It forms prostrate mats on exposed mountain slopes and ridges and produces creeping stems with the capacity of rooting, and thereby, clonal growth personal observations. Fragmentation of plant material and re-rooting further down the slope increases the probability of its survival in a harsh and unstable environment. In the present study, we investigated the spatial genetic structure of the Alpine endemic woody plant, S.
So far, most studies dedicated to alpine or subalpine calcicolous species has been focused on the herbaceous plants e. Stehlik et al.
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Alpine zones are important areas of global biodiversity because they host a high diversity of cold-adapted specialists, including many endemic species. Nevertheless, global warming is expected to cause an upward shifting of plant species in the high mountain systems and, consequently, the habitats available for the alpine and nival plants may be significantly limited leading to extinction of some of them Rangwala and Miller ; Steinbauer et al. Thus, population genetic data gained for alpine species may be useful not only in determining historical events but also in predicting the ability of taxa to respond to current climate change.
In this study, genetic analyses were used with the aim of answering the following questions: 1 What is the pattern of geographic distribution of the genetic diversity of S. Initially, a total of 30 nSSRs markers originally designed for Salix sp. Barker et al. Tuskan et al. Amplification was conducted according to the thermal profile presented in Tuskan et al. Genotypes were scored manually using GeneMapper 4.
Raw2Gen software I. Chybicki, Kazimierz Wielki University, Poland, unpubl. Deviation from Hardy—Weinberg equilibrium was tested using an exact test implemented in GenePop v. The multilocus parameters of genetic diversity for populations, including average number of alleles A , private alleles per population P A , average number of effective alleles A E , allelic richness A R , expected heterozygosity H E , observed heterozygosity H O and inbreeding coefficient F IS were estimated using GenAlEx v.
The analysis was run with , MCMC cycles, with every th cycle sampled and a burn-in of 50, Finally, pairwise population comparisons based on F ST were performed in Arlequin v. Evidence of a recent bottleneck was evaluated using the M -ratio method Garza and Williamson implemented in INEst 2. The M -ratio value is expected to be lower in populations that have experienced a bottleneck than in populations in mutation-drift equilibrium Garza and Williamson The analysis was run under the two-phase mutation model TPM with the proportion of multi-step mutations pg set as 0.
The reduction in the M -ratio was verified by comparing the mean observed M -ratio M to the simulated M -ratio generated under mutation-drift equilibrium MReq. To evaluate the significance of a deficiency in the M -ratio, the Wilcoxon signed-rank test based on coalescent simulations consisting of 10 6 iterations was applied. Haplotypes were defined as unique combinations of size variants across the cpSSRs.
The analysis was performed based on a non-spatial admixture model with correlated allele frequencies without prior information of population location. The optimal number of K clusters was used with the clustering of groups option in which populations with known coordinates are used as clustering units. After the testing stage, an analysis was run for ten replicates of K ranging between 1 and To evaluate the effect of past and present climatic conditions on the geographic range of S. The climatic information available in the WorldClim database Hijmans et al.
To construct the models for the current species range, 19 bioclimatic variables were used at a 30 arc-sec resolution Hijmans et al. Analyses were performed as a bootstrap with 10 replicates.
The maximum number of iterations was set to 10, and the convergence threshold to 0. To evaluate the model accuracy, the receiver operating characteristic ROC curve and value of area under the curve AUC were used.
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An AUC value close to 0. The list of species occurrence records that was used to model the range of S. Detailed information on the polymorphisms of the nSSR loci that were used in this study is presented in Online Resource 1. In total, alleles were identified among individuals at ten nSSR loci. Null alleles were detected in all loci, with an average frequency approaching 0. The population pairwise F ST ranged from 0. MR the mean observed M -ratio, MReq the M -ratio generated under mutation-drift equilibrium, p value probability of significant test for the deficiency in M -ratio based on Wilcoxon signed-ranks test.
We did not find a similar correlation for the cpSSR dataset.
Refugial areas as explained in Fig. Some geographic pattern of differentiation corresponding to the main regions of the Alps was detected Fig. The most easterly situated populations 11 and 2 were mostly assigned to cluster I and they were the most distinct from the rest of the populations. In particular, population 11 from the Central Eastern Alps the Sarntal Alps showed only limited overlap with the gene pools of other inferred clusters.
