Positive selection of the long-wavelength opsin gene in South American cichlid fishes

Cichlid fishes use their vision for recognition of other fishes, feeding, and in habitat selection. Neotropical cichlids can be found in a range of different habitats differing in their light regimes, and therefore it is interesting to determine if this is associated with molecular variation of genes responsible for expressing visual pigments. Here, we studied codon variation of the LWS gene in cichlids from South America, and compared it with the variation among species from the African Great Lakes. Partial fragments of this gene were sequenced, including spectral tuning sites. There were notable differences in codons under selection between Neotropical and African cichlids, with Neotropical species exhibiting an overall higher genetic variation than African species, but weaker positive selection. This study provides novel data that contributes to our understanding of the evolution of the visual system in Neotropical cichlids.