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Urban sea snakes shed stripes — and pollutants

Claire Goran / University of New Caledonia

Scientists report a normally-banded species of sea snake is evolving darker skin to get rid of manmade pollutants. Some insects, like the peppered moth, evolved "urban melanism" for better camouflage in polluted environments, but this is the first time something similar has been seen in a marine animal. It also suggests at least one species of sea snake may be adapting to pollution, though just how well it's working remains to be seen.

What they did: The scientists examined populations of turtle-headed sea snakes and museum specimens throughout Southeast Asia and Australia, and found a clear association between dark coloration and urban pollution or military activity. They found that the all-dark snakes were twice as likely to shed their skin, and that those sheds had more contaminants. Finally, they looked at another kind of sea snake called banded sea kraits, and found that even on a single snake, the dark stripes had more pollutants than light stripes.

A long-standing mystery: "We've known for a while some groups of these snakes were jet black, but we didn't know why," Richard Shine of the University of Sydney, Australia tells Axios. He's been studying sea snakes for 20 years. "We looked at habitat, mating systems — we even dragged different colored ropes behind a boat to see which they preferred."

It stayed a mystery until Shine's collaborator Claire Goran, a marine biologist at the University of New Caledonia, was reading a paper that found melanin helped dark-colored pigeons shed more toxins through their feathers than light-colored pigeons. It was her idea to look at the levels of pollutants in snake skin.

A small challenge: The researchers still need to determine whether dark-skinned snakes survive better in polluted water than striped snakes. Unfortunately, says Shine, that's easier said than done. They're a long-lived species. "Some of the first snakes I marked are still swimming," he tells Axios.

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