Distinguishing Acuña cactus, a federally endangered species, from its close relatives using genetic information

Shannon Fehlberg, Desert Botanical Garden

The Acuña cactus, Echinomastus erectocentrus var. acunensis, is an endangered species with a restricted distribution in the Sonoran Desert in southern Arizona and northern Sonora, Mexico. Population-level genetic analyses for this species are lacking, and taxonomic boundaries between E. erectocentrus var. acunensis and its close relatives E. erectocentrus var. erectocentrus and E. johnsonii are unclear. Detailed morphological data that have been collected for these three taxa indicate the existence of a geographical cline from the Mojave Desert to the Sonoran Desert. The goal of this project is to document genetic diversity within and among populations of E. erectocentrus var. acunensis, as well as between E. erectocentrus var. acunensis and its close relatives. The addition of genetic data to our current knowledge of morphology and distribution may enable us to form stronger species definitions, make more accurate field identifications, and begin to clarify taxonomic confusion in the group. To acquire genetic data, seven known populations of E. erectocentrus var. acunensis, three populations of E. erectocentrus var. erectocentrus and four populations of E. johnsonii were visited, and more than 230 spine or floral tissue samples were taken. DNA was extracted, and data were collected for 11 microsatellite regions specifically developed for these taxa, and two microsatellite regions previously developed for Sclerocactus. Standard population genetic measures were used to determine genetic variation and structure, and observed genetic differentiation was compared to the current morphological understanding of the group. These analyses help improve our knowledge of the genetic structure of E. erectocentrus var. acunensis populations and inform our understanding of species boundaries and evolutionary relationships within the group, thereby allowing us to refine conservation and management plans aimed at protecting and restoring populations of this endangered species.