期刊
ANNALS OF BOTANY
卷 107, 期 3, 页码 443-454出版社
OXFORD UNIV PRESS
DOI: 10.1093/aob/mcq260
关键词
Pilosella echioides; cytotype co-existence; cytotype distribution; flow cytometry; free mating; ploidy variation; triploid; sympatry
资金
- Academy of Sciences of the Czech Republic [KJB601110813, AV0Z60050516]
- Charles University in Prague [1207/2007]
- Ministry of Education, Youth and Sports of the Czech Republic [MSM 0021620828, MSM 6007665806]
- Ministry of Culture of the Czech Republic [MK00002327201]
- Czech Science Foundation [206/08/H049]
Background and Aims A detailed knowledge of cytotype distribution can provide important insights into the evolutionary history of polyploid systems. This study aims to explore the spatial distribution of different cytotypes in Pilosella echioides at various spatial scales (from the whole distributional range to the population level) and to outline possible evolutionary scenarios for the observed geographic pattern. Methods DNA-ploidy levels were estimated using DAPI flow cytometry in 4410 individuals of P. echioides from 46 populations spread over the entire distribution range in central Europe. Special attention was paid to the cytotype structure in the most ploidy-diverse population in south-west Moravia. Key Results Five different cytotypes (2x, 3x, 4x, 5x and 6x) were found, the last being recorded for the first time. Although ploidy-uniform (di- or tetraploid) sites clearly prevailed, nearly one-quarter of the populations investigated harboured more (up to all five) cytotypes. Whereas penta-and hexaploids constituted only a minority of the samples, a striking predominance of the triploid cytotype was observed in several populations. Conclusions The representative sampling confirmed previous data on cytotype distribution, i.e. the spatial aggregation of mixed-ploidy populations in south-west Moravia and Lower Austria and the predominance of ploidy-uniform populations in other parts of the area investigated. Recurrent origin of polyploids from diploid progenitors via unreduced gametes and their successful establishment are considered the key factors promoting intrapopulational ploidy mixture ('primary hybrid zones'). As an alternative to the generally accepted theory of cytotype co-existence based on the development of different means of inter-ploidy reproductive isolation, it is suggested that a long-term ploidy mixture can also be maintained in free-mating populations provided that the polyploids originate with a sufficient frequency. In addition, the prevalence (or subdominance) of the triploid cytotype in several mixed-ploidy populations represents the first evidence of such a phenomenon in plant systems with exclusively sexual reproduction.
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