Adaptive radiation in the Afrotropical region of the Paleotropical genusLissocephala(Drosophilidae) on the pantropical genusFicus(Moraceae)

Abstract.Of sixty‐three extant genera of Drosophilidae, the genusLissocephalais unique in having produced a diverse radiation superimposed on a plant‐insect mutualism.Lissocephalais 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 ofFicus(Moraceae), solely in the African floristic region. A paradox results from the consideration that only the African radiation is linked with a strict diversification onFicusspecies, 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 byLissocephalain the African mainland (twenty‐two fig species have yielded twenty‐threeLissocephalaspecies, 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‐breedingLissocephalalineages (thejunctaandsanugroups) observed from male terminalia is further supported on the basis of 28S nuclear DNA divergence. Evolutionary scenarios are discussed whereby the two AfricanLissocephalalineages might have diverged on the African mainland or arisen independently from Oriental ancestors. Although the possibility remains that thejunctaandsanulineages set foot independently on the African mainland, it is more likely that there was a single colonization event for a commonjuncta—sanuancestor. A stepwise host‐fig transfer would then have occurred on the African mainland. The AfricanLissocephalaancestor would have first spread among theSycomorusfigs and only secondarily among theGaloglychiafigs.