Describing the whiskers of a semi-aquatic caniform: the Eurasian Otter ( Lutra lutra )

Recent research has identified specializations in whisker shape and material in aquatic species, such as pinnipeds, that serve to increase the stiffness of their whiskers to allow for precise positioning underwater. The whiskers of semi-aquatic species are thought to be somewhat intermediary between aquatic and terrestrial species, but have been fairly overlooked, especially when compared to pinnipeds, which are easily trained and widely available in zoological collections. In this study, we describe the whiskers of the Eurasian Otter (Lutra lutra), including their shape, layout, musculature, movement, and control behaviours. Lutra lutra have 38 to 43 long mystacial whiskers. Taper, base width, and length are strong predictors of whisker shape. Whisker arrangement varies somewhat between individuals, especially in the 5 dorsal-most rows, which are rather disorganized with regard to both layout and intrinsic musculature. The whiskers can be protracted underwater using intrinsic muscles, as well as adapted extrinsic muscles (Pars interna profunda and Pars maxillaris). Whisker movements are common in L. lutra, as well as other contact-related control behaviors, including contact-induced asymmetry. The large numbers of whiskers, the regularity of whisker movements and specializations in whisker shape and muscles demonstrate the importance of whisker sensing in L. lutra. Despite this, L. lutra whiskers lack any adaptations in cross-sectional shape, such as oval shapes and undulations that occur in phocids. Nevertheless, studying the whiskers of semi-aquatic mammals reveals their specialized sensory adaptations to the aquatic environment, and can give us insights into the evolution of mammalian somatosensory systems.