BACKGROUND AND AIMS: Although the large variation in genome size among different species is widely acknowledged, the occurrence and extent of variation below the species level are still controversial and have not yet been satisfactorily analysed. The aim of this study was to assess genome size variation in six ploidy levels (2n = 3x-8x) of the polyploid Allium oleraceum over a large geographical gradient and to search for potential interpretations of the size variation. METHODS: The genome sizes of 407 individuals of A. oleraceum collected from 114 populations across Europe were determined by flow cytometry using propidium iodide staining. The genome size variation was correlated with spatial, climatic and habitat variables. KEY RESULTS: The mean holoploid genome size (2C DNA) was 42·49, 52·14, 63·34, 71·94, 85·51 and 92·12 pg at the tri-, tetra-, penta-, hexa-, hepta- and octoploid levels, respectively. Genome size varied from a minimum of 2·3 % in the octoploids to a maximum of 18·3 % in the tetraploids. Spatial structuring of genome size was observed within the tetra- and pentaploids, where 2C DNA significantly increased with both latitude and longitude, and correlated with several climatic variables, suggesting a gradient of continentality. Genome size in hexaploids showed low variation, weak correlation with climatic variables and no spatial structuring. Downsizing in monoploid genome size was observed between all cytotypes except for heptaploids. Splitting populations into western and eastern European groups resulted in strong differences in monoploid genome size between groups in tetra- and pentaploids but not in hexaploids. The monoploid genome sizes of the cytotypes were similar in the western group but diverged in the eastern group. CONCLUSIONS: Complex patterns of holoploid and monoploid genome size variation found both within and between A. oleraceum cytotypes are most likely the result of several interacting factors, including different evolutionary origins of cytotypes via hybridization of parental combinations with different genome sizes in the south-western and south-eastern part of Europe, introgression between cytotypes, and antropic dispersal. The role of broad-scale and fine-scale environmental variables in shaping genome size is probably of minor importance in A. oleraceum.
- MeSH
- Allium genetika metabolismus MeSH
- biologická adaptace MeSH
- buněčné jádro genetika MeSH
- chromozomy rostlin genetika MeSH
- délka genomu * MeSH
- DNA rostlinná analýza genetika MeSH
- ekosystém MeSH
- genetická variace MeSH
- genom rostlinný * MeSH
- hybridizace nukleových kyselin MeSH
- molekulární evoluce MeSH
- podnebí MeSH
- polyploidie * MeSH
- propidium metabolismus MeSH
- průtoková cytometrie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Evropa MeSH
BACKGROUND AND AIMS: Despite extensive study of polyploidy, its origin, and ecogeographical differences between polyploids and their diploid progenitors, few studies have addressed ploidy-level structure and patterns of ecogeographical differentiation at various spatial scales using detailed sampling procedures. The pattern of coexistence of polyploids in the geophyte Allium oleraceum at the landscape and locality scale and their ecology were studied. METHODS: Flow cytometry and root-tip squashes were used to identify the ploidy level of 4347 plants from 325 populations sampled from the Czech Republic using a stratified random sampling procedure. Ecological differentiation among ploidy levels was tested by comparing sets of environmental variables recorded at each locality. KEY RESULTS: Across the entire sampling area, pentaploids (2n = 5x = 40) predominated, while hexaploids (2n = 6x = 48) and tetraploids (2n = 4x = 32) were less frequent. The distribution of tetra- and hexaploids was partially sympatric (in the eastern part) to parapatric (in the western part of the Czech Republic) whereas pentaploids were sympatric with other cytotypes. Plants of different ploidy levels were found to be ecologically differentiated and the ruderal character of cytotypes increased in the direction 4x --> 5x --> 6x with the largest realized niche differences between tetra- and hexaploids. Most populations contained only one ploidy level (77 %), 22 % had two (all possible combinations) and 1 % were composed of three ploidy levels. The majority of 4x + 5x and 5x + 6x mixed populations occurred in sympatry with uniform populations of the participating cytotypes in sites with ecologically heterogeneous or marginal environment, suggesting secondary contact between cytotypes. Some mixed 4x + 6x populations dominated by tetraploids being sympatric and intermixed with uniform 4x populations might represent primary zones of cytotype contact. Almost no mixed accessions were observed on the fine spatial scale in mixed populations. CONCLUSIONS: The results provide evidence for adaptive differences among ploidy levels, which may contribute to their complex distribution pattern. The prevalence of asexual reproduction, limited dispersal and equilibrium-disrupting processes may support local coexistence of cytotypes.
- MeSH
- Allium klasifikace genetika růst a vývoj MeSH
- ekologie MeSH
- ploidie MeSH
- polyploidie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Česká republika MeSH
