Interspecific Hybridization Can Generate Functional Novelty in Cichlid Fish

The role of interspecific hybridization in evolution is still being debated. Interspecific hybridization has been suggested to facilitate the evolution of ecological novelty, and hence the invasion of new niches and adaptive radiation when ecological opportunity is present beyond the parental species niches. On the other hand, hybrids between two ecologically divergent species may perform less well than parental species in their respective niches because hybrids would be intermediate in performance in both niches. The evolutionary consequences of hybridization may hence be context-dependent, depending on whether ecological opportunities, beyond those of the parental species, do or do not exist. Surprisingly, these complementary predictions may never have been tested in the same experiment in animals. To do so, we investigate if hybrids between ecologically distinct cichlid species perform less well than the parental species when feeding on food either parent is adapted to, and if the same hybrids perform better than their parents when feeding on food none of the species are adapted to. We generated two first-generation hybrid crosses between species of African cichlids. In feeding efficiency experiments we measured the performance of hybrids and parental species on food types representing both parental species niches and additional 'novel' niches, not used by either of the parental species but by other species in the African cichlid radiations. We found that hybrids can have higher feeding efficiencies on the 'novel' food types but typically have lower efficiencies on parental food types when compared to parental species. This suggests that hybridization can generate functional variation that can be of ecological relevance allowing the access to resources outside of either parental species niche. Hence, we provide support for the hypothesis of ecological context-dependency of the evolutionary impact of interspecific hybridization.