The sea snake’s vision evolved to regain color

An international team of scientists researching the genetic history of sea snakes has found that the species has improved their color vision in response to living in a brighter and more colorful marine environment.

“Our research has found that the annulated sea snake has four intact copies of the opsin SWS1 gene,” said PhD candidate Isaac Rossetto, from the University of Adelaide’s School of Biological Sciences who led the research.

“Two of these genes have ancestral ultraviolet sensitivity, and two of the genes have developed new sensitivities to the longer wavelengths that dominate oceanic habitats.

“The earliest snakes lost much of their ability to see color due to their dim-light burrowing lifestyle.

“However, their sea snake descendants now occupy a much brighter and spectrally complex marine environment. We believe that recent gene duplication has dramatically expanded the range of colors sea snakes can see.”

The team examined published reference genomes to examine the visual opsin gene in five ecologically distinct species of elapids. They looked at gene data from Hydrophis cyanocinctus, or the annulated sea snake, a species of venomous snake found in tropical and subtropical regions of Australia and Asia.

The team included scientists from the University of Adelaide, University of Plymouth and the Vietnam Academy of Science and Technology. They published their findings in a journal Genome Biology and Evolution.

Many animals have lost opsin throughout their lineage history as they have adapted to new habitats, but it is rare to see an opsin gain.

“Humans have a similar sensitivity to color, while cats and dogs are partially color blind like early snakes,” said Mr Rossetto.

“It is quite unique and interesting that these snakes appear to have obtained and diversified their opsin, when other land-to-sea transition animals do the opposite.”

“Basically, there’s only been one other case in reptiles that we think this has occurred.”

The newly acquired color vision opsin has also been noted in the semi-aquatic Helicopter snake.

Evidence of color vision in hydrophilic snake was first published in 2020, but this new research shows that it is the result of gene duplication, not gene polymorphism. This means that extended color vision is more common among species than previously thought.

“With polymorphism it’s a bit of a lottery – only a few individuals have a wider range of color sensitivity. But now we know that there are many aberrant copies of the gene, so color vision is expected to be seen in all members of this species,” said Rossetto.