Résumé
The history of sweet potato in the Pacific has long been an enigma.
Archaeological, linguistic and ethnobotanical data suggest that
prehistoric human-mediated dispersal events contributed to the
distribution in Oceania of this American domesticate. According to the
“tripartite hypothesis”, sweet potato was introduced into Oceania from
South America in pre-Columbian times, and was then later newly introduced,
and diffused widely across the Pacific, by Europeans via two historically
documented routes from Mexico and the Caribbean. Although sweet potato is
the most convincing example of putative pre-Columbian connections between
human occupants of Polynesia and South America, the search for genetic
evidence of pre-Columbian dispersal of sweet potato into Oceania has been
inconclusive. Our study attempts to fill this gap. Using complementary
sets of markers (chloroplast and nuclear microsatellites), and both modern
and herbarium samples, we test the tripartite hypothesis. Our results
provide strong support for prehistoric transfer(s) of sweet potato from
South America (Peru-Ecuador region) into Polynesia. Our results also
document a temporal shift in the pattern of distribution of genetic
variation in sweet potato in Oceania. Later re-introductions, accompanied
by recombination between distinct sweet potato genepools, have reshuffled
the crop’s initial genetic base, obscuring primary patterns of diffusion
and at the same time giving rise to an impressive number of local
variants. Moreover, our study shows that phenotypes, names and neutral
genes do not necessarily share completely parallel evolutionary histories.
Multidisciplinary approaches thus appear necessary for accurate
reconstruction of the intertwined histories of plants and humans.