Tag: color

Science

Through Glowing Eyes: What Do Cats See?

mehshadoweye

Meredith Hemphill

mehshadoweye

Encyclopaedia Felidae now has a Patreon! Go to www.patreon.com/EncyclopaediaFelidae if you want to help support this content!

Joon has a strange habit. Well, a lot of strange habits, actually, but I’m thinking of one in particular. She will stare up at the ceiling at night and yowl. At first, I thought she was hearing our upstairs neighbors. Then I remembered that we lived on the top floor. Is my cat insane, or are there demons in the walls? There’s no way to know. I now live in a detached, single-family home, and she still does the same thing. I’ve never known any other cat to do that, but cats are infamous for looking off into space intently and kind of spookily. Obviously, cats and humans see the world very differently. If you have ever wondered what on Earth your cat is looking at, or just how the world appears to them, then you have come to the right place.

Eyeball diagram
Image from Cat-World.com

Let’s start with the basics: eyeballs. The fundamental structure of the cat eye is pretty similar to that of a human, but there are some important differences that affect how they perceive what’s in front of them. If you haven’t taken an anatomy class since high school and need a refresher on what the parts of the eye in the diagram at left do, the National Eye Institute has a short video that goes over the highlights.

Although it doesn’t so much affect the way they see, while we’re on the subject of eyes it bears mentioning that cats, like many other mammals, have a nictitating membrane inside of their eyelids. This membrane, often called the “third eyelid,” is a semi-transparent, whitish color, and cats close it when they need to protect their eyes from scratches, like if they’re squeezing through a bush [1]. The nictitating membrane should not be visible normally; this could be a sign of inflammation or disease and is a reason to visit the vet [1, 2].

As with most things about the cat body, their eyes are exquisitely adapted to the life of a crepuscular hunter. “Crepuscular” means most active at dawn and dusk, when they are able to maximize the proportion of prey animals they have access to. Both cats and humans have forward-facing eyes, but the position of cat eyes gives them a somewhat wider field of view, about 200 degrees to our 180 degrees [3-5]. Cats also have much larger eyes than humans relative to the size of their heads, allowing them to take in more light in the dimmer hours of the early morning and late evening [2].

Another feature that helps cats see in dim light is a layer of reflective cells behind their retinas called the tapetum lucidum, which is Latin for bright/shining carpet. The tapetum lucidum is common in nocturnal and crepuscular mammals. The mirror-like cells reflect light that has gone through the retina back for a second pass. When you take a picture of your cat with the flash or open the door to find them in a dark room and see their eyes seeming to glow like some kind of hellspawn, that’s just their tapetum lucidum reflecting light at you.

Green cat eyes
Elliptical pupils mean more control over light – Image by Christel SAGNIEZ from Pixabay

There is research to suggest that the slit, vertical pupils of cats are also an adaptation to a crepuscular habit. It allows their pupils to change in size drastically for greater control over the amount of light that reaches their retinas [6]. The change in pupil area between the constricted and dilated states is estimated to be 135- to 300-fold, while human pupils can only change in size about 15-fold [6]. Think about how much the amount of sunlight can change around dawn and dusk, versus during the daylight hours when humans are meant to be most active. The ability to significantly adjust the amount of light let into the eye has likely served cats well.

All this means that cats can see much, much better than we can in low light. However, everything in biology involves trade-offs. For one, cats are rather near-sighted. They can only see clearly up to about 20 ft (6 m) away, while humans can resolve details at 100-200 ft (30-60 m) [3-5]. Cats have also prioritized one type of retinal cell, or photoreceptor, over another.

Cone cells help see details and colors. Rod cells are excellent at absorbing dim light and catching quick movements. Humans have lots of cones, including three types that specialize in picking up the colors red, green, and blue. Cats have lots of rods instead, six to eight times as many as humans [1, 4]. This assists in seeing in low light and in picking up the small, rapid movements of prey [3].

This heightened awareness of tiny movements may also explain the way cats seem to look at nothing. They may just have noticed something too small to register with you. Or your house is haunted. Who knows? Although the abundance of rod cells has great advantages for cats, it causes them to have less visual acuity and poorer color vision than humans. Obviously, they have done quite well for themselves even so. After all, did you see that ghost zip through your kitchen? I don’t think so.

