Allozyme variability within and among varieties of Isomeris arborea (Capparaceae)

The pattern of genetic variation within and among 13 natural populations (294 individuals) representing the four varieties of Isomeris arbórea (Capparaceae) throughout its range in California was investigated with allozyme electrophoresis. Thirty enzyme loci were examined. Low genetic diversity within populations (A = 1.18, P = 0.139, HE = 0.051 and Ho = 0.051) and significant genetic differentiation among populations (FST = 0.462) were found. A relatively large number of private alíeles (9) were detected as well as several unique alíeles confined to single varieties. We found a relatively high proportion of total genetic diversity (45%) among varieties and a significant correlation (P < 0.001) between FST and geographic distance. Multiple regression analyses demonstrated clines in genetic diversity measures, from East to West and South to North. Multiple Correspondence Analysis (MCA) clearly demonstrated division into a minimum of two groups. The above observations together with low gene flow estimates suggest genetic drift by isolation may have been critical to the current genetic structure of the species. We tentatively argue, based on our results, that variety globosa may be deserving of subspecies status.