Author ORCID Identifier

https://orcid.org/0000-0002-7422-8185

Semester

Spring

Date of Graduation

2026

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Craig Barrett

Committee Member

Jennifer Hawkins

Committee Member

Stephen DiFazio

Committee Member

Loren Albert

Committee Member

Cynthia Huebner

Abstract

Invasive species can cause environmental and economic damage, but can offer unique opportunities to study rapid evolution and adaptation in novel environments. Microstegium vimineum (stiltgrass) is a prolific invasive grass in the eastern United States. Historical herbaria collections were used to identify patterns of invasion history and population dynamics over a spatial and temporal scale. Analyses of plastid genomes reveal a complex invasion history, including a single introduction in the southern United States linked to Japan and multiple repeated introductions in the northern United States from various source populations. Spread of introduced populations provide evidence of admixture among previously geographically isolated populations. A common garden experiment with phenotypic and genotypic data from nearly 400 individuals demonstrated that multiple traits associated with invasiveness vary significantly across populations, correlate with awn presence and latitude, and show signatures of selection, indicating evidence of rapid adaptive divergence post-introduction. Phylogenomic analyses using the Angiosperms353 dataset clarify the evolutionary relationships of Microstegium and Leptatherum, corroborating previous taxonomic revisions splitting Microstegium and revising Leptatherum. Historical hybridization and polyploid events were revealed in the lineages of both Microstegium and Leptatherum. This study provided a comprehensive analysis of the ecological, genetic, and evolutionary mechanisms underlying the success history of M. vimineum in the invasion process. Additionally, this study highlighted the roles of key invasion hypotheses including propagule pressure, habitat filtering, phenotypic plasticity, polyploidy, and adaptation in shaping the invasion dynamics of M. vimineum. This integrative approach demonstrates how combining historical specimens, genomic, and phenotypic data can elucidate the processes driving plant invasions and identify the pathways that promote invasiveness in a species.

Invasive species, stiltgrass, evolution, phylogenetics

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