Function, form and evolution of food processing in salamanders

在脊椎动物中，摄食系统进化出了显著多样化的专业化，从而允许开发各种食物来源。除了最初获得一种食物外，口腔内加工，即机械地减少口腔内的食物，在进化适应程序中发挥了重要作用，以成功地利用特定营养环境中的食物来源。从鱼类到哺乳动物，所有主要脊椎动物的加工机制都是已知的，加工设备的形式和功能以及粉碎、研磨或刺穿食物在主要群体之间和主要群体内部可能有很大不同，但颅骨、颌骨和下支具系统的有节奏和周期性的协调运动似乎是一个共同的特征。虽然羊膜动物(蜥蜴和哺乳动物)和类似鱼的脊椎动物的加工机制是深入研究的主题，但利沙比目动物的加工机制在很大程度上还没有被研究，尽管利萨姆比目动物由于其在四足动物中的系统发育地位而很重要。事实上，火蜥蜴以其相对保守的身体规划、或多或少转变为陆地形式的水生鳃幼体以及通常具有双峰生活方式的成虫为研究水陆过渡的功能方面提供了一个很好的机会，因此是理解和重建发生在我们自然历史上的一个主要进化转变--鱼到四足动物转变--的功能变化的关键。在这里，我们提出了一个在耶拿和国外进行为期三年的研究项目，以研究8个主要蜥蜴科12个物种的加工机制的功能、形成和进化方面的问题。我们邀请了一个年轻的国际专家团队，他们的研究重点从实验动物学到古生物学和一名博士生都不同，我们的目标是协同解决以下问题：火蜥蜴体内处理系统的多样性，觅食发生的环境(水生和陆地事件)，不同食物类型如何影响处理协调，以及火蜥蜴在变态过程中运动模式如何变化。由于一个物种可以施加的咬合力对食物种类和相应的加工机制(例如，咀嚼时)有重大影响，我们将测量各种火蜥蜴的咬合力，并模拟同一物种的足形(即未变态)和变态个体的咬合力，以解决变态过程中结构重塑的功能后果问题。最后，通过将火蜥蜴加工的综合知识与两栖动物关键类群化石的头骨、颌骨和下颚形态的现有信息相结合，我们旨在构建一个两栖动物和其他四足动物谱系中摄食和加工机制如何进化的机械进化情景。

In vertebrates, the feeding system has evolved a remarkable diversity of specialisations that allow exploitation of a great variety of food sources. Besides the initial acquisition of a food item, intraoral processing, i.e. mechanically reducing food within the mouth, has played a major role in evolutionary adaptive procedures to successfully exploit food sources in a given trophic environment. Processing mechanisms are known for all major vertebrate clades, from fishes up to mammals and form and function of the processing apparatus to crush, grind, or puncture food items can differ substantially between and within major groups, but rhythmic and cyclic coordinated movements of skull, jaws and hyobranchial system seem to be a common feature. While processing mechanisms in amniotes (sauropsides and mammals) and fish-like vertebrates were subject of intense research, processing mechanisms in lissamphibians are largely unstudied though lissamphibians are important due to their phylogenetic position within tetrapods. In fact, salamanders with their relatively conservative body plan, the aquatic gill-bearing larva that metamorphoses to a more or less terrestrial form and adults with often bimodal lifestyles offer a great opportunity to study functional aspects of aquatic-terrestrial transitions and are therefore key to understand and reconstruct functional changes that happened across one of the major evolutionary transitions of our natural history: the fish-to-tetrapod transition. Here, we propose a research project designed to be conducted in Jena and abroad for three years to study function, form and evolutionary aspects of processing mechanisms in 12 salamander species from 8 major salamander families. Involving a young and international team of specialists with different research focuses from experimental zoology up to palaeontology and one PhD-student, we aim to synergistically tackle questions on the diversity of processing systems within salamanders, how the environment where feeding occurs (aquatic vs. terrestrial events) or how different food types influence processing coordination and how movement patterns change across metamorphosis in salamanders. As bite forces that can be exerted by a species have a significant impact on the food repertoire and accordingly the processing mechanism used (e.g. when chewing), we will measure the bite force in a variety of salamanders and simulate bite mechanics in paedomorphic (i.e. not metamorphosed) and metamorphosed individuals of the same species to address questions of the functional consequences of the structural remodelling across metamorphosis. Finally, by combining the integrative knowledge on salamander processing with available information of skull, jaws and hyobranchial morphology of fossil amphibian key-taxa we aim to construct a mechanistic evolutionary scenario how feeding and processing mechanisms might have evolved in amphibians and other tetrapod lineages.