AOBPreview originally published online on February 4, 2009
Annals of Botany 2009 103(6):963-974; doi:10.1093/aob/mcp016
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Towards resolving the Knautia arvensis agg. (Dipsacaceae) puzzle: primary and secondary contact zones and ploidy segregation at landscape and microgeographic scales
1,*
tech1
ek2,3
Urfus2,3ová2,3
1 Department of Botany, Faculty of Science, University of South Bohemia, Braniovská 31, CZ-370 05 
eské Bud
jovice, Czech Republic
2 Institute of Botany, Academy of Sciences of the Czech Republic, CZ-252 43 Pr
honice, Czech Republic
3 Department of Botany, Faculty of Science, Charles University in Prague, Benátská 2, CZ-128 01 Prague, Czech Republic
* For correspondence. E-mail filip.kolar{at}gmail.com
Received: 20 October 2008 Returned for revision: 1 December 2008 Accepted: 18 December 2008 Published electronically: 4 February 2009
Background and Aims: Detailed knowledge of variations in ploidy levels and their geographic distributions is one of the key tasks faced in polyploid research in natural systems. Flow cytometry has greatly facilitated the field of cytogeography by allowing characterization of ploidy levels at both the regional and population scale, and at multiple stages of the life cycle. In the present study, flow cytometry was employed to investigate the patterns and dynamics of ploidy variation in the taxonomically challenging complex Knautia arvensis (Dipsacaceae) and some of its allies (K. dipsacifolia, K. slovaca) in Central Europe.
Methods: DNA ploidy levels were estimated by DAPI flow cytometry in 5205 adult plants, 228 seedlings and 400 seeds collected from 292 Knautia populations in seven European countries. The flow cytometric data were supplemented with conventional chromosome counts. A subset of 79 accessions was subjected to estimation of the absolute genome size using propidium iodide flow cytometry.
Key Results and Conclusions: Five different ploidy levels (from 2x to 6x) were found, with triploids of K. arvensis being recorded for the first time. The species also exhibited variation in the monoploid genome size, corresponding to the types of habitats occupied (grassland diploid populations had larger genome sizes than relict and subalpine diploid populations). Disregarding relict populations, the distribution of 2x and 4x cytotypes was largely parapatric, with a diffuse secondary contact zone running along the north-west margin of the Pannonian basin. Spatial segregation of the cytotypes was also observed on regional and microgeographic scales. The newly detected sympatric growth of diploids and tetraploids in isolated relict habitats most likely represents the primary zone of cytotype contact. Ploidy level was found to be a major determinant of the strength of inter-cytotype reproductive barriers. While mixed 2x + 4x populations virtually lacked the intermediate ploidy level at any ontogenetic stage, pentaploid hybrids were common in 4x +6x populations, despite the cytotypes representing different taxonomic entities.
Key words: Contact zone, cytogeography, flow cytometry, genome size, hybridization, Knautia arvensis, ploidy mixture, polyploidy, relict, reproductive isolation, serpentine
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