Conclusions
We showed that repeated origin of sympatric ecomorphs differing in lip size within the East African Labeobarbus provides a nice example for studying ecological speciation. The six pairs of sympatric ecomorphs that have been equally divergent in phenotype (thick-lipped vs. common lips) were at various stages of ecological and genetic differentiation. This example of ecological speciation represents a continuum from polymorphism in phenotype via trophic resource partitioning (with various strengths) to genetic divergence. This assumedly starts as an intra-population strategy to broaden the food spectrum via temporally/seasonally differential niche. However, in some circumstances, polymorphism in lip size may be a major contributor to trophic shift and consequently to divergent selection and ecological speciation, for example in the Didessa River (see also example from cichlids - Elmer et al., 2010).