Sea snakes regain color vision thanks to rare genetic evolution

Summary: A new study shows that the annular sea snake has evolved to perceive more colors than its ancestors.

The snakes initially lost their color vision as they adapted to a lifestyle of burrowing under dim light, but sea snakes living in brighter marine environments have regained color vision.

Two of the four intact copies of the snake’s SWS1 opsin gene have developed novel sensitivities to the longer wavelengths that prevail in oceanic habitats, allowing for better color discrimination.

Major Events:

  1. The annular sea snake possesses four intact copies of the SWS1 opsin gene, two of which have developed novel sensitivities to longer wavelengths.
  2. This adaptation likely allows sea snakes to better distinguish potential predators, prey or mates against a colorful sea background.
  3. The reappearance of color vision in sea snakes contrasts with the evolution of opsin in mammals such as bats, dolphins and whales, which have undergone further loss of opsin to adapt to water and dim light.

Source: Oxford University Press USA

A new article in Genomic biology and evolution discovered that the ringed sea snake, a venomous snake found in the waters around Australia and Asia, appears to have evolved to see an expanded palette after their ancestors lost the ability response to environmental changes.

Color vision in animals is mainly determined by genes called visual opsins. Although there have been numerous loss of the opsin gene during the evolution of tetrapods (the group that includes amphibians, reptiles, and mammals), the emergence of new opsin genes is extremely rare.

This shows a snake.
The original snakes lost two visual opsin genes during their burrowing stage under dim light and could perceive only a very limited range of colors. Credit: Neuroscience News

Prior to this study, the only evolution of new opsin genes in reptiles appeared to have occurred in Helicoptera genus of snakes from South America.

This study used published reference genomes to visually examine opsin genes in five ecologically distinct soft snake species.

The history of elapids, a family of snakes that includes cobras and mambas in addition to annular sea snakes, offers the opportunity to investigate the molecular evolution of visual genes.

The original snakes lost two visual opsin genes during their burrowing stage under dim light and could perceive only a very limited range of colors.

However, some of their descendants now live in brighter environments; Two lineages of antelope have even moved from terrestrial to marine environments within the last 25 million years.

Researchers here have found that the annular sea snake possesses four intact copies of the opsin gene SWS1. Two of these genes have ancestral UV sensitivity, and two have developed novel sensitivities to the longer wavelengths that dominate ocean habitats.

The study’s authors believe this sensitivity could help snakes better distinguish colors to distinguish predators, prey and/or potential mates against a colorful sea background.

This is significantly different from the evolution of opsin in mammals such as bats, dolphins and whales during ecological transition; they lose extra opsin as they adapt to water and dim light.

Lead author of the paper, Isaac Rossetto, said: ‘The first 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 greatly expanded the range of colors sea snakes can see.

«For reference, we humans have a similar extended color sensitivity, while cats and dogs are partially colorblind like those early snakes.»

About this optic neuroscience and genetics research news

Author: Daniel Luzer
Source: Oxford University Press USA
Contact: Daniel Luzer – Oxford University Press USA
Image: Image credited to Neuroscience News

Initial research: Open access.
“Short-wavelength-sensitive Opsin transcriptional function in sea snakes: Evidence of re-expanded color sensitivity after ancestral regression” by Isaac Rossetto et al. Genomic biology and evolution


abstract

Functional duplication of short-wavelength-sensitive Opsin in sea snakes: Evidence of color sensitivity re-expanded after ancestral regression.

Color vision is mediated by ancient and spectrally distinct cone opsins. However, while there have been numerous loss of the opsin gene during the evolution of tetrapods, evidence for the acquisition of opsin through functional duplication is extremely scarce.

Previous studies have shown that a number of second marine soft snakes have acquired extended «UV-blue» sensitivity through changes at the major spectral regulatory amino acid sites of the Opsin gene. 1 short wavelength (SWS1).

Here, we use the elapid reference genome to show that the molecular origin of this adaptation involves proximal, repeated duplication of the SWS1 gene in a purely marine environment. Hydrophis cyanocinctus. This species possesses four intact SWS1 genes; two of these genes have ancestral UV sensitivity and two have sensitivities derived from longer wavelengths that dominate marine habitats.

We propose that this remarkable expansion of the sea snake’s opsin repertoire functions to compensate for the ancestral loss of two medium-wavelength opsins in the earliest (dimmed light-adapted) snakes. ). This creates a striking contrast to the evolution of opsins during ecological transition in mammals.

Like snakes, early mammals lost two cone pigments; however, lines such as bats and cetaceans lose extra opsin during adaptation to low light.

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