CHLOROPLAST DNA PHYLOGEOGRAPHY OF THE ARGAN TREE OF MOROCCO

Polymorphisms in the chloroplast genome of the argan tree (Sapotaceae) , an endemic species of south-western Morocco, have been detected by r estriction site studies of PCR-amplified fragments. A total of 12 chlo roplast DNA (cpDNA) and two mitochondrial DNA (mtDNA) fragments were a mplified and digested with a single restriction enzyme (HinfI). Polymo rphisms were identified in six of the cpDNA fragments, whereas no mtDN A polymorphisms were detected in a survey of 95 individuals from 19 po pulations encompassing most of the natural range of the species. The c pDNA polymorphisms allowed the identification of 11 haplotypes. Two li neages, one in the south-east and the other in the north-west, divide the range of the argan tree into two distinct areas. The level of gene tic differentiation measured at the haplotype level (G(STc) = 0.60) (i .e. with unordered haplotypes) was smaller than when phylogenetic rela tionships were taken into account (N-STc = 0.71-0.74) (ordered haploty pes), indicating that population history must be considered in the stu dy of the geographical distribution of cpDNA lineages in this species. If contrasted with the level of nuclear genetic differentiation measu red in a previous study with isozymes (G(STn) = 0.25), the results ind icate a relatively high level of gene flow by seeds, or conversely a r elatively low level of gene flow by pollen, as compared with other tre e species. Goats and camels could have played an important role in dis seminating the fruits of this tree.