Genomic and Genetic Comparisons in Three Species of Rhamnaceae On and Off Serpentine Soil
Mentor:Thomas Vandergon, Professor of Biology, Pepperdine University
Members of the family Rhamnaceae are dominant within Southern California shrub chaparral. Among these, the genera Ceanothus and Rhamnus are well represented. Many species of Ceanothus, are restricted to specific ecotypes and these habitats may be widely dispersed including on Serpentine Soils. Two common and widely distributed Rhamnus species, R. crocea and R. californica are also known to exist on serpentine soils. Serpentine soils restrict plants due to the presence of heavy metals and a paucity of calcium. Prior research in plant species has shown both genetic and genomic differences related to growing in stress conditions. We hypothesize that there will be genetic or genomic differences between populations of Rhamnaceae growing on or off serpentine soils. Here we examined the genome size variation of C. cuneatus, R. crocea and R. californica using flow cytometry and microsatellite DNA analysis. The genome sizes of C. cuneatus populations were not significantly different from other measured populations (about 1.25 pg/genome) or between populations on or off serpentine soil. The genome size of R. crocea populations were the smallest recorded for Rhamnaceae to date (about 0.78 pg/genome) and were not significantly different between populations on or off serpentine soil. Rhamnus californica did not yield usable genome size data due to high noise. Microsatellite DNA analyses showed no a genetic difference between adjacent populations of C. cuneatus, but did show significant differences in adjacent populations of R. crocea and R. californica growing on or off serpentine soils.