Amplified fragment length polymorphism (AFLP) markers reveal that population structure of triploid dandelions (Taraxacum officinale) exhibits both clonality and recombination

Abstract

Highly variable amplified fragment length polymorphism (AFLP) fingerprints of triploid apomictic dandelions obtained from three localities in an area where diploids are lacking were analysed to infer the predominant modes of reproduction. The distribution of markers was analysed using character compatibility to infer whether many genotypes agree with a tree-like structure in the data set. The presence of incompatible character state combinations (matrix incompatibility; MI) was used as a measure of genetic exchange. The detection of overrepresented genotypes, of which some were widespread, confirmed asexual reproduction. Not all genotypes were overrepresented; approximately half of the genotypes in the three localities were found only once. Because, in terms of genotype frequencies, only a part of the genetic variation is described, more important aspects of the molecular data such as relationships between markers or genotypes have been studied. The analysis of character compatibility indicated a disagreement of the data with a clonal structure. Nearly all genotypes contributed to MI and this contribution varied considerably among genotypes in each sampled locality. A gradual decrease of matrix incompatibility upon successive deletion of genotypes showing the highest contribution to MI indicated that marker distribution of virtually all genotypes disagreed with a tree-like structure in the data. This result suggested that many genotypes were separated by one or more sexual generations. Consistent with this conclusion was the fact that markers that show a low probability of contributing to MI are different in every sampled locality, which is most easily explained as the result of recombination. Apparently, asexual reproduction has resulted in overrepresented, widespread genotypes but sexual recombination has also substantially contributed to genetic variation in the sites studied.

Genetic diversity and reproductive biology in ecotypes of the facultative apomict Hypericum perforatum L.

“…Our molecular and cytometric investigations have demonstrated large numbers of apomictic clonal lineages, as has been found in other apomictic species (Noyes and Soltis, 1996;Chapman et al, 2000;Van Der Hulst et al, 2000). Clonal diversity is likely to be correlated with the facultative nature of apomixis, as occasional sex leads to genetic diversity that is later fixed by apomixis.…”

“…The presence of plant groups sharing the same multilocus genotype in a given population is often the most robust and significant evidence of agamic reproduction (Van Der Hulst et al, 2000). Considering the total number of different genotypes observed in the analysed populations, 43.5% (37/85) were represented by more than one individual, a result inconsistent with what would be expected from a purely sexually reproducing population.…”

“…Various experimental studies have reported the existence of distinct multilocus genotypes (ie clones) in apomictic plant populations (Ellstrand and Roose, 1987;Noyes and Soltis, 1996;Chapman et al, 2000;Van Der Hulst et al, 2000), although the source of this genetic diversity remains largely unexplained. Clonal diversity within a population reflects the sexual genetic pool from which the clones originated, the frequency of clonal origin, and the somatic mutations that subsequently accumulate in established clones (Meirmans and Van Tienderen, 2004).…”

Evolution of Triploidy in Apios Americana (Leguminosae) Revealed by Genealogical Analysis of the Histone H3-D Gene

“…This variability increases the likelihood of forming successful triploid genotypes that could adapt to new environments, and gives the opportunity for autotriploids to be better fit than their diploid progenitors in these new habitats (Mooney and Johnson 1965). This also should be true for other plant species in which multiple origins of autotriploidy have been documented (Haufler et al 1985;van der Hulst et al 2000;Takamiya et al 2001). Indeed, our study showing multiple origins of autotriploidy, as well as others suggesting an important role of triploidy in tetraploid formation (Harlan and deWet 1975;deWet 1980;Haufler et al 1985;Ramsey and Schemske 1998), suggest that triploidy may play an important role in plant evolution, given the preponderance of polyploidy in flowering plants in general (Stebbins 1950;Grant 1981;Masterson 1994;Otto and Whitton 2000).…”

“…For triploid taxa, multiple origins constitute an important contribution to genetic diversity, and more origins means an increased probability of producing successful genotypes. To date, clear examples of recurrent autotriploid evolution in natural plant populations involve two ferns, Cystopteris protrusa (Haufler et al 1985) and Diplazium doederleinii (Takamiya et al 2001), and the angiosperm Taraxacum officinale (van der Hulst et al 2000). In addition, although somaclonal mutation has been reported in some clonal organisms (e.g., King and Schaal 1990;Corradini et al 2002), it has yet to be described in triploids.…”