Experimental evidence for adaptive phenotypic plasticity in a rock-dwelling cichlid fish from Lake Victoria

We demonstrate adaptive phenotypic plasticity (PP) in Neochromis greenwoodi, a rock-dwelling haplochromine cichlid from Lake Victoria. Adaptive phenotypic plasticity will enhance the chance of survival and reproduction in changing or novel environments. For rock-dwelling cichlids it may contribute to the success of settlement after migration between rocky outcrops or islands, since newly colonized patches of rock may offer different food regimes and different competitors. In our experiments, we simulated such situations by raising fry on different diets and with different competitors. We chose diet treatments in such a way that we could predict the direction of anatomical changes from functional demands. We expected an indirect effect of interspecific competition: selectively removing one prey-type by the competing species would leave N. greenwoodi with the other. We found the predicted phenotypic responses to food in trophic traits of N. greenwoodi. However, in the current experimental set-up we did not find a differentiating effect of species of competitor. We discuss the possible role of PP in allopatric and sympatric speciation.