Genetic and developmental origins of a unique foraging adaptation in a Lake Malawi cichlid genus

Significance Biologists have long been captivated by novel traits because they provide insights into both the origin of and constraints on morphological variation. The iconic adaptive radiations of cichlid fishes have led to incredible diversity of form, including some species with an exaggerated snout. This novelty is mechanically integrated with the upper jaw, appears to be under directional selection, and is found in one of the most ecologically successful cichlid lineages. We used protein manipulation, gene expression, and genetic mapping to implicate the Tgfβ pathway in the development of this unusual trait. Given the functions of Tgfβ signaling in tissue proliferation, migration, invasion, and organ fibrosis, this represents an example of the cooption of existing pathways in the evolution of novelty.