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

(2012) ANNALS OF BOTANY. 109(4). p.709-720
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Abstract
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). 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. 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 F-1 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. 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 F-1 generation.
Keywords
Dactylorhiza praetermissa, genetic analysis, Dactylorhiza incarnata, AFLP, hybridization, morphology, polyploidy, reproductive isolation, triple hybrid, INTERSPECIFIC HYBRIDIZATION, INCARNATA ORCHIDACEAE, HYBRID ZONES, GENETIC DIFFERENTIATION, DECEPTIVE POLLINATION, POLYPLOID COMPLEX, EUROPEAN RUSSIA, EVOLUTION, PLANTS, INTROGRESSION

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Chicago
De Hert, Koen, Hans Jacquemyn, Sabine Van Glabeke, Isabel Roldàn-Ruiz, Katrien Vandepitte, Leen Leus, and Olivier Honnay. 2012. “Reproductive Isolation and Hybridization in Sympatric Populations of Three Dactylorhiza Species (Orchidaceae) with Different Ploidy Levels.” Annals of Botany 109 (4): 709–720.
APA
De Hert, Koen, Jacquemyn, H., Van Glabeke, S., Roldàn-Ruiz, I., Vandepitte, K., Leus, L., & Honnay, O. (2012). Reproductive isolation and hybridization in sympatric populations of three Dactylorhiza species (Orchidaceae) with different ploidy levels. ANNALS OF BOTANY, 109(4), 709–720.
Vancouver
1.
De Hert K, Jacquemyn H, Van Glabeke S, Roldàn-Ruiz I, Vandepitte K, Leus L, et al. Reproductive isolation and hybridization in sympatric populations of three Dactylorhiza species (Orchidaceae) with different ploidy levels. ANNALS OF BOTANY. 2012;109(4):709–20.
MLA
De Hert, Koen, Hans Jacquemyn, Sabine Van Glabeke, et al. “Reproductive Isolation and Hybridization in Sympatric Populations of Three Dactylorhiza Species (Orchidaceae) with Different Ploidy Levels.” ANNALS OF BOTANY 109.4 (2012): 709–720. Print.
@article{8096143,
  abstract     = {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). 
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. 
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 F-1 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. 
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 F-1 generation.},
  author       = {De Hert, Koen and Jacquemyn, Hans and Van Glabeke, Sabine and Rold{\`a}n-Ruiz, Isabel and Vandepitte, Katrien and Leus, Leen and Honnay, Olivier},
  issn         = {0305-7364},
  journal      = {ANNALS OF BOTANY},
  keyword      = {Dactylorhiza praetermissa,genetic analysis,Dactylorhiza incarnata,AFLP,hybridization,morphology,polyploidy,reproductive isolation,triple hybrid,INTERSPECIFIC HYBRIDIZATION,INCARNATA ORCHIDACEAE,HYBRID ZONES,GENETIC DIFFERENTIATION,DECEPTIVE POLLINATION,POLYPLOID COMPLEX,EUROPEAN RUSSIA,EVOLUTION,PLANTS,INTROGRESSION},
  language     = {eng},
  number       = {4},
  pages        = {709--720},
  title        = {Reproductive isolation and hybridization in sympatric populations of three Dactylorhiza species (Orchidaceae) with different ploidy levels},
  url          = {http://dx.doi.org/10.1093/aob/mcr305},
  volume       = {109},
  year         = {2012},
}

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