Genomic differentiation and conservation relevance of isolated marginal Primula farinosa populations in Central-Eastern Europe.

INTRODUCTION: Quaternary climatic oscillations produced heterogeneous range dynamics in European cold-adapted plants. Primula farinosa L. has been discussed in the context of the interglacial expansion model for moisture-demanding cold-adapted species. However, it remains unclear whether isolated low-elevation populations in Central European calcareous fens and wet meadows represent long-term relicts or recently established populations.

METHODS: We used RADseq-derived SNPs from four sampling localities in the Balaton Region of Hungary and one low-elevation comparative locality at Lipce in the Julian Alps, Slovenia, to assess population-genomic structure, differentiation, allelic diversity and demographic history. Population structure was analyzed using SNP-based maximum-likelihood tree inference, PCA, model-based ancestry clustering and pairwise FST estimates. We further quantified rarefied allelic richness and private allelic variation and performed exploratory population-specific historical effective population-size trajectories from folded site-frequency spectra.

RESULTS: Population structure analyses revealed pronounced differentiation between Lipce and the Hungarian samples. Within Hungary, the two neighbouring localities of Lesencetomaj and Tapolca were nearly indistinguishable, whereas Köveskál and Nemeshany populations showed stronger differentiation and reduced allelic diversity. Rarefied allelic richness was highest in Lipce and Lesence and lowest in Nemeshany, with Köveskál only slightly richer. Collectively, the Balaton Region carried a distinct allelic pattern and comparable rarified richness at the broader regional scale. Demographic reconstructions suggested population-specific effective population-size changes over recent to Late-Glacial timescales, although older intervals were weakly resolved and exact timing was uncertain.

DISCUSSION: Low-elevation Primula farinosa populations in Hungary and Slovenia are strongly differentiated, and this isolation is unlikely to be explained solely by recent anthropogenic wetland fragmentation. The higher rarefied allelic richness of Lipce and Lesence suggests that these populations retain less-eroded genetic variation, whereas the depauperate allelic profiles of Köveskál and especially Nemeshany are consistent with recent founder effects, bottlenecks, strong drift or long-term small effective population size. These findings indicate that the Balaton Region populations represent a conservation-relevant and regionally differentiated component of P. farinosa genomic diversity. Although the exact timing and historical origin of their isolation remain unresolved, the observed genomic pattern is compatible with, but does not demonstrate, long-term regional persistence, including a possible Late Glacial refugial scenario.