Is a zebra white with black stripes, or black with white stripes?

This article was reviewed by Zhao Xumao, a young researcher at Lanzhou University

The most recognizable feature of zebras is their black and white fur. This color scheme contrasts sharply with the browns and greens of their habitat: the treeless savannah and savannah woodlands of eastern and southern Africa. Have you ever wondered if zebras are white with black stripes or black with white stripes? Many people would assume that since zebras usually have lighter hairs than darker hairs on their bellies, zebras should have black stripes on a white background. But this is not the case.

There are three known living zebras: the plains zebra (Equus quagga), the mountain zebra (Equus zebra), and the Grevy's zebra (Equus grevyi), and their stripe patterns vary. An extinct subspecies of the plains zebra, the quagga (Equus quagga quagga), even had only a few stripes on its head, neck, and mane. Each individual zebra's stripes are also unique: some zebras have dark stripes that are black, others are brown, and some zebras have stripes only on their bodies, not their legs.

Zebras don't all have the same coat color, but they all have the same skin color: black. But the question we want to discuss is whether zebras' "hair" is white with black stripes or black with white stripes. "Although zebras have black skin, their hair color is determined by a different set of developmental processes, just as light-skinned humans can have dark hair," said Tim Caro, a behavioral and evolutionary ecologist and conservation biologist at the University of California, Davis. So to answer this question, we need to study the cells that produce pigment in zebra hair (melanocytes).

Every hair, no matter how dark or light, comes from a follicle filled with melanocytes, according to a 2005 review article in the Journal of Investigative Dermatology. These cells produce melanin, a pigment that determines the color of hair and skin: large amounts of melanin result in dark colors, such as dark brown or black; small amounts result in light colors, such as brown or blonde.

The black hair of a zebra is full of melanin, but the white hair does not have melanin. This is because the hair follicles that grow white hair "turn off" the melanin production process of the melanocytes. So black is the default color of zebra hair, and white is the stripes.

The exact biological process by which zebras develop their stripes is unclear. The African striped mouse (Rhabdomys pumilio) also has light and dark stripes on its furry body. According to a 2016 study published in Nature, the Alx3 gene in the African striped mouse is more active on light stripes than on dark stripes. The researchers found that Alx3 blocks the master regulator gene responsible for the development of melanocytes, causing the hair in the corresponding areas to become lighter.

So why do zebras have white stripes on a black background? According to a study published in the Proceedings of the Royal Society B in 2020 by Caro and colleagues, this unique pattern can protect against flies. After they covered horses with solid-colored, striped, or plaid blankets, they found that African gadflies (which bite horses and zebras and can carry diseases that are fatal to equines) were significantly more likely to land on solid-colored blankets.

Okapi

"There are very few mammals that have stripes as high-contrast as zebras," Carroll said. "Only the okapi has similar stripes on its rump, but other than that, no other animal has really distinct black and white stripes. I suspect that the fly-repellent function of the black and white stripes is unique to equids, as they are very susceptible to diseases carried by certain gadflies in Africa."

Source: Global Science (ID: huanqiukexue)

Written by Jennifer Welsh

Compiled by: Zheng Yuhong

Original link:

https://www.livescience.com/zebras-black-and-white

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