Gradients of Mechanical Properties in Taenioglossan Radular Teeth is Linked with Specific Function and Ecological Niche

Biological composites usually display graded heterogeneities in structure and mechanical properties, enabling proper functioning. The radula, one important molluscan autapomorphy and the organ for food processing, is well examined in the light of its morphology, but the mechanical properties that enable an efficient acting of the radular teeth on the ingesta with a simultaneous reduction of structural failure are not known for the vast majority of gastropods. In this case study, we employed nanoindentation technique, to measure mechanical properties (hardness and Young’s modulus) on three distinct localities of an individual radular tooth in taenioglossan radular teeth of African paludomid gastropods with distinct ecological niches (preferred feeding substrate). A gradual distribution of measured properties along the teeth was found in species foraging on solid or mixed feeding substrates, but soft substrate feeders exhibit teeth almost homogeneous in their biomechanical properties. We hypothesize, that large-scale gradients are not abundant in all biological materials and that the presence of functional gradients is rather directly linked with their specific function and in general with the species ecology.