Abstract
Scots pine (Pinus sylvestris L.) and the taxa from the P. mugo complex can hybridize in the contact zones and produce fertile hybrids. A unique example of an early Holocene relict population of P. sylvestris and P. uliginosa (a taxon from the P. mugo complex) growing on the tops of Jurassic sandstone rocks is located in Błędne Skały (Sudetes). Phenotypically, there are trees resembling P. sylvestris, P. uliginosa and intermediate forms between them. We expected that some of P. sylvestris and/or P. uliginosa-like trees could be in fact cryptic hybrids resembling one of the parental phenotypes. To address this question, we examined randomly sampled individuals, using a set of plastid (cpDNA), nuclear (nDNA) and mitochondrial (mtDNA) markers as well as biometric characteristics of needles and cones. The results were compared to the same measurements of allopatric reference populations of the P. sylvestris and the P. mugo complex (Pinus mugo s.s, P. uncinata and P. uliginosa). We detected cpDNA barcodes of the P. mugo complex in most individuals with the P. sylvestris phenotype, while we did not detect cpDNA diagnostic of P. sylvestris within P. uliginosa-like trees. These results indicate the presence of cryptic hybrids of the P. sylvestris phenotype. We found only three typical P. sylvestris individuals that were clustered with the species reference populations based on needle and cone characteristics. Most trees showed intermediate characteristics between P. sylvestris and P. uliginosa-like trees, indicating intensive and probably long-lasting hybridization of the taxa at this area and subsequent gene erosion of parental species.
Highlights
Hybridization and introgression are important evolutionary factors that increase species variation and may lead to speciation [1,2,3,4,5,6]
The results indicated the higher success of pollination, when taxa of the P. mugo complex were the pollen donors, and possible back-crossing of hybrids with both parental species
We investigated the hybridization processes in the pine population in Błedne Skały to verify (i) if there are any hybrids among P. sylvestris-like and/or P. uliginosa-like trees which resemble one of the parental trees; (ii) if there are any patterns of successful hybridization as compared to some earlier works (iii) to what extent the level of genetic variation of this small and isolated population is comparable to variation in much bigger reference populations of pure species
Summary
Hybridization and introgression are important evolutionary factors that increase species variation and may lead to speciation [1,2,3,4,5,6]. These two processes concern mostly related species, which do not express isolation mechanisms such as phenological barriers [7] and post-pollination barriers to fertilization [8]. Forests 2020, 11, 1086 frequent [9,10,11,12] Considering their long generation time and lifespan, the relatively recent divergence between dwarf mountain pine (P. mugo Turra) and Scots pine (P. sylvestris L.) [13] resulted in their similar genetic variation at neutral loci [14]. The unequivocal identification of hybrids is difficult based on morphological and anatomical characteristics alone
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