Visual opsin gene expression evolution in the adaptive radiation of cichlid fishes of Lake Tanganyika

Tuning the visual sensory system to the ambient light is essential for
survival in many animal species. This is often achieved through
duplication, functional diversification, and/or differential expression of
visual opsin genes. Here, we examined 753 new retinal transcriptomes from
112 species of cichlid fishes from Lake Tanganyika to unravel adaptive
changes in gene expression at the macro-evolutionary and ecosystem level
of one of the largest vertebrate adaptive radiations. We found that,
across the radiation, all seven cone opsins – but not the rhodopsin – rank
among the most differentially expressed genes in the retina, together with
other vision-, circadian-rhythm-, and haemoglobin-related genes. We
propose two new visual palettes characteristic of very shallow- and
deep-water living species, respectively, and show that visual system
adaptations along two major ecological axes, macro-habitat and diet, occur
primarily via gene expression variation in a subset of cone opsin genes.