First Advisor

McGlaughlin, Mitchell

Date Created



Sclerocactus glaucus is an endemic Colorado species that is federally threatened under the Endangered Species Act. Sclerocactus glaucus is losing habitat due to disturbance by oil and gas exploration, urbanization, open range cattle grazing and recreational land use. Due to the low number of wild populations, conservationists question the genetic integrity of the species. Field biologists have observed S. glaucus populations with individuals possessing morphological characteristics of the closely related and widely distributed Sclerocactus parviflorus. Individuals from 28 populations of S. glaucus, 9 populations of S. parviflorus, and 1 population of S. cloveriae were sampled. Microsatellite analysis using 13 variable loci was used to determine population structure, degree of hybridization, gene flow, and diversity levels of these species. Chloroplast DNA analysis was also used to determine diversity, phylogenetic relationships, and direction of gene flow. Using genetic tools, the analyses established that S. glaucus populations remain diverse and mostly untainted by hybridization. These data also demonstrate that morphology is not reliable for identification of species or hybrids within this cluster of species. Characters that historically designated S. parviflorus, such as hooked spines, were found not to be good indicators for species determination. Two populations of S. glaucus were misidentified as S. parviflorus and one of these populations is a genetically pure population with no genetic introgression from S. parviflorus. Species divisions appear to be closely tied to geographical location with S. parviflorus located only to the east of Grand Junction. Two distinct groups of S. glaucus are distinguished by the river drainage systems in which they are located. Land managers and conservationists now have the genetic information to move forward with preserving populations of S. glaucus.

Abstract Format



Biology; Genetics; Sclerocactus glaucus; Sclerocactus parviflorus; Microsatellite analysis; Botony


107 pages

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