For lots of animals—humans included—lazing about in the sunshine is one of life's greatest pleasures. But unfortunately, this leisure comes with a cost: 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?
"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 put on animals and that has led to many mechanisms of reacting to it."
Some of these mechanisms are obvious: hair, fur, wool, feathers and scales (鱼鳞) on many creatures create a barrier between sunshine and skin.
But, "marine mammals (海洋哺乳动物) , 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 sunburn from the whales' hours spent breathing and socializing at the surface. But crucially, they also discovered that whales have specialized mechanisms that help them cancel out this burn. "The common adaptation of cetaceans is that they appear to be very effective at repairing damage," she said.
Some whales generate colors that darken and protect their skin; others have genes (基因) that set off a protective stress response in the skin. There are even whales that have developed a hard, keratinized layer (角质层) 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.
