Clonal diversity in taraxacum officinale (compositae), an apomict

Abstract

SUMMARYAllozyme analysis, morphological characters, and histocompatibility relationships have revealed unexpected amounts of clonal diversity within and among populations of unisexual animals. Plant studies, likewise, have shown that genetic diversity exists in populations of plants that have restricted recombination. However, no work has been done which investigates the extent of genotypic diversity within and among populations of an obligate apomict.This study surveyed 22 North American populations of Taraxacum officinale, an obligate gametophytic apomict. Over 20 individuals from each population were assayed electrophoretically for three enzyme systems representing five different migration zones. Seed colour was used to determine seven phenological classes that, when combined with the allozyme morphs, resulted in 47 discernible clones among 518 individuals sampled. Chromosome analysis revealed the ploidy level to be triploid in all cases. The number of clones per population ranged from 1-13, with a mean of 50. Sixty-six per cent of the clones were restricted to single populations, and the mean number of populations containing a particular clone is 21. One widespread clone was found in all but three of the populations. Diversity values, expressed as clones per individual, indicate that T officinale proved to be more genotypically diverse than other clonal plants previously studied. Spearman's Rank Correlation test failed to show a correlation of diversity with latitude or elevation.

Genetic structure of a population sample of apomictic dandelions

“…In the literature of apomictic dandelions there are essentially two ways of interpreting populations. A population sample may comprise, randomly sampled apomictic dandelions (eg Lyman and Ellstrand, 1984;Menken et al, 1995;Van der Hulst et al, 2000). Alternatively, a population sample may correspond to a set of apomicts, selected on the basis of certain morphological features that are diagnostic for microspecies (eg Hughes and Richards, 1988;.…”

“…Outside areas in Central Europe (Den Nijs and Sterk, 1980) and Asia (Richards, 1973), where diploid sexuals are found, dandelions are almost exclusively polyploid and obligate apomicts. Despite the lack of sexuals in these areas, it is not exceptional to find tens of different genotypes co-occurring in meadows, pastures or verges (Lyman and Ellstrand, 1984;Van der Hulst et al, 2000, and unpublished results). The wealth of genotypes present in regions where sexuals are lacking could be the result of immigration from regions where sexuals and apomicts co-occur and hybridise.…”

The genetic structure of populations of sexual and asexual Taraxacum (dandelions)

“…Usberti and Jam (1978) have investigated the facultatively agamospermous grass Panicum maximum, but the only studies we can trace on obligate agamosperms have been in Taraxacum by Ford and Richards (1985), and van Oostrum et aL (1985). Unfortunately the work by Lyman and Ellstrand (1984) is hampered by the absence of any taxonomic information. These studies, notably van Oostrum et a!., fulfill the predictions as to the structure of populations of agamosperms.…”

Apomictic parthenogenesis and genotypic diversity in Cypridopsis vidua (Ostracoda: Cyprididae)

“…However, a variety of studies have now shown that this view is incorrect. Studies of morphological, chromosomal, allozymic, and histocompatibility diversity have revealed abundant variation on both macro- (Lyman and Ellstrand, 1984;Hebert et a!., 1988) and microgeographic scales (Hebert and Crease, 1980;Hoffmann, 1986;Ellstrand and Roose, 1987).…”