The demographic history of Castanea sativa Mill. in southwest Europe: A natural population structure modified by translocations.

Abstract

In domesticated species, translocation of materials can alter natural demographic patterns; this may have occurred in Castanea sativa (European chestnut), a species conserved in several refuges, with a long domestication history for nut production. Bayesian analysis of population genetic structure in marginal areas and in the centre of C.sativa range, considering spatial information and making corrections for unbalanced size, allowed visualization of a genetic structure that was subsequently analysed by approximate Bayesian computation to assess its natural demographic history and test the origin of some hypothetical translocated germplasm. We obtained evidence of C.sativa population contraction during the earliest Pleistocene, resulting in a split into eastern (Greek) and western (Italian and Iberian) populations. The northern Iberian population, in the Eurosiberian area, is one of the vestiges that remained after the contraction that split the global Tertiary population. A secondary encounter, occurred from Middle to Upper Pleistocene, which explains the hybrid origin of the Western Mediterranean population present in Italy and in the centre and south of the Iberian Peninsula. It has been demonstrated that a germplasm translocation from Italy to the Central Iberian Range may have occurred. Recent translocations have hybridized with the local northern Iberian population, producing naturalized populations with high diversity. The populations of C.sativa in southwestern Europe have a genetic structure compatible with a natural origin, in which signs of population contractions and expansions caused by climatic oscillations since the Late Miocene have been imprinted.