A study from the University of Adelaide has found that olive sea snakes have a light-sensing ability in their skin that allows them to ‘see’ through their tails to avoid predators.
The international study led by the University of Adelaide has discovered found the adaptation allowed olive sea snakes (Aipysurus laevis) to move their tails away from light, which the researchers believe is meant to keep the tail hidden from predators.
Study lead author Jenna Crowe-Riddell, a PhD candidate in the University of Adelaide’s School of Biological Sciences, said that sea snakes live their entire lives at sea swimming with a vulnerable paddle-shaped tail.
“Olive sea snakes swim around looking for prey but often they rest during the day and they’ll curl up under a rock or coral,” she said.
“They have this light sensing ability in their tail in order for them to know or sense where their tail is at any time. It keeps them hidden from sharks and other predators.”
The olive sea snakes, which usually grow to a meter in length but can reach up to two meters, are one of three species, out of 60 total sea snake species that have the unique ability to sense light in the skin of their tails.
“Because sea snakes have long bodies, the tail-paddle is a large distance from the head, so it benefits from having a light-sense ability of its own,” said Crowe-Riddell.
Crowe-Riddell and a team of researchers at the University of Adelaide tested for light-sensitive tails in eight species of sea snakes using RNA sequencing and found that three species have the light-sense ability due to a gene linked to the protein melanopsin.
She also believes that the olive sea snake is the only reptile “out of more than 10,000 reptile species, that was known to respond to light on the skin this way.”
“Using RNA sequencing, we could tell what genes are actually active when you shine a light on the skin,” she said.
Melanopsin is most commonly used by animals to sense overall light levels in their environment but, according to Crowe-Riddell, is used differently in other species.
She said the sea snakes are not the only animals to have a similar adaptation using the melanopsin protein.
“There are some amphibians like frogs that have it in their skin. Instead of moving away, they use it for colour change,” she said.
“It is even used by some animals, including humans for regulating sleep cycles by sensing overall light levels in the environment.”
The ability of the snakes to ‘see’ light through their tail could have evolved in the ancestor of six closely related Australian sea snake species, according to Crowe-Riddell.
“Our research has found that surprisingly, it’s not all sea snakes, it’s just a few species,” she said.
Crowe-Riddell said a similar adaptation has also evolved in other marine species that look like sea snakes and that similar physiology could be a reason for the ability.
“The same thing has evolved in some long bodied fish and some forms of salamanders that have long bodies and paddle shaped tails. It might be convergent with that, it might even be a driving factor,” she said.
“I think it’s something that is quite rare, it may be [because of] a particular combination of expression patterns that just happened, and then it seemed to be really useful for those species that they have just retained the ability.”