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).