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PDF, English - main document Download (46MB) | Lizenz: Living on the edge - the evolutionary history, edaphic adaptations and conservation prospects of the Cheddar Pink, Dianthus gratianopolitanus by Schöne, Alexandra Katharina underlies the terms of Creative Commons Attribution-NonCommercial-NoDerivatives 4.0

Abstract

The Cheddar Pink (Dianthus gratianopolitanus Vill., Caryophyllaceae) is an endangered, herbaceous perennial native to Central Europe, currently facing population decline. To understand its evolutionary history and biogeographic patterns, we sampled 130 populations and 1705 individuals across its entire distribution range, from southern France to Poland and the British Isles and used nuclear AFLP data, maternally inherited plastid haplotype variation, whole plastome sequence information, and cytological data.

The absence of spatial genetic variation, the high rate of mixed plastid haplotypes, and the lack of spatial structure in the plastome tree suggest postglacial gene flow, favoring a scenario of once widespread distribution with secondary fragmentation. While AFLP data revealed a genetic division between southern and northern groups, plastid haplotype variation did not show clear biogeographic patterns but did highlight southwestern richness. Differences in bedrock type, calcareous in the south and siliceous in the north, coincide with AFLP groupings, suggesting edaphic factors may influence the differentiation and adaptation of D. gratianopolitanus. Genetic and cytological data strongly support the existence of refugia in southern France: Although clear evidence for a northern German/Czech refugium is lacking, the survival of now-extinct small populations in western Germany near Belgium, with subsequent expansion, is a possibility. A third genetic group in Baden-Württemberg, located in the contact zone between northern and southern groups, might result from survival in unknown refugia or represent a melting pot scenario. The colonization of the British Isles likely originated from French populations, specifically from the (Pre-)Alps, expanding through Belgium and into the Isles, as supported by genetic assignment and plastid haplotypes.

To further investigate local adaptations, cuttings of D. gratianopolitanus from both calcareous and siliceous regions were cultivated and used in a reciprocal transplant experiment in the Botanical Garden in Heidelberg. After one year of growth on triassic shell limestone, porphyry, and serpentine soils, fitness parameters and leaf elemental composition were assessed. Additionally, flowering time and behavior were recorded for individuals from the entire distribution range, as well as D. gratianopolitanus subsp. moravicus cultivated in the Botanical Garden in 2022 and 2023, respectively. While the results revealed only small adaptations in elemental uptake they indicated that plants from calcareous bedrock invested more in vegetative growth, potentially enhancing vegetative reproduction and competitiveness on restricted limestone outcrops. In contrast, plants from siliceous origins exhibited higher flowering rates, promoting gene flow and faster colonization in more open habitats. Although a trend towards earlier flowering between 2013 and 2022/23 was observed, higher early spring and summer temperatures alone likely do not suffice to trigger the earlier flowering.

In addition, eleven metapopulations originating from both calcareous and siliceous regions were analyzed using nuclear AFLP data and plastid haplotypes. The genetic structuring revealed varying patterns of connectivity and degrees of isolation, that could indicate either recent gene flow or remnants of past connections. Ecological niche modeling under current and future climate scenarios revealed that southern populations are more affected by drought stress, while northern populations are limited by minimum temperatures. The siliceous group displayed a broader climatic niche, while the more specialized calcareous group might be more vulnerable to climate change. Although current climatic conditions predict a wider suitable area than presently occupied, future scenarios indicate a significant reduction in suitable habitats, with a trend towards higher elevations and northern migrations. These findings underscore the need for conservation strategies that target all subpopulations, preserve genetic variation, and potentially re-establish dispersal routes to ensure the survival of this species.