Abstract
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.
Highlights
Whiskers are present on the faces of almost all mammals (Ahl, 1986, 1987; Bauer, Reep, & Marshall, 2018; Ginter, DeWitt, Fish, & Marshall, 2012)
Many aquatic mammals are considered whisker specialists (Bauer et al, 2018; Grant & Arkley, 2015), and we suggest that they have a different whisker morphology, better able to cope with sensing in an aquatic environment
The quick and easy scanning and analysis methods that we propose here are able to accurately capture gross measures of whisker curvature and taper, enabling lots of data to be collected for comparative analyses
Summary
Whiskers are present on the faces of almost all mammals (Ahl, 1986, 1987; Bauer, Reep, & Marshall, 2018; Ginter, DeWitt, Fish, & Marshall, 2012). They are specialised vibrotactile sensors that can guide behaviours such as navigation, locomotion, foraging, and social interactions (Grant & Arkley, 2015). Whisker specialists are species that can actively move their whiskers to sense, and include rodents, insectivores, and pinnipeds (Grant & Arkley, 2015; Muchlinski, Wible, Corfe, Sullivan, & Grant, 2020), suggesting that whiskers are especially useful for animals that live in dark, complex environments. Whisker morphology can vary between species, for example, many phocids have undulating, beaded whiskers (Ginter et al, 2012; Ginter, Fish, & Marshall, 2010; Hanke et al, 2010; Rinehart, Shyam, & Zhang, 2017), and aquatic mammals are thought to have more innervated whiskers than terrestrial species
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