Scientists: Sea Snakes Have Been Adapting to See Underwater for 15 Million Years

Blue-lipped sea krait (Laticauda laticaudata), Anemone Reef, Thailand. (By jon hanson on flickr. – https://www.flickr.com/photos/jonhanson/90795890/, CC BY-SA 2.0, Link)

(CN) — Sea snakes have been gradually adapting their underwater vision capabilities over the past 15 million years — an impressive biological feat according to scientists.

A study, published Thursday in Current Biology by the University of Plymouth in the United Kingdom, documents how a team of researchers sought to better understand how exactly sea snakes have been adapting to their underwater homes. Researchers were specifically interested to find out how sea snakes, which first entered marine environments several million years ago, have stacked up evolutionarily to their land-based counterparts.

Scientists discovered sea snakes have undergone some remarkably rapid changes during their time underwater and have far outpaced their terrestrial cousins.

The researchers examined a number of both land- and sea-based snake species from a number of locations, such as through fieldwork in Asia and Australia. Researchers even studied snake species found in the collections of historical museums.

One crucial element researchers wanted to explore was the opsin genes found inside snake species, a special type of gene that helps produce visual pigments that are responsible for a snake’s visual spectrum sensitivity. Data taken from those genes, coupled with information from a snake’s lenses and other retinal components, helped researchers understand how a sea snake’s visual abilities have formed and changed throughout generations.

Researchers found the visual pigments have seen significant adaptive diversification over the past few million years alone, particularly when compared to land and amphibious snake species. This diversification has allowed sea snakes to see a wider array colors and ultraviolet ranges when navigating the depths of sea, which gives them a distinctive advantage when avoiding predators and stalking prey.

This is particularly impressive given that most snakes, despite having descended via evolution from some exceptionally visual and sight-centric lizards, have rather limited color vision due to the darker, more confined lifestyles of their immediate ancestors.

Bruno Simões, who led the research and is a lecturer in Animal Biology at the University of Plymouth, said one explanation for how sea snakes have grown to adapt in a relatively short amount of time is that the harsh and unforgiving nature of their environment has given them little choice.

“In the natural world, species obviously have to adapt as the environment around them changes,” Simões said in a statement accompanying the study. “But to see such a rapid change in the sea snakes’ vision over less than 15 million years is truly astonishing. The pace of diversification among sea snakes, compared to their terrestrial and amphibious relatives, is perhaps a demonstration of the immensely challenging environment they live in and the need for them to continue to adapt in order to survive.”

One example the study points out is how a particular species of sea snake have seen some impressive expansions of their UV-Blue sensitivity. Researchers point out that sea snakes often have difficult journeys in their day-to-day bids for survival, given that many hunt and scavenge around the sea floor for food but must return to the surface for air at least once every couple of hours. This journey, which can often take sea snakes to more than 260 feet below the surface, can be fraught with danger from other sea dwellers.

But an expanded depth to their UV-Blue vision sensitivity gives many sea snakes the ability to navigate and thrive in the blue waters.

Researchers also found, in a somewhat surprising discovery, that from a genetic perspective sea snakes share these adaptive genetic properties with fruit-loving primates. This is due to the fact that some primates have a unique genetic ability that allows the copies of their genes to be slightly less-than identical, resulting in an improved color vision spectrum for the primate.

Through this same process, sea snakes are also able enhance their underwater eyesight according to the study.

Simões believes that these abilities may also serve sea snakes well going forward. With so many sea snakes threatened by unlawful fishing activity and shifting factors in the oceans due to climate change, a sea snake’s genetic diversity and ability to adapt may give the species a much-needed edge in an ever-changing world.

“Many sea snakes are endangered by illegal fishing, bycatch and also by changes in the oceans as a result of climate change,” Simões said in an email. “Sensory is central for animal survival and reproduction and adaptive visual systems discovered by my study in sea snakes will be important for this lineage to adapt to changes in their environments.”

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