A newborn zebra foal with bizarre polka-dot markings has recently been photographed in the Maasai Mara National Reserve in Kenya. This is the first time that this unusual pattern has ever been seen among zebras in the Maasai Mara.
This rare black zebra foal was first spotted and photographed early one fine September morning near the Mara River by Antony Tira, a respected Maasai tour guide and photographer at the Matira Bush Camp in the Reserve.
“At first, I thought it was a zebra that had been captured and painted or marked for purposes of [researching] migration,” Mr. Tira told the Daily Nation, a Kenyan newspaper. “I was confused when I first saw it.”
After carefully studying the foal, Mr. Tira realized he was looking at a newborn zebra with a pigment disorder.
Most Popular In: Science
NASA Now Has Alien Life-Hunting Robot Explorers That Only Phone Home When They’ve Hit The Jackpot
The Coronavirus Was Detected In Sewage In March Of 2019, Far From Wuhan, China
African Dust Storms Are The Latest ‘New’ Old Weather Phenomena
He photographed the peculiarly marked zebra foal and posted the images to the Matira Bush Camp’s Facebook page. According to the Daily Nation, the photographs generated a lot of attention and unleashed a human “stampede” in the reserve. Everyone wanted to see this foal. Tour guides were quickly enlisted to take eager tourists and photographers to the lookout area where the newborn zebra and his mother were located.
The following morning, and before the news got out in a big way, several more people saw this rare zebra foal.
“I was out looking for rhinos to photograph early that morning”, said Frank Liu, a professional photographer who provided the pictures of this foal for this piece. “We spent a couple hours [searching] around sunrise and failed. That’s when we stumbled upon this mutated zebra that was discovered just the day before.”
Mr. Liu’s reaction was similar to Mr. Tira’s the previous morning.
“At first glance, he looked like a different species altogether,” Mr. Liu said in email. Although he’d never seen such a strangely marked zebra before, Mr. Liu quickly realized Tira’s striking appearance is the result of a pigment disorder.
This rare zebra foal was given the name, “Tira”.
“The name ‘Tira’ was coined by the local Maasai guide who first found him on Sep 13,” Mr. Liu explained in email. “There is a general rule within the park; whoever finds an animal of significance gets to name it. Tira was the surname of the guide who found him.”
This rare black zebra is probably not “pseudo-melanistic”
Because this zebra foal has some white spots and a few small, incomplete white stripes, it is not completely black, so its distinctive coat pattern has been described in the media as “pseudo-melanistic”. (Keep in mind that zebra foals are chocolate brown with white stripes when they’re born and the brown darkens to black as the animal matures.)
“I do not know the origin of the term pseudo-melanism, but I think it is fair to say that is a popular and undefined term, used to refer to very rare animals that exhibit an apparent abnormality in the stripe pattern process such that light stripes are excluded from much of the trunk and back, but are more common on the extremities”, said geneticist Greg Barsh, a faculty investigator at the HudsonAlpha Institute for Biotechnology and a Professor Emeritus at Stanford University. Professor Barsh is an expert on the genetic mechanisms that underlie differences in individual appearance, a specialty that provides important insights into basic biology as well as human disease.
“This animal is different from most others that have been described as pseudo-melanistic”, Professor Barsh added. “[I]t is probably better described as ‘spotted’ or ‘partially spotted’.”
Black zebra stripes are created by melanins, a group of pigments that provide yellow, red, brown or black color to hair and skin. Melanins are synthesized by specialized cells known as melanocytes.
“In other animals where the biology and genetics are understood, ‘melanism’ refers to increased production of a specific pigment type”, Professor Barsh explained in email.
Are Tira’s black coloration and general lack of stripes the result of having too many melanocytes or are his melanocytes producing too much melanin?
“There are a variety of mutations that can disturb the process of melanin synthesis and in all of those disorders, the melanocytes are normally distributed but the melanin they make is abnormal”, Professor Barsh said.
One such color variant that may be the result of normal numbers of melanocytes producing abnormal melanin pigments is the “blonde” or “golden” zebra, a faded-out white zebra that occasionally pops up in Kenya and Tanzania. [an Albino?]
What we’re seeing in Tira is probably something different from a lack of melanocytes because melanocytes are uniformly and ubiquitously distributed throughout zebra skin.
“If you shave a zebra, it is completely black”, Professor Barsh pointed out.
“We think that in a partially spotted zebra like Tira, the melanocytes are still uniformly and ubiquitously distributed, however the melanocytes don’t know where they are on the body”, Professor Barsh elaborated. “In other words, partial spotting in zebras is not an abnormality of melanin synthesis but instead is an abnormality of melanocyte identity.”
