Skeletal and dental development of larval batrachians: The influence of developmental processes on the evolution of novelties and the evolution of neobatrachian diversity.

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The cartilaginous or bony skull is the central innovation of vertebrates. Its structure is highly complex, and its functions range from protecting the brain and important sensory organs to enabling effective food intake. During ontogeny, the skull is initially built from cartilage. Unlike bone, cartilage can develop more quickly and with less energy intake, which favours its early appearance. The cartilaginous precursor skeleton is predominantly replaced by bone during further development. The tadpole stage is central to the diversification of the anura. The separation of larvae and adults in terms of physiology, morphology and ecology allows aquatic and terrestrial habitats to be effectively exploited independently. Anuran tadpoles can be distinguished from adult frogs by their spherical bodies and long, muscular tails. In addition to these features, the mouth region of the tadpoles is crucial for their success and diversity. The mouth is surrounded by an oral disc. It typically consists of an upper and lower lip. Both are surrounded by one or more rows of keratinized structures called labial teeth. This project will compare the skeletal development of Batrachia and the development of the anuran labial teeth. Using histology, immunohistochemistry, clearing and staining and µ-CT, the skeletal development of different Anura and Urodela will be analysed and described. Comparison of sequences using heterochrony plot, Parsimov-based Genetic inference and Anatomical Network Analysis will provide insights on heterochronic shifts in the respective developmental sequences and the modularity of the developing skull, as well as reconstructing the ancestral developmental sequences. Any developmental changes will be identified and characteristics of skeletal development of different taxa will be defined. They will also be compared with the characteristics of skeletal development in other vertebrates. Previous results have shown, that the sequence of skeletal development in anuran larvae differs from that in other vertebrates. A comparison with urodelan larvae will provide information on whether this is an exclusive batrachian feature and how the skeletal development of Urodela should be classified. The development of the labial teeth of different anurans will be investigated and described at the cellular level using scanning electron microscopy, transmission electron microscopy and histology. One result of the project will be the first detailed description of the development of this structure. Overall, the project will increase our knowledge on the development of batrachian larvae and improve our understanding of the mechanisms underlying the evolution of skeletal development.