In an evolutionary rarity, sea snakes may have regained lost color vision
Most snakes can only see the colors blue and green, along with ultraviolet light in some cases. New research, however, suggests that sea snakes have evolved to actually regain the wider-color vision of their earliest ancestors.
Snakes evolved from lizards, which scientists believe could see in full color. Because those early snakes adopted a low-light burrowing lifestyle, however, they lost that ability over time. That said, they did develop a sensitivity to ultraviolet light, which helped them to see in the dark.
When some snakes took to life in bright, shallow ocean waters, color vision became useful again. Among other things, it could help them them pick out prey, predators and potential mates against multi-colored backgrounds.
In order to see if the snakes did regain color vision, scientists from The University of Adelaide, The University of Plymouth and The Vietnamese Academy of Science and Technology analyzed the previously published genomes of five ecologically distinct species of snakes. All of the snakes were members of the elapid family.
It was found that one species, the annulated sea snake (Hydrophis cyanocinctus) is unique in that it has four copies of a gene known as opsin SWS1, instead of the usual two. Opsin SWS1 is responsible for the different types of visual pigments that allow vertebrates to perceive different wavelengths of light.
"Two of these genes have the ancestral ultraviolet sensitivity, and two have evolved a new sensitivity to the longer wavelengths that dominate ocean habitats," said University of Adelaide PhD candidate Isaac Rossetto. "We believe that recent gene duplications have dramatically expanded the range of colors sea snakes can see."
The scientists additionally state that while it's not uncommon for animals to lose opsin genes throughout the course of evolution, it is very rare for them to gain new ones – or in this case, perhaps previously used ones.
The research is described in a paper that was recently published in the journal Genome Biology and Evolution.