Journal Article

Reproductive isolation and hybridization in sympatric populations of three <i>Dactylorhiza</i> species (Orchidaceae) with different ploidy levels

Koen De hert, Hans Jacquemyn, Sabine Van Glabeke, Isabel Roldán-Ruiz, Katrien Vandepitte, Leen Leus and Olivier Honnay

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 109, issue 4, pages 709-720
Published in print March 2012 | ISSN: 0305-7364
Published online December 2011 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcr305
Reproductive isolation and hybridization in sympatric populations of three Dactylorhiza species (Orchidaceae) with different ploidy levels

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

The potential for gene exchange between species with different ploidy levels has long been recognized, but only a few studies have tested this hypothesis in situ and most of them focused on not more than two co-occurring species. In this study, we examined hybridization patterns in two sites containing three species of the genus Dactylorhiza (diploid D. incarnata and D. fuchsii and their allotetraploid derivative D. praetermissa).

Methods

To compare the strength of reproductive barriers between diploid species, and between diploid and tetraploid species, crossing experiments were combined with morphometric and molecular analyses using amplified fragment length polymorphism markers, whereas flow cytometric analyses were used to verify the hybrid origin of putative hybrids.

Key Results

In both sites, extensive hybridization was observed, indicating that gene flow between species is possible within the investigated populations. Bayesian assignment analyses indicated that the majority of hybrids were F1 hybrids, but in some cases triple hybrids (hybrids with three species as parents) were observed, suggesting secondary gene flow. Crossing experiments showed that only crosses between pure species yielded a high percentage of viable seeds. When hybrids were involved as either pollen-receptor or pollen-donor, almost no viable seeds were formed, indicating strong post-zygotic reproductive isolation and high sterility.

Conclusions

Strong post-mating reproductive barriers prevent local breakdown of species boundaries in Dactylorhiza despite frequent hybridization between parental species. However, the presence of triple hybrids indicates that in some cases hybridization may extend the F1 generation.

Keywords: AFLP; Dactylorhiza incarnata; Dactylorhiza praetermissa; genetic analysis; hybridization; morphology; polyploidy; reproductive isolation; triple hybrid

Journal Article.  8233 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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