By Sarah Marks
Edited by Kelsey Gray and Sam Stadmiller
The internet is full of cats. They’re cute, they’re aloof, and apparently really bad at spelling. Some of the most recognizable cats on the internet, after Grumpy Cat, are Siamese cats. Their distinct coloring (dark ears, face, feet, and tail on a pale body), called point coloration, makes them easily identifiable.
Siamese cat with its distinctive coloring pattern wondering what those silly humans are looking at… probably. (Photo by Cindy McCravey – originally posted to Flickr as Neighbor’s Siamese, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=3969632)
One of my favorite facts about Siamese cats is that their coloring is temperature dependent! The cooler the part of the cat’s body, the darker the fur. If you’ve ever played outside in the snow, you know the first things to get cold are your fingers, toes, and nose. This is because the extremities of your body lose more heat than your core. Similarly, Siamese cats are cooler at their paws, nose, and tail, making their fur darker there as well.
Scientists first tested the idea that Siamese cat coloring is temperature dependent in the 1930s by bringing Siamese cats to Moscow and caring for them in rooms kept at -3oC to 16oC (about 26oF to 60oF). This contrasts with the warmer temperatures in which the average pampered house cat lives. While the cats’ bodies were cream colored when they arrived in Russia, the cats eventually shed their fur and became noticeably darker in the cooler temperatures.
To make sure that this color change really was because of the temperature, the scientists hypothesized that if they kept an area of the cat’s body that had dark fur warm, then it would become lighter. To test this, they shaved a portion of the cat’s fur and covered it with a bandage that would keep the cat’s skin warm. Sure enough, when the hair grew back, it was lighter than the surrounding fur that had been continuously exposed to the cooler temperatures.
The cause of this temperature dependence in Siamese cats is related to a mutation in the protein, tyrosinase. Tyrosinase is involved in making melanin, which is the same pigment found in your eyes and skin. The more melanin that there is, the darker the fur will be. While the tyrosinase in our bodies works well at body temperature (37oC or 98oF), a mutation in tyrosinase in Siamese cats causes it to work best at room temperature (25oC or 77oF). (A cat’s normal body temperature is about 38-39oC or 101-102oF.) Therefore, at the cooler parts of the cat’s body, the tyrosinase works more efficiently, produces more pigment, and therefore darker fur.
One remaining mystery is how this mutation changes tyrosinase’s optimal temperature. Any ideas?