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Title: Genetic diversity and structure in the rare Colorado endemic plant Physaria bellii Mulligan (Brassicaceae)

item Richards, Christopher

Submitted to: Conservation Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2006
Publication Date: 8/1/2007
Citation: Kothera, L., Richards, C.M., Carney, S.E. 2007. Genetic diversity and structure in the rare Colorado endemic plant Physaria bellii Mulligan (Brassicaceae). Conservation Genetics 8:1043-1050.

Interpretive Summary: This study examines the genetic diversity and differentiation of a rare endemic perennial plant found along the Front Range of the northern Colorado. Analysis made use of novel Bayesian estimators of the common genetic differentiation parameter, Fst. In addition we demonstrate that the spatial arrangement of populations in this species correlated to and north south gradient in genetic variation. These data suggest that populations are exchanging genes in a stepping stone-like manner. These baseline data are critical in making informed management decisions and for identifying populations for ex situ collection.

Technical Abstract: Physaria bellii (Brassicaceae) is a rare, outcrossing perennial endemic to shale and sandstone outcrops along the Front Range of northern Colorado, USA. This species is locally abundant, but ranked G2/S2 - imperiled because of threats to its habitat and a small number of populations – according to NatureServe’s standardized ranking system. Leaf tissue from ten populations was analyzed with ISSR (Inter-Simple Sequence Repeat) markers to discern the amount of genetic diversity and degree of population subdivision in P. bellii. Genetic diversity was moderate (0.22) and a moderately high degree of population structure was found (FST calculated using two algorithms ranged from 0.17 - 0.24). An AMOVA partitioned most of the variation among individuals within populations (76%), and the remainder among populations (24%). Results from a Principal Coordinates analysis were consistent with the geographic distribution of populations. A Mantel test of the correlation between genetic and geographic distances was highly significant (P < 0.001). The pattern of variation thus appears to be distributed along a gradient, and efforts to conserve this species should involve preserving enough populations so that gene flow between populations is not interrupted.