title: The impact of hybridization on long-term persistence of polyploid Dactylorhiza species.
abstract: OBJECTIVE
  Hybridization may pose severe threats to the long-term survival of the parental taxa through introgression and the formation of hybrid swarms. However, when the resulting hybrids show strong male and female sterility, backcrossing and introgression are unlikely to occur, but the parental species may suffer from reduced male and female fitness.
  
  
  METHODS
  We assessed the impact of hybridization on the long-term persistence of two food-deceptive orchids in the genus Dactylorhiza (the common Dactylorhiza maculata and the rare D. sphagnicola). The extent of hybridization was investigated using both molecular markers and morphometric measurements. To determine the strength of postmating reproductive isolation, hand pollinations were conducted between pure and hybrid individuals. Finally, fruit set and seed viability of open-pollinated plants were determined in sympatric and allopatric populations to investigate the impact of hybridization on the reproductive output of the pure parental species.
  
  
  RESULTS
  Our results showed that postmating reproductive isolation was weak and that hybridization occurred frequently within the studied sympatric population. Although hybrids were characterized by very low female fitness, mainly because of strongly reduced seed viability, backcrossing appeared to occur and was asymmetric toward the rare D. sphagnicola. Fruit set and seed viability of open-pollinated plants were also significantly lower in the sympatric population than in the allopatric populations, indicating that hybridization and ongoing introgression incurred fitness costs in the pure parental species.
  
  
  CONCLUSIONS
  Overall, our results suggest that extensive hybridization can affect the long-term viability of the parental species through the combined effect of introgression following interspecific hybrid fertilization and reduced fitness of the parental species.
authors: KU Leuven, Biology Department, Plant Population and Conservation Biology, Kasteelpark Arenberg 31, B-3001 Heverlee, Belgium hans.jacquemyn@kuleuven.be.
authors: Hans
authors: H
authors: Jacquemyn
authors: KU Leuven, Biology Department, Plant Population and Conservation Biology, Kasteelpark Arenberg 31, B-3001 Heverlee, Belgium.
authors: Sascha
authors: S
authors: van der Meer
authors: Research Institute for Nature and Forest, Kliniekstraat 25, B-1070 Brussels, Belgium.
authors: Rein
authors: R
authors: Brys
mesh_terms: D001530:Belgium; D056084:Genetic Fitness; D006824:Hybridization, Genetic; D029595:Orchidaceae / Q000235:genetics*; D054817:Pollination; D011123:Polyploidy; D060047:Reproductive Isolation
keywords: hybridization; introgression; long-term population viability; plant fitness