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上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进食模式。 在两栖动物（即青蛙，蝾螈和螈）中，可以粘在猎物物品上并将猎物拉入口中的粘性舌头进化了好几次。两栖动物的粘性舌头的使用范围从舌头伸出下巴的尖端到高速发射舌头到远程目标。对于一个成功的进食事件，舌头和猎物表面之间的连接需要在几毫秒内建立，并且需要足够强大，以将猎物从基底上抬起。然而，这些舌头的弯曲的实际原因仍然模糊不清。舌头的形状、表面结构和粘性粘液的结合可能对舌头和猎物之间的紧密联系很重要。舌头的表面特性，舌头的解剖结构，和粘液的贡献仍然有待检查下考虑的猎物的舌头粘附对象的表面。本研究旨在揭示两栖动物舌头的结构原理和表面特性，这些特性是陆生两栖动物在捕食过程中舌头与猎物相互作用的基础。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）将与光学和电子显微镜（SEM和TEM）相结合，系统地研究从毫米到纳米尺度的两栖动物舌头表面。工程方法（压痕），然后将被用来检查两栖动物舌头的表面和材料特性。两栖类舌头的表面解剖学和特征的信息将由高分辨率的三维（3D）计算机模型补充。这种解剖学和功能的描述舌头表面和它们的属性将结合实验方法来量化两栖动物舌头的可变表面上的性能。 为此，我们将分析捕捉到的高速视频序列，我们将测量作用在猎物上的体内粘附力。通过揭示两栖动物舌头的解剖结构、物理和化学性质以及性能属性，本研究将全面了解两栖动物的舌头-猎物相互作用-一种天然的高性能粘附系统。

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.