INTEGRATING EVO-DEVO AND PALAEONTOLOGY ON THE STUDY OF THE ORIGIN AND EVOLUTION OF THE TYMPANIC MEMBRANE IN DIAPSIDA

Abstract

This project is dedicated to the study of the tympanic ear in Diapsida (snakes, lizards, tuatara, crocodylians, birds, and their extinct relatives), a group of amniotes with a long evolutionary history (c. 300 Ma), and that encompasses great diversity and morphological disparity in the extinct and extant lineages. The main goal consists in establishing a hypothesis for one of the longest-standing debate in evolutionary biology: the occurrence of single or multiple origins of the tympanic ear in Diapsida and its subgroups. For that, a detailed study of one of its components, the tympanic membrane, will be conducted promoting an interface between Evo-Devo and Palaeontology. Using CT-Scans and histological sections, we intend to provide a detailed characterization of the distinct stages of the embryonic development of the otic region in lizards Tropidurus catalanensis, caimans Caiman latirostris, and birds Gallus gallus. Still on the developmental part of this study, the gene expression in three different stages (initial, intermediate, membrane fully-developed) of the developmental processes of the otic will also be compared using transcriptomic analyses (RNAseq). Analyses of fossil materials of diapsids composes the palaeontological aspect of this project. These will seek to identify the presence/absence of the osteological correlates (determined on the basis of the morphology of the living species) of the tympanic membrane in fossil taxa. Developmental and palaeontological data will be integrated in order to formulate a new hypothesis regarding the levels of homology (i.e. classic homology vs deep homology) of the tympanic membrane in Diapsida and subgroups. Using modern techniques, and combining two distinct fields in the investigation of the origin of the tympanic ear in Diapsida represents a conceptual and methodological innovation, with implications for different areas of Biology.