Ecomorphology reveals Euler spiral of mammalian whiskers

• Published in: Journal of morphology (1931) Vol. 281; no. 10; pp. 1271 - 1279
• Main Authors: Dougill, Gary, Starostin, Eugene L., Milne, Alyx O., Heijden, Gert H. M., Goss, Victor G. A., Grant, Robyn A.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.10.2020
• Subjects: Animals; curvature; Linear Models; Mammals - anatomy & histology; mechanoreception; morphology; Multivariate Analysis; Principal Component Analysis; touch; vibrissae; Vibrissae - anatomy & histology; Vibrissae - innervation; mechanoreception; touch; morphology; vibrissae; curvature
• ISSN: 0362-2525; 1097-4687
• DOI: 10.1002/jmor.21246

Whiskers are present in many species of mammals. They are specialised vibrotactile sensors that sit within strongly innervated follicles. Whisker size and shape will affect the mechanical signals that reach the follicle, and hence the information that reaches the brain. However, whisker size and shape have not been quantified across mammals before. Using a novel method for describing whisker curvature, this study quantifies whisker size and shape across 19 mammalian species. We find that gross two‐dimensional whisker shape is relatively conserved across mammals. Indeed, whiskers are all curved, tapered rods that can be summarised by Euler spiral models of curvature and linear models of taper, which has implications for whisker growth and function. We also observe that aquatic and semi‐aquatic mammals have relatively thicker, stiffer, and more highly tapered whiskers than arboreal and terrestrial species. In addition, smaller mammals tend to have relatively long, slender, flexible whiskers compared to larger species. Therefore, we propose that whisker morphology varies between larger aquatic species, and smaller scansorial species. These two whisker morphotypes are likely to induce quite different mechanical signals in the follicle, which has implications for follicle anatomy as well as whisker function. Mammalian whiskers have a linear curvature as a function of their length and, when normalised, can be mapped onto an Euler spiral. Here, 687 whiskers from terrestrial (red), arboreal (green), semi‐aquatic (black), and aquatic (blue) mammals are mapped onto a single Euler spiral. This indicates that mammalian whiskers have a shape that is conserved over a range of species.