Chloroplast DNA phylogeography suggests a West African centre of origin for the baobab, Adansonia digitata L. (Bombacoideae, Malvaceae)

Abstract

The African baobab (Adansonia digitata L.) is an emblematic, culturally important, and physically huge tropical tree species whose natural geographical distribution comprises most of tropical Africa, but also small patches of southern Arabia, and several Atlantic and Indian Ocean islands surrounding the African continent, notably including Madagascar. We analysed the polymerase chain reaction-restriction fragment length polymorphism of five chloroplast DNA fragments obtained from 344 individuals of A. digitata collected from 74 populations covering the entire extant distribution range of the species. Our goal was to reconstruct the phylogeographical history of the species and, if possible, to identify its centre of origin, which has been a subject of controversy for many decades. We identified five haplotypes whose distribution is clearly geographically structured. Using several species of Adansonia and of closely related genera as outgroups, the haplotypes showed a clear phylogeographical pattern of three groups. Two are phylogenetically related to the outgroup taxa, and are distributed in West Africa. The third group is substantially more differentiated genetically from outgroup species, and it corresponds to southern and eastern Africa, Arabia and the Indian Ocean islands, including Madagascar. According to our results, the tetraploid A. digitata, or its diploid progenitor, probably originated in West Africa and migrated subsequently throughout the tropical parts of that continent, and beyond, by natural and human-mediated terrestrial and overseas dispersal.

Baobabs on Kubu Island, Botswana – A dendrochronological multi-parameter study using ring width and stable isotopes (δ13C, δ18O)

“…With their enormous size and their distinctive and often bizarre appearance, the African baobabs have attracted the attention of many researchers of various disciplines (adanson 1759;livinGstone 1868;poCk tsy et al 2009;riedel et al 2012). The species are geographically distributed in (semi-)arid and partly semi-humid tropical Africa south the Sahara (wiCkens 1979;Fig.…”

Endophytes as potential pathogens of the baobab species Adansonia gregorii: a focus on the Botryosphaeriaceae

“…Beard (1990) outlined the "floatation" hypothesis; seed pods of the "proto-baobab" floated across the Indian Ocean from Madagascar, landed on the NW coast of Australia and were then successful in germinating and establishing in this area. Leong Pock et al (2009) hypothesised that an ancestor of Adansonia migrated from the neotropics to West Africa, where seed pods germinated and that anthropogenic movement spread this species to Madagascar and Australia, indicating the centre of origin to be Africa, not Madagascar. Current work (J.…”

Three new <I>Graphium</I> species from baobab trees in South Africa and Madagascar

“…These results suggest that these fungi have some degree of host or substrate specificity. In a recent study, Pock Tsy et al (2009) showed that baobab trees probably originated in West Africa and subsequently spread to other parts of the world where they speciated. The similarity in fungi isolated from different tree species on separate land masses, raises intriguing questions regarding the movement of fungi between these areas.…”