Winter is coming, and as some of us prepare to trade swimsuits for snowsuits, we may find a few extra pounds under our winter coats.
Animals are smart. They never take their coats off.
But what does animal skin look like under fur or hair—especially strikingly patterned animals such as big cats and zebras? Reader Christian Meyer asked Weird Animal Question of the Week to investigate.
WHAT LIES BENEATH
The short answer is it depends on the animal.
All mammalian hair colour is dictated by melanin-producing cells, called melanocytes, that live within hair follicles. Melanocytes that live between follicles control skin colour, says Greg Barsh, a geneticist at Hudson Alpha Biotechnology Institute in Huntsville, Alabama.
The two systems are controlled by different genes, hormones, and other factors, says Barsh, who studies the genetics of animal colour patterns.
"We know that in situations where stripes are apparent in the hair, they are not apparent in skin," Barsh says, citing domestic cats, domestic dogs, horses, zebras, and cheetahs as examples.
Cheetahs (pictured, an animal named George at Zoo Miami) are actually not closely related to big cats, and thus have different skin colours. PHOTOGRAPH BY JOEL SARTORE, NATIONAL GEOGRAPHIC PHOTO ARK
For instance, zebra skin is black under their black-and-white striped coats. Giraffe skin is a uniform light tan that's similar in colour to that of its coat, and its patterns are not visible, Mads Bertelsen, a materials scientist at Denmark's Copenhagen University, says via email. (Read: "Stripes don't protect Zebras from predators".)
Cheetahs—which are actually more closely related to small cats—“definitely do not have spots or lines on their [tan] skin,” says Vincent van der Merwe, a biologist at South Africa’s Endangered Wildlife Trust. (Learn more about van der Merwe's work as a cheetah matchmaker.)
Giraffes have light tan skin, similar to their coat colour. PHOTOGRAPH BY JOEL SARTORE, NATIONAL GEOGRAPHIC PHOTO ARK
However big cats, such as tigers, have skin patterns that mirror their fur, says van der Merwe. The same goes for snow leopards, as seen in this video of a captive cat undergoing a surgical procedure to relieve kidney stones and this photo of a shaved snow leopard cub.
That's likely because the coloured hair follicles embedded in the skin are visible, similar to a man's five-o'clock shadow, Barsh says.
Boone Smith, an independent big cat researcher who has shaved the skin of wild cougars to draw blood or place tags, has also observed the animals have the same skin colour. Their fur is varying degrees of brown, white, grey, and even black hair, and the "follicles seem to give the skin a slightly different contrast."
Polar bears have black skin that allows them to absorb more sunlight in the frigid Arctic. PHOTOGRAPH BY JOEL SARTORE, NATIONAL GEOGRAPHIC PHOTO ARK
When the bears moult out of their dense undercoat in the spring, “wee patches of black skin” are visible, Hedman says.
“The hair, if you take a couple of strands, looks clear,” Hedman says, though the bears look “bone white on the ice” because of the way the hair scatters light. This also helps the predators blend into their polar environment.
Male drills (pictured, a five-month-old captive drill) have blue and pink rumps that signal their social ranking. PHOTOGRAPH BY JOEL SAROTRE, NATIONAL GEOGRAPHIC PHOTO ARK
Though the blue pigments are not completely understood, they're likely linked to sexual selection. (In mandrills, colour has been linked to social status.)
“Their fur does the opposite,” Bercovich says. It’s “quite black when born, but turns to brindle-grey when older.”
Oh, we have no idea what that feels like.
Header Image: Zebras (such as this Burchell's zebra, photographed at Zoo Atlanta) have black skin under their striped coats. PHOTOGRAPH BY JOEL SARTORE, NATIONAL GEOGRAPHIC PHOTO ARK