Phylogeography of two hybridizing southern beeches (Nothofagus spp.) with different adaptive abilities

CAROLINA SOLIANI; LEONARDO GALLO; PAULA MARCHELLI

TREE GENETICS & GENOMES

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2012 vol. 8 p. 659 - 673

1614-2942

In phylogenetically related plant species, hybrid-ization can influence their current genetic structure. Long-lasting hybridization may be related to persistence in sharedglacial refugia, where the differential abilities of eachspecies to survive could have provided adaptations tochanging environmental conditions. In temperate SouthAmerican forests at the Patagonia region, the pattern ofQuaternary glaciations offered several opportunities forrefuge. At mid-latitudes (42° to 44° S), particular topo-graphic characteristics determined different glaciation pat-terns, defining the existence of a transitional zone. Westudied two widespread Nothofagus species (Nothofaguspumilio, Nothofagus antarctica) characterized by contrast-ing plasticity. We screened 40 coupled populations withthree cpDNA markers and found 14 different haplotypes.Both species presented significant phylogeographic struc-ture (NST≥GST, p>0.001), with two geographically segre-gated lineages (north?south). A latitudinal cline in thedistribution of genetic diversity was determined, with mostvariable populations in the north (35°?41° S). Populationdiversity diminished to southern latitudes, but a particularsituation occurs between 42°S and 44°S. The transitionzone, a putative refuge area, presented unique haplotypes.The more plastic species, N. antarctica, probably persistedin more refuge areas, which could be reflected in its higherlevels of diversity. In these species, sympatric distributionexplains introgression (IG>IGe), but the differential levelsof haplotype sharing between N. pumilio and N. antarcticaat population level are relevant to the understanding ofphylogeographic patterns. Hybridization may have facili-tated recruitment in the onset of postglacial colonization bymiddle to long-distance pollen dispersal. In the currentscenario of climate change, the presence of hybrids withdifferent plastic responses is of remarkable importance.