The Drosophilidae Associated with Tropical African Figs.

In the tropical African region the entire drosophilid genus Lissoceplzala and Drosophila $mu species group have evolved a close association with endemic figs (Ficus spp., Moraceae). We previously described the biology of a few of these figdependent drosophilids (Lachaise, 1977). We report here on a further investigation in evergreen rainforests, mainly in western Africa, that has yielded information bearing on 19 fig species harboring 35 figbreeding drosophilids. The information shows that these fig-dependent drosophilids represent a major evolutionary pathway of the tropical African drosophilid fauna. Small chalcidoid Hymenoptera of the family Agaonidae are absolutely necessary for fig pollination. There are about 900 species of figs in the Old and New World tropics and, with only very rare exceptions where strict specificity appears to break down (Wiebes, 1979), there is clear evidence of a one-to-one relationship between species of fig and wasp (Wiebes, 1963, 1966; Ramirez, 1970). As White (1978) says “It seems impossible to avoid the conclusion that the speciation of Ficus and of the agaonid has been concomitant, i.e., that each incipient species of Ficus has evolved in parallel with an incipient species of wasp.” The possible parallel evolution of some African drosophilids with the figlwasp system is of particular interest. The life histories of figs form the object of an abundant literature. Detailed synthetic articles include Wiebes (1977, 1979), Galil (1977), Janzen ( 1 9 7 9 ~ ) and Valdeyron and Lloyd (1979). A summary of the major facts needed for understanding the biology of fig drosophilids follows.