Department of Mammalogy and Paleoanthropology, Center of Natural History (CeNak), Universität Hamburg, Martin-Luther-King-Platz 3, 20146 Hamburg, Germany; Functional Morphology and Biomechanics, Zoological Institute, Christian-Albrechts-Universität zu Kiel, Am Botanischen Garten 9, 24118 Kiel, Germany.
Functional Morphology and Biomechanics, Zoological Institute, Christian-Albrechts-Universität zu Kiel, Am Botanischen Garten 9, 24118 Kiel, Germany.
Acta Biomater. 2021 Nov;135:458-472. doi: 10.1016/j.actbio.2021.07.073. Epub 2021 Aug 4.
The molluscan radula, a thin membrane with embedded rows of teeth, is the structure for food processing and gathering. For proper functioning, radular failures must be either avoided or reduced when interacting with the preferred food, as this might be of high significance for the individual fitness. Thus, the analysis of structural failure in radular teeth could be included in studies on trophic specializations. Here, we tested the failure of non-mineralized, chitinous radular teeth from taxa, belonging to an African paludomid species flock from Lake Tanganyika and surrounding river systems. These species are of high interest for evolutionary biologists since they represent a potential result of an adaptive radiation including trophic specialisations to distinct substrates, the food is attached to. In a biomechanical experiment a shear load was applied to tooth cusps with a force transducer connected to a motorized stage 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, could be documented. Wet teeth were able to resist higher forces, because of their increased flexibility and the flexibility of the embedding membrane, 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 with wear-minimizing elements, as described for Polyplacophora and Patellogastropoda. Since the documented mechanical behaviour of radular teeth and the maximal forces, teeth resist, can directly be related to the gastropod ecological niche, both are here identified as an adaptation to preferred feeding substrates. STATEMENT OF SIGNIFICANCE: The radula, a chitinous membrane with teeth, is the molluscan feeding structure. Here we add onto existing knowledge about the relationship between tooth's mechanical properties and species' ecology by determining the tooth failure resistance. Six paludomid species (Gastropoda) of a prominent species flock from Lake Tanganyika, foraging on distinct feeding substrates, were tested. With a force transducer wet and dry teeth were broken, revealing the high influence of water content on mechanical behaviour and force resistance of teeth. Higher forces were needed to break wet radulae due to an increased flexibility of teeth and membrane, which resulted in an interlocking or twisting of teeth. Mechanical behaviour and force resistance were both identified as trophic adaptations to feeding substrate.
软体动物的齿舌，是一种带有嵌入式齿列的薄膜，是进行食物处理和采集的结构。为了正常运作，当与首选食物相互作用时，必须避免或减少齿舌的故障，因为这对个体的适应性可能非常重要。因此，分析齿舌结构的故障可以包括在研究营养特化方面。在这里，我们测试了来自坦噶尼喀湖及其周边河流系统的非洲 paludomid 种团的分类群的非矿化、几丁质齿舌的故障。这些物种对进化生物学家非常感兴趣，因为它们代表了适应辐射的潜在结果，包括对不同基质的营养特化，食物就附着在这些基质上。在生物力学实验中，使用力传感器将剪切力施加到齿尖上，该传感器连接到一个电动台上，直到结构故障发生。随后测量断裂区域并计算断裂应力。由于实验是在干燥和湿润条件下进行的，因此可以记录下水含量对牙齿能够承受的力的高度影响。湿齿能够承受更高的力，因为它们的柔韧性增加，并且嵌入膜的柔韧性使它们能够滑动或从相邻的牙齿获得支撑。这种机制可以被理解为一种集体效应，减少了结构故障而无需使用耐磨最小化元素进行矿化，如多板纲和腹足纲所描述的那样。由于齿舌的机械行为和牙齿所能承受的最大力可以直接与腹足动物的生态位相关，因此这两者都被确定为对首选食物基质的适应。意义声明：齿舌，是一种带有牙齿的几丁质膜，是软体动物的进食结构。在这里，我们通过确定牙齿的抗故障能力，在牙齿的机械性能和物种生态之间的关系方面增加了现有知识。测试了来自坦噶尼喀湖的一个突出种团的六种 paludomid 物种（腹足纲），它们以不同的摄食基质为食。使用力传感器，对湿齿和干齿进行了断裂测试，揭示了水含量对牙齿机械行为和力阻力的高度影响。由于牙齿和膜的柔韧性增加，导致牙齿相互锁合或扭曲，因此需要更大的力才能折断湿齿舌。机械行为和力阻力都被认为是对摄食基质的营养适应。
