Chloroplast DNA variation and reticulate evolution in sexual and apomictic sections of dandelions

Abstract

Sequencing of the trnL-trnF intergenic spacer in chloroplast DNA (cpDNA) from 237 sexual and apomictic species of dandelions (genus Taraxacum) from Europe, Asia and arctic North America revealed 46 haplotypes, which differed mainly by a variable number of polymorphic tRNA pseudogenes next to the trnF gene. The haplotypes could be divided into 20 cpDNA lineages, but independent duplications and deletions of the pseudogene copies made it difficult to further reconstruct the phylogeny. Intraspecific cpDNA variation was found in the primitive sexual T. serotinum. However, in contrast to a recent study, no cpDNA variation was detected within 12 apomictic species representing a variety of haplotypes. The cpDNA haplotype may therefore help to define these critical apomicts. On the other hand, the genetic variation may easily be overestimated, if the clones are not correctly identified, because some morphologically similar microspecies carried very different haplotypes. In all, 36 sections of the genus were sampled. Four primitive, mainly sexual, sections only displayed a group of ancient haplotypes, whereas morphologically more advanced sections often exhibited many different haplotypes from up to seven cpDNA lineages. In the latter cases, the lineages were rarely unique to a certain section. For example, the two most widespread haplotypes, belonging to different lineages, were found together in nine sections. This suggests that significant gene flow has occurred among the advanced sections, although sexual reproduction is not currently known in several of them. The result is consistent with the reticulate distribution of morphological characters among the sections.

Studying allozyme variation in sexual and apomictic Taraxacum and Pilosella (Asteraceae) populations

“…Thus, the above evidence from literature and our data cast some doubt on the a priori view on low genetic diversity in apomictic populations, as well as, in many cases, on lower variation in these species as compared to the sexual ones. This conclusion is based on the results obtained by a number of authors in theoretical [10], morphological, isozyme [13], and more recent DNA studies [7,52,53,66,67]. High isozyme genetic polymorphism was also found in population of uniparental animal species, e.g., species of Daphnia (Crustaceae) [68,69], Pycnoscelus (Insecta) [70], Prionocypris and Candona (Ostracoda) [71], Lacerta (Reptilia) [72][73][74].…”

Relationships in Taraxacum section Arctica s.l. (Asteraceae, Cichorieae) and allies based on nrITS

“…SOLBRIG & SIMPSON 1974;FORD & RICHARDS 1985;MOGIE 1985;BATTJES et al 1992), later chloroplast DNA and occasionally nuclear ribosomal DNA as well as microsatellites (e.g. WITTZELL 1999;MES et al 2002;KIRSCHNER et al 2003;VA-ŠUT et al 2004) were used for detection of clonal diversity, genetic population structure, genetics of reproduction and gene flow but only some of these papers dealt with phylogenetic systematics (WITTZELL 1999;MES et al 2000;MES et al 2002;KIRSCHNER et al 2003). These molecular phylogenetic approaches based on cpDNA which is maternally inherited in most angiosperms resulted in considerable ces within Taraxacum during this study, but the low level of sequence divergence does not point at a relaxed selection pressure on certain sequences.…”

Notes on the genus Taraxacum in Slovakia. I. Taraxacum sect. Hamata: a new group of dandelions in Slovakia

“…Hamata H. Øllgaard: a new group of dandelions in Slovakia Taraxacum sect. Hamata is an evolutionary advanced section (Wittzell 1999;Kirschner et al 2003), and it is comprised exclusively of triploid apomicts. Morphologically, it is very close to section Ruderalia, from which it was separated (Øllgaard 1983).…”