Ancient Humans Influenced the Current Spatial Genetic Structure of Common Walnut Populations in Asia.
Common walnut (Juglans regia L) is an economically important species cultivated worldwide for its wood and nuts. It is generally accepted that J. regia survived and grew spontaneously in almost completely isolated stands in its Asian native range after the Last Glacial Maximum. Despite its natural geographic isolation, J. regia evolved over many centuries under the influence of human management and exploitation. We evaluated the hypothesis that the current distribution of natural genetic resources of common walnut in Asia is, at least in part, the product of ancient anthropogenic dispersal, human cultural interactions, and afforestation. Genetic analysis combined with ethno-linguistic and historical data indicated that ancient trade routes such as the Persian Royal Road and Silk Road enabled long-distance dispersal of J. regia from Iran and Trans-Caucasus to Central Asia, and from Western to Eastern China. Ancient commerce also disrupted the local spatial genetic structure of autochthonous walnut populations between Tashkent and Samarkand (Central-Eastern Uzbekistan), where the northern and central routes of the Northern Silk Road converged. A significant association between ancient language phyla and the genetic structure of walnut populations is reported even after adjustment for geographic distances that could have affected both walnut gene flow and human commerce over the centuries. Beyond the economic importance of common walnut, our study delineates an alternative approach for understanding how the genetic resources of long-lived perennial tree species may be affected by the interaction of geography and human history.
Institute of Agro-environmental and Forest Biology, National Research Council, Porano, Terni, Italy.
Paola
P
Pollegioni
U.S.D.A. Forest Service, Hardwood Tree Improvement and Regeneration Center, Department of Forestry and Natural Resources, Purdue University, West Lafayette, Indiana, United States of America.
Keith E
KE
Woeste
Institute of Agro-environmental and Forest Biology, National Research Council, Porano, Terni, Italy.
Francesca
F
Chiocchini
The Institute of Archaeological and Monumental Heritage, National Research Council, Tito Scalo, Potenza, Italy.
Stefano
S
Del Lungo
Institute of Agro-environmental and Forest Biology, National Research Council, Porano, Terni, Italy.
Irene
I
Olimpieri
Institute of Agro-environmental and Forest Biology, National Research Council, Porano, Terni, Italy.
Virginia
V
Tortolano
Earth Trust, Little Wittenham, Abingdon, Oxfordshire, United Kingdom.
Jo
J
Clark
Sylva Foundation, Little Wittenham, Oxfordshire, United Kingdom.
Gabriel E
GE
Hemery
Institute of Agricultural Biology and Biotechnology, National Research Council, Milan, Italy.
Sergio
S
Mapelli
Institute of Agro-environmental and Forest Biology, National Research Council, Porano, Terni, Italy.
Maria Emilia
ME
Malvolti
D001208:Asia; D051456:Gene Flow / Q000235:genetics; D005843:Geography; D006801:Humans; D031324:Juglans / Q000235:genetics*; D009754:Nuts / Q000235:genetics*; D014197:Trees / Q000235:genetics