Architecture of vibrissae in eight rodent species of Ctenohystrica (Rodentia): A comparative SEM study

Abstract

Our study was conducted within the framework of comparative functional morphology of mammalian skin (Sokolov 1982) and “Trichomorphology” (Hausmann 1930; 1944; Teerink 1991) focusing in particular on specialized tactile organs such as whiskers (vibrissae). The architecture of vibrissae was studied for the first time using SEM in the relict rodent Laonastes aenigmamus and in some other representatives of the clade Ctenohystrica (Rodentia): Ctenodactylus gundi, Pectinator spekei, Proechimys guyannensis, Echimys sp., Trichomys apereoides, Chinchilla lanigera, and Octodon degus with the aim to identify the specific characters for each species. The vibrissal architecture is specific and polymorphic: the rod shape and structure of the medulla show differences between species of different genera and differ from those of guard hairs and spines of the same species. In L. aenigmamus, the vibrissal medulla is peculiar in its internal structure, which, together with the structure of guard hairs in this species, confirms its phylogenetically distinct position within Ctenohystrica. For the compared species, the complex medulla is with variously arranged systems of keratinized septa and different degrees of development of air spaces between them (ranging from unstructured and irregular to uni- or biserial ladder-like, cellated or pyramidal). The vibrissae have a non-specialized cuticle serving mostly for protection during tactile contacts, which distinguishes it from the diverse and multifunctional cuticle of guard hairs, spines, and quills. The tactile function of vibrissae is corroborated by the presence of scuff marks, scratches and even cuticle loss at the tip and on the ventral side of the rod, a thickened dense cortex and a poorly developed medullar layer but diverse its internal architecture, which provides only a very limited thermal protection, unlike that of the hair pelage. The SEM study of vibrissal architecture is a promising line of research, because a better knowledge of vibrissae may contribute to the biology and biomimetics.