The Pyrenees as a cradle of plant diversity: phylogeny, phylogeography and niche modeling of Saxifraga longifolia

The current distribution of most species results from ecological niche, past distribution, and migrations during glacial-interglacial periods and in situ evolution. Here, we disentangle the colonization history of Saxifraga longifolia Lapeyr., a limestone plant abundant in the Pyrenees and rare in other Iberian mountains and the African Atlas. Our working hypothesis is that the current distribution results from the shrinkage of a more extensive distribution in previous cold periods. We sampled 160 individuals of 32 populations across the whole distribution range and sequenced four DNA regions (rpl32-trnL, rps16-trnQ, trnS-trnG, and ITS). Ecological conditions were modeled to identify factors promoting high genetic diversity and long-term persistence areas for S. longifolia. In addition, we inferred phylogenetic relationships, phylogeographic divergence, genetic diversity, and migration routes. Seven plastid haplotypes were found, of which six occur in the Pyrenees and one in the High Atlas (Morocco). Discrete phylogeographic analysis (DPA) estimated migration routes predominantly from the Pyrenees to the other areas. Colonization events to those areas appear to have taken place recently given that the rest of the Iberian mountains do not harbor exclusive haplotypes. Iberian-Northern African distribution was inferred to be the result of long-distance dispersal because the split between Iberian and High Atlas haplotypes is estimated to have taken place in the last 4 million years ago when the Strait of Gibraltar was already open. Migrations from the Pyrenees to the south may have been favored by a corridor of predominant limestone rocks along Eastern Iberia, followed by successful overcoming the Strait of Gibraltar to reach northern Africa.