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Only populations 3 and 14 from this group presented high admixture with other gene pools. Interestingly, the most northerly located population 9 the Glarus Alps showed a genetic mixture of the western and eastern alpine gene pools cluster I and III, respectively Fig. Considering the major cluster only, some geographic specificity appeared and indicated the distinctiveness of the populations from the Western and Eastern Alps. However, both the western and eastern distribution domains were inhabited with populations showing a large intermixing of a few clusters that occurred in those areas Fig.
Interestingly, in some populations, there were individuals that represented exclusive BAPS clusters, which were not detected elsewhere. Especially, the monotypic population 6 and the polytypic populations 7 and 8, all three from the inner part of the massif, were characterized by unique genetic structure. In populations 7 and 8 some individuals formed own clusters, while the remaining ones were grouped into clusters found in the Western and Eastern Alps populations 7 and 8, respectively. MaxEnt-modelled geographic distributions under a current, and b Last Glacial Maximum climate conditions.
Our study shows that S. However, the number of size variants that were obtained from the three cpSSR loci in S. According to M -ratio, five populations 3, 5, 7, 8 and 11 experienced a bottleneck effect. Generally, detection of demographic decline with M -ratio indicates that the bottleneck lasted several generations and population has recovered Williamson-Natesan In the case of S.
As purely stochastic process, bottleneck leads to long-term reduction of effective population sizes. Consequently, it results in loss of allelic and gene diversity and may distort the inter-population differentiation pattern. The genetic barriers among populations detected using nSSRs correspond roughly to the general division of the genetic diversity of Alpine biota into four groups encompassing the South-Western, Western, Central and Eastern Alps Schmitt Less pronounced yet still noticeable was the division into two parts that agrees with the genetic division assuming the western and eastern domain Thiel-Egenter et al.
Specifically, the homogenization of the diversity among populations at the Western Alps was apparent in which a single cluster predominated cluster II ; only populations 1 and 3 from this group displayed considerable admixture from other gene pools cluster I. Slightly more differentiation and admixing were visible in populations from the eastern part of the Alps. Cluster III prevailed in the most easterly located populations 11 and 12, possibly indicating a south-eastern or even eastern colonization route Fig.
However, denser sampling in the Eastern Alps would be highly recommended to make clear inferences about eastern Alpine refugia and their contribution in recolonization.
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Many high-alpine species show clear edaphic limitations that may determine the possibility of survival and the genetic structure Alvarez et al. Siliceous substrate dominates mainly in the inner Alps, which were covered with ice sheets during the glaciation period Kelly et al. Consequently, wider possibilities for refugial persistence are predicted for calcicolous plants such as S.
The south-western periphery of the Alps remained largely free of ice during the Pleistocene and was characterized by suitable calcareous habitats Ehlers and Gibbard ; Naciri and Gaudeul This part of the Alps is frequently described as a refugial area for numerous herbaceous plant e. Gaudeul et al. With considerable support, this part of the Alps was indicated by MaxEnt as the main area of S.
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Interestingly, MaxEnt indicated also more southerly located the Apuan Alps in the Northern Apennines as a potential area of the species survival of the glacial period, but there is no additional evidence in support of this possibility, therefore, the niche modelling can be here an artefact. Moreover, the applied model was based on bioclimatic variables without considering the other important factors affecting the distribution of species, such as substrate type or orographic complexity.
The genetic analysis also revealed a significant structure among the populations inhabiting the south-western part of the Alps, especially in the cpSSRs. Specifically, population 1 located in the Maritime Alps was characterized with a distinct genetic makeup that was confirmed by both marker systems nSSRs and cpSSRs , and this may be expected due to its long-term isolation. A founder effect or long-term in situ persistence under isolation could result in the genetic impoverishment of population 1. However, which of those two processes was responsible for the reduction in genetic diversity cannot be fully explained with our genetic data.
The genetic diversity was above average in most of the populations from this region that is one of the indicators of refugial status. Population 12 the Dolomites , in particular, was characterized by the highest average number of alleles, private alleles and expected heterozygosity.
This population, along with population 14, belongs to the area of southern-alpine peripheral refugium between Lake Como and the Dolomites, where many other species probably survived during the LGM e. Interestingly, population 9 from the Glarus Alps refers to the eastern-alpine populations. It is located in the Western Alps near the border with the Eastern Alps , but more northerly and closer to putative northern alpine peripheral refugia. This population was second in terms of genetic diversity. Nevertheless, regarding S.
Conversely, their genetic distance and structure were rather close, suggesting considerable postglacial gene flow in this longitudinal direction. Nevertheless, it is acknowledged to be an important glacial refugium for many high-mountain plants e.
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