Cones mediate vision in daylight (photopic vision) and color vision, while rods mediate vision in dim light (scotopic vision). Cones and rods are the photoreceptors of the retina. Visual perception in mammals is initiated by phototransduction, which converts light into an electrical signal in photoreceptor cells by signal transduction ( Lamb, 2013). It follows that vision impacts animal fitness by affecting survivorship through mating, foraging, and predator avoidance behaviors. Examples of diurnal species (∼20% of mammals) include primates and squirrels. These species inhabit poor light environments underwater (e.g., aquatic cetaceans), underground (e.g., mole rats), or in caves (e.g., bats) ( Heesy and Hall, 2010 Bennie et al., 2014). In order to adapt to different light environments, they have activity patterns classified as nocturnal (night-active), diurnal (day-active), crepuscular (twilight-active), or non-circadian ( Smale et al., 2003).Īpproximately, two-thirds of mammals (including their ancestors) are nocturnal. Mammals occupy a variety of light niches. 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.Įxtant mammals include eutherians (placental mammals), metatherians (marsupials), and monotremes (egg-laying mammals). Macropus-specific amino acid substitutions in opsin genes ( LWS and SWS1), in particular, may be an adaptation for crepuscular vision in this genus via opsin spectral sensitivity tuning. We also show evidence of rapid evolution and positive selection of bright-light vision genes in the common ancestor of Macropus (kangaroos, wallaroos, and wallabies). We found that four genes ( GUCA1B, GUCY2F, RGR, and SWS2) involved in retinal phototransduction likely became functionally redundant in the ancestor of marsupials, a group of largely obligate nocturnal mammals. Here, we used integrative approaches to investigate the molecular evolution of 112 vision-related genes across 19 genomes representing most marsupial orders. This includes diurnal (day-active) and crepuscular (twilight-active) species. While most mammals are night-active (nocturnal), many have adapted to novel light environments. Vision plays an essential role in the life of many animals.
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