Evolution and development of evolutionary novelties during anuran ontogenesis

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Evolutionary novelties are morphological structures that enable new functions or further specialize ancestral functions in an organism. How such innovations evolved and which mechanisms led to their development are essential questions in the field of developmental biology.The composition of the cartilaginous skeleton of anuran tadpoles is unique among vertebrates. The jaw of tadpoles consists of two additional cartilages. The suprarostral cartilage is part of the upper jaw, whereas the infrarostral cartilage is part of the lower jaw of larval anurans. The infrarostral cartilage is situated between the anterior tips of the two Meckel´s cartilages. Between the infrarostral and Meckel´s cartilage the unique intramandibular joint is present. Several anurans exist which develop further additional cartilages. Depending on their respective position, these cartilages are called sub-meckelian, admandibular or adrostral cartilage. Genetic signaling, which controls ontogenesis of an organism and ensures that it develops in a certain way, must be responsible for the evolution and development of evolutionary novelties. Investigations in Xenopus laevis have shown that the the nkx-genes bapx1 and zax may have been involved in the evolution of the infrarostral and adrostral cartilage.We will investigate the musculoskeletal development of three different frogs to obtain a comprehensive overview on the ontogenesis of anurans. This overview will provide information about the sequence of the musculoskeletal development, about the influence of the specific feeding habit on the development and about the specific development of several anuran novelties. Additionally, the influence of selected nkx-genes on the evolution and development of these novelties will be investigated.We will study musculoskeletal morphogenesis using classic histology and modern approaches such as immunohistochemistry, confocal laser scanning microscopy and μ-computed tomography. To investigate and manipulate the gene expression of various nkx-genes, pharmacological substances and CRISPR/Cas9 will be used. Spatial and temporal gene expression will be studied using whole mount in situ hybridization and quantitative PCR.This project will significantly expand our knowledge of the musculoskeletal development of larval frogs. Furthermore, it will advance our understanding of the mechanisms responsible for the evolution of evolutionary novelties.