Sea snakes may have undergone an evolutionary change that restored their ability to perceive colors, according to a recent study published in Genome Biology and Evolution by Oxford University Press.
The research focused on the annulated sea snake, a venomous species found in the waters around Australia and Asia, and revealed that it has developed an extended range of color vision as a response to environmental shifts.
Color vision in animals is primarily influenced by visual opsins, a set of genes responsible for this sensory capability. While the loss of opsin genes has been observed in the evolutionary history of tetrapods (which include amphibians, reptiles, and mammals), the emergence of new opsin genes is exceedingly rare. Until now, the only known instance of new opsin gene evolution in reptiles was found in certain species of Helicops, a snake genus from South America.
To investigate the molecular evolution of vision genes, the study utilized previously published reference genomes and examined visual opsins in five distinct species of elapid snakes, a snake family that encompasses cobras, mambas, and the annulated sea snake. This family provides an excellent opportunity to study the evolution of vision genes due to the varying ecological backgrounds of its members.
Early snakes lost two visual opsin genes during their phase of burrowing in dim-light conditions, resulting in limited color perception. However, some of their descendants have since adapted to brighter environments, with two lineages even transitioning from terrestrial to marine habitats over the past 25 million years.
Researchers discovered that the annulated sea snake possesses four intact copies of the opsin gene SWS1. Two of these genes retained the ancestral ultraviolet sensitivity, while the other two have evolved to detect longer wavelengths, which are prevalent in oceanic habitats.
The team speculates that this newfound sensitivity enables sea snakes to discern colors more effectively, aiding them in differentiating predators, prey, and potential mates against the vibrant marine backgrounds.
This evolutionary pattern stands in stark contrast to that of mammals such as bats, dolphins, and whales, which experienced further opsin losses during their adaptation to dim-light and aquatic environments.
Isaac Rossetto, the lead author of the study, explained, “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.”
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