Tollefsrud M.   Sperisen C.  

Paternal introgression from Siberian spruce (Picea obovata) to Norway spruce (P. abies): tracing pollen and seed flow with chloroplast and mitochondrial DNA

Reporter: Tollefsrud M.

Norway spruce (Picea abies (L.) Karst.) and Siberian spruce (Picea obovata Lebed.) are closely related and occupy a large parapatric area across the whole of northern Eurasia. It has been suggested that a wide zone of hybridization along the Ural Mountains separates the European Norway spruce from the Siberian spruce. In this study we analysed maternally (mitochondrial DNA, mtDNA) and paternally (chloroplast DNA, cpDNA) inherited markers in 50 spruce populations to study genetic differentiation and introgressive hybridization between them. We used partial sequences of the cpDNA trnT- trnF region and size variants of the mtDNA nad1 region, the latter by extending a previous data set. Fourteen mtDNA and four cpDNA haplotypes were identified, and distinct genetic division was detected between Norway spruce and Siberian spruce. In the mtDNA marker, a 9-bp polymorphism differentiated populations in the northern Urals and east Siberia from populations along and west of the Ural Mountains. This division largely corresponded to two highly differentiated genetic (SAMOVA) groups both in the mtDNA dataset (FCT = 0.685) and in the cpDNA dataset (FCT = 0.438), suggesting that the main border between the taxa is to the east of the Ural Mountains. However, the paternally inherited cpDNA marker showed extensive introgression from Siberian spruce into the entire range of Norway spruce, and the maternally inherited mtDNA haplotypes of Norway spruce are also found across the Ural Mountains. Introgression via pollen thus acts as a mechanism of dispersal of Siberian spruce genes into the northern European gene pool of Norway spruce. No phylogeographic structure was detected in Siberia, consistent with a single glacial refugium for Siberian spruce, but only little variation was detected with the markers surveyed here.

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