Conservation genetics of Stylophorum diphyllum (Papaveraceae): investigating the genetic diversity and differentiation of peripheral and core populations across the range

Many species-at-risk reach the edge of their range as disjunct and isolated populations. These peripheral populations may harbour unique genetic diversity crucial for future range shifts, or they may lack genetic diversity due to isolation or small population size. As such it is important to assess the genetic diversity and differentiation of these populations. We used 1,838 SNPs to evaluate the differentiation and genetic diversity in six Canadian (peripheral) and eight US (core) populations of wood-poppy (Stylophorum diphyllum), a perennial wildflower that is endangered at the northern limit of its range. We also compared these 14 populations to seeds from two commercial seed providers to determine if commercial sources are introgressing into wild populations. We found strong differentiation between core and peripheral populations, low levels of gene flow among both core and peripheral populations, and low to moderate levels of genetic diversity across the range with a decrease in heterozygosity in peripheral populations. We also noted that the commercial populations were genetically distinct from all natural sampled populations, with no evidence of introgression between commercial seeds and either Canadian or US populations. Our study indicates that peripheral and core populations form unique conservation units and therefore the conservation and recovery of the wood-poppy in Canada is necessary to conserve the full range of genetic diversity within the species.