Combined analysis of nuclear and mitochondrial markers provide new insight into the genetic structure of North European Picea abies

Abstract

Norway spruce of northern Europe expanded at the end of the last glacial out of one refugium in Russia. To provide a detailed insight into how the genetic structure in the northern European lineage of this species has been shaped by postglacial migration, recurrent pollen flow and marginality, we here compare variation at seven highly variable nuclear microsatellite loci in 37 populations (1715 trees) with mitochondrial DNA variation. Microsatellite diversity was high (H E ¼ 0.640) and genetic differentiation was low (F ST ¼ 0.029). The microsatellite structure supported a mitochondrial DNA (mtDNA)-based hypothesis of two migration routes out of a single Russian refugium; one northwestern over Finland to northern Scandinavia, and one southwestern across the Baltic Sea into southern Scandinavia. Microsatellite diversity was maintained along the southwestern migration routes, whereas a significant decrease was observed towards the north. In contrast, the mtDNA diversity suggested higher amounts of historical gene flow towards the north than along the southwestern migration route. This suggests that the loss of nuclear diversity after postglacial colonization has been efficiently replenished by pollen-mediated gene flow in the south. Towards the north, smaller effective population size because of more limited seed and pollen production may have caused decreased nuclear diversity and increased inbreeding, reflecting the ecological marginality of the species in the north.

Population at the edge: increased divergence but not inbreeding towards northern range limit in Acer campestre

“…This kind of spatial pattern is generally found in tree species (e.g. Tollefsrud et al 2009;Grivet et al 2009), although such studies often require large spatial scales (Comps et al 2001;Coart et al 2005). This is because trees are often characterised by wide distribution, high potential for gene flow and strong human impact, including forest management and translocation of seed material (Petit and Hampe 2006).…”

“…For example, in many European trees the geographic distribution of genetic diversity reflects the process of postglacial recolonisation (Comps et al 2001;Coart et al 2005;Tollefsrud et al 2009;Grivet et al 2009). In consequence, genetic diversity tends to decrease with the distance from refugia (generally northwards), even if no sharp differences in a species' current density can be found.…”

“…In such conditions recurrent consanguineous mating can lead to genetic purging (Pujol et al 2009), weakening inbreeding depression and opening potential for further increase of inbreeding. When fragmentation is due to ecological conditions, like in marginal habitats, inbreeding can be especially adaptive because it can help avoiding decreased fecundity (Fischer and Matthies 1997;Busch 2005;Mimura and Aitken 2007;Michalski and Durka 2007;Johnson et al 2009;Tollefsrud et al 2009). Nonetheless, because empirical studies provided a mixed support for this prediction, it was argued that in many cases populations experienced fragmentation only recently, so that the observed inbreeding level still reflects more the historical conditions rather than the reduced population size (Aguilar et al 2008).…”

Comment on “Glacial Survival of Boreal Trees in Northern Scandinavia”

“…The distribution of other mtDNA and nuclear DNA markers (8)-combined with palaeoecological evidence of small scattered, perhaps palynologically silent, early Picea populations in Scandinavia (9), including a possible Late Glacial (but not LGM) occurrence on a Swedish nunatak (10)-suggest several immigrations along both northern and southern routes after deglaciation. This scenario would explain the observed genetic diversities from Russia to Scandinavia (8). Furthermore, LGM Picea populations south of the ice with HapA could have spread north during deglaciation, meanwhile becoming extinct in their southern refugia.…”

Genetic and historical studies on the origin of Norway spruce in Białowieża Primeval Forest in Poland

“…This forest complex resembles the virgin lowland forests that originally covered Central Europe (Faliński 1968). According to pollen data, Białowie_ za was colonized with spruce from a refugium in the Middle Russian Upland (Latałowa and van der Knaap 2006;Tollefsrud et al 2009). Genetic data support this finding but additionally indicate that the Norway spruce in Białowie_ za comes from the Eastern Carpathian refugium as well (Dering 2008).…”