What can whiskers tell us about mammalian evolution, behaviour, and ecology?

• Published in: Mammal review Vol. 52; no. 1; pp. 148 - 163
• Main Authors: Grant, Robyn A., Goss, Victor G. A.
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01.01.2022
• Subjects: behaviour; Carnivora; Comparative studies; Conservation; Ecology; Evolution; Laboratory animals; Mammalia; Mammals; marsupials; Muscles; Prey; Rodentia; sensory ecology; Species; Tinbergen; Vibrissae
• ISSN: 0305-1838; 1365-2907
• DOI: 10.1111/mam.12253

Most mammals have whiskers; however, nearly everything we know about whiskers derives from just a handful of species, including laboratory rats Rattus norvegicus and mice Mus musculus, as well as some species of pinniped and marsupial. We explore the extent to which the knowledge of the whisker system from a handful of species applies to mammals generally. This will help us understand whisker evolution and function, in order to gain more insights into mammalian behaviour and ecology. This review is structured around Tinbergen’s four questions, since this method is an established, comprehensive, and logical approach to studying behaviour. We ask: how do whiskers work, develop, and evolve? And what are they for? While whiskers are all slender, curved, tapered, keratinised hairs that transmit vibrotactile information, we show that there are marked differences between species with respect to whisker arrangement, numbers, length, musculature, development, and growth cycles. The conservation of form and a common muscle architecture in mammals suggests that early mammals had whiskers. Whiskers may have been functional even in therapsids. However, certain extant mammalian species are equipped with especially long and sensitive whiskers, in particular nocturnal, arboreal species, and aquatic species, which live in complex environments and hunt moving prey. Knowledge of whiskers and whisker use can guide us in developing conservation protocols and designing enriched enclosures for captive mammals. We suggest that further comparative studies, embracing a wider variety of mammalian species, are required before one can make large‐scale predictions relating to evolution and function of whiskers. More research is needed to develop robust techniques to enhance the welfare and conservation of mammals. The majority of whisker research has been focused on rodents, marsupials, and pinnipeds, and we use these studies to infer patterns in many mammalian species. There are similarities in whisker form across mammals; for example, whiskers are all touch‐sensitive, slender, curved tapered hairs, with a common muscle architecture. This conservation of form suggests that early mammals had whiskers, and that they may have even been functional in therapsids. There were also some differences in whisker form between species. Some species are equipped with especially long and sensitive whiskers, and these tend to be nocturnal, arboreal species, and aquatic species, which hunt moving prey. We propose that comparative biology offers opportunities to explore associations with whisker function and evolution in mammals. Such research should also inform us of habitat features that are important for different species, which also has implications for animal welfare and enrichment. Whiskers can be used for isotope and hormonal analyses, which has conservation applications. This review highlights that if we wish to extend our understanding of how whisker form relates to function, then research must extend to encompass a wider range of species.