From the morphospace to the soundscape: Exploring the diversity and functional morphology of the fish inner ear, with a focus on elasmobranchs

Abstract

Fishes, including elasmobranchs (sharks, rays, and skates), present an astonishing diversity in inner ear morphologies; however, the functional significance of these variations and how they confer auditory capacity is yet to be resolved. The relationship between inner ear structure and hearing performance is unclear, partly because most of the morphological and biomechanical mechanisms that underlie the hearing functions are complex and poorly known. Here, we present advanced opportunities to document discontinuities in the macroevolutionary trends of a complex biological form, like the inner ear, and test hypotheses regarding what factors may be driving morphological diversity. Three-dimensional (3D) bioimaging, geometric morphometrics, and finite element analysis are methods that can be combined to interrogate the structure-to-function links in elasmobranch fish inner ears. In addition, open-source 3D morphology datasets, advances in phylogenetic comparative methods, and methods for the analysis of highly multidimensional shape data have leveraged these opportunities. Questions that can be explored with this toolkit are identified, the different methods are justified, and remaining challenges are highlighted as avenues for future work.

Finite element modelling of sound transmission in the Weberian apparatus of zebrafish ( Danio rerio )

“…However, the emergence of high-resolution μCT imaging has revolutionized our ability to visualize and model the detailed anatomy of these structures three-dimensionally [ 32 ]. The development of computing power and biomechanical software using finite element methods and reconstruction of natural objects allows modelling of the physical interactions and relationships among multiple component parts with widely varying sizes and properties [ 57 ]. The combination of high-resolution CT imaging and advanced biomechanics simulation tools has opened new avenues for realistically modelling the function of conductive hearing apparatus and investigating their mechanical behaviour, which is also the methodology basis of this study.…”