Revelation of sound-induced motion patterns of fish auditory structures: a new experimental tomography-based 4D approach

• Applicants: Professor Dr. Martin Heß; Dr. Tanja Schulz-Mirbach
• Subject Area: Sensory and Behavioural Biology ; Systematics and Morphology (Zoology)
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 491091951

Modern bony fishes (Teleostei) show a high diversity in auditory abilities and in the morphology of the corresponding structures such as the otoliths in the inner ears and the swimbladder. Despite this enormous diversity, experimental evidence providing insights into the basic principles of the functional interaction of auditory structures is rare and focuses on a few model species such as goldfish or zebrafish. This is due to the difficulty to evaluate the motion patterns of auditory structures in-situ without exposing them surgically. In previous projects at the European Synchrotron Radiation Facility, we developed a setup that enabled visualizing the sound-induced motion of fish auditory structures in a non-invasive way. The moving structures, however, were captured only in 2D plus time, thereby ignoring their three-dimensionality and hampering interpretations of their functional interplay.In our planned project, we therefore envisage a new 4D (three spatial dimensions plus time) tomography-based approach at the Swiss Light Source to characterize the sound-induced interaction from the swimbladder through the Weberian ossicles to the otoliths. To address the variability of the auditory structures, we will compare six otophysan species, namely the cypriniform species Danio rerio, Pangio kuhlii, and Sewellia lineolata, and the siluriform species Kryptopterus vitreolus, Ancistrus dolichopterus, and Corydoras aeneus. Specifically, we aim to develop a setup to capture the in-situ motion with high spatio-temporal resolutions. This will, for the first time, allow to quantify the motion patterns of the auditory structures in their 3D aspect depending on the sound component (sound pressure versus sound-induced particle motion), frequency, sound level, and species.In previous studies at the Swiss Light Source, we tested a prototype of a 20mL-miniature standing wave tube-like setup for time-resolved tomography (pixel size: 2.75µm; framerate: 2kHz) which can be run under sound pressure or sound-induced particle motion conditions. Based on this, we will increase the spatial (pixel size: < 1.0µm) and temporal resolutions (framerate: 20kHz) by implementing a new microscope at the TOMCAT beamline. Motion patterns will be quantified in terms of rotation and translation using a data processing pipeline.Our study will fundamentally enhance the knowledge of sound transmission in teleosts by characterizing the path of sound-induced motion from the swimbladder to the inner ears while testing hypotheses on the function of the Weberian apparatus formulated decades ago. The outcomes will yield vital input for future studies modelling motion patterns in fishes not available for lab experiments such as endangered or fossil species. Our methodological developments will unlock novel biomechanical applications and benefit ongoing studies which, for example, elucidate the effects of pathologic ear structures on the motion of the auditory ossicles in the human middle ear.

• DFG Programme: Research Grants
• International Connection: Austria, Switzerland
• Partner Organisation: Schweizerischer