There remains some debate as to the color vision of cats. They definitely see some color. According to some scientists, they may see the world in shades of blue, gray, and yellow [4]. A 2014 study found that cats may actually be able to see some colors in the ultraviolet spectrum, so while they can’t see all the colors we can, it’s possible that they can see colors we can’t [7]. This is because the lenses of their eyes don’t remove all the ultraviolet rays before light reaches their retina, unlike ours, which absorb UV [7]. The study found that the lenses of cats allowed 58.9% of UVA radiation through [7]. Whether there is an evolutionary advantage to this remains unknown.

Brown tabby cat face
The feline cornea allows UVA rays through – Photo from Pixabay at Pexels

Perhaps the greatest question of all is, how do our cats see us? A lot of research has been conducted to assess whether animals recognize faces, and a wide variety of species, including wasps and fish, have been demonstrated to recognize the faces of their own species. Recognizing the faces of other species is a much more difficult task, however. I personally couldn’t recognize the face of a wasp, in all fairness, although I do know just about every stripe and speck on my Joon-bug. Then again, it helps that she’s got so many of those. Well, it turns out that to cats, all human people look alike. Fair enough, honestly.

Lomber and Cornwell trained dogs and cats to choose one of two images presented for a treat, regardless of which image they chose [8]. The image pairs were 1) their handler and an unfamiliar human face, 2) an animal they lived with and an unfamiliar animal’s face, 3) a natural scene they’d learned before and a new one, or 4) two unfamiliar natural scenes [8]. Dogs and cats both showed a strong preference for the face of a familiar animal and a familiar natural scene, choosing that which they knew at least 85% of the time [8]. Dogs kept up the preference for the face of their handler, but cats only chose the familiar human face 54.5% of the time, equivalent to a coin flip [8].

Cats are certainly capable of recognizing their people, but they evidently do not recognize our faces, although they can recognize each other’s faces. As animals that are just barely domesticated, and only because they chose to be, perhaps this should be no surprise. What need would a cat have to recognize human faces in its wild state? Cats have met us a lot farther over than the middle. It’s the least we can do to try and see things their way.

If you want to actually see what the world would look like through a cat’s eyes, artist Nickolay Lamm took simple photographs and then manipulated them to appear as they would to a cat, then juxtaposed the two images [3]. You can see the results of the project in the Wired article linked below.

Works Cited

  1. Gelatt, K.N. (2018, August). Eye structure and function in cats. Merck Vet Manual. https://www.merckvetmanual.com/cat-owners/eye-disorders-of-cats/eye-structure-and-function-in-cats
  2. Farricelli, A. (2019, August 12). The anatomy of a cat’s eye. PetHelpful. https://pethelpful.com/cats/The-Anatomy-of-a-Cats-Eye
  3. Drake, N. (2013, October 16). This is how cats see the world. Wired. https://www.wired.com/2013/10/cats-eye-view/
  4. Thrive. (2019, April 12). Can cat’s see color? https://resources.thrivevet.com/can-cats-see-color/
  5. Ghose, T. (2013, October 16). Feline vision: How cats see the world. Live Science. https://www.livescience.com/40459-what-do-cats-see.html
  6. Calderone, J. (2018, June 30). Here’s why cats have such strange, haunting eyes, explained by science. Science Alert. https://www.sciencealert.com/here-s-why-cats-have-such-weird-eyes
  7. Douglas, R.H. and Jeffery, G. (2014). The spectral transmission of ocular media suggests ultraviolet sensitivity is widespread among mammals. Proceedings of the Royal Society B, 281(1780). https://doi.org/10.1098/rspb.2013.2995
  8. Lomber, S.G. and Cornwell P. (2005). Dogs, but not cats, can readily recognize the face of their handler. Journal of Vision, 5(8), 49, 49a. https://doi.org/10.1167/5.8.49

Published September 6th, 2020

Updated September 30th, 2023

Science

Coat Color Genetics

mehshadoweye

Meredith Hemphill

mehshadoweye

Encyclopaedia Felidae now has a Patreon! Go to www.patreon.com/EncyclopaediaFelidae if you want to help support this content!

