For lots of animals — humans included — lazing about in the sunshine is one of life's greatest pleasures. But unfortunately, this pastime comes with a cost: the skin-sizzling ordeal known as sunburn. And, while its most likely victims are the fairer-skinned among us, animals are at risk of sunburn, too.
But if this can happen to animals too, why, then, don't we ever see sunburned fish, or scarlet elephants?
"If you think of it, the sun has been here forever in terms of our planet, and all individuals have been exposed to it," said Karina Acevedo-Whitehouse, a molecular epidemiologist from the Autonomous University of Queretaro, in Mexico. "So, it's a pretty strong selective pressure that the sun has imposed on animals and that has led to many mechanisms of counteracting it." [Why Does Being in the Heat Make Us Feel Tired?]
Some of these mechanisms are obvious: Hair, fur, wool, feathers and scales on many creatures create a barrier between sunshine and skin. These adaptations are so effective that the only time they really fail is when humans intervene. For instance, domesticated pigs — bred to have less hair — are more sensitive to sun damage than their wild cousins.
Animals with naturally hairless, unscaled skin must resort to other methods of self-protection. Elephants and rhinos not only have thicker hides; they also regularly coat themselves in dust or mud to create a rudimentary sunscreen. When conditions are extreme, most animals retreat to the shade or take refuge in burrows. "All of that is helping animals to cope, so we don't see a lot of sunburn [in these species]," Acevedo-Whitehouse told Live Science.
Some species up the ante by producing a unique brand of sunscreen from their own cells. Taifo Mahmud, a molecular biologist at Oregon State University, has discovered genetic traits in fish, birds, reptiles and amphibians that enable them to produce a compound called gadusol, which creates protection against ultraviolet (UV) rays in the sun. "Most vertebrates, except mammals, have the genes responsible for producing gadusol," Mahmud told Live Science. So far, they've proved that only zebrafish actually use this compound as a protectant against UV rays. But now scientists are looking into how humans might exploit this trait for our skin.
Why don't we — and other mammals — produce gadusol? "It has been proposed that early mammals were nocturnal. Was that because they lost the genes that produce gadusol? We don't know," Mahmud said. "I think it would be interesting to figure out if fur and thicker skin were developed later in their evolution."
Not to be outdone, gadusol-deprived mammals have developed their own sophisticated mechanisms of protection. Hippos are known to secrete a scarlet liquidfrom their pores that looks just like blood — and it wasn't until 2004 that a group of Japanese scientists discovered that the orangey-red compounds in this skin-coating fluid protected hippos from UV rays, according to a report in the journal Nature (opens in new tab). Other animals focus their sun protection in the most vulnerable parts of their bodies.Giraffes, for example, produce more protective melanin in their tongues— giving them a darker hue — because they spend most of their lives with their tongues exposed to the sun as they pry tender leaves off trees.
So, do animals ever get sunburned? Yes. "Marine mammals, and specifically cetaceans [whales, dolphins and porpoises], are an exception because they don't have fur; they don't have scales," said Acevedo-Whitehouse, who has been studying sunburn in whales for over five years.
In skin samples taken from the backs of blue, sperm and fin whales on their cross-ocean migrations, Acevedo-Whitehouse and her colleagues discovered signs of sunburnfrom the whales' hours spent breathing and socializing at the surface, according to a 2013 study published in the journal Scientific Reports (opens in new tab). But crucially, they also discovered that whales have specialized mechanisms that help them counteract this burn. "The common adaptation of cetaceans is that they appear to be very effective at repairing damage," she said.
Some whales generate pigments that darken and protect their skin; others have genes that trigger a protective stress response in the skin. There are even whales that have developed a hard, keratinized layer that protects the delicate skin below. "We were excited to see there isn't really evidence of skin cancer in whales," Acevedo-Whitehouse said. Now, they're trying to understand precisely how those healing mechanisms work.
From protective coats, to self-made sunscreen, to rapid healing, these sun-smart animals may one day give us the clues we need to save our own skin.
Original article on Live Science.