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Genetic variation among populations of the Bakersfield cactus, Opuntia basilaris var. treleasei, based on amplified fragment length polymorphisms
Opuntia basilaris Engelm. & Bigelow var. treleasei (J.M. Coult.) Toumey (OBT), commonly known as Bakersfield cactus, is endemic to parts of Kern County, California. O. b. var. treleasei is one of four varieties of Opuntia basilaris and is state and federally listed as endangered (USFWS 1990). The purpose of this study was to assess the genetic differentiation between OBT and Opuntia basilaris var. basilaris (OBB), and within and among populations of OBT throughout its range. Samples were collected from 200 individual plants representing 32 populations of OBT and one population of OBB and were analyzed using amplified fragment length polymorphisms (AFLP). The AFLP protocol was successfully used to differentiate between an outgroup population of OBB and the great majority of the sampled populations of OBT using 195 polymorphic fragments. Two dendrograms were created using unweighted pair group method with arithmetic mean (UPGMA); one for all individuals and the other where each population was treated as a discreet unit. In the dendrogram based on all individuals, most samples did not cluster as distinct geographic populations, suggesting little genetic differentiation, due to a partial or complete restriction of gene flow, among the majority of OBT populations. Extensive genetic variation was found within and among OBT populations based on an analysis of molecular variance (AMOVA). Twenty three percent of the genetic differentiation was found among fragmented populations and 77%from within individuals of OBT populations suggesting that genetic variation exists between individuals within the OBT populations analyzed. In the UPGMA diagram by population, all five of the Wheeler Ridge populations clustered together. Moreover, three of the Wheeler Ridge populations formed a distinct cluster in a principal coordinates analysis (PCoA) suggesting some level of genetic structure among OBT populations. The only population with a large sample size where virtually all representative samples grouped together was for ‘OEO2’, which is located in the eastern portion of the Southern San Joaquin Valley. The results of this population genetics study will likely be useful in the conservation management of this endangered taxon.
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