Comparative tongue anatomy of the rakali (Hydromys chrysogaster) and greater stick-nest rat (Leporillus conditor) (Rodentia; Muridae)

Abstract

For many mammals, the tongue provides an important functional interface with the environment through roles including manipulating, ingesting, and mechanically processing food items. As such, the adaptations of the tongue reflect different physical properties of an animal’s diet. We sought to investigate whether adaptations of the tongue are apparent in two native Australian rodents that have divergent dietary niches: the semiaquatic and mixed feeding rakali (Hydromys chrysogaster) and the arid dwelling, herbivorous stick-nest rat (Leporillus conditor). Both species retained many lingual features typical of rodents. A notable difference was a large, annular pad surrounding the single circumvallate papilla in H. chrysogaster, suggesting an enhanced gustatory function, which would be consistent with adaptation to a semiaquatic, mixed diet. In contrast, L. conditor appeared to have reduced gustatory sensitivity and mechanical dexterity, consistent with crushing their preferred succulent plant forage and manipulating sticks for nest building. The descriptions provide a novel view of the evolution of soft tissues within Australian endemic rodents.