Summary: A new study reveals 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, regained color vision.
Two out of four intact copies of the snake’s opsin gene SWS1 evolved a new sensitivity to longer wavelengths dominant in ocean habitats, enabling better color discrimination.
The annulated sea snake possesses four intact copies of the opsin gene SWS1, two of which have evolved a new sensitivity to longer wavelengths.
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 contrasts the evolution of opsins in mammals like bats, dolphins, and whales, which experienced further opsin losses adapting to dim-light and aquatic environments.
Source: Oxford University Press USA
A new paper in Genome Biology and Evolution finds that the annulated sea snake, a species of venomous snake found in ocean waters around Australia and Asia, appears to have evolved to see an extended palette of colors after its ancestors lost that ability in response to changing environments.
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 group including amphibians, reptiles, and mammals), the emergence of new opsin genes is extremely rare.
Before this study, the only evolution of new opsin genes within reptiles appeared to have occurred in species of Helicops, a genus of snake from South America.
This study used published reference genomes to examine visual opsin genes across five ecologically distinct species of elapid snakes.
The history of elapids, a family of snakes that includes cobras and mambas in addition to the annulated sea snake, presents an opportunity to investigate the molecular evolution of vision genes.
Early snakes had lost two visual opsin genes during their dim-light burrowing phase and could only perceive a very limited range of colors.
However, some of their descendants now occupy brighter environments; two elapid lineages have even moved from terrestrial to marine environments within the last 25 million years.
Researchers here found that the annulated sea snake possesses four intact copies of the opsin gene SWS1. Two of these genes have the ancestral ultraviolet sensitivity, and two have evolved a new sensitivity to the longer wavelengths that dominate ocean habitats.
The study’s authors believe that this sensitivity may provide the snakes with better color discrimination to distinguish predators, prey and/or potential mates against colorful marine backgrounds.
This is dramatically different from the evolution of opsins in mammals like bats, dolphins, and whales during ecological transitions; they experienced further opsin losses as they adapted to dim-light and aquatic environments.
“The earliest snakes lost much of their ability to see color due to their dim-light burrowing lifestyle,” said the paper’s lead author Isaac Rossetto.
“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.”
About this visual neuroscience and genetics research news
Functional Duplication of the Short-Wavelength-Sensitive Opsin in Sea Snakes: Evidence for Reexpanded Colour Sensitivity Following Ancestral Regression
Color vision is mediated by ancient and spectrally distinct cone opsins. Yet, while there have been multiple losses of opsin genes during the evolution of tetrapods, evidence for opsin gains via functional duplication is extremely scarce.
Previous studies have shown that some secondarily marine elapid snakes have acquired expanded “UV–blue” sensitivity via changes at key spectral tuning amino acid sites of the Short-Wavelength Opsin 1 (SWS1) gene.
Here, we use elapid reference genomes to show that the molecular origin of this adaptation involved repeated, proximal duplications of the SWS1 gene in the fully marine Hydrophis cyanocinctus. This species possesses four intact SWS1 genes; two of these genes have the ancestral UV sensitivity, and two have a derived sensitivity to the longer wavelengths that dominate marine habitats.
We suggest that this remarkable expansion of the opsin repertoire of sea snakes functionally compensates for the ancestral losses of two middle-wavelength opsins in the earliest (dim-light adapted) snakes. This provides a striking contrast to the evolution of opsins during ecological transitions in mammals.
Like snakes, early mammals lost two cone photopigments; however, lineages such as bats and cetaceans underwent further opsin losses during their adaptation to dim-light environments.