Range, extending from King County, Washington, to Humboldt County, California.
To assess whether these genetic lineages corresponded with morphological differentiation, morphometric analyses were conducted on 103 specimens using light microscopy and scanning electron microscopy (SEM). The most consistent morphological differences were found in coxal spine structure and multivariate comparisons of body proportions, with M. sp. distinguishable from M. pacificus and M. magnus. Although some overlap in morphometric traits was observed, particularly within M. pacificus, these data supported species-level divergence.
This study presents the first phylogeographic and integrative taxonomic analysis of Mundochthonius in North America. Results highlight cryptic diversity within the genus and identify the Cascade Range as a primary biogeographic barrier. These findings underscore the value of combining genetic, morphological, and geographic data to resolve species boundaries in poorly studied arthropod groups.
Rights
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Persistent Identifier
https://archives.pdx.edu/ds/psu/44203
Recommended Citation
Montoya-Cowan, Amanda Rai, "Systematics and Phylogeography of Mundochthonius Chamberlin, 1929, in the Pacific Northwest (Chelicerata, Pseudoscorpiones)" (2025). Dissertations and Theses. Paper 6964.