Comparative Phylogeography of Castanea Species

摘要

The genus Castanea consists of seven species that are disjunctly distributed in Asia, Europe and North America. Phylogenetic analysis of Castanea using DNA sequence data from six variable regions of the chloroplast genome indicated migration of extant Castanea species from Asia westward to Europe and North America. Cycles of Pleistocene glaciation and environmental events like the spread of chestnut blight were major determinants of historical migration and current genetic diversity in North American Castanea species. Chloroplast and nuclear sequence information revealed two lineages within American chestnut (C. dentata), one which is closely related to Allegheny chinkapin (C. pumila var. pumila) haplotypes from the southern Appalachian region, indicative of hybridization in refuge zones. The other American chestnut lineage expanded in northerly direction following the Last Glacial Maximum, and was accompanied by a gradual loss of diversity. Ozark chinkapins (C. pumila var. Ozarkensis) show high sequence homology with the most frequently occurring Allegheny chinkapin haplotype from Virginia and North Carolina. Ancestral Allegheny chinkapin haplotypes can be detected in populations along the Gulf Coast, while haplotypes in Virginia share regions of the chloroplast genome with Ozark and ancestral haplotypes, suggesting multiple colonization routes and suture zones of chloroplast lineages in the Appalachian Mountains. This knowledge will be useful for development of conservation management strategies and successful reintroduction of blight resistant American chestnut into the Appalachian mountain ecosystem.