The riddle behind zebra stripes

Brenda Larison, University of California, Berkeley

How the zebra got its stripes might at first seem like an esoteric question. But it has fascinated many generations and is embedded in the lore of Africa. It is also a question that offers a great educational tool by helping the general public understand how evolution shapes the variation we see in nature.

I began studying the question out of pure curiosity. But could it be more? Could the answer to why zebras are striped provide any benefits to society? There are many ideas about the advantages that stripes might confer on zebras.

Three ideas have some support: that stripes help zebra escape predation, avoid biting flies, and keeping cool. I’ll take up each of these ideas in turn, while speculating about the societal benefits that could obtain if they were proven to be true.

Predation and the dazzle effect

The most well-known idea about why zebras are striped is that they help them escape predation. The thought is that the dazzle effect of their stripes confuses the predator about either distance, speed, direction of movement, or where one zebra ends and the other begins.

The dazzle effect has already been put to use. In the first world war, ships were painted with bold black and white patterns in the hopes of making them less vulnerable to attack.

Research is mixed as to whether stripes actually lend such an advantage to zebras or might instead make them easier to catch. Once we understand whether stripes make something harder or easier to capture, rest assured that technology will make use of the fact.

Stripes as insect repellent

It has also been suggested that zebra stripes keep disease-carrying flies, such as tsetses and horseflies, from biting. Nagana, a form of sleeping sickness carried by tsetse flies, is a serious deterrent to livestock rearing in parts of Africa. Much research has gone into trying to mitigate this problem.

Researchers are working on not only why zebras are striped, but how. By trying to work out the genetic basis, we might one day be able to breed zebra-striped livestock. I can just see a herd of zebra striped cows contentedly munching away in a swarm of confused tsetse flies.

This solution for livestock would be a double-edged sword, though. The inability to rear livestock is one reason some areas of Africa are safe from human encroachment and are left for wildlife.

At any rate, the waterbuck may have already stolen the zebra’s thunder. Researchers have discovered that waterbuck give off an odour that deters tsetse flies. Collars exuding this smell are now being developed for livestock to wear. This is very much like your dog or cat wearing a flea collar.

Stripes to stay cool

There is another idea about the function of zebra stripes that could have an impact on their survival, and could possibly benefit humans and the rest of the planet. Collaborators and I recently discovered that the strength of striping in one species of zebra, the widespread plains zebra, varies with temperature.

The more stripy zebra are found in hot, tropical climates. Preliminary experiments also suggest that strong black and white stripes may help keep zebras cool under the tropical sun.

Zebra stripes differ.
Brenda Larison

If the biting fly hypothesis is true, temperature may also influence how many parasites they carry. Clearly this matters for zebra in the face of climate change. Zebra in regions of Africa that have seasonally cooler temperatures have subtler striping and often lack stripes on the legs.

Should climate change render these regions hotter, these less stripy zebras may have insufficient ability to thermoregulate and they may be subject to bites by flies that now harbour more parasites. Either of these could pose serious problems for zebras if their populations cannot evolve stronger striping quickly enough.

On a more positive note, if zebra stripes can truly create cooling, imagine an inexpensive cooling system for buildings that requires no energy input once in place. Instead of turning on the air conditioning, just roll out a black and white striped cover onto your roof during hot spells. This could significantly reduce energy usage and help mitigate climate change.

Only time will tell whether any of these ideas pan out. Meanwhile, I work simply to satisfy my curiosity, and hopefully yours.

The Conversation

Brenda Larison is Assistant Adjunct Professor, Department of Ecology and Evolutionary Biology at University of California, Berkeley

This article was originally published on The Conversation. Read the original article.

Pottoka Piornal ponies WE

This entry was contributed to Wild Equus by Lucy Rees, member and researcher of the Wild Equus Network (WEN). You can visit the Pottokas en Piornal website, where you will find more details about her work with the feral pottoka ponies.


Species: Equus caballus

Subspecies/Breed/Type: Pottoka (Basque Pony)

Country: Spain

Region/Province/Range: Sierra de Tormantos, Piornal (Extremadura-Caceres)

Population type: Feral

Management Authority:  Pottokas en Piornal

Estimated Population size: about 40 horses (2015)

Census August 2015

Foals 2015 m 5 (+ 1 that died) f 3

Yearlings    m 4 (b, 3n) f. 3  (d, 2n)

2 y-olds      m 1 (b)  f  4

3 & above   m 5 (b, 4s) f  15

Total 40, m 15, f 25
b= bachelor, s=stallion, n= still with natal band, d=dispersed  – 9/15 mares foaled. = 60%.

