Oscillation Maintains Polymorphisms — a Model of Lateral Asymmetry in Two Competing Scale-eating Cichlids

Scale-eating cichlids in Lake Tanganyika exhibit lateral asymmetry polymorphism in their mouth-opening. Frequency of left- and right-handed phenotypes oscillates around unity. In the southern shore of the lake, two scale-eaters coexist in similar densities, where their oscillation synchronize. This phenomena is analysed by a time delay differential equation model, and new mechanisms which maintains polymorphism is discovered. In a wide range of parameters, the oscillation keeps the frequencies of the same phenotype in the two species at a similar level, and prevents the fixation of one phenotype in either species.