Amphibian sticky tongues: functional morphology, biomechanics, and evolution of a natural high performance adhesive system

在脊椎动物进化过程中，从水生栖息地到陆地栖息地的转变与陆地生命的许多特化有关。虽然早期的四足动物可能以水生猎物为食，但用于捕获和运输猎物的舌头的进化导致了几种新的陆地捕食模式。在两栖动物（如青蛙、蝾螈和无尾螈）中，可以粘住猎物并将猎物拉进嘴里的粘性舌头进化了好几次。两栖动物粘附舌头的使用范围很广，从舌头伸出到下巴顶端，到以高速向远处的目标发射舌头。为了成功的进食，舌头和猎物表面之间的连接需要在几毫秒内建立起来，并且需要足够强大以将猎物从基底上提起。然而，这些舌头粘连的真正原因仍然不清楚。舌头的形状、表面结构和黏性粘液的结合很可能是舌头和猎物紧密联系的重要因素。舌头表面特性、舌头解剖结构和黏液的作用还有待研究，要考虑到舌头附着的猎物表面。该项目旨在揭示两栖动物舌头的结构原理和表面特性，这些结构原理和表面特性是陆生两栖动物捕食过程中舌头与猎物相互作用的基础。将应用最先进的成像技术微计算机断层扫描（µCT）和原子力显微镜（AFM），结合光学和电子显微镜（SEM和TEM），系统地研究两栖动物舌头表面从毫米到纳米尺度。工程方法（压痕）将被用来检查两栖动物舌头的表面和材料特性。有关两栖动物舌头表面解剖和特征的信息将由高分辨率的三维（3D）计算机模型补充。这种舌头表面及其特性的解剖和功能描述将与实验方法相结合，以量化两栖动物舌头在可变表面上的表现。为此，我们将分析捕捉捕食打击的高速视频序列，我们将测量作用于猎物的体内粘附力。本研究通过揭示两栖动物舌头的解剖结构、物理化学性质和性能属性，将对两栖动物舌头与猎物的相互作用——一种天然的高性能粘接系统——有一个全面的认识。

The transition from aquatic to terrestrial habitats during vertebrate evolution was related to numerous specializations for a life on land. While early tetrapods presumably fed on aquatic prey, the evolution of a tongue for prey capture and transport resulted in several new modes of terrestrial feeding. Within amphibians (i.e. frogs, salamanders, and caecilians), adhesive tongues that can stick to prey items and that will pull the prey into the mouth evolved several times. The use of adhesive tongues in amphibians ranges from protruding of the tongue over the tip of the jaw to ballistically firing the tongues at high speeds to remote targets. For a successful feeding event, the connection between the tongue and the surface of the prey items needs to be established within a few milliseconds and needs to be strong enough to lift the prey off the substrate. The actual cause of the adhesiveness of these tongues, however, remains obscure. It is likely that the combination of tongue shape, surface structure, and adhesive mucus is important for the tight connection between tongue and prey. The contributions of tongue surface properties, tongue anatomy, and mucus remain to be examined under consideration of the surfaces of the prey objects to which the tongues adhere. This project aims to reveal the structural principles and surface properties of amphibian tongues that underlie the tongue-prey interaction during the feeding strike in terrestrial amphibians. The state of the art imaging techniques micro computed tomography (µCT) and atomic force microscopy (AFM) will be applied in combination with light and electron microscopy (SEM and TEM) to systematically study the surface of amphibian tongues from the millimeter to the nanometer scale. Engineering approaches (indentation) will then be used to examine the surface and material properties of amphibian tongues. Information on the surface anatomy and characteristics of amphibian tongues will be complemented by high resolution three dimensional (3D) computer models. This anatomical and functional description of tongue surfaces and their properties will be combined with an experimental approach to quantify the performance of amphibian tongues on variable surfaces. For this, we will analyze high-speed video sequences that capture the feeding strike and we will measure the in vivo adhesive forces that act on the prey. By revealing the anatomy, the physical and chemical properties, and the performance attributes of amphibian tongues, this study will result in a comprehensive view of the tongue-prey interaction in amphibians - a natural high performance adhesive system.