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

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.

Temperature as a constraint on the timing and duration of African elephant foraging trips

“…Despite the fact that the timing of visits to waterholes reduces the average temperature experienced during the whole trip, it seems that it puts elephants at risk of overheating due to the final march towards waterholes undertaken in the afternoon heat. We argue that this risk may be lower than expected because elephants can quickly cool down at the waterhole by drinking, bathing, wallowing, or spraying themselves (Dunkin et al 2013;Mole et al 2016), thanks to the water retention properties of their skin structure (Lillywhite and Stein 1987;Martins et al 2018).…”

“…The elephants' mass and volume, and the absence of sweat glands, make it difficult for them to lose heat, increasing the risk of overheating (Wright 1984;Wright and Luck 1984). Biophysical studies highlighted anatomical and morphological adaptation in elephants favoring heat dissipation through ear flapping (Koffi et al 2014;Phillips and Heath 1992;Wright 1984) or sufficient passive evaporative cooling (Wright and Luck, 1984) through cracks in the skin (Lillywhite and Stein, 1987;Martins et al, 2018). Finescale behavioral adjustments such as shade-seeking, dust-bathing, or wetting, also could be critical for their physiology, especially under high water and thermal constraints when physiological adaptations are not suficient (Kinahan et al 2007;Mole et al 2016;Thaker et al 2019).…”

The postembryonic transformation of the shell in emydine box turtles

“…Some notable case studies that might be explained by function‐induced changes are the postembryonic emergence of the atypical cranio‐facial hinge of parrots (Tokita, ), as well as the evolutionarily novel maxillary hinge of bolyerine snakes (Frazzetta, , ). There is already a growing body of literature corroborating that trait patterning or repatterning is often a correlated structural response to trait function (Martins et al, ; Milinkovitch et al, ; M. L. Zelditch, Wood, & Swiderski, ). Thus, successful differentiation of many adaptive phenotypes might be underlain by both biochemical and biomechanical mechanisms acting across embryonic and postembryonic life stages of organisms (e.g., epigenetic bone remodeling; Young & Badyaev, ).…”

Textured Building Façades: Utilizing Morphological Adaptations Found in Nature for Evaporative Cooling

“…The network of wrinkles on the surface of an elephant's skin enhances their thermoregulation by retaining water in the crevasses across the skin allowing for 5-10 times the retention of water than a flat surface, supporting thermoregulation through evaporative cooling for a longer time [19]. Wrinkles also self-shade and create convective currents that augment cooling [20].…”