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 subgroup sister species, including D. santomea, the newly discovered endemic from São Tomé island. The evolutionary divergence of these genes is of special interest as it is suspected to result from physiological evolution via gene duplication. This paper describes the relationship between the geographical origin of the various strains and the patterns of mating and phylogeny, focusing on the evolution of D. santomea and its relationship to other species and their niches. The Amyrel and Amy data indicate that, contrary to expectations, the sympatric insular D. yakuba population is less closely related to D. santomea than allopatric mainland ones, suggesting that the extant insular D. yakuba population on São Tomé results from a recent secondary colonization. Data for sympatric and allopatric D. yakuba suggest that D. santomea arose from a mainland D. yakuba parental stock when montane habitats of the Cameroon volcanic line extended to lower altitudes during colder and less humid periods. Despite their different modes of evolution and different functions, the Amyrel and Amy genes provide remarkably consistent topologies and hence reflect the same history, that of the species.