Glacial history of Saxifragawahlenbergii (Saxifragaceae) in the context of refugial areas in the Western Carpathians

Abstract

Despite the wealth of data available for mountain phylogeography, local-scale studies focused on narrow endemic species remain rare. Yet, knowledge of the genetic structure of such species biogeographically linked to a restricted area is of particular importance to understand the history of the local flora and its diversity patterns. Here, we aim to contribute to the phylogeographical overview of the Western Carpathians with a genetic study of Saxifragawahlenbergii, one of the most characteristic endemic species of this region. We sampled populations from all discrete parts of the species' distribution range to apply sequencing of selected non-coding cpDNA and nuclear ribosomal DNA (ITS) regions, as well as Amplified Fragment Length Polymorphism (AFLP) fingerprinting. First, while ITS sequences showed weak diversification, the genetic structure based on cpDNA sequences revealed two well-differentiated groups of haplotypes. One of them is restricted to the main center of the distribution range in the Tatra Mountains (Mts), while the second group included a series of closely related haplotypes, which in most cases were unique for particular isolated groups of populations in peripheral mountain ranges and in the south-eastern part of the Tatra Mts. AFLP fingerprinting also revealed a pattern of divergence among populations, while only partly corroborating the division observed in cpDNA. Taking into account all the data, the pattern of genetic structure, supported by the high levels of unique genetic markers in populations, may reflect the historical isolation of populations in several local refugia during the last glacial period. Not only the center of the range in the Tatra Mts, but also other, neighboring massifs (Malá Fatra, Nízke Tatry, Chočské vrchy, Muránska planina), where populations are characterized by separate plastid DNA haplotypes, could have acted as separate refugia.

Keywords: AFLP; Tatra Mts; haplotype; high mountain plant; narrow endemic; phylogeography; refugial areas.

Figure 1.

Location of studied populations of Saxifragawahlenbergii and their genetic variability based on DNA sequence data A distribution of 11 populations of S.wahlenbergii and haplotypes and ribotypes in the populations B haplotype network based on the combined chloroplast regions: rps16-trnK and rpl32-trnL C ribotype network based on ITS region. Networks obtained from TCS based on a 95% connection limit. The relative sizes of circles in networks are proportional to haplotype and ribotype frequencies. For population acronyms see Table 1.

Figure 2.

MrBayes tree based on the combined plastid rps16–trnK and rpl32–trnL regions of Saxifragawahlenbergii (reduced dataset; see text for details). Numbers at nodes, in the order shown, correspond to posterior probabilities estimated in MrBayes. For population acronyms see Table 1.

Figure 3.

Phylogeographic structure within of Saxifragawahlenbergii based on AFLP dataset (55 individuals from 10 populations) A Principal Component Analysis diagram, ordination at 1 vs 2 vs 3 axes B Neighbor-Net diagram with the bootstrap values derived from an analysis of 2,000 replicates above 50% has been given. Both diagrams were prepared based on the Nei-Li coefficient. For population acronyms see Table 1.

Figure 4.

A The histograms representing the assignment of 55 individuals of Saxifragawahlenbergii to different clusters by Bayesian spatial clustering (STRUCTURE software). Each vertical bar corresponds to an individual, highlighted in gray for clarity, contrasting with the cluster assignments, respectively, at K = 2 and K = 3 B in P(Data) values in function of K are shown. For population acronyms see Table 1.