Shift in cytotype frequency and niche space in the invasive plant Centaurea maculosa

Authors

  • Urs A. Treier,

    Corresponding author
    1. Department of Biology, Unit of Ecology and Evolution, University of Fribourg, Chemin du Musée 10, CH-1700 Fribourg, Switzerland
    2. Department of Biological Sciences, Systematic Botany, Aarhus University, Ny Munkegade 114, Building 1540, DK-8000 Århus C, Denmark
    •  Present address: Department of Biological Sciences, Systematic Botany, Aarhus University, Ny Munkegade 114, Building 1540, DK-8000 Århus C, Denmark. E-mail: urs.treier@gmail.com

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  • Olivier Broennimann,

    1. Department of Ecology and Evolution, University of Lausanne, The Biophore, CH-1015 Lausanne, Switzerland
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  • Signe Normand,

    1. Department of Biological Sciences, Systematic Botany, Aarhus University, Ny Munkegade 114, Building 1540, DK-8000 Århus C, Denmark
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  • Antoine Guisan,

    1. Department of Ecology and Evolution, University of Lausanne, The Biophore, CH-1015 Lausanne, Switzerland
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  • Urs Schaffner,

    1. CABI Europe–Switzerland, Rue des Grillons 1, CH-2800 Delémont, Switzerland
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  • Thomas Steinger,

    1. Department of Biology, Unit of Ecology and Evolution, University of Fribourg, Chemin du Musée 10, CH-1700 Fribourg, Switzerland
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    •  Present address: Agroscope Changins-Wädenswil ACW, CP 1012, CH-1260 Nyon, Switzerland.

  • Heinz Müller-Schärer

    1. Department of Biology, Unit of Ecology and Evolution, University of Fribourg, Chemin du Musée 10, CH-1700 Fribourg, Switzerland
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  • Corresponding Editor: B. B. Casper.

Abstract

Polyploidy is often assumed to increase the spread and thus the success of alien plant species, but few empirical studies exist. We tested this hypothesis with Centaurea maculosa Lam., a species native to Europe and introduced into North America approximately 120 years ago where it became highly invasive. We analyzed the ploidy level of more than 2000 plants from 93 native and 48 invasive C. maculosa populations and found a pronounced shift in the relative frequency of diploid and tetraploid cytotypes. In Europe diploid populations occur in higher frequencies than tetraploids and only four populations had both cytotypes, while in North America diploid plants were found in only one mixed population and thus tetraploids clearly dominated. Our results showed a pronounced shift in the climatic niche between tetraploid populations in the native and introduced range toward drier climate in North America and a similar albeit smaller shift between diploids and tetraploids in the native range. The field data indicate that diploids have a predominately monocarpic life cycle, while tetraploids are often polycarpic. Additionally, the polycarpic life-form seems to be more prevalent among tetraploids in the introduced range than among tetraploids in the native range. Our study suggests that both ploidy types of C. maculosa were introduced into North America, but tetraploids became the dominant cytotype with invasion. We suggest that the invasive success of C. maculosa is partly due to preadaptation of the tetraploid cytotype in Europe to drier climate and possibly further adaptation to these conditions in the introduced range. The potential for earlier and longer seed production associated with the polycarpic life cycle constitutes an additional factor that may have led to the dominance of tetraploids over diploids in the introduced range.

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