Molecular evolution of vision-related genes may contribute to marsupial photic niche adaptations

Vision plays an essential role in the life of many animals. While most mammals are night-active (nocturnal), many have adapted to novel light environments. This includes diurnal (day-active) and crepuscular (twilight-active) species. Here, we used integrative approaches to investigate the molecular evolution of 112 vision-related genes across 19 marsupial genomes representing most marsupial orders. We found that four genes (<em>GUCA1B</em>, <em>GUCY2F</em>, <em>RGR</em>, and <em>SWS2</em>) involved in retinal phototransduction likely became functionally redundant in the ancestor of marsupials, a group of largely obligate nocturnal mammals. We also show evidence of rapid evolution and positive selection of bright-light vision genes in the common ancestor of <em>Macropus</em> (kangaroos, wallaroos, and wallabies). <em>Macropus</em>-specific amino acid substitutionsin opsin genes (<em>LWS</em> and <em>SWS1</em>), in particular, may be an adaptation for crepuscular vision in this genus via opsin spectral sensitivity tuning. Our study set the stage for functional genetics studies and provides a stepping-stone to future research efforts that fully capture the visual repertoire of marsupials.