Isozyme Variation and Ploidy Levels within the Apomictic Ranunculus auricomus Complex: Evidence for a Sexual Progenitor Species in Southeastern Austria

Abstract:

Allozyme variation of 11 enzymes in each of three populations of the diploid species Ranunculus notabilis and the tetraploid R. variabilis of the predominantly apomictic R. auricomus complex has been studied by horizontal starch gel electrophoresis. Genetic interpretation of electrophoretic patterns is supported by chromosome counts and densitometric ploidy level determination. R. notabilis is confirmed as diploid (2 n = 16), and R. variabilis as tetraploid (2 n = 32). Two triploids and one tetraploid individual were sorted out as putative hybrids. Genetic variability measures based on both allelic frequencies and genotype frequencies were calculated for 13 polymorphic loci. Allelic and genotypic variation in R. notabilis is similar to other sexual plants, and the species is shown to be an outbreeder and not a dihaploid apomict. Corresponding values in R. variabilis confirm a previously assumed clonal population structure. A higher frequency of observed heterozygotes in R. variabilis indicates its hybridogenous origin and the lack of meiosis. Putative hybrids showed combinations of morphological phenotype and electrophoretic patterns of both species. Genetic identity is high among species (0.905), but still lower than within species (R. notabilis: 0.965, R. variabilis: 0.940); corresponding distance values allow a clear separation of the two species in a dendrogram. Genetic identity and distance values between R. notabilis and R. variabilis resemble those of other progenitor-derivative species pairs. The results favour the hypothesis that R. notabilis is an ancient sexual species of the R. auricomus complex and also one progenitor of the presumably allopolyploid R. variabilis.

Isozymes - apomixis - polyploidy - chromosome numbers - Feulgen densitometry - hybridization - phylogeny - Ranunculus auricomus complex.

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