A species left behind by glaciation: Appalachian Mustard lineage dispersal due to climate change during the Ice Ages

The research presented here pertains to the population genetics of a diploid glacial relict mustard, Draba ramosissima (Brassicaceae), in the Appalachian Mountains and associated foothills. Draba ramosissima is a diploid Appalachian perennial herb found primarily on limestone-rocky outcrops and is endemic to the area. Draba ramosissima's closest relatives are in Siberia and Beringia based on previous phylogenetic analysis. These data led us to conclude that the original Draba lineage was of Asian descent during the time of glaciation cycles of the Pleistocene. With this research, we have been observing the present-day habitat, specifically the stability of the habitat, as well as collecting phylogenetic and population genetic data for its entire distribution. The research is testing the hypothesis that the lineages that gave rise to the diploid Draba ramosissima were pushed throughout the North American continent and were unable to retreat with the melting ice sheet that once boarded the Appalachian mountains, and can be classified as a “glacial relic” species. Preliminary population genetic data of a subset of sites also indicates population structure typical for glacial relict species. We have gathered data from both SERNEC and iNaturalist, compiling all known sightings of Draba ramosissima throughout the Appalachian mountains and across six states (Kentucky, Maryland, North Carolina, Tennessee, Virginia, and West Virginia). Methods used for this research are population sampling, sub-genomic analysis using ddRADtag and Illumina sequencing, population genetic statistics, phylogenetic, and phylogeographic analysis, and potentially chromosomal observations. At the moment have procured population samples from Virginia and West Virginia in 2025, and will be collecting in the rest of the aforementioned states in early spring 2026. We will use this genetic data to test for relatedness of the populations throughout the Appalachian mountains to explore the effects of glaciation on speciation.