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Orchid colonization: multiple parallel dispersal events and mosaic genetic structure in Dactylorhiza majalis ssp. lapponica on the Baltic island of Gotland.

Författare:
  • Mikael Hedrén
  • Sofie Nordström Olofsson
  • Ovidiu Paun
Publiceringsår: 2018-06-28
Språk: Engelska
Sidor: 1019-1031
Publikation/Tidskrift/Serie: Annals of Botany
Volym: 122
Nummer: 6
Dokumenttyp: Artikel i tidskrift
Förlag: Oxford University Press

Abstract english

Background and Aims The island of Gotland in the Baltic Sea had no contact with surrounding continental areas since the withdrawal of the Weichselian ice sheet at ca 17 ka BP. Plants present on Gotland must have arrived by long distance dispersal, so populations are expected to exhibit reduced levels of genetic diversity compared with surrounding mainlands. However, orchids have very small seeds, which appear well-adapted for long-distance dispersal, and they should therefore be less affected than other plant species by colonization bottlenecks. The aim of this study was to analyse the genetic structure of orchids colonizing isolated islands, using the marsh orchid Dactylorhiza majalis ssp. lapponica as case study.
Methods More than 500 samples from 27 populations were analysed for 15 plastid and eight nuclear marker loci. Population diversity and differentiation patterns were compared for nuclear and plastid marker systems and analysed in relation to geographic location.
Key Results We found high genetic diversity but no clear geographic structure of genetic differentiation between populations on Gotland. However, the between-population differentiation in plastid and nuclear markers were correlated and the greatest diversity was found at sites at comparatively high elevations, which were the first to emerge above the water after the ice age.
Conclusions The regional population on Gotland has been established by a minimum of four dispersal events from continental regions. Subsequent gene flow between sites has not yet homogenized the differentiation pattern originating from initial colonization. We conclude that long-distance seed dispersal in orchids has a strong impact on structuring genetic diversity during periods of expansion and colonization, but contributes less to gene flow between populations once a stable population structure has been achieved.

Background and Aims

The island of Gotland in the Baltic Sea has had no contact with surrounding continental areas since the withdrawal of the Weichselian ice sheet at approx. 17 ka BP. Plants present on Gotland must have arrived by long-distance dispersal, so populations are expected to exhibit reduced levels of genetic diversity compared with populations on surrounding mainlands. However, orchids have very small seeds, which appear well adapted to long-distance dispersal, and they should therefore be less affected than other plant species by colonization bottlenecks. The aim of this study was to analyse the genetic structure of orchids colonizing isolated islands, using the marsh orchid Dactylorhiza majalis ssp. lapponica as a case study.


Methods

More than 500 samples from 27 populations were analysed for 15 plastid and eight nuclear marker loci. Population diversity and differentiation patterns were compared for nuclear and plastid marker systems and analysed in relation to geographical location.


Key Results

We found high genetic diversity but no clear geographical structure of genetic differentiation between populations on Gotland. However, the between-population differentiation in plastid and nuclear markers were correlated and the greatest diversity was found at sites at comparatively high elevations, which were the first to emerge above the water after the Ice Age.


Conclusions

The regional population on Gotland has been established by a minimum of four dispersal events from continental regions. Subsequent gene flow between sites has not yet homogenized the differentiation pattern originating from initial colonization. We conclude that long-distance seed dispersal in orchids has a strong impact on structuring genetic diversity during periods of expansion and colonization, but contributes less to gene flow between populations once a stable population structure has been achieved.

Keywords

  • Botany
  • Genetics
  • Ecology

Other

Published
  • ISSN: 0305-7364
Mikael Hedrén
E-post: mikael [dot] hedren [at] biol [dot] lu [dot] se

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