Disentangling the role of hybridization in the evolution of the endangered Arizona cliffrose (<Emphasis Type="Italic">Purshia subintegra</Emphasis>; Rosaceae): a molecular and morphological analysis |
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Authors: | Steven E Travis Joanne E Baggs Joyce Maschinski |
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Institution: | (1) USGS National Wetlands Research Center, 700 Cajundome Blvd., Lafayette, LA 70506, USA;(2) Present address: Department of Biological Sciences, University of New England, 11 Hills Beach Road, Biddeford, ME 04005, USA;(3) The Arboretum at Flagstaff, 4001 S. Woody Mountain Rd., Flagstaff, AZ 86001, USA;(4) Present address: USDA Forest Service, Humboldt-Toiyabe National Forest, 1200 Franklin Way, Sparks, NV 89431, USA;(5) Present address: Fairchild Tropical Botanic Garden Research Center, 11935 Old Cutler Rd., Miami, FL 33156, USA |
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Abstract: | Hybridization may threaten the conservation status of rare species through genetic assimilation and may confound the ability
to distinguish among taxa. We studied these issues in an endangered shrub, Purshia subintegra (Rosaceae), known from four populations growing on limestone outcrops in central Arizona (USA). Using amplified fragment
length polymorphisms (AFLP) and the Bayesian clustering algorithm implemented in STRUCTURE, we identified three distinct genetic
lineages among Arizona Purshia subintegra and P. stansburiana. An initial split divided San Carlos Basin P. subintegra (considered P. pinkavae by Schaack) from northern P. stansburiana populations (FST = 0.394). A subsequent split separated northern P. stansburiana from two P. subintegra populations at Horseshoe Lake and Burro Creek (FST = 0.207), which comprised a nearly perfect admixture of the two lineages identified in the initial analysis. In the Verde
River Valley P. subintegra is sympatric with P. stansburiana and exhibited an average 27% P. stansburiana genes for 5 of 6 stands analyzed, indicating ongoing hybridization and backcrossing with P. subintegra. Individuals carrying >90% P. subintegra markers are identifiable 68% of the time based on morphology, with leaf lobing, leaf size, and leaf length acting as the
most reliable indicators of taxonomic status. However, the genetic and morphological distance correlation among individuals
was low (r = 0.17, P = 0.0002), indicating that morphology cannot always accurately predict genetic admixture or taxonomy. Overall, our study
confirmed the genetic distinctiveness of the San Carlos Basin population, an ancient natural hybrid origin of P. subintegra, and the presence of a hybrid swarm in the Verde Valley, whose conservation value may lie in its heightened genetic diversity. |
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Keywords: | Hybridization AFLPs Discriminant function analysis Transition zone Arizona |
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