Date of Thesis

Summer 2024

Description

Premise: The glacial cycles of the Pleistocene period likely had a profound impact on the genetic diversity and phylogeographic patterns of numerous plant taxa in North America. However, the genetic diversity of rare, limestone-endemic woody species has not been highlighted. This study assesses genetic diversity in Paxistima canbyi A. Gray (Canby’s mountain lover or rat stripper), a rare limestone endemic small woody plant.

Methods: We investigated the genetic diversity of P. canbyi using genomic Single Nucleotide Polymorphism (SNP) data from 165 individuals from 14 populations sampled from across the entire range distribution. We first; de novo assembled the SNP dataset using ipyrad and then estimated Ploidy levels of P. canbyi using the observed heterozygosity and the ratio of DNA sequences through a Bayesian assignment method-based R package, gbs2ploidy. We subsequently use a hard-filtered SNP dataset containing only biallelic SNPs to make inferences on the genetic diversity of the extant P. canbyi populations.

Results: Our results reveal P. canbyi is a polyploid species. Also, genetic diversity within the extant populations seems to be moderately high with observed heterozygosity higher than expected. Also, there appears to be a significant level of differentiation between populations with the overall FST calculated to be 0.390. Except for two populations in West Virginia who (even with large numbers of individuals) appear to be inbred, most P. canbyi populations are not inbred as heterozygotes were observed to be abundant (FIS = -0.273). Using a cross-entropy criterion in a population structure analysis, we also identified fourteen genetic clusters with all populations except four, which form two unique genetic clusters.

Conclusion: Almost all P. canbyi populations are distinct genetic units that share some ancestral genetic variation even under genetic isolation. Despite promising inferences regarding the genetic health of the species, some populations may not persist without control of the invasive scale insect. While all populations have high genetic diversity and are not yet inbred, the genetic isolation observed across all the populations within the disjunct distributions indicates that these populations may be at risk of future inbreeding depression, especially within the Smoke Hole and Blue Rock populations in West Virginia.

Keywords

Paxistima canbyi, Genetic diversity, Central Appalachian Mountains, Cumberland-Allegheny Interior Low Plateaus, Rare plants

Access Type

Masters Thesis

Degree Type

Master of Science

Major

Biology

First Advisor

Christopher T. Martine

Second Advisor

Melody P. Sain

Third Advisor

Scott Schuette

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