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Keywords:

  • Chloroplast microsatellites;
  • conservation;
  • genetic clusters;
  • haplotype sharing;
  • historical demography;
  • hybridization;
  • Pinus mugo complex;
  • Pinus sylvestris;
  • post-glacial recolonization;
  • western Europe

Abstract

Aim  Our aims were to test whether morphological species of mountain pines were genetically supported in the western part of the distribution range of the Pinus mugo species complex (Pinus mugo Turra sensu lato), to resolve genetically homogeneous clusters of populations, to determine historical demographic processes, and to assess the potential hybridization of mountain pines with Scots pine, Pinus sylvestris L.

Location  Populations were sampled in the Iberian System, the Pyrenees, the French Mont Ventoux, Vosges and Jura mountains, the German Black Forest and throughout the Alps. This corresponded to a range-wide sampling for mountain pine sensu stricto (Pinus uncinata Ram.) and to a sampling of the western parts of the ranges of dwarf mountain pine (Pinus mugo Turra sensu stricto) and bog pine/peatbog pine [Pinus rotundata Link/Pinus × pseudopumilio (Willk.) Beck].

Methods  In total, 786 individuals of Pmugo sensu lato from 29 natural populations, and 85 individuals of Psylvestris from four natural populations were genotyped at three chloroplast microsatellites (cpSSRs). Populations were characterized for standard genetic diversity statistics and signs of demographic expansion. Genetic structure was explored using analysis of molecular variance, differentiation statistics and Bayesian analysis of population structure (BAPS).

Results  One hundred haplotypes were identified in Pmugo sensu lato. There was a stronger differentiation between geographical regions than between morphologically identified taxa (P. mugo sensu stricto, Puncinata and Protundata/P. ×pseudopumilio). Overall genetic differentiation was weak (GST = 0.070) and displayed a clear phylogeographic structure [NST = 0.263, NST > NST (permuted), P < 0.001]. BAPS identified a Pyrenean and an Alpine gene pool, along with several smaller genetic clusters corresponding to peripheral populations.

Main conclusions  The core regions of the Pyrenees and Alps were probably recolonized, respectively by Puncinata and Puncinata/Pmugo sensu stricto, from multiple glacial refugia that were well connected by pollen flow within the mountain chains. Pinus rotundata/P. × pseudopumilio populations from the Black Forest, Vosges and Jura mountains were probably recolonized from various glacial populations that kept their genetic distinctiveness despite late glacial and early Holocene expansion. Marginal Puncinata populations from the Iberian System are compatible with elevational shifts and long-term isolation. The causes of haplotype sharing between Pmugo sensu lato and Psylvestris require further research.