Areas of immediate contact of different cytotypes offer a unique opportunity to study evolutionary dynamics within heteroploid species and to assess isolation mechanisms governing coexistence of cytotypes of different ploidy. The degree of reproductive isolation of cytotypes, that is, the frequency of heteroploid crosses and subsequent formation of viable and (partly) fertile hybrids, plays a crucial role for the long-term integrity of lineages in contact zones. Here, we assessed fine-scale distribution, spatial clustering, and ecological niches as well as patterns of gene flow in parental and hybrid cytotypes in zones of immediate contact of di-, tetra-, and hexaploid Senecio carniolicus (Asteraceae) in the Eastern Alps. Cytotypes were spatially separated also at the investigated microscale; the strongest spatial separation was observed for the fully interfertile tetra- and hexaploids. The three main cytotypes showed highly significant niche differences, which were, however, weaker than across their entire distribution ranges in the Eastern Alps. Individuals with intermediate ploidy levels were found neither in the diploid/tetraploid nor in the diploid/hexaploid contact zones indicating strong reproductive barriers. In contrast, pentaploid individuals were frequent in the tetraploid/hexaploid contact zone, albeit limited to a narrow strip in the immediate contact zone of their parental cytotypes. AFLP fingerprinting data revealed introgressive gene flow mediated by pentaploid hybrids from tetra- to hexaploid individuals, but not vice versa. The ecological niche of pentaploids differed significantly from that of tetraploids but not from hexaploids.

Department of Botany Faculty of Science Charles University Prague Czech Republic

Department of Botany Faculty of Science Charles University Prague Czech Republic ; Institute of Botany The Czech Academy of Sciences Průhonice Czech Republic

Division of Conservation Biology Vegetation Ecology and Landscape Ecology Department of Botany and Biodiversity Research University of Vienna Vienna Austria

Division of Conservation Biology Vegetation Ecology and Landscape Ecology Department of Botany and Biodiversity Research University of Vienna Vienna Austria ; Vienna Institute for Nature Conservation and Analyses Vienna Austria

Division of Systematics and Evolutionary Botany Department of Botany and Biodiversity Research University of Vienna Vienna Austria

Division of Systematics and Evolutionary Botany Department of Botany and Biodiversity Research University of Vienna Vienna Austria ; GLORIA co ordination Center for Global Change and Sustainability University of Natural Resources and Life Sciences Vienna Vienna Austria ; Institute for Interdisciplinary Mountain Research Austrian Academy of Sciences Innsbruck Austria

Institute of Botany University of Innsbruck Innsbruck Austria

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