Date Approved

8-13-2025

Graduate Degree Type

Thesis

Degree Name

Biology (M.S.)

Degree Program

Biology

First Advisor

Timothy Evans

Second Advisor

Charlyn Partridge

Third Advisor

Jennifer Winther

Academic Year

2024/2025

Abstract

Small, isolated populations often have low genetic diversity and low potential for adaptation in response to environmental changes. Alternatively, isolated communities are often more likely to display local adaptations and over time speciate. The Great Lakes Region is home to over 50 vascular plant species that are disjunct from the species’ core populations. Agoseris glauca (Asteraceae) is a Great Lakes disjunct and Michigan state threatened species geographically isolated from its core range by 900 km. This study uses Genotyping by Sequencing to assess the population genetics of A. glauca for two Michigan disjunct populations and five western populations in the core range of the species. Specific goals were to 1) determine the amount of genetic variation in Michigan populations of A. glauca and several populations throughout the primary range of the species; and 2) determine whether the Great Lakes populations of A. glauca survived the last glaciation in a glacial refugium, are present due to pre or postglacial vicariance, or are the products of more recent dispersal. Cluster analysis and hierarchical F statistics were used to assess relationships among all seven populations. In all models, populations in Montana and Utah were different than all populations east of the Rocky Mountains. Two South Dakota populations and the Minnesota population were closely related to each other, and the Michigan populations were likewise closely related. Michigan populations show genetic distance from the South Dakota and Minnesota populations in our pairwise FST, and at K= 4 form their own cluster. At K=3 these Michigan populations cluster with South Dakota and Minnesota populations. These results indicate low genetic health for all populations east of the Rocky Mountains, and postglacial expansion with vicariance. Future studies will be carried out to determine approximate time of divergence and possible local adaptations in the threatened Michigan populations.

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