Genetic variation within and geographical relationships between four natural populations of Virgilia oroboides (tribe Podalyrieae: Fabaceae)

Virgilia oroboides has a large indigenous range encompassing most of the south-western coastal areas of the Cape Province, South Africa, where it exhibits considerable morphological variation. Four populations of V. oroboides were examined by horizontal starch gel electrophoresis to assess levels and patterns of genetic variation and to estimate the amount of genetic differentiation among populations at 37 protein coding loci. Leaf extracts were surveyed for 22 proteins, and gene produts of 37 loci revealed genetic variation at 17 (46%) thereof. The percentage of polymorphic loci range from 29.73-43.24% (0.95 criterion), values of 1.35-1.49 (± 0.09) were obtained for the mean number of alleles per locus, and average heterozygosities per locus were calculated at 0.127-0.198. No statistical significant difference between heterozygosity values was obtained when fewer (25 compared to 50) individuals were analysed. The mean genotypic distance index (Nei, 1978 = 0.0185) suggests a low degree of differentiation between populations. Geographic relationships reflect gradual isolation of the western populations, which may have become restricted to a few moist sites as a result of a decrease in total forest area in response to long-term climatic changes. This isolation and subsequent selection may have resulted in a depletion of genetic variation from the eastern to the western regions Estimates of elapsed divergence times suggest that these populations diverged 0.02-0.18 million years ago.