Theses and Dissertations

ORCID

https://orcid.org/0000-0003-1374-0895

Advisor

Folk, Ryan

Committee Member

Goût, Jean-François

Committee Member

Mlsna, Todd

Committee Member

Welch, Mark

Date of Degree

5-15-2026

Original embargo terms

Immediate Worldwide Access

Document Type

Dissertation - Open Access

Major

Biological Sciences

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Arts and Sciences

Department

Department of Biological Sciences

Abstract

Hybridization, or the flow of genetic materials between varieties or species, shapes evolution by generating novel genotypes, altering allele frequencies, and driving diversification. Yet, the rate at which hybridization occurs is heterogeneous across the tree of life and the ecological and evolutionary factors that govern its occurrence remain poorly understood. This dissertation examines how conserved biotic and abiotic niches influence hybridization and uses integrative methods to delimit species boundaries within Heuchera (Saxifragaceae), a genus notable for widespread interspecific gene flow and cryptic morphological diversity. Results reveal that hybridization is most frequent where pre- and postzygotic barriers are weak, as with Heuchera, and suggest that the occurrence of poor barriers may be incidental to life history differences among species. Our investigations using Heuchera reveal that frequent hybridization in plants is highly correlated to plant taxa where floral traits and pollinator interactions are conserved, highlighting biotic niche conservatism as a key predictor of gene flow. Additionally, population-level phylogenetic analyses and ancestral niche reconstructions reveal that Pleistocene glaciation caused range disturbances that created localized refugia, facilitating historical hybridization, multiple independent chloroplast capture events, and cytonuclear discord; highlighting abiotic niche conservatism as another key predictor of gene flow. Using a refined multiprong species delimitation pipeline, a new species from Coahuila, Mexico was described; and species boundaries in the highly reticulate H. americana complex were resolved, identifying five species and three varieties despite extensive admixture. Collectively, these findings illustrate that organismal traits and ecological interactions shape hybridization, stress the importance of population level sampling for reconstructing complex evolutionary histories, and provides a pragmatic framework for delimiting species in syngameons. This work advances understanding of how niche divergence influences rates of hybridization across the tree of life.

Sponsorship (Optional)

NSF CAREER program (NSF DEB-2337784), Mississippi State University Biology Faculty Fund Research Award (Spring 2020), American Society of Plant Taxonomists (ASPT) Graduate Research Grant, International Association for Plant Taxonomy (IAPT) Research Grant, Society of Systematic Biologists Graduate Research Award, an Oskar H. Zernickow Endowed Fund, a Mississippi State University Strategic Research Initiative (SRI) Student Research & Scholarly Activity Funding Program, and Mississippi State University Biology Faculty Fund Research Award

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