Journal Article

Genome Size Variation and Species Relationships in <i>Hieracium</i> Sub-genus <i>Pilosella</i> (Asteraceae) as Inferred by Flow Cytometry

Jan Suda, Anna Krahulcová, Pavel Trávníček, Radka Rosenbaumová, Tomáš Peckert and František Krahulec

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 100, issue 6, pages 1323-1335
Published in print November 2007 | ISSN: 0305-7364
Published online October 2007 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcm218
Genome Size Variation and Species Relationships in Hieracium Sub-genus Pilosella (Asteraceae) as Inferred by Flow Cytometry

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims Hieracium

sub-genus Pilosella (hawkweeds) is a taxonomically complicated group of vascular plants, the structure of which is substantially influenced by frequent interspecific hybridization and polyploidization. Two kinds of species, ‘basic’ and ‘intermediate’ (i.e. hybridogenous), are usually recognized. In this study, genome size variation was investigated in a representative set of Central European hawkweeds in order to assess the value of such a data set for species delineation and inference of evolutionary relationships.

Methods

Holoploid and monoploid genome sizes (C- and Cx-values) were determined using propidium iodide flow cytometry for 376 homogeneously cultivated individuals of Hieracium sub-genus Pilosella, including 24 species (271 individuals), five recent natural hybrids (seven individuals) and experimental F1 hybrids from four parental combinations (98 individuals). Chromosome counts were available for more than half of the plant accessions. Base composition (proportion of AT/GC bases) was cytometrically estimated in 73 individuals.

Key Results

Seven different ploidy levels (2x–8x) were detected, with intraspecific ploidy polymorphism (up to four different cytotypes) occurring in 11 wild species. Mean 2C-values varied approx. 4·3-fold from 3·53 pg in diploid H. hoppeanum to 15·30 pg in octoploid H. brachiatum. 1Cx-values ranged from 1·72 pg in H. pilosella to 2·16 pg in H. echioides (1·26-fold). The DNA content of (high) polyploids was usually proportional to the DNA values of their diploid/low polyploid counterparts, indicating lack of processes altering genome size (i.e. genome down-sizing). Most species showed constant nuclear DNA amounts, exceptions being three hybridogenous taxa, in which introgressive hybridization was suggested as a presumable trigger for genome size variation. Monoploid genome sizes of hybridogenous species were always between the corresponding values of their putative parents. In addition, there was a good congruency between actual DNA estimates and theoretical values inferred from putative parental combinations and between DNA values of experimental F1 hybrids and corresponding established hybridogenous taxa.

Conclusions

Significant differences in genome size between hawkweed species from hybridogenous lineages involving the small-genome H. pilosella document the usefulness of nuclear DNA content as a supportive marker for reliable delineation of several of the most problematic taxa in Hieracium sub-genus Pilosella (including classification of borderline morphotypes). In addition, genome size data were shown to have a good predictive value for inferring evolutionary relationships and genome constitution (i.e. putative parental combinations) in hybridogenous species.

Keywords: Agamic complex; AT/GC base ratio; DNA C-value; flow cytometry; genome composition; genome size; hawkweeds; Hieracium sub-genus Pilosella; hybridization; nuclear DNA content; polyploidy; taxonomy

Journal Article.  8486 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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