Sexually active male haplochromine cichlid fishes possess pronounced yellow ovoid spots on the anal fm, which mimic eggs of the female and have therefore been called egg dummies (Wickler, 1962b).It is thought that divergence in egg dummy characteristics can considerably reduce gene flow and in this way may trigger off reproductive isolation. Two ways in which egg dummy divergence can develop are described. Both mechanisms may have been operating, at the same time and in the same area, in different species, (...) or possibly even in a single species. (shrink)