title: Rethinking the history of common walnut (Juglans regia L.) in Europe: Its origins and human interactions.
abstract: Common walnut (Juglans regia L) is an economically important species cultivated worldwide for its high-quality wood and nuts. It is generally accepted that after the last glaciation J. regia survived and grew in almost completely isolated stands in Asia, and that ancient humans dispersed walnuts across Asia and into new habitats via trade and cultural expansion. The history of walnut in Europe is a matter of debate, however. In this study, we estimated the genetic diversity and structure of 91 Eurasian walnut populations using 14 neutral microsatellites. By integrating fossil pollen, cultural, and historical data with population genetics, and approximate Bayesian analysis, we reconstructed the demographic history of walnut and its routes of dispersal across Europe. The genetic data confirmed the presence of walnut in glacial refugia in the Balkans and western Europe. We conclude that human-mediated admixture between Anatolian and Balkan walnut germplasm started in the Early Bronze Age, and between western Europe and the Balkans in eastern Europe during the Roman Empire. A population size expansion and subsequent decline in northeastern and western Europe was detected in the last five centuries. The actual distribution of walnut in Europe resulted from the combined effects of expansion/contraction from multiple refugia after the Last Glacial Maximum and its human exploitation over the last 5,000 years.
authors.affiliation: Institute of Agro-environmental and Forest Biology, National Research Council, Porano, Terni, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Pollegioni
authors.affiliation: 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.
authors.forename: Keith
authors.initials: K
authors.lastname: Woeste
authors.affiliation: Institute of Agro-environmental and Forest Biology, National Research Council, Porano, Terni, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Chiocchini
authors.affiliation: The Institute of Archaeological and Monumental Heritage, National Research Council, Tito Scalo, Potenza, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Del Lungo
authors.affiliation: Institute of Agro-environmental and Forest Biology, National Research Council, Porano, Terni, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Ciolfi
authors.affiliation: Institute of Agro-environmental and Forest Biology, National Research Council, Porano, Terni, Italy.
authors.forename: Irene
authors.initials: I
authors.lastname: Olimpieri
authors.affiliation: Institute of Agro-environmental and Forest Biology, National Research Council, Porano, Terni, Italy.
authors.forename: Virginia
authors.initials: V
authors.lastname: Tortolano
authors.affiliation: Earth Trust, Little Wittenham, Abingdon, Oxfordshire, United Kingdom.
authors.forename: Jo
authors.initials: J
authors.lastname: Clark
authors.affiliation: Sylva Foundation, Little Wittenham, Oxfordshire, United Kingdom.
authors.forename: Gabriel E
authors.initials: GE
authors.lastname: Hemery
authors.affiliation: Institute of Agricultural Biology and Biotechnology, National Research Council, Milan, Italy.
authors.forename: Sergio
authors.initials: S
authors.lastname: Mapelli
authors.affiliation: Institute of Agro-environmental and Forest Biology, National Research Council, Porano, Terni, Italy.
authors.forename: Maria Emilia
authors.initials: ME
authors.lastname: Malvolti
mesh_terms: D001208:Asia; D063368:Balkan Peninsula; D005060:Europe; D005580:Fossils; D014644:Genetic Variation; D005828:Genetics, Population / Q000266:history / Q000379:methods; D049690:History, Ancient; D006801:Humans; D031324:Juglans / Q000235:genetics* / Q000254:growth & development; D018895:Microsatellite Repeats / Q000235:genetics*; D011058:Pollen / Q000235:genetics