Five tabby kittens
Colorful kittens – Photo from Pixabay

I majored in genetics as an undergraduate, so whenever I see a cat with unusual patterning or coloration, I can’t help but wonder what molecular wizardry made that possible. Cat fanciers have long wanted to unlock the mysteries of feline traits. While breeders began to puzzle out the patterns before DNA was determined to be the blueprint of heredity, there are still some mysteries to be solved. However, the more obvious traits have been mapped onto the feline genome, and there are even DNA tests for breeders or uncommonly curious pet owners who want to know what genes their cats carry. Today I want to cover the basics of coat color genetics, but I’ll start with a quick overview of genetics so no one gets lost. Feel free to skip it if you know you don’t need it.

Genetics: A Primer

DNA (deoxyribonucleic acid) is the molecule on which all the necessary information to build an organism is stored. Each unit of storage in the DNA is called a gene, and genes code for proteins. Proteins serve an incredibly wide variety of biological functions in the organism, including providing structure and metabolizing food into energy. There can be multiple different versions of a gene in the gene pool of a species. These different versions are called alleles.

Because an individual inherits half of their DNA from each of their parents, they have two copies of each gene. There are species for which this isn’t true, but it is for most vertebrates, including cats and humans. So each individual should have two copies of every gene, with a notable exception that we will get to later, but some alleles are dominant to others, so not every allele will be expressed. In the case of simple dominance, dominant alleles will be expressed if they are present. However, if the individual has inherited a recessive allele from both parents, they will express the recessive trait.

If you’re confused, I recommend looking up a more thorough overview of basic genetics before proceeding. There is much more to be said on the point, and I will do my best to explain as I go along, but it is only going to be more complicated from here. Now, let’s talk about what makes cats so very colorful!

Tom and the Monochromatic Fur Coat

Cats have two coat color pigments: eumelanin, which is black or brown, and pheomelanin, which is red or yellow. The primary coat color gene produces eumelanin. There are three alleles. The dominant allele, B, leads to black fur. The b allele is recessive to B and produces less pigment, leading to a brown coat, sometimes called “chocolate.” The b1 allele is recessive to both B and b, and it leads to a light brown or “cinnamon” coat.

The pheomelanin gene has a dominant allele, XO, that produces a red/orange coat color instead of or in addition to the color at the black/brown locus. The recessive allele, Xo, produces no reddish pigment. The pheomelanin gene is different in that it is located on the X-chromosome. In mammals, females have two X-chromosomes and males have one X and one Y, with some exceptions because biology is complicated.

So tom cats only have one gene for orange pigment, which they inherit from their mother. That is why toms are either ginger or black, but only very rarely both. But she-cats can have a XO and a Xo allele, causing them to have patches of both orange and black. This pattern is called tortoiseshell, or calico if they also have white patches. Tortoiseshell and calico toms can be born if they have two X-chromosomes and a Y or a similar chromosomal anomaly.

White cat with plush cow
White cat with odd eyes. Also a cow. – Photo by Samson Andreea on Pexels

50 Shades of White

White patches are due to the piebald spotting gene, where the recessive, s, allele codes for no white. If a cat has just one dominant allele, S, less than half of their fur will be white, and the white patches are often restricted to the feet, face, chest, and underside. If they have two dominant alleles, more than half of the cat will be white. It’s possible that they may even be completely white.

There are two other ways that a cat may be white, genetically speaking. The dominant white gene, as the name suggests, produces solid white cats with at least one dominant W allele. These cats are likely to be deaf, especially those with blue eyes and odd eyes. Those with odd eyes tend to be deaf in the ear on the same side as the blue eye. Rarely, white cats may be albino. There are two alleles that cause albinism, both recessive and both defective versions of the allele coding for the tyrosine enzyme. Cats with two c alleles are true albinos and have a translucent white pelt with pink eyes. Two ca alleles produce a white coat with pale blue eyes. There is no association of deafness with albino cats.

A Dilute Shade of Pale

The dilution gene is capable of modifying the appearance of other colors. The dominant allele produces the normal coloration. Two recessive alleles causes the pigment granules to clump in the hair shaft and leave large areas without pigment. The result is a lighter, or diluted, coloring. Black cats become grey, known as “blue” in the breeding world. Chocolate becomes lilac, cinnamon becomes fawn, and ginger, or “red,” becomes cream.

This covers the basics, although certain breeds can have unique alleles, such as the amber allele at the orange locus in Norwegian Forest Cats. I will cover the genetics of coat patterns another week. Until then, enjoy this picture of my gorgeous blue-cream calico.

Published February 20, 2020

Updated June 20, 2022