Of the 6 that did not foal, 4 were 3 y-o that foaled last year at 2, 1 is 3 y-o,  1 unknown (mare not seen for 3 months)


Details of Population

1200ha. of mountain between 700m and 1500m. , with two deep gorges. Lower-lying areas are oak wood (about 400ha) with scattered chestnut plantations, the latter mainly unavailable to the ponies. The rest is mainly high, dense heather, Spanish broom, bracken and rock, with occasional areas of grass.

Average winter temperature 2.8º; snow may cover areas over 1000m for up to a month. Average summer temperature 20.8º . Water is abundant except in dry summers when all but two springs may dry up. The ponies practice seasonal vertical migration.

The area may also be grazed by up to 600 goats. Occasional red deer, groups of fallow deer, wild boar, fox, martin, jineta, rabbits (few), walkers and cyclists share the area. No large predators.

The population was set up as an open-access study facility for equine researchers and students with non-invasive projects. All ponies can be identified individually and their life history is known. Pottokas are Basque ponies whose DNA variation corresponds to a wild, not domesticated breed. Ours have no management except culling to limit numbers.

Their social organization corresponds to other older feral populations: natal bands, home ranges (around 300ha.), natal dispersal, bachelor bands often joined by dispersing fillies. Three have tamed themselves but the rest cannot be touched although they admit close observation.

Population growth has been limited by culling. In 2014 one entire band (young stallion, old mare, her daughter and grand-daughter) were removed. In 2015 11 ponies (3 y-o stallion, 7 y-o mare, her yearling son, and 7 fillies of 1 and 2 years old were removed). The individuals were chosen to minimize social disruption, being mostly fillies in natal dispersal. To reduce possible conflicts each band was rounded up separately and the youngsters removed.

Despite apparent lack of good forage the ponies are in extremely good condition although lactating mares lose weight at the end of the summer. The ponies show an astonishing ability to self-heal even severe wounds. Parasite burden is negligible.

Structure and demographics

4 single-stallion natal bands, one bachelor band.
The population was set up in 2007/8 in Catalonia with two bands each of one stallion and three mares. On moving the population to its present location in 2011, a 3 year-old unrelated stallion was introduced.

Of the 11 foals conceived in Catalonia 9 were female. In Extremadura 20 colts and 19 fillies have been born.
Mortality:
12 y-o mare, piroplasmosis (Catalonia, 2007)
colt 6 months killed by hippies (c, 2008)
14 y-o stallion, infection from broken tooth (Extremadura, 2014)
12 y-o mare, herbicide poisoning (Extremadura, 2013)
yearling colt, eating plastic bag (E, 2014)
foal 3 weeks (E. 2015)
2 disappeared colts.

About half the fillies become pregnant as yearlings, giving a very fast-growing, female-skewed  population (see culling, below). Fillies that foal at 2 do not foal at 3. Colts begin (inefficiently) to form natal bands at 3 years old.

Issues worth noting and needed actions

a) Legal imperative to microchip, which causes stress and social disruption and is extremely difficult in practice. The European regulations allow exemption in wild or feral ponies but the Extremadura authorities do no recognize this.
b) Damage to fences and walls caused by herds of goats, whose owner refuses to use the gates, cause escapes, social disruption and conflicts with the police.

Bibliography and further reading

Genetic analysis in the basque pony-pottoka breed. Preliminary results

Genetic variability in two spanish horse populations: Preliminary results

Pottoka’s behaviour and training

El caballo al final de la última glaciación en el período postglacial

Hippo gets zebra foal across the river

A cool little video of how a zebra foal drifting away during a Mara River crossing manages to get to shore with the help of a female hippo.
Many tourists visit the Mara River crossings every year, in hopes of witnessing one of the most spectacular and popular animal migrations known. Images portraying the ‘red in tooth and claw’ struggle of Wildebeest and Zebra to get to better grazing grounds abound.
Incidents like these are still few and scattered, but are always a breath of fresh air.
An image of the heroine hippo and the zebra foal on shore.
Incidentally, the same hippo was reported to have helped a Wildebeest calf in a similar incident, only 10 minutes before.
African wildlife - Mother hippo rescues a baby wildebeest in Kenya
Image taken by the Sanctuary Olonana Camp Manager

Read more about these sightings here:

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