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Oaks ( Quercus, Fagaceae) are the dominant tree genus of North America in species number and biomass, and Mexico is a global center of oak diversity. Understanding the origins of oak diversity is key to understanding biodiversity of northern temperate forests., A phylogenetic study of biogeography, niche evolution and diversification patterns in Quercus was performed using 300 samples, 146 species. Next-generation sequencing data were generated using the restriction-site associated DNA ( RAD-seq) method. A time-calibrated maximum likelihood phylogeny was inferred and analyzed with bioclimatic, soils, and leaf habit data to reconstruct the biogeographic and evolutionary history of the American oaks., Our highly resolved phylogeny demonstrates sympatric parallel diversification in climatic niche, leaf habit, and diversification rates. The two major American oak clades arose in what is now the boreal zone and radiated, in parallel, from eastern North America into Mexico and Central America., Oaks adapted rapidly to niche transitions. The Mexican oaks are particularly numerous, not because Mexico is a center of origin, but because of high rates of lineage diversification associated with high rates of evolution along moisture gradients and between the evergreen and deciduous leaf habits. Sympatric parallel diversification in the oaks has shaped the diversity of North American forests. [ABSTRACT FROM AUTHOR]

The article provides information on some aspects of the genus Quercus or Mexican oak, including its taxonomy, diversity, distribution, and ecology. It indicates that the genus Quercus is a woody plant found in the Northern Hemisphere and has 500 species worldwide and more than 200 in the Americas. It claims that Mexico has the greatest wealth of species of the genus Quercus because of the prominence of its physical geography.

We tested the effects of hybridization and introgression on the levels of leaf fluctuating asymmetry (FA) in a hybrid zone between Quercus magnoliifolia and Quercus resinosa at the Tequila volcano, Jalisco state, Mexico, in which the species are distributed along an altitudinal gradient ranging from 1400 to 2100 m. Bayesian clustering analysis was performed with STRUCTURE on data for eight nuclear microsatellite loci to assign individuals from reference populations and from the hybrid zone to pure or hybrid genotypic classes. To test the performance of the assignment procedure and to determine optimal thresholds for genetic assignment pure, hybrid and backcrossed genotypes were simulated (from the allelic frequencies found in real pure populations of the two species) and reanalyzed with STRUCTURE. Leaf FA and morphological identification of parental and hybrid individuals were obtained using geometric morphometric techniques. We found genetic and morphological evidence of a hybrid zone by secondary contact at the Tequila volcano. The genotypes and phenotypes were significantly correlated with altitude along the mountain, but no correlation between them was found. FA was higher in F1 hybrids and backcrossed genotypes than in pure species. Levels of FA were more correlated with the proportion of genetic ancestry of each individual than with leaf morphology or altitude, supporting the hypothesis that hybridization is associated with development instability potentially caused by disruption of coadapted gene complexes characteristic of each species. [ABSTRACT FROM AUTHOR]