Divergence between Drosophila santomea and allopatric or sympatric populations of D. yakuba using paralogous amylase genes and migration scenarios along the Cameroon volcanic line

We have used two paralogous genes (Amyrel and Amy) of the amylase multigene family to reconstruct the phylogeny of the nine Drosophila melanogaster su bgroup sister species, including D. santomea, the newly discovered endemic from Sao Tome island. The evolutionary divergence of these genes is of spec ial interest as it is suspected to result from physiological evolution via gene duplication. This paper describes the relationship between the geograp hical origin of the various strains and the patterns of mating and phylogen y, focusing on the evolution of D. santomea and its relationship to other s pecies and their niches. The Amyrel and Amy data indicate that, contrary to expectations, the sympatric insular D. yakuba population is less closely r elated to D. santomea than allopatric mainland ones, suggesting that the ex tant insular D. yakuba population on Sao Tome results from a recent seconda ry colonization. Data for sympatric and allopatric D. yakuba suggest that D . santomea arose from a mainland D. yakuba parental stock when montane habi tats of the Cameroon volcanic line extended to lower altitudes during colde r and less humid periods. Despite their different modes of evolution and di fferent functions, the Amyrel and Amy genes provide remarkably consistent t opologies and hence reflect the same history, that of the species.