Convergent phenotypic evolution of the visual system via different molecular routes: How Neotropical cichlid fishes adapt to novel light environments

How predictable is evolution? This remains a fundamental but contested issue in evolutionary biology.When independent lineagescolonize the same environment, we are presented with a natural experiment that allows us to ask if genetic and ecologicaldifferences promote species-specific evolutionary outcomes or whether species phenotypically evolve in a convergent mannerin response to shared selection pressures. If so, are the molecular mechanisms underlying phenotypic convergence the same?In Nicaragua, seven species of cichlid fishes concurrently colonized two novel photic environments. Hence, their visual systemrepresents a compelling model to address these questions, particularly since the adaptive value of phenotypic changes is wellunderstood.By analyzing retinal transcriptomes, we found that differential expression of genes responsible for color vision (coneopsins and cyp27c1) produced rapid and mostly convergent changes of predicted visual sensitivities. Notably, these changesoccurred in the same direction in all species although there were differences in underlying gene expression patterns illustratingnonconvergence at the molecular level. Adaptive phenotypes evolved deterministically, even when species differ substantially inecology and genetic variation. This provides strong evidence that phenotypic evolution of the visual system occurred in responseto similar selective forces of the photic environment.KEY WORDS: Color vision, crater lake, cyp27c1, molecular