Date of Award
12-1-2025
Document Type
Dissertation
Degree Name
Ph.D. in Biological Science
First Advisor
Jason Hoeksema
Second Advisor
Brice Noonan
Third Advisor
Ryan Garrick
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Mycorrhizal fungi form mutualistic symbioses with most land plants, occurring primarily as arbuscular mycorrhizal (AM) fungi or ectomycorrhizal (ECM) fungi. Pulsatilla patens, an herbaceous perennial widely distributed across Eurasia and North America, belongs to a plant family historically known only to form AM associations. However, recent discoveries of ECM P. patens individuals in northeastern Poland raise questions about the mycorrhizal status and evolutionary trajectory of this species. Because ECM formation in this lineage is likely evolutionarily recent, P. patens offers a valuable system for investigating the ecological and historical factors that facilitate the emergence of ECM symbiosis.
Chapter 1 assessed the biogeography of P. patens mycorrhizal associations across 31 locales in North America and Europe. ECM individuals were restricted to forested European locales, particularly in Poland, Slovakia, and Romania, and ECM presence was strongly correlated with increased canopy cover. DNA sequencing revealed associations with generalist ECM fungi, especially Tomentella species. Importantly, all ECM individuals also formed AM associations, indicating that P. patens is dual-mycorrhizal and that ECM acquisition does not require loss of the ancestral AM symbiosis.
Chapter 2 used a common-garden experiment to test whether ECM formation is driven by environmental factors (light availability) or genetically influenced by seed origin. ECM developed only in plants grown from seeds sourced from an ECM-present European locale and only under shaded conditions. These individuals associated with fungi in the Helotiales, demonstrating that ECM formation can occur ex situ without neighboring ECM trees. The roles of light availability, seed origin, and fungal inoculum require further investigation.
Chapter 3 explored potential historical explanations for the patchy distribution of ECM P. patens by evaluating four preliminary hypotheses involving climatic history, distributions of ECM fungi, co-refugia with ECM trees, and potential hybridization with Pulsatilla pratensis. These exploratory results highlight promising directions for future phylogeographic testing.
Overall, this work demonstrates that mycorrhizal status in P. patens varies across its range, that ECM formation is facilitated by both environmental and genetic factors, and that dual mycorrhizal associations can occur in recently evolved ECM plants. These findings advance our understanding of the ecological and evolutionary processes that promote the emergence of novel mycorrhizal symbioses.
Recommended Citation
Draud, Savannah Lane, "Investigating the Origins of Symbiosis Using A Novel Mycorrhizal Interaction in Pasque Flowers (Pulsatilla Patens)" (2025). Electronic Theses and Dissertations. 3510.
https://egrove.olemiss.edu/etd/3510