Tuesday, June 19, 2007 - 4:30 PM
Ponderosa Pines (Boise Centre on the Grove)

Population Genetics of the Rare Polyploid, Lepidium papilliferum (Brassicaceae), a Southwest Idaho Endemic

Amy J. Stillman, Stephen J. Novak, Ian C. Robertson, and James F. Smith. Boise State University, Boise, ID

Rare plant species typically exhibit low levels of genetic diversity within populations and high levels of genetic differentiation among populations. Several mechanisms may counter the genetic consequences of rarity such as polyploidy or an outcrossing mating system. However, for rare species whose size and distribution may already be limited, habitat destruction and fragmentation can alter historic patterns of gene flow and increase the risk of genetic erosion. Lepidium papilliferum, slickspot peppergrass, is a rare polyploid, insect-pollinated, herbaceous plant, endemic to sagebrush steppe communities of southwestern Idaho. Plants exhibit a naturally patchy distribution, occurring in specialized microhabitats called slick spots. Habitat destruction and fragmentation has lead to a decline in this species. Enzyme electrophoresis was used to determine the amount and distribution of genetic diversity within and among 25 populations of L. papilliferum. Across all populations, 10 of 11 loci (91%) were polymorphic, with an average of 4.27 alleles per locus. On average, the disjunct Jarbidge populations exhibited higher levels of polymorphic loci (P = 80.1%) compared with the Snake River Plain populations (P = 58.1%) and similar number of alleles per locus, A = 2.16 and 2.09, respectively. Measures of genetic diversity were positively correlated with population size for all populations, however this trend was most pronounced in Snake River populations. Genetic differentiation (GST) among all populations was 0.109. Among populations of each region, GST was 0.042, indicating that the majority of genetic differentiation among all populations is due to genetic differences between the two regions.