Morpho-functionality of the toothed whale external ear canal

Tesi en modalitat de cotutela: Universitat Politècnica de Catalunya i Universita degli studi di Padova While marine, anthropogenic noise pollution is a scientific and societal matter of concern, there is limited knowledge on how sea animals, particularly cetaceans, perceive their environment through sounds. Toothed whales, like all cetaceans, show a series of astonishing morphological and physiological evolutionary adaptations, of which one of the most striking can be found in the complex configuration of the hearing apparatus. The external ear canal, although no longer considered a direct actor in the sound reception process, also shows surprising adaptation with many active structures and a complex peripheral innervation, although basic knowledge on its morphology is inconclusive at the moment. This study aimed at providing fundamental knowledge on the morphology of the external ear canal in various toothed whales, associated to its sensory capabilities with in-depth morphological descriptions of its shape and course, lumen and content, epithelium, glands, lymphoid tissue, vascularization, innervation, muscular tissue, cartilage, fat and connective tissue. Furthermore, specific attention was given to the identification and morphological characterization of the sensory formations associated with the external ear canal, and the comparison with the terrestrial cetartiodactyl external ear canal, to gain perspective of a comprehensive understanding of the cetacean sensory abilities. Post-mortem samples were gathered during necropsies of wild toothed whales, in an international collaborative effort. The tissues were inspected macroscopically and subjected to microscopic studies including immunohistochemical analyses using antibodies specific for nervous tissue, various histochemical techniques, ultrastructural investigation using transmission electron microscopy, and 3D reconstruction from histological slides of the ear canal and associated tissues. The winding structure of the external ear canal revealed a complex organ that comprises a physiological function reflected in its delicate anatomical structures, all of which are discussed in detail. Remarkably, the innervation showed an extensive intramural nervous plexus with the predominant presence of simple lamellar corpuscles, similar to Pacinian corpuscles although without an outer core or capsule. There were differences in conformation along the canal, from a network that fully encompasses the ear canal to