Hybridization in contact zone between temperate European pine species

Abstract

Hybridization studies are important to advance our understanding of the interspecific gene flow and its evolutionary consequences in closely related species. Hybridization and admixture patterns were assessed in a contact zone and reference populations of European pine species using sequence data from 26 nuclear genes and a species-diagnostic cpDNA marker. Reference populations formed three distinct genetic clusters comprising Pinus sylvestris, Pinus mugo/Pinus uliginosa, and Pinus uncinata. Evidence of population structure was found only in P. uliginosa. Based on phenotypic characteristics and molecular data, we identified five groups of individuals in the contact zone in Poland, comprising forms of the parental species and intermediates that were most probably the result of interspecific crosses. A combination of nuclear gene sequence data and a diagnostic organelle marker were used to show that hybridization is frequent in the contact zone and results in hybrid trees with distinct phenotypic identity. The influence of selection in maintaining hybrid phenotypes in environments unsuited to parental species was inferred from nucleotide polymorphism data. A lack of admixture in reference populations suggests that hybridization has not occurred during post-glacial migration and so the contact zone represents a distinct, active example of ongoing evolution. Pine populations in this zone will be a valuable system for studying the genetic basis of hybrid advantage in environmental conditions untypical of pure parental species.

Cross-amplification and multiplexing of cpSSRs and nSSRs in two closely related pine species (Pinus sylvestris L. and P. mugo Turra)

“…Furthermore, the marker that exhibits species-specific allelic patterns (PCP30277) seems ideal for studies of interspecific gene flow in the species' contact zones. Such studies accompanied by analyses of sequence variation at candidate genomic regions will help to address questions related to the role of hybridization in evolution of P. sylvestris and P. mugo (Wachowiak et al, 2015(Wachowiak et al, , 2016. Our study clearly confirms that cross-amplification seems to be a good first choice alternative to the de novo development of microsatellite markers, especially for species with poor genomic resources.…”

“…Alleles scored for these loci did not overlap when the two species were taken into account. Only 2 bp difference was observed for PCP45071 and it does not seem to be a species-specific polymorphism as compared to other studies (Wójkiewicz & Wachowiak, 2016). The difference for PCP30277 was at least 14 bp (Table 2), and this locus can be useful as a diagnostic marker to track interspecific gene flow in the species' contact zones.…”

“…With respect to population genetics of forest tree species, microsatellites have proved to be useful neutral molecular markers in studies focusing on genetic diversity (e.g. Chybicki et al, 2011;Litkowiec et al, 2015;Wójkiewicz & Wachowiak, 2016), mating systems (e.g. Lian et al, 2001) and gene mapping (e.g.…”

Spatial Pattern of the Mitochondrial and Chloroplast Genetic Variation in Poland as a Result of the Migration of Abies alba Mill. from Different Glacial Refugia

“…By contrast, the results in this study for cpDNA were consistent with strong gene flow via pollen, and the secondary contact between the two lineages of A. alba populations led to the homogenization of genetic structure primarily by the transport of only pollen from the Balkan refugium after isolation during the LGM. Such an exchange of genetic information between refugia would produce hybrid individuals with the creation of new genotypic combinations resulting in transgressive phenotypes well outside the paternal norms that are widely considered to be better adapted to new, local environmental conditions [46][47][48]. Moreover, the results of this study did not support the prior presumption concerning the distinctiveness of the Sudeten and Carpathian A. alba populations based on previous studies using isoenzyme markers [22,23] and provenance experiments [49][50][51].…”

Improved recovery of ancient DNA from subfossil wood – application to the world's oldest Late Glacial pine forest

“…To distinguish between the two potential species, Scots pine and mountain pine, we took advantage of a species‐specific single nucleotide polymorphism (SNP), located at position 150 of the plastid trn F‐ trn L intergenic spacer (Wachowiak et al ., ). This SNP was found to be diagnostic in more than 30 populations of Scots pine (carrying a cytosine) and species of the Pinus mugo Turra complex (carrying an adenine) from throughout Europe (Jasińska et al ., ; Wachowiak et al ., ), indicating that this SNP is fixed between the two taxa. This was further confirmed in two mixed stands of Scots pine and mountain pine located on Uetliberg mountain (data not shown).…”