High genetic diversity at the extreme range edge: nucleotide variation at nuclear loci in Scots pine (Pinus sylvestris L.) in Scotland

Abstract

Nucleotide polymorphism at 12 nuclear loci was studied in Scots pine populations across an environmental gradient in Scotland, to evaluate the impacts of demographic history and selection on genetic diversity. At eight loci, diversity patterns were compared between Scottish and continental European populations. At these loci, a similar level of diversity (y sil ¼ B0.01) was found in Scottish vs mainland European populations, contrary to expectations for recent colonization, however, less rapid decay of linkage disequilibrium was observed in the former (r ¼ 0.0086 ± 0.0009, r ¼ 0.0245 ± 0.0022, respectively). Scottish populations also showed a deficit of rare nucleotide variants (multi-locus Tajima's D ¼ 0.316 vs D ¼ À0.379) and differed significantly from mainland populations in allelic frequency and/or haplotype structure at several loci. Within Scotland, western populations showed slightly reduced nucleotide diversity (p tot ¼ 0.0068) compared with those from the south and east (0.0079 and 0.0083, respectively) and about three times higher recombination to diversity ratio (r/y ¼ 0.71 vs 0.15 and 0.18, respectively). By comparison with results from coalescent simulations, the observed allelic frequency spectrum in the western populations was compatible with a relatively recent bottleneck (0.00175 Â 4N e generations) that reduced the population to about 2% of the present size. However, heterogeneity in the allelic frequency distribution among geographical regions in Scotland suggests that subsequent admixture of populations with different demographic histories may also have played a role.

Signatures of volcanism and aridity in the evolution of an insular pine (Pinus canariensis Chr. Sm. Ex DC in Buch)

“…A similar pattern was also found for nuclear gene analysis in P. sylvestris in Scotland (Wachowiak et al, 2011), suggesting that admixture of populations with different demographic histories has played a role in shaping current genetic diversity patterns.…”

High genetic similarity between Polish and North European Scots pine (Pinus sylvestris L.) populations at nuclear gene loci

“…Nucleotide sequence analysis at several nuclear loci also provided little evidence for the effects of recent (post-glacial) population size changes during migration and suggested bottlenecks in the mid-to-late Pleistocene ). Nucleotide variation in Scottish populations was not compatible with a simple recolonization model (Wachowiak et al 2010) and some evidence for possible northern refugia has been suggested by ancient DNA studies (Parducci et al 2012). Regardless of migration trajectories, postglacial expansion of the species was accompanied by adaptation to local environments as evident from quantitative genetic studies in Scots pine that showed large variation of morphological (growth dynamics, wood quality), physiological, growth traits and stress response across the environmental gradient related to photoperiod and temperature (Salmela et al 2013;Hurme et al 1997).…”

Genetic variation for needle traits in Scots pine (Pinus sylvestris L.)

“…The fragmented remnants that endure are 39 estimated to cover only one percent of the area that was once occupied (McVean and Ratcliffe, 40 1962). Despite this dramatic contraction, native Scots pine populations have retained levels of 41 molecular genetic diversity comparable to those observed in continental European populations 42 (Wachowiak et al, 2011(Wachowiak et al, , 2013. Moreover, they continue to survive under a wide variety of 43 environmental conditions within this limited geographic area.…”

“…As previously little to no spatial genetic structure has been 369 identified among native pinewoods (Provan et al, 1998, Wachowiak et al, 2011, it is plausible 370 that the differences and trends observed have an adaptive basis, and it would be of interest to 371 investigate whether the same patterns can be observed in situ. 372…”

“…60 Local adaptation can be described in terms of a balance between gene flow and selection: 61 specifically, it occurs only if differential selective pressures are of sufficient strength to overcome the 62 homogenising effects of gene flow (Kawecki and Ebert, 2004). Scots pine is wind-pollinated and a 63 highly outcrossing tree species (Muona and Harju, 1989;, and in 64 Scotland genetic structure has been shown to be extremely low for nuclear and chloroplast markers 65 which are subject to pollen-mediated gene flow (Provan et al, 1998, Wachowiak et al, 2011 …”