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Polyploid evolution in the European orchid genus Nigritella: evidence from DNA fingerprinting

Författare:
  • David Ståhlberg
Publiceringsår: 1999
Språk: Engelska
Dokumenttyp: Rapport

Sammanfattning

The genus Nigritella (Orchidaceae-Orchidinae) is a complex of species at four different ploidy levels. Fourteen taxa at species or subspecies level have been distinguished. The triploid N. nigra ssp. nigra is endemic to Scandinavia, whereas the remaining taxa are confined to different mountain regions in Central and Southern Europe. The polyploids are of hybrid origin and have arisen from taxa at lower ploidy levels by allopolyploidization. By using a recently developed PCR based DNA fingerprinting technique (AFLP), I have investigated the evolutionary history of the genus. I have also considered the genetic relationship between Nigritella and the closely related genus Gymnadenia.

Tetraploid members of Nigritella are supposed to be the result of hybridization between diploids and triploids. The latter may have contributed unreduced gametes. Three different ancient triploid taxa would explain the origin of all present-day tetraploids. Nigritella nigra ssp. nigra and the other – today probably extinct – triploids may have survived the last glacial maximum in different Central and Southern European refugia. They may then have mixed with populations of diploids, thereby giving rise to new, tetraploid taxa.

All the polyploids displayed several DNA bands that were rare or absent in the extant diploids. It is therefore reasonable to assume that ancestral diploids, somewhat different from present-day taxa, have been involved – at least in the formation of the intermediate triploid forms.

The diploid samples only partly clustered in accordance with morphologically defined entities. Plants with the same geographic origin tended to cluster together, regardless of taxonomic belonging.

The polyploids are mainly apomicts, but in spite of this fact, certain taxa varied in a complex way. This pattern could partly be explained by recurrent polyploidization, by which a given taxon may have several independent origins. The number of origins was estimated for different taxa, and varied between one and seven.

It is not necessary to amalgamate the genera Nigritella and Gymnadenia. They were well separated from each other. Bigeneric hybrids clustered in between, and the origin of Gymnigritella runei was confirmed: this rare Scandinavian tetraploid is most likely the result of hybridization between N. nigra ssp. nigra and G. conopsea.

Disputation

Nyckelord

  • Biology and Life Sciences
  • AFLP
  • apomixis
  • evolution
  • Gymnadenia
  • Gymnigritella
  • hybridization
  • Nigritella
  • polyploidy
  • systematics

Övriga

Unpublished

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