Collective Effect of Damage Prevention in Taenioglossan Radular Teeth is Related to the Ecological Niche

Abstract

The molluscan radula, a thin membrane with embedded rows of teeth, is the structure for mechanical food processing and gathering. For proper functioning, radular failures must be either avoided or reduced, as this might be of high significance for the individual fitness. The factors, leading to the structural failure of teeth, are related to trophic specializations of species. Here, the failure of non-mineralized, chitinous radular teeth from an African paludomid species flock, inhabiting Lake Tanganyika and surrounding river systems, were tested in a biomechanical experiment. These species are of high interest for evolutionary biologists, since they represent a potential result of an adaptive radiation. With a force transducer attached to a motorized stage, a shear load was applied to tooth cusps until structural failure occurred. Subsequently broken areas were measured, and breaking stress was calculated. As the experiments were carried out under dry and wet conditions, the high influence of the water content on the forces, teeth were capable to resist to, could be documented. Wet teeth were able to resist to higher forces, because their flexibility was higher, which enabled them either to slip away or to gain support from adjacent teeth. This mechanism can be understood as collective effect reducing structural failure, without the mineralisation by wear-minimizing elements, as described for Polyplacophora and Patellogastropoda. As the documented mechanical behaviour of radular teeth is related to the gastropod ecological niche, it can thus be identified as an adaptation to preferred feeding substrates.