Résumé
Genetic diversity of contemporary domesticated species is shaped by both
natural and human-driven processes. However, until now, little is known
about how domestication has imprinted the variation of fruit tree species.
In this study, we reconstruct the recent evolutionary history of the
domesticated almond tree, Prunus dulcis, around the Mediterranean Basin,
using a combination of nuclear and chloroplast microsatellites (i.e. SSRs)
to investigate patterns of genetic diversity. Whereas conservative
chloroplast SSRs show a widespread haplotype and rare locally distributed
variants, nuclear SSRs show a pattern of isolation by distance with clines
of diversity from the East to the West of the Mediterranean basin, while
Bayesian genetic clustering reveals a substantial longitudinal genetic
structure. Both kinds of markers thus support a single domestication
event, in the eastern side of Mediterranean basin. In addition,
model-based estimation of the timing of genetic divergence among those
clusters is estimated sometime during the late Holocene, a result that is
compatible with human-mediated dispersal of almonds out of its center of
origin. Still, the detection of region-specific alleles suggests that gene
flow from relictual wild pre-glacial populations (in North Africa) or from
wild counterparts (in the Near-East) could account for a fraction of the
diversity observed.