Influence of water content on mechanical behaviour of gastropod taenioglossan radulae

Abstract

One molluscan autapomorphy is the radula, the organ used for feeding. Here, for the first time, the performance and failure of taenioglossan radular teeth were tested in a biomechanical experiment which in turn allowed building hypotheses about tooth functionalities. Shear load was applied to tooth cusps with a force transducer until structural failure occurred, the broken area was measured, and finally breaking stress was calculated. These experiments were carried out under dry and wet conditions. Our results show that certain tooth types can resist higher stresses and are rather specialised to loosen food items from a surface, whereas other teeth can only gather food particles. The experiments additionally illustrate the high influence of the water content on the resulting breaking stress. When wet teeth were tested, their ductility and ability to avoid being fractured by an obstacle increased. Their flexibility also allowed them support from teeth of adjacent tooth rows, which made the whole system less prone to failure. Our results were compared with the previous data on the mechanical properties and feeding simulations. This study provides a keystone for further comparative studies aiming at connecting diversity of radulae with their possible adaptations to the ingesta.

From the knitting shop: the first physical and dynamic model of the taenioglossan radula (Mollusca: Gastropoda) aids in unravelling functional principles of the radular morphology

“…Our results indicate that centrals are not affected by stress and strain, marginals are highly affected, and laterals are intermediate [55]. (v) By breaking stress experiments, documenting the force needed to break teeth, we found that centrals are capable of resisting the highest stresses, followed by the laterals, and finally marginal teeth [56,57]. During these experiments, we observed that native (wet) centrals and laterals can interlock with adjacent teeth and thus resist higher stresses (collective effect), whereas the wet (native) marginal teeth are capable of twisting and bending.…”

“…By almost all manipulations of the model, we observed a tight interlocking and formation of a stiff array due to the interaction of the laterals, which is clearly a kind of 'collective effect' leading to a proper stress distribution and thus to the reduction of the structural failure, when interacting with ingesta (for stress distribution through the interlocking of teeth, see also [2,32,[56][57][58][59][60][61][62]). The centrals usually do not form a stiff array with the adjacent central teeth but enable the stabilization of each transversal tooth row by lateral interlocking with the lateral teeth.…”

“…By finite-element analysis (FEA), three-dimensional morphology can be consolidated with material property data, resulting in computer-aided simulations of an individual structure's mechanical behaviour [55]. Our approach was strictly computer-based first, but meanwhile subsequently translated into the physical world in form of breaking stress experiments on real radulae, where the shear load was applied to individual tooth cusps of the whole radula with a needle, measuring simultaneously the breaking force and documenting behaviour of teeth (bending, twisting and relying on other teeth) [56,57]. These experiments partially verified the previous computerbased FEA simulations, but additionally, we discovered that significantly higher force was needed to break wet teeth than dry ones, even though wet biological materials are usually softer than dry ones.…”

“…to obtain a simplistic but realistic physical model capable of mimicking proper degrees of freedom during the motion and interaction of radular parts (teeth, alary processus) when the underlain supporting structures (buccal mass muscles with odontophoral cartilages) were manipulated. We decided to build the radula of Spekia zonata (Woodward, 1859) (Gastropoda, Caenogastropoda, Cerithioidea, Paludomidae) from Lake Tanganyika, since tooth material properties, threedimensional morphology, tooth position on membrane and mechanical behaviour are known and stress and strain simulations have been previously performed [2,31,[52][53][54][55][56]63]. Additionally, since this radula is taenioglossan (containing only seven teeth per tooth row), it does not contain many individual parts and is thus less complex.…”

Elemental analyses reveal distinct mineralization patterns in radular teeth of various molluscan taxa

“…We thus propose that specific cross-linking conditions of the chitin due to tanning 1 , fiber arrangement, and density 22 , 23 , 26 , 28 , 31 , 88 , 143 – 145 rather cause the heterogeneities in mechanical properties. We previously also detected that the capability of wet teeth to rely on one another and to redistribute the mechanical stress increases the radula’s resistance to structural failure in paludomid gastropods 146 , 147 . This altogether probably enables the feeding on harder ingesta types.…”