Hybridization Processes in Putative Hybrid Swarms of Scots Pine and Mountain Dwarf Pine as Revealed by Chloroplast DNA

Abstract

Gene flow among individual trees of Pinus sylvestris and P. mugo putative hybrid swarms in Slovakia was followed at four localities using the species-diagnostic cpDNA trnV-trnH/Hinf I restriction profile. Variable proportions of P. sylvestris and P. mugo haplotypes were revealed among the sampled localities. Low between-habitus consistency of the trees and their cpDNA haplotypes indicates the hybrid nature of the swarms. Molecular analysis based on mutual comparison of the haplotypes of a given tree and its embryos suggests direct and reciprocal hybridization between trees of the P. sylvestris and P. mugo haplotypes. Besides conspecific embryos resulting from hybridization of trees with the same haplotype (P. sylvestris × P. sylvestris and P. mugo × P. mugo), hybrid embryos of P. sylvestris × P. mugo (8.03%) and P. mugo × P. sylvestris (11.50%) were also detected in open-pollinated offspring. The results are discussed from the standpoint of primary and introgressive hybridization between the parental species.

Hybridization in contact zone between temperate European pine species

“…A lack of hybrids from crossings between P. mugo as a maternal and P. sylvestris as a paternal tree, but putative hybrid individuals from reverse crossing combinations (with P. mugo as a pollen donor), were found based on a joint analysis of cpDNA, isozymes, and phenotypic characteristics of trees (Wachowiak and Prus-Głowacki 2008) and at nuclear genes in a P. sylvestris and P. mugo population (Kormutak et al 2014). Cryptic hybrids between P. sylvestris and P. uncinata were found in the sympatric populations of the species (Jasińska et al 2010).…”

“…Our data clearly indicate that the markers applied in our study can accurately discriminate pure parental species. These markers provide a large resource of SNP information for future use in tracking interspecific gene flow and evaluating species composition in other contact zones where individuals with mixed morpho-anatomical characteristics have been described (e.g., in the Alps (Christensen 1987a), Slovakia (Kormutak et al 2014)). Hybrids can exhibit intermediate trait values, combine traits from both parents, and/or exhibit extreme trait values as compared to the parental species (Gross and Rieseberg 2005).…”

Molecular Insight into Genetic Structure and Diversity of Putative Hybrid Swarms of Pinus sylvestris × P. mugo in Slovakia

“…To provide evidence of P. sylvestris × mugo hybridization at the localities, several studies on paternally inherited chloroplast DNA markers were conducted in the past, revealing significant proportions of hybrid embryos, especially in Zuberec (41.1-58.7%) and Obsivanka (5-17.5%) [17,18]. These markers could also be used to test for hybridity of individual trees.…”