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The skin of African elephants is covered with a pattern of cracks that resembles damaged asphalt, dry mud in the sun or the polar landscape of the Earth. This pattern helps the elephant retain water on its surface and cool off in hot weather in the savannah. Swiss researchers have now determined that the reason was not due to the shrinkage of the skin (as some had suspected) but rather to a true fracture of the outermost layer of skin of the elephant.
Unlike humans, African elephants do not have sweat glands or sebum. This means that she can not keep her skin moist and flexible on her own or cool down, which can make things very difficult for an elephant living in a dry, warm habitat. Fortunately, the animal has come up with a clever solution: its wrinkled skin retains water and mud that cool the elephant by evaporation and also serve to fight against pests.
The applied mud does not fall easily because the skin is carved by a fine pattern of millions of channels that allow the spreading and retention of 5 to 10 times more water than a flat surface.
An interdisciplinary team of researchers led by Michel Milinkovitch, professor in the Department of Genetics and Evolution at the University of Geneva, now indicates that the cutaneous channels of the African elephant are cracks caused by local bending stress of the epidermis. Three main factors are responsible for this effect: hyper-keratinized and shedding skin that develops on a network of millimeter elevations.
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Researchers have shown by computer simulations that flexural stress accumulates between different levels of skin elevation as the skin thickens to crack formation, rejecting the hypothesis of "shrinkage cracking". ".
Mechanical instabilities such as cracks in the pavement are not common in living beings. Previously, Milinkovitch's laboratory had shown that the crocodile's scale pattern was formed by skin fold, a dynamic similar to the cracking of mud drying. Now, Swiss researchers have shown that African elephant skin has not only fissure-like channels, but that it is really a physical fissure of the keratinized epidermis.
Back of the lower limbs of a person with ichthyosis. Credit: Walter Howard, Dr. T.R. Bailey / April 4, 1888.
It is striking that the skin morphology of the African elephant is very similar to that of humans with ichthyosis vulgaris – a genetic disease that occurs in 1 in 250 people and is responsible for dry skin. flaky. Future studies that could confirm the analogy with molecular and cellular biology could lead to new treatments for this pathology.
"This correspondence would also show that similar mutations occurred independently in evolutionary lineages of humans and elephants were unfavorable in the first and adaptive in the second," says Michel Milinkovitch.
The results appeared in the newspaper Nature Communications.
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