For elephants, cracked and wrinkly skin is a good thing
Crevices in mighty mammal are more common in non-living materials. Nick Carne reports.
The channels visible on the skin of the African bush elephant (Loxodonta africana) are physical cracks caused by bending in the early years, new research suggests.
The intricate network of interconnected crevices is quite distinct from the more obvious elephant wrinkles and is rare in biological systems. It is normally non-living materials that crack.
And it is an African thing. Asian elephants do not have them.
Why the channels are there has been known for some time. They retain five to 10 times more water than a flat surface, which impedes dehydration and improves thermal regulation, and they help mud stick, which offers protection from parasites and the African sun.
To work out how they got there, a team of researchers from Europe and South Africa, led by Michel Milinkovitch from Switzerland’s University of Geneva, decided to take a closer look, using microscopy, computed tomography and a custom physics-based lattice model.
The team’s conclusion, in a paper published in Nature Communications, is that the cracks are only in the skin’s outermost layer, the stratum corneum, and are caused by bending stress of the progressively growing epidermis.
The layer is brittle and gets progressively thicker because it doesn’t tend to peel.
“Here we show that the African elephant not only exhibits physiological and genuine physical cracking of its stratum corneum but that this process is also mechanistically distinct from the archetypal tensile cracking caused by frustrated shrinkage,” the researchers write.
In support of these conclusions, they note that new-born elephants do not have channels, and that in adults they disappear when the outer layer of skin is removed. Below the surface, L. africana is similar its Asian counterpart.
Why African elephants have cracked skin and Asian ones don’t requires further study, the researchers say, although adaption to different environments is likely to play a part.
Also worth exploring is the observation that a parallel appears to exist between the physiological characteristics of the bush elephant’s skin and that of humans affected by Ichthyosis vulgaris, a disorder which causes dry, scaly skin.