Origin and maintenance of intrapopulational cytotype mixture in an alpine plant species (Senecio carniolicus), Asteraceae)
Runtime: 2008 - 2012
Polyploidy, i.e., the multiplication of chromosome sets is recognized as a major force in plant speciation, but the factors and their interactions underlying the origin and maintenance of cytotype co-occurrence (cytotype mixture) remain insufficiently understood. Here, we address those questions in a complex system of cytotype mixture, the eastern Alpine Senecio carniolicus (Compositae) that comprises up to three co-occurring cytotypes (diploids, tetraploids, hexaploids). Applying a multitude of different methods (DNA sequencing, AFLP fingerprints, habitat analysis, transplantation and crossing experiments), the phylogenetic relationships among those cytotypes were resolved and isolating factors allowing the co-occurrence of cytotypes and their relevance for each cytotype were identified. Specifically, the major results are:
(1) Diploids comprise two longitudinally separated lineages with the polyploids being autopolyploid derivatives of the eastern lineage. As these lineages are also morphologically differentiated, they warrant taxonomic recognition emphasizing the commonly underestimated relevance of autopolyploidy for lineage diversification and speciation.
(2) Cytotypes show different, yet overlapping habitat requirements in line with the current understanding of ecological differentiation as one of the main factors fostering cytotype establishment and allowing cytotype co-occurrence. Furthermore, habitat displacement, i.e., the stronger differentiation of ecologically similar species in sympatry than in allopatry, reinforces ecological differentiation, thus widening the conditions for cytotype co-occurrence.
(3) Post-pollination reproductive isolation is decoupled from habitat differentiation, as only crosses involving diploids show strongly reduced seed set and seedling survival, whereas crosses between tetraploids and hexaploids produce ample hybrid offspring. Differential dynamics at contact zones of different cytotypes as well as putatively higher adaptational potential of polyploids may lead to differing range dynamics caused by global change.
University of Innsbruck, Institute of Botany (AT)
- Charles University Prague (CZ)
- CSIC Real Jardín Botánico de Madrid (ES)
- University of Vienna, Department of Systematic and Evolutionary Botany (AT)