A new study published in Genome Biology and Evolution reveals that the annulated sea snake has evolved to perceive a wider range of colors than its ancestors. Early snakes lost their color vision during their adaptation to dim-light burrowing lifestyles, but sea snakes, which inhabit brighter marine environments, have regained color vision.
The study focused on the annulated sea snake, a venomous snake found in ocean waters around Australia and Asia. Color vision in animals is primarily determined by genes called visual opsins. While there have been multiple losses of opsin genes during the evolution of tetrapods, the emergence of new opsin genes is extremely rare.
Before this study, the only known evolution of new opsin genes within reptiles appeared to have occurred in species of Helicops, a snake genus found in South America. However, the researchers used published reference genomes to examine visual opsins in five ecologically distinct species of elapid snakes, which include cobras, mambas, and the annulated sea snake.
They found that the annulated sea snake possesses four intact copies of the opsin gene SWS1, two of which have evolved a new sensitivity to longer wavelengths dominant in ocean habitats. This adaptation potentially enables sea snakes to better distinguish predators, prey, or potential mates against colorful marine backgrounds.
The re-emergence of color vision in sea snakes is in stark contrast to the evolution of opsins in mammals like bats, dolphins, and whales. These mammals experienced further opsin losses as they adapted to dim-light and aquatic environments.
Isaac Rossetto, the lead author of the study, explains, “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 brighter and more spectrally-complex marine environments. We believe that recent gene duplications have dramatically expanded the range of colors sea snakes can see. For reference, us humans have a similarly expanded sensitivity to colors, while cats and dogs are partially color-blind much like those early snakes.”
The findings of this study shed light on the unique evolution of color vision in vertebrates and how different species adapt to their diverse environments. This research was conducted by a team of scientists from various institutions, including Oxford University Press USA.