Tertiary remnants and Holocene colonizers: Genetic structure and phylogeography of Scots pine reveal higher genetic diversity in young boreal than in relict Mediterranean populations and a dual colonization of Fennoscandia

Abstract

Aim: Scots pine is one of the dominant tree species in forest ecosystems of the temperate and boreal zones in Eurasia. Since the Tertiary, it has persisted also in the Mediterranean region, forming relict populations. In this study, we investigate rangewide genetic diversity of Scots pine, aiming to provide comprehensive information on the phylogeography and genetic resources of the species.Location: Europe and Asia. Methods: Thirteen paternally inherited chloroplast microsatellite (cpSSR) loci were used to investigate the genetic structure of 62 populations from Fennoscandia and 30 populations from the Mediterranean. We also surveyed variability of two maternally inherited mitochondrial DNA (mtDNA) regions and additionally included literature data from 156 populations (248 populations in total).Results: Scots pine retains an overall high genetic diversity in the chloroplast genome but, unexpectedly, the historically younger populations from Fennoscandia showed statistically higher mean intrapopulation diversity than the Mediterranean stands (0.807 and 0.750, respectively). The latter also contained a lower number of private cpSSR haplotypes.Population differentiation with respect to mtDNA was higher (G ST = 0.628) than at cpSSR (G ST = 0.015) indicating an efficient pollen-mediated gene flow among refugial populations of the species. One novel haplotype mtDNA was found, increasing the number of known mitotypes for the species from 4 to 5. The geographic distribution of mitotypes was structured into four groups corresponding to the main refugial areas of the species. Main conclusions: Genetic impoverishment of the Mediterranean populations may enhance their vulnerability to future environmental changes. The spatial distribution of two mitotypes in Fennoscandia, featuring predominance of mitotype a in Norway and Sweden and mitotype b in Finland, gives strong support for dual colonization of that region from south-eastern (Finland) and south-western (Sweden) directions. These results thus provide new insights into both Holocene expansion of Scots pine and the present distribution of species' genetic resources. | 541 DERING Et al.

Colonization history of Scots pine in Eastern Europe and North Asia based on mitochondrial DNA variation

“…At the same time our work was based on samples obtained from natural populations and was free from such kind of errors. The distribution of the mitochondrial DNA haplotypes based on the nad7 and nad1 markers in the combined data of Naydenov et al (2007), Pyhajarvi et al, (2008), Buchovska et al (2008), Dering et al (2017) and this study is presented in Fig. S1 (Supplemental data).…”

“…The analysis was performed at K = 2, 3, 4, 5 and 6. The geographic distribution of the mitochondrial DNA haplotypes identified in our study was manually drawn, and the distribution of mitotypes that is based on the nad7 and nad1 markers from the data of obtained in Naydenov et al (2007), Pyhajarvi et al, (2008), Buchovska et al (2008), Dering et al (2017) and our study was constructed using the program PhyloGeoViz (Tsai, 2010).…”

“…As a result, traces of historical demographic events, such as decline, expansion, isolation and migration of populations are better preserved in the genetic structure of populations identified by such markers. The mitochondrial DNA was widely used in studies of genetic structure and phylogeography of Scots pine (Sinclair et al 1999;Soranzo et al 2000;Cheddadi et al 2006;Naydenov et al 2007;Pyhäjärvi et al 2008;Vidyakin et al 2012;Buchovska et al 2013;Bernhardsson et al 2016;Dering et al 2017). In addition to Mediterranean refugia, which were common for many forest species, the geographical distribution of mitochondrial DNA haplotypes (mitotypes) showed additional potential northern sources of post-glacial recolonization of Scots pine in northern Europe and Asia (Naydenov et al 2007;Pyhäjärvi et al 2008).…”

Cold adaptation drives variability in needle structure and anatomy in Pinus sylvestris L. along a 1,900 km temperate–boreal transect

“…The prevalence of low LMA, thin needles in southern Scandinavian sites may thus be linked to the combination of high moisture availability and relatively moderate temperature conditions resulting from proximity of the warm oceanic current. Alternatively, it might be a result of historical differentiation of populations on opposite shores of the Baltic Sea, perhaps related to the pathways of post‐glacial colonization of Scandinavia (Dering et al., ) or introduction of non‐native genotypes in Southern Sweden. In either case, the similarity of needle cross‐sectional dimensions between southern and northern sites suggests that traits from this group are not crucial components of cold‐climate adaptation in P. sylvestris .…”

Variability of morphological needle traits of Scots pine (Pinus sylvestris L.) among populations from mountain and lowland regions of Poland

“…Although it is known that the most important glacial refugia of Scots pine are located on the Iberian Peninsula, the Balkans and Italy (Cheddadi et.al. 2006), it is conceivable that aside from the main refugial area pine could have probably survived in smaller refugia in other parts of Eurasia, including the Pieniny and Tatra Mountains (Wielkie Koryciska and Małe Koryciska) (Staszkiewicz 1993;Ralska-Jasiewiczowa 2004Naydenov et al 2007Pyhäjärvi et al 2008) and also as it is suggested in a recent extensive study of 92 Scots pine population based on mtDNA and cpSSR, there is a possibility of existence cryptic northern refugia, which can explain discordance with the phenomenon of "southern richness and northern purity" observed in this population (Dering et al 2017).…”