Martin Galgóci

Needle structure was analyzed in three Juniperus communis taxa from different localities in central Slovakia. The main aim was to test the hybrid origin hypothesis of J. communis nothovar. intermedia (Schur) Nyman, defined as a cross between J. communis L. ssp. communis and J. communis ssp. nana (Hook.) Syme. While DNA-based analyses remain the most reliable tool for inferring evolutionary history, comparative needle morphology can provide complementary evidence, including diagnostic traits for taxonomic delimitation. In this study, we evaluated three morphometric and sixteen anatomical needle traits, measured via microscopy in ten shrubs per taxon. The analyses indicated that most traits in nothovar. intermedia matched one of the parents, with only two traits proving strongly diagnostic, separating all three taxa: needle length, which showed an intermediate mean phenotype in nothovar. intermedia (R² = 0.824, p = 0.011; between parents), and vascular bundle height, which displayed a transgressive pattern (R² = 0.552, p = 0.031; between parents). Although the diagnostic value of individual traits for hybrid detection was generally weak, a phylogenetic network analysis based on six diagnostic traits that separated individuals of the parental taxa provided evidence for reticulate evolution. These results support the hybrid origin of J. communis nothovar. intermedia and highlight needle traits with potential value for distinguishing ssp. communis and ssp. nana in natural populations, which may assist in taxonomic delimitation and inform future conservation assessments.

The Pinus mugo complex (P. mugo Turra s. l. or P. mugo aggregate) is an important fragment of European dendroflora, which is characterized by high variability, reticulate evolution, and several hybrid zone populations in different parts of Europe. Here we tried to explore the admixture structure of four putative hybrid zones between P. mugo Turra (s. str.) and P. sylvestris L. in Slovakia, using Bayesian ancestry inference with microsatellites. Unexpectedly, compared to nine reference populations, the results showed no elevated allelic diversity in our four locations. However, there was a high marker information content for ancestry based on the reference samples (δ _C or D _K = 0.451). The individual admixture proportions of P. sylvestris averaged at 0.529, 0.419, and 0.292 in the three locations, with the distribution ranging from unimodality to bimodality. These data support the presence of hybrid zones, but only in association with peatland habitats. In a typical calcicolous pine relict examined, no hybrids were detected, which contrasts earlier reports. The unexpected absence of elevated diversity, including the differences in hybrid zones’ modality within the same habitat, might be explained by population bottlenecks due to anthropogenic peatland degradation during the 1960s to 1980s, when intensive drainage in the region occurred. The study highlights the evolutionary, ecological and conservation value of the studied bog populations.

Pollen viability in three Juniperus taxa native to Slovakia was investigated using in vitro germination test. The highest germination percentage and longest pollen tubes were surprisingly found in J. communis var. intermedia (Shur) Sanio which is believed to be a putative hybrid between J. communis var. communis L. and J. sibirica Lodd. Germination rate of the hybrid averaged at 78.70% as compared with 64.96% and 60.83% of the pollen germination in the corresponding parental species. The same tendency holds for the pollen tube length reaching 38.68 μm in the putative hybrid, 31.39 μm in J. communis var. communis and 28.08 μm in J. sibirica. At the taxa level, the above given data were statistically highly significant in both pollen viability characteristics. Highest viability of J. communis var. intermedia pollen does not corroborate the widespread notion postulating reduced fertility of the plant interspecific hybrids. Additional tests are suggested to verify the hybrid nature of the putative hybrid population using DNA based population study and artificial crossing experiments involving the putative parental species J. communis var. communis and J. sibirica.

The study investigates the population structure, hybridization, and adaptation of Juniperus communis sensu lato in the context of recent habitat fragmentation across Europe, using inter-Primer Binding Site (iPBS) markers and needle morphometry. Three operational taxonomic units, all native to Slovakia, are analyzed: J. communis ssp. communis, J. communis ssp. nana, and their putative hybrid, J. communis ssp. communis var. intermedia. The results show a moderate overall structure (𝛷𝑃𝑇=0.115, 𝑝=0.001), indicating high gene flow within ssp. communis and low gene flow between ssp. communis and ssp. nana. However, the inter-subspecies differentiation dropped significantly after correcting for non-neutral loci, which implies adaptive divergence despite substantial gene flow. This conclusion is further supported by admixture regression and 𝛷𝑃𝑇-𝑄𝑆𝑇 comparison. In needle morphometry, we find genetic differentiation by selection to be relatively important compared to phenotypic plasticity. This can be highly relevant for conservation measures due to the risk of outbreeding depression. Finally, we identify var. intermedia as the hybrid of the two subspecies, suggesting it as an evolutionary significant unit.

The genetic structures of the four putative hybrid swarms of Pinus sylvestris × P. mugo in Slovakia were analyzed in terms of individual admixture proportions calculated via inter-primer binding site (iPBS) marker loci. This work aimed to reevaluate the hybrid swarms’ differentiation status as postulated in the previous studies at both population and genomic levels. The study confirmed intermediate divergence of each of the swarms examined. Based on 80-loci hybrid index scores, we have revealed the presence of introgressive and intermediate hybrids with frequencies corresponding to differentiation estimates. Surprisingly, irrespective of individual phenotypes, the most frequent intermediates were found in Sucha Hora (29.5%) and Obsivanka (28.6%) populations, which resemble rather pure P. mugo and were previously considered as bimodal hybrid zones with a negligible amount of hybrids. The remaining hybrid zone population Zuberec seems to be highly introgressed to P. sylvestris, while Tisovnica is clearly inclined to P. mugo. The results and different methodologies are discussed.

Generally acknowledged reduction of the interspecific hybrid fertility was utilized in evaluation of the putative hybrid swarms of Scots pine (Pinus sylvestris L.) and mountain dwarf pine (P. mugo Turra) viability under field conditions. Pollen viability and seed quality of the trees from the four contact zones of P. syl­vestris and P. mugo in Slovakia were compared with the corres­ponding characteristics of the pure populations of these spe­cies from three reference localities. Pollen germination percentage was comparable in contact zones and control populations of the species. Statistically significant differences between the parent and hybrid groups were detected in pollen tube length only. In general, pollen tubes of the pure species populations were longer than those in contact zones. At the cone level, the individuals from contact zones possessed shor­ter cones than the trees of pure species populations P. mugo and P. sylvestris. This was paralleled by a lower number of seeds per cone in contact zones and higher amount of seeds per cone in the P. mugo population. Striking differences between individuals of the contact zones and reference populations were revealed also in germination potentials of their seeds. Significantly higher proportions of germinating seeds was found in the reference populations of P. mugo and P. sylvestris than in their contact zones. Contrary to seed quality parame­ters mentioned above, the fractions of filled but non-germina­ting seeds and amounts of empty seeds were higher in contact zones than in the parental species populations, indicating hig­her frequency occurrence of abortive embryogenesis in the former. The lower fertility characteristics of the individuals from contact zones indicate their hybrid nature.