Functional gradients facilitate tactile sensing in elephant whiskers

Keratin composites enable animals to hike with hooves, fly with feathers, and sense with skin. Mammalian whiskers are elongated keratin rods attached to tactile skin structures that extend the animal's sensory volume. We investigated the whiskers that cover Asian elephant (Elephas maximus) trunks and found that they are geometrically and mechanically tailored to facilitate tactile perception by encoding contact location in the amplitude and frequency of the vibrotactile signal felt at the whisker base. Elephant whiskers emerge from armored trunk skin and shift from a thick, circular, porous, stiff base to a thin, ovular, dense, soft tip. These functional gradients of geometry, porosity, and stiffness independently tune the neuromechanics of elephant trunk touch to facilitate highly dexterous manipulation while ensuring whisker durability.