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(Inside Science) – A gangrene bite in Africa, a 40-year-old curiosity and garden experiments that are still complaining about her daughters have united to tell one thing to Alison Cobb: rays help zebras to keep their blood cold. A new study published today in the Journal of Natural History shows that stripes can create air streams that give zebras a kind of natural air conditioning system helping them to protect themselves from the scorching sun.
"It's about thermoregulation to avoid heat and cold," said retired amateur naturalist Cobb, who led the research with her zoologist husband, Stephen Cobb. Other scientists argue that the main reason for scratching is to deter biting insects.
At the age of four, 85-year-old Cobb questions zebra striping for the first time after reading Rudyard Kipling's story "How did the leopard get its spots?" . But the camouflage seemed to be a bad explanation for Cobb, in the light of his own observations in Africa of lions crisscrossing the herds of zebras deciding which one to eat. She had also seen zebras spend a lot of time under the hot midday sun – more than the antelopes that lived in the same area – and she thought the scratches might help them cope with the heat.
Forty years ago, she made her first experiment by spreading colored coats of felt in the sun on oil drums filled with water and taking the temperature of the water to the water. inside. Without direct access to research animals, she used her three daughters aged 8, 9 and 10 years old. She made them wear rugby shirts sewn with zebra and she crawled her "lab animals" on all fours in the sun in England.
"They always complain about it. They are now 60 years old, "said Cobb.
But when she touched the different stripes on their back, they could tell him what was black and what was white without seeing. But that still did not give him a full explanation: if the white dots were colder, why did they have black wicks? Moreover, thanks to her long experience with horses, she knew that animals sweated a lot and she still did not know how perspiration would interact with different colored stripes.
She did not have a chance to approach zebras before her 70th birthday when she and her husband returned to Africa to test her idea about a couple of captive zebras living on private ranches in Kenya. December 2003. They measured the temperatures of the adjacent black and white bands on various parts of the zebras every 15 minutes throughout the day, as well as the ambient temperature of the air near the animals. They also took similar measures of a zebra skin wrapped around horse-shaped clothes left in the sun on the ranch.
The research was not without losses: Stephen Cobb was bitten by a territorial stallion and his injury turned into gangrene. "He still has a scar," said Alison Cobb.
But their research proved enlightening. They found that the temperature of the black and white bands differed greatly between live animals, with the differences being greater at the hottest times of the day. The bands on the inanimate skin showed a similar difference between the black and white bands, but the highest temperatures of the black bands were 15 degrees Celsius warmer than the maximum temperatures of the black bands of live zebras.
The couple of researchers believe that these differences in temperature are enough to cause small swirls of air. In living zebras, these airflows could help cool the zebras during the hottest hours of the day by accelerating the evaporation of sweat.
The Cobbs also noted that live zebras were able to stick their black hair in the air at some of the hottest hours of the day. They hypothesize that this behavior could also help regulate the heat, although the mechanism is still unclear.
Gabor Horvath, a researcher at Eotvos Lorand University in Budapest, who studied zebra stripes but did not participate in Cobbs' research, does not believe that thermoregulation is the primary function of zebra stripes.
"Such suspected convective air swirls could be formed exclusively over striped horizontal surfaces," he said in an e-mail. "If the main purpose of zebra bands was to cool through these swirls of air, only the almost horizontal areas of the back of zebras should be scratched."
Tim Caro, a wildlife biologist at the University of California, Davis, who also studied zebra stripes but did not participate in Cobbs' research, said it was an interesting descriptive study of temperature differences between black and white striped stripes. However, he does not think the article improves our understanding of the main factors behind the evolution of these band patterns in animals. His research and those of Horvath and others indicate that stripes could deter insects from landing.
"We are absolutely certain that it is a fight against biting flies," said Caro, adding that tsetse flies and horse flies that harass zebras in Africa may carry deadly diseases such as African horse sickness, equine influenza and a form of sleeping sickness called nagana. "They simply can not afford to let these biting flies land on their coats."
At the same time, Caro still thinks that scratches have thermal consequences for zebras. He, Horvath and the Cobbs agree that there is probably not a single reason why zebras have evolved into stripes.
Inside Science is a nonprofit, editorial and independent print, electronic and video journalism press service, owned by the American Institute of Physics.
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