Tira’s melanocytes either lost their internal biological GPS or they have amnesia.
Inbreeding may increase the number of abnormally patterned wild zebras
Does inbreeding play a role in abnormally colored or patterned zebras?
“Because the spotted and partially spotted animals tend to be more frequent in areas that have been subject to habitat fragmentation, and in which the census sizes are low, we do, indeed, suspect that inbreeding (and genetic drift) contribute to the phenotype”, Professor Barsh replied in email.
Historically, plains zebras had a very large range that encompassed the vast grasslands, shrublands and savannahs of eastern and south-eastern Africa, stretching from South Sudan, Ethiopia, Uganda and Kenya down to the southern coasts of South Africa (Figure 1). Thanks to hunting, ranching, farming and habitat loss, their current range consists of small, highly fragmented and isolated patches within their historic range. This raises the question: do particular pattern abnormalities tend to appear in particular locations?
“In general, spotted and partially spotted animals have been observed in the northern part of the species’ range, while ‘pseudo-melanistic’ animals have been observed in the southern part of the species’ range”, Professor Barsh replied in email.
Three species of zebras have been described based on body size and stripe morphology, as well as several other distinguishing traits. One of those species, the plains zebra, Equus quagga (formerly Equus burchellii) is easily recognized just by its stripes, which are broader than those of the other two zebra species, although even amongst plains zebras, there is a consistent, clearly visible gradient of differences in stripe patterns between northern and southern plains zebra populations.
Work carried out by Brenda “Ren” Larison (Figure 1), an Assistant Adjunct Professor at the University of California, Los Angeles (UCLA), and an expert in plains zebra ecology and evolution, has shown that northern populations of plains zebras have broader and more defined striping compared to southern populations, which have fewer, and thinner, stripes and less striping on their under parts, legs and hindquarters. Additionally, southern populations of plains zebras have brown “shadow stripes” between each black and white stripe. These shadow stripes are either absent or very faint in northern zebras.
The extinct quagga, one of six recognized subspecies of plains zebra that was range-limited to the southernmost tip of South Africa, is an example of reduced striping, and of extreme shadow striping.
Abnormally marked zebras are more likely to die young
Just what is the function of zebra stripes?
“We are pretty sure that stripes have an adaptive function, but the evidence for one function over the other is not strong,” Professor Larison replied in email.
“Stripes may have a number of functions [ref]: thermoregulation may be one [ref], avoiding biting flies may be one [ref; also more here], they may also have an anti-predator role [ref]. Those are the only hypotheses I’m aware of with some data to back them up”, Professor Larison said in email. “But a lot of the evidence is a bit indirect as doing the necessary experiments with live zebras would be expensive, logistically difficult and ethically problematic.”
“Although many hypotheses have been put forward for the function of stripes in the past, a wave of recent research shows that only one stands up to scientific scrutiny”, Tim Caro, a Professor Emeritus at the University of California, Davis, said in email. Professor Caro is a behavioral and evolutionary ecologist, and conservation biologist, who is an expert on the function of zebra stripes.
“Comparative, observational and experimental evidence coming from three independent laboratories all support the fact that stripes prevent biting flies (horse flies) from landing on them successfully. Moreover, by using striped cloth coats placed on horses, we now know the mechanism by which stripes prevent controlled landings on striped coats [ref; also more here],” Professor Caro explained in email.
“The outstanding question is what diseases are carried by biting flies that are so dangerous for zebras.”
Might Tira’s health be harmed or his lifespan cut short because he lacks stripes?
“The loss of whatever function stripes may provide could result in negative impacts, but I imagine that the biggest issue is not the loss of function due to lack of stripes, but simply not blending in to the herd due to lack of stripes”, Professor Larison said in email. “One of the advantages of living in a herd is protection from predators either due to a simple dilution effect or because large groups can create what is known as predator confusion; difficulty picking out and sticking with a target [ref]. Being obviously different from other members of the herd will likely make this foal stand out and make it an easier target for predators. This effect may be the main reason why such variants are so rare.”
Although abnormally patterned or colored zebras are born from time to time, they rarely survive to breeding age, either because they stand out from a bedazzling crowd of stripes in the eyes of hungry lions or because abnormal color or pattern are linked to other important traits in zebras, such as eyesight, night vision or speedy running.
I asked Mr. Liu, the photographer, how Tira is doing so far.
“I revisited the zebra a few days later and by then it was too far away from the road to photograph,” Mr. Liu said in email. “I did talk to the park rangers and they said they are keeping a close eye on him and he is looking healthy. He was still very close to his mother at all times.”
Here’s a video of Tira recorded by a recent guest of the Maasai Mara: