Multilocus data reveal deep phylogenetic relationships and intercontinental biogeography of the Eurasian-North American genus Corylus (Betulaceae).

The evolutionary history of the genus Corylus, a tertiary disjunct lineage consisting of approximately 15-20 taxa with New and Old World distribution, has not been fully studied using molecular tools. In this research, we reconstructed comprehensive phylogenies of this genus using multiple datasets (genome-wide SNPs; complete chloroplast genomes; and nuclear ribosomal ITS sequences) based on detailed sampling of 17 Corylus species currently recognized. Divergence times were estimated using a fossil calibrated relaxed clock model, and ancestral area reconstruction were inferred using Bayesian binary MCMC (BBM) method and the dispersal-extinction-cladogenesis (DEC) model. Phylogenetic incongruences were detected from datasets, with nuclear SNP and ITS phylogenies supporting four major clades that correspond well with morphological traits, while chloroplast phylogeny revealed geographic partitioning. Recombination and introgressive hybridization played important roles in Corylus diversification. Molecular dating and biogeographical analyses unambiguously revealed that Corylus originated in Southwest China during the middle Eocene. The westward migration of Phyllochlamys (Clade C) and Colurnae (Clade D) and the uplift of Qinghai-Tibet Plateau drove the formation of European taxa, whereas the transoccanic migration crossing the Bering Land Bridge of Siphonochlamys (Clade B) and Phyllochlamys (Clade C) led to the occurrence of North American taxa. The topographic heterogeneity and climatic oscillations from Miocene to Pleistocene made East Asia the diversity center for Corylus. This study offers important insights into the phylogenetic relationships and biogeography history of the genus Corylus.
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