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Nat Commun. 2018 Oct 2;9(1):3865. doi: 10.1038/s41467-018-06257-3.

Locally-curved geometry generates bending cracks in the African elephant skin.

Author information

1
Laboratory of Artificial & Natural Evolution (LANE), Department of Genetics & Evolution, University of Geneva, Geneva, 1211, Switzerland.
2
SIB Swiss Institute of Bioinformatics, Geneva, 1211, Switzerland.
3
Mammal Research Institute, University of Pretoria, Hatfield, 0028, South Africa.
4
Zoo African Safari, Plaisance du Touch, 31830, France.
5
Department of Anatomy & Physiology, University of Pretoria, Hatfield, 0028, South Africa.
6
Adventures with Elephants, Bela Bela, D1000 LP, South Africa.
7
Zoo Basel, Basel, 4054, Switzerland.
8
Réserve Africaine, Sigean, 11130, France.
9
School of Anatomical Sciences, University of the Witwatersrand, Johannesburg, Braamfontein, 2000, South Africa.
10
Laboratory of Artificial & Natural Evolution (LANE), Department of Genetics & Evolution, University of Geneva, Geneva, 1211, Switzerland. Michel.Milinkovitch@unige.ch.
11
SIB Swiss Institute of Bioinformatics, Geneva, 1211, Switzerland. Michel.Milinkovitch@unige.ch.

Abstract

An intricate network of crevices adorns the skin surface of the African bush elephant, Loxodonta africana. These micrometre-wide channels enhance the effectiveness of thermal regulation (by water retention) as well as protection against parasites and intense solar radiation (by mud adherence). While the adaptive value of these structures is well established, their morphological characterisation and generative mechanism are unknown. Using microscopy, computed tomography and a custom physics-based lattice model, we show that African elephant skin channels are fractures of the animal brittle and desquamation-deficient skin outermost layer. We suggest that the progressive thickening of the hyperkeratinised stratum corneum causes its fracture due to local bending mechanical stress in the troughs of a lattice of skin millimetric elevations. The African elephant skin channels are therefore generated by thickening of a brittle material on a locally-curved substrate rather than by a canonical tensile cracking process caused by frustrated shrinkage.

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