Nothofagus species merge and diverge in complex landscapes

PREMOLI, A. C.; ACOSTA M. C.; MATHIASEN, P.

Bento Gonçalves, Rio Grande do Sul, Brazil

Simposio; IV Brazilian Symposium on Plant Molecular Genetics; 2013

Sociedade Brasileira de Genética

Forest landscapes of Patagonia have suffered from large-scale modifications such as a presence of physical barriers that have affected patterns of gene flow of tree species. This is in addition to changes in climate and environmental heterogeneity that produced ecologically divergent selective forces in sympatric taxa. Subgenus Nothofagus is restricted to temperate areas of South America. It consists of five tree species, with distinct life histories traits, most of which are regionally widespread. Species of subgenus Nothofagus are dominant tree taxa in all forest types. They are morphologically and ecologically distinct, although pollen undistinguishable. Even though they grow under contrasting environmental settings they produce hybrids in sympatry or after disturbance. We used nuclear and chloroplast DNA (cpDNA) sequences in combination with molecular dating methods to analyze patterns of among- and within-species divergence throughout their entire range in the southern Andes. Phylogenetic analyses yielded widespread nuclear and chloroplast discordance. Whereas nuclear DNA depicted phylogenetic relationships, chloroplast DNA yielded a shared geographic structure significantly controlled by geology. Concordant cpDNA was due to ancient hybridization and repeated chloroplast capture. Paleobasins and marine transgressions that occurred during the late Tertiary produced long-lasting vicariant events while pre-Miocene massifs functioned as land-dispersal corridors. Hybridization and introgression facilitated long-distance pollen dispersal followed by a selective regime favoring each ecologically-distinct Nothofagus. Adaptive divergence in the absence of complete reproductive barriers in spatial and temporally heterogeneous environments of Patagonia acted as reassurance for long-term species? persistence.