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Phylogeography of Populus alba (L.) and Populus tremula (L.) in Central Europe: secondary contact and hybridisation during recolonisation from disconnected refugia


The central aim of this paper is to clarify the picture of postglacial recolonisation and the reconstruction of refugia of Populus alba (L.) and Populus tremula (L.) in the light of hybridisation of the two species. We focussed our study on Central and Southeastern Europe including reference samples from Spain, Sweden and Northern Africa.We investigated 414 individuals of 26 populations using restriction fragment length polymorphisms (PCR-RFLPs) in six maternally inherited chloroplast markers. Altogether, 57 haplotypes were analysed of which four indicated hybridisation events in the past. Phylogeographic structure was found for P. alba with low diversity in Eastern Europe versus high diversity in Italy and Central Europe. A lack of phylogeographic structure was assessed for P. tremula as expected for a boreal forest tree, and diversity was evenly distributed in the studied populations. Two main refugia were identified for P. alba in Italy and Romania. A previously described hybrid zone between species in Central Europe turned out also to be a zone of contact between southern and eastern chloroplast lineages in P. alba. In contrast, P. tremula recolonised its present habitats in Central Europe from several refugia near the former ice cap. We assume separate disconnected refugia for P. alba and P. tremula and suggest an immigration scenario involving the mixing of colonisation routes and interspecific introgression to be responsible for the observed patterns.

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We thank Wilfried Nebenführ, Hans Herz, Christian Fraissl, Franz Kovacs, Denes Bartha, Marius Sorin Nica and Adrian Ipati, for their help with sampling. We also thank Davorin Kajba, Sasa Bogdan, Attila Benke, Stefano Castiglione, Santiago González-Martínez, Helena Cvrčková and Pavlina Máchová for providing us with samples. We thank Maria del Carmen Calderón Pérez for her great help in the laboratory. Helpful advice on statistical analysis was given by Remy Petit. We thank Karl-Manfred Schweinzer for helping in designing the haplotype maps. This study was financially supported by the city of Vienna (Jubiläumsfonds der Stadt Wien für die Österreichische Akademie der Wissenschaften, J-6/2005), a DOC-fFORTE grant to B. Fussi (Österreichische Akademie der Wissenschaften) and by grant NE/E016731/1 of the British NERC to CL.

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Correspondence to Barbara Fussi.

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Communicated by O. Savolainen

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Additional supporting information can be found in the online version of this article:

Appendix S1

Sampling locations and number of haplotypes per population (PDF 107 kb)

Appendix S2

Haplotype definition of eight variable fragments (PDF 37 kb)

Appendix S3

Haplotype distribution in Europe and Northern Africa (PDF 487 kb)

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Fussi, B., Lexer, C. & Heinze, B. Phylogeography of Populus alba (L.) and Populus tremula (L.) in Central Europe: secondary contact and hybridisation during recolonisation from disconnected refugia. Tree Genetics & Genomes 6, 439–450 (2010). https://doi.org/10.1007/s11295-009-0262-5

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  • Postglacial recolonisation
  • Hybridisation
  • cpDNA
  • Populus alba
  • Populus tremula