Electronic Theses and Dissertations

Date

2024

Document Type

Thesis

Degree Name

Master of Science

Department

Biology

Committee Chair

Jennifer Mandel

Committee Member

Emily Puckett

Committee Member

Shawn Brown

Abstract

Genetic diversity among and within populations of species is critical for survival in our rapidly changing world. Conservation genomics links studies of population genomic variation with conservation managers to provide scientific data for species management strategies. The whorled sunflower, Helianthus verticillatus (Asteraceae), is an endangered plant species endemic to the southeastern United States. Only five populations were known to exist, in Alabama, Georgia, and Tennessee, until about seven years ago when additional populations of the species were discovered in Mississippi and Virginia. Population genetic work using microsatellites revealed that the Mississippi population (known as MSCC) was genetically distinct from all other populations. Since this study, more populations have been discovered in Mississippi with a unique phenotype that does not match the description of any known Helianthus species. Some stems have a whorled leaf morphology, which is typically used to distinguish H. verticillatus from relative species. However, some stems have an opposite (and even alternate) leaf morphology. Helianthus verticillatus’ sister species, H. grosseserratus, is known to display both the opposite and alternate leaf morphology found in the newly discovered Mississippi populations and has geographic overlap in Mississippi. These factors made H. grosseserratus a great candidate to test for past admixture with H. verticillatus, which could have played a role in the evolutionary history of the newly discovered Mississippi populations. In this thesis work, I have used a conservation genomic approach to investigate the patterns of genetic diversity across all known populations of H. verticillatus and determine if the newly discovered Mississippi populations are genetically distinct compared to populations of H. verticillatus and H.grosseserratus. Despite being federally endangered and rare, H. verticillatus has comparable levels of genetic diversity to its much more common and widespread sister species, H. grosseserratus, at the genome-wide level. Three unique genetic clusters were identified within the whorled sunflower: 1) Alabama2, 2) Alabama1/Georgia/Virginia, and 3) the Tennessee populations. Collecting seed from each cluster will help preserve as much genetic diversity as possible for the protection of this endangered species. Additionally, the MSCC population should not be classified as H. verticillatus, reducing the number of extant populations to six. The Mississippi Helianthus sp. populations are genetically distinct from both H. grosseserratus and H. verticillatus. The Helianthus sp. populations exhibit signatures of slight gene flow from both the Tennessee H. verticillatus populations and some H. grosseserratus populations. However, the evolutionary history of these populations is likely more complex than previously hypothesized, as results do not suggest that they are solely introgressed from H. grosseserratus and H. verticillatus. There may be unsampled populations or species that have contributed to the ancestry of these Helianthus sp. populations, and the use of different species of Helianthus in these analyses may result in different findings. The goal of this thesis was to provide local conservation agencies with information to foster implementation of the best conservation plans to protect the federally endangered plant species, Helianthus verticillatus. The results from this work will alter conservation recommendations for the whorled sunflower, as well as for the new Mississippi populations.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to ProQuest.

Notes

Open Access

Download

Share

COinS