Haplotype variation in a mitochondrial tandem repeat of Norway spruce (Picea abies) populations suggests a serious founder effect during postglacial re-colonization of the western Alps

Populations from 13 elevational transects of Norway spruce [Picea abies (L. ) Karst] across the Alpine range were sampled to elucidate the geographical pattern of genetic variation in relation to postglacial re-colonization an d to study elevational effects on haplotypic diversity. We assessed fragmen t length variation in a tandem repeat region of the mitochondrial (mt) nad1 intron 2. This maternally inherited genetic marker is suited to infer migr ation as it is dispersed by seed only. A total of 10 haplotypes was found, most of which were due to repeat copy number variation. An analysis of mole cular variance (AMOVA) showed that overall population differentiation was h igh (F-ST = 0.41), and it revealed a significant differentiation between mo nomorphic western and moderately to highly variable eastern Alpine populati ons. This phylogeographic pattern may be explained by a founder effect duri ng postglacial. re-colonization. An early arriving haplotype, assumed to or iginate from a western Carpathian refugium, could expand into suitable habi tats, reducing the chances for establishment of subsequently arriving haplo types. On the other hand, the high variation in populations within an Itali an transect of the south-eastern Alps may be the consequence of merging mig ration pathways from and close distance to putative glacial refugia, most l ikely those assumed in the Carpathian mountains and on the Balkan peninsula or possibly in the central plains of Italy. An effect of elevation on hapl otypic diversity was not evident, though a low, but significant, partition of total genetic variation was attributed to among-population variation in one Italian transect. Various factors, such as vertical seed dispersal and forest management, may account for blurring an otherwise established patter n of genetic variation on a small geographical scale.