Function, form and evolution of food processing in salamanders

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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.