Genetic Analyses of the Federally Endangered Echinacea laevigata using Amplified Fragment Length Polymorphisms (AFLP) - Inferences in Population Genetic Structure and Mating System

Abstract

Echinacea laevigata is a federally endangered species and a close relative of the medicinally important E. purpurea. The species has 24 recognized populations restricted to four states (VA, NC, SC, GA). To determine the population structure and outcrossing rate across the range of the species, we conducted AFLP analysis using four primer combinations for 22 populations. The genetic diversity of this species was found to be high based on the level of polymorphic loci (200 of 210 loci; 95.24%) and Nei's gene diversity (ranging from 0.1398 to 0.2606; overall 0.2611). There was significant population genetic differentiation (GST of 0.2941), suggesting possible adaptation to local environments. Results from the AMOVA analysis suggest that a majority of the genetic variance is attributed to variation within populations (70.26%). These results are congruent to a previous allozyme study that examined the genetic makeup of 11 of the 24 populations, excluding any Georgia populations. An isolation by distance (IBD) analysis indicated that genetic differentiation among populations is a function of geographic distance, although long-distance gene dispersal (LDGF) between some populations was suggested based on the NJ tree. An estimate of the outcrossing rate based on genotypes of progenies from six of the 22 populations using a multilocus estimate was 0.833-1.2, where 1.2 is considered complete outcrossing, suggesting that the species is predominantly outcrossing. The remaining populations of E. laevigata have significant levels of population diversity, which is encouraging because the long-term survival of this species will depend on moderate to high levels of genetic diversity and management efforts can focus on other issues instead of increasing the genetic diversity.