Whiskers That Don’t Whisk: Unique Structure From the Absence of Actuation in Elephant Whiskers

2024

Miscellaneous

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Whiskers are so named because these hairs often actuate circularly, whisking, via collagen wrapping at the root of the hair follicle to increase their sensing volumes. Elephant trunks are a unique case study for whiskers, as the dorsal and lateral sections of the elephant proboscis have scattered sensory hairs that lack individual actuation. We hypothesize that the actuation limitations of these non-whisking whiskers led to anisotropic morphology and non-homogeneous composition to meet the animal's sensory needs. To test these hypotheses, we examined trunk whiskers from a 35-year-old female African savannah elephant (Loxodonta africana). Whisker morphology was evaluated through micro-CT and polarized light microscopy. The whiskers from the distal tip of the trunk were found to be axially asymmetric, with an ovular cross-section at the root, shifting to a near-square cross-section at the point. Nanoindentation and additional microscopy revealed that elephant whiskers have a composition unlike any other mammalian hair ever studied: we recorded an elastic modulus of 3 GPa at the root and 0.05 GPa at the point of a single 4-cm-long whisker. This work challenges the assumption that hairs have circular cross-sections and isotropic mechanical properties. With such striking differences compared to other mammals, including the mouse (Mus musculus), rat (Rattus norvegicus), and cat (Felis catus), we conclude that whisker morphology and composition play distinct and complementary roles in elephant trunk mechanosensing.

@misc{Schulz24-SICBA-Whiskers,
  title = {Whiskers That Don’t Whisk: Unique Structure From the Absence of Actuation in Elephant Whiskers},
  author = {Schulz, Andrew and Kaufmann, Lena and Brecht, Michael and Richter, Gunther and Kuchenbecker, Katherine J.},
  howpublished = {Abstract presented at the Society for Integrative and Comparative Biology Annual Meeting (SICB)},
  address = {Seattle, USA},
  month = jan,
  year = {2024},
  doi = {},
  month_numeric = {1}
}