Are Zebras Black with White Stripes or White with Black Stripes?

According to the principles of embryology, the real/original color of zebras is BLACK. The white color is actually the stripe around the main black background of their body. There has long been a popular belief that zebras were white animals with black stripes, but scientifically, it turns out to be the opposite.

There is no denying that zebras are without a doubt one of the most exotic and stunning horse species, but there are also plenty of questions about these beautiful beasts:

1) Are zebras white with black stripes or black with white stripes?

2) What is the purpose of having such a peculiar pattern on their bodies?

Look no further, because researchers have finally landed on some answers!

In the Medieval era, people believed that zebras had white bodies with black stripes. The proof of this hypothesis lay in the fact that they had white underbellies. This makes logical sense; white, being a lighter color, would be the base to a darker black.

Zebra Lying

White Underbelly (Credits:Wojciech PLONKA/Shutterstock)

However, recent studies have proven otherwise. Zebras are actually black on the surface with white stripes!

The skin cells of most animals—zebras and humans included—produce a pigment called melanin. This gives humans our skin color and hair color, and zebras their black color. However, in the case of zebras, instead of being all black, some skin cells are instructed to not produce melanin; those are the white stripes that we see.

Zebra embryos are completely black. The white stripes appear during the last embryonic stage.

How is the striping pattern formed on zebras?

The striping is mainly formed due to selective pigmentation. As mentioned, zebra embryos are completely black, while the white stripes appear at the last embryonic stage. Melanocyte skin cells produce the pigments that give color to the fur. Certain chemical messengers determine which melanocytes deliver the melanin to certain hairs; those appear black, while those that don’t receive the melanin appear white.

tabanid-zebra-cartoon1

The pigmentation is controlled by the activation or inhibition of specific genes. In the zebra’s case, those areas with white stripes are where the pigmentation gene has been inhibited. Black is the actual color of the fur, and the white patches are simply the areas that have little or no pigmentation. The fact that the skin beneath a zebra’s fur is black further supports this conclusion.

This pattern of pigmentation is called selective pigmentation.

Different zebra species can be identified by differences in their stripe pattern. These differences in stripe patterns have to do with how cells differentiate, a process wherein stem cells turn into other cells with a particular function (like liver cells, or skin cells) when embryos develop.

During this development, a type of cell called neural crest cells move around the forming embryo and form different cell types like brain, bone, muscle and skin cells or melanocytes. As these neural crest cells differentiate into melanocytes, many genes are turned on or off.

Depending on when these genes get turned on, the stripe patterns form accordingly. Research has shown that the earlier the melanocyte matures, the thicker the zebra’s stripes will be. This is an example of heterochrony. In simple terms, it is the difference in the timing and duration of certain genes being turned on or off between different organisms.

While we know this much, the molecular pathways and which genes are involved remain a mystery. In 2016, however, a study published in Nature suggested that the gene Alx3 is involved in stripe formation. They didn’t study the gene in zebras, since they’re hard to keep in a lab, so they opted for a rodent, the African striped mouse.

Alx3 is a transcription factor. A transcription factor is a molecule, usually a protein, that turns on or off certain genes. It is like a switch master. The release or activation of transcription factors is strictly controlled in the cell. When its job is done, the cell calls it off duty until it is needed again.

Alx3 was found before pigmented stripes. It also suppresses Mitf, which controls melanocyte differentiation, leading to light-colored stripes.

While these were findings in rodents, evolutionarily speaking, it could help scientists determine the purpose of stripes, whether they are on zebras or any other creature!

What is the Purpose of a Zebra’s Stripes?

This question doesn’t have a single, straightforward answer; there are several hypotheses:

1) Camouflage

A zebra’s stripes actually work as camouflage to deter its main predators: lions and hyenas. Since the animals herd together, experts believe that the mass of stripes can confuse predators by acting as an optical illusion, effectively blending their figures together. Therefore, a herd of zebras can create the optical illusion of a giant mass, thus deterring any predators from taking on the herd alone.

zeb

2) Regulate body temperature

Zebras spend a lot of time grazing on open plains, which means that they must bear the intense African heat for long periods of time. Zebras with the most prominent torso stripes generally live in the Northern, equatorial region of their range, whereas those with less prominent torso stripes are more commonly found in the Southern, cooler regions of the range. This geographic distribution supports the stripes’ proposed utility as heat-regulating tools.

Both of the above ideas have been popular theories in the past, but they don’t have much evidence to support them.

3) Flies and other pests

Tsetse flies are a big problem for animals in tropical Africa. These parasitic flies cause the disease Trypanosomiasis in both animals and humans. One hypothesis with some evidence supporting it is that zebra stripes confuse the flies. A study published in 2014 in Nature found that the flies, which you would imagine to be a common pest for Zebras, are less likely to sit on black-and-white striped surfaces.

In 2019, Japanese researchers painted cows black and white and found that fly bites reduced by 50%. They have proposed this method as a possible prevention technique for the spread of disease through these tsetse flies.

And there you have it… a zebra is a black horse with white stripes because they don’t want flies to suck their blood!

Suggested Reading

References

  1. University of California, Santa Barbara Science Line
  2. Zebra Stripes Not for Camouflage – UC Davis
  3. UC Davis
  4. Nature Communications
The short URL of the present article is: http://sciabc.us/b4gR4
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About the Author:

Ishan is a Mechanical Engineer from Mumbai University, India and is obsessed with science, food and all things football. He is a self proclaimed cyclist, runner and a professional procrastinator.

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