Adaptive radiation in the Afrotropical region of the Paleotropical genus Lissocephala (Drosophilidae) on the pantropical genus Ficus (Moraceae)

Of sixty-three extant genera of Drosophilidae, the genus Lissocephala is unique in having produced a diverse radiation superimposed on a plant-insect mutualism. Lissocephala is basically Paleotropical, with twenty-three Afrotropical and eight Oriental and Australasian species, and seemingly the adaptive radiation occurred on a taxonomically restricted group of host-plants, species of Ficus (Moraceae), solely in the African floristic region. A paradox results from the consideration that only the African radiation is linked with a strict diversification on Ficus species, even though this host plant genus is more diverse in the Oriental region. The focus of the present work is to document the diversity of host-figs exploited by Lissocephala in the African mainland (twenty-two fig species have yielded twenty-three Lissocephala species, but similarities in numbers between insects and plants does not seemingly result from species specificity), and to show that the clear-cut divide between the two African strictly fig-breeding Lissocephala lineages (the juncta and sanu groups) observed from male terminalia is further supported on the basis of 28S nuclear DNA divergence. Evolutionary scenarios are discussed whereby the two African Lissocephala lineages might have diverged on the African mainland or arisen independently from Oriental ancestors. Although the possibility remains that the juncta and sanu lineages set foot independently on the African mainland, it is more likely that there was a single colonization event for a common juncta—sanu ancestor. A stepwise host-fig transfer would then have occurred on the African mainland. The African Lissocephala ancestor would have first spread among the Sycomorus figs and only secondarily among the Galoglychia figs.