Isozyme variation under different modes of reproduction in two clonal winter annuals, Sedum rosulato-bulbosum and Sedum bulbiferum (Crassulaceae)

We studied isozyme variation in two annual species that produce bulbils, Sedum rosulato-bulbosum , which includes both sexually reproducing plants and obligate clonal plants that result from triploidy (fertile and sterile S. rosulato-bulbosum , respectively), and an obligate clonal plant, Sedum bulbiferum , to examine the relationship between reproductive mode and isozyme variation. The sterile S. rosulato-bulbosum population exhibited no genotypic variation, but showed high genetic variation (gene diversity, H _e  = 0.60) because five of the six loci that we analyzed were heterozygous. Almost all ramets of S. bulbiferum across 20 populations shared an identical isozyme phenotype, although we could not identify the genetic basis of the phenotype. In contrast, fertile S. rosulato-bulbosum exhibited genotypic variation across the species, but comprised genotypically uniform and polymorphic populations whose genotypic variations correlated positively with the genetic variations within the populations ( H _e at the genet level per population ranged from 0.08 to 0.37). Genetic drift and habitat conditions inhibiting seedling recruitment may have caused this among-population variation. The results for sterile and fertile S. rosulato-bulbosum suggest that exclusive clonal reproduction causes low genotypic variation, but maintains genetic variation within individuals. Factors that affect the maintenance of genetic variation in these plants are discussed on the basis of these findings.