Résumé
Aim: Phylogeography of fruit trees is challenging due to the recurrent
exchanges between domesticated and wild populations. Here we tested the
eastern refugium hypothesis (ERH) for the carob tree, Ceratonia siliqua,
which supports its natural and domestication origins in the Eastern
Mediterranean and a feral origin in the West. Location: Mediterranean
basin Taxon: Ceratonia siliqua L., Leguminosae Methods: Divergence time of
the divergence between the carob tree and its sister species (C.
oreothauma) was estimated based on two nuclear and one plastid sequences.
Variation from four plastid regions and 17 nuclear microsatellite loci
were used to decipher genetic structure in the carob tree and to test
coalescent-based models by an Approximate Bayesian Computation (ABC)
approach. We assessed our hypotheses by examining palaeobotanical records
and hindcasting the past distribution of the carob tree at the
Mid-Holocene, Last Glacial Maximum (LGM) and Last Interglacial (LIG) using
species distribution modelling (SDM). Results: The split between C.
oreothauma and C. siliqua was estimated at 6.4 Ma, and a first divergence
within C. siliqua at 1.3 Ma. After a presence since the Oligocene,
Ceratonia was found in the Western and the Eastern Mediterranean in the
fossil records during the Pleistocene. Plastid and nuclear markers,
characterized by low allelic richness, revealed a strong west-east genetic
structuring. Approximate Bayesian computation (ABC) analyses rejected the
ERH. Main conclusions: Our study supports a severe population decline
during LIG. The strong west-east divergence and the occurrence of four
lineages within C. siliqua provided support for a new hypothesis of
multiple domestications of the carob tree from native populations
throughout the Mediterranean basin.