Not All Zebra Have stripes!
Plains zebra (Equal quagga) are an iconic African plains species, being easily identifiable by their distinctive black and white stripes. But plains zebra are now been seen with more unusual coat patterns. Instead of stripes, some have spotted or large, black splotches, and even golden coats with lighter stripes. In 2019, researchers in the Masai Mara National Reserve, Kenya, recorded a polka-dotted foal, which had white spots covering its darker brown body
These rarely found coat patterns are often caused by genetic mutations in which the production of melanin (a natural pigment) has been altered. Scientist Brenda Larison, has found an unusually high number, about 5%, of plains zebra with abnormal coat patterns, near Lake Mburo, Uganda.
In an interview with National Geographic, Larison said that “the observation [of the oddly patterned zebras] led me to wonder: is part of the reason that I’m seeing so many is because this population is inbred?”
To discover more, Larison along with fellow researchers, investigated population genetic health and genetic structure in plains zebra. They ran genetic analyses on 140 plains zebras from nine different locations, including Etosha and Kruger National Parks. Their analysis included seven individuals who had unusual coat patterns. The data was then analysed to find out the relationships between population structure, genetic diversity, inbreeding and abnormal phenotypes.
Not surprisingly, they found that smaller, more isolated zebra populations had lower genetic diversity. But, they also found that these isolated groups were more likely to produce abnormally striped zebras. This suggested that these genetic mutations are caused by poor genetic diversity, with one of the reasons these herds are isolated from other zebra populations might be due to a result of habitat fragmentation.
Although their study only included seven zebras with these odd patterns, their results could indicate a highly visible warning about the future of plains zebra.
Concern for plains zebra long-term survival
It is thought that by not having stripes, unusually patterned zebra are more vulnerable to predators, as researchers only found polka dotted foals, but no mature dotted adults. Larison is also researching the link between a zebra’s stripes and biting insects – do their stripes help to avoid them been bitten by tsetse flies, and if so, does this help them to avoid sleeping sickness?
Larison’s study found that zebras are becoming genetically closer within their own populations. In turn, these isolated populations are growing more genetically distant from other zebra populations. This means that these isolated populations could eventually lead to new subspecies of plains zebra.
“We found that there are populations that are possibly diverging more than they would under normal circumstances, because of human population pressure.”
Brenda Larison
This is of conservation concern. Inbreeding, with a lack of gene flow, can cause infertility, disease and other genetic defects. If isolated zebra populations become too genetically different from each other, then the opposite of inbreeding can occur – outbreeding – which can also cause abnormalities from genes being too dissimilar. The only way to make sure that this does not happen is through conservation strategies, such as translocating zebra, so that new genes are brought into a herd, ensuring their long-term survival.
Plains zebra are the least threatened of the three zebra species, but it is thought that their numbers have dropped by 25% since 2002, with around 500,000 plains zebra across the whole of Africa.
Habitat fragmentation is caused by human development, such as putting up fencing, which squeezes mammal populations into small pockets of land. This prevents them from migrating to other areas, and also stops them from breeding with other herds.
Find out more
Brenda Larison works at the Department of Ecology and Evolutionary Biology, University of California, Los Angeles. She researches Zoology, Ecology and Evolutionary Biology with her interests including the evolution of phenotypic diversity and conservation genetics. Her current research projects focus on the genomic and evolutionary basis of striping in plains zebras, and conservation genomics in Grevy’s and plains zebras and common loons.
You can read her article Resolving the Riddle of Why the Zebra Has Stripes online and find her study – Population structure, inbreeding and stripe pattern abnormalities in plains zebras – in Molecular Ecology.
Main photograph – Zebra herd with melanistic foal, © Brenda Lairson