Chloroplast DNA variation in a rainforest tree (Aucoumea klaineana, Burseraceae) in Gabon

One of the dominant savannah colonists in Gabon is Aucoumea klaineana or Ok oume (Burseraceae), an endemic species which belongs to a monotypic genus. Chloroplast DNA (cpDNA) variation was studied in this species by means of P CR amplification of 40 kb of cpDNA sequences, followed by restriction analy sis of the resulting fragments. No insertion/deletion events were noted, an d a single point mutation was found. The level of differentiation among the 19 populations studied was relatively low (G(ST) = 0.54) compared to other plant species (mean of 0.76), in agreement with the pioneer status of the species. However, cpDNA diversity was geographically structured, with the l ess frequent haplotype occurring only in populations from southern Gabon. T his distribution might suggest either that there were two ancient source po pulations of Okoume, one in the north and the other in the south, from whic h the colonizing process of the savannah began after the last ice age, or a lternatively that there was one polymorphic source in the south. The low le vel of cpDNA diversity could indicate that Okoume populations in these refu gia were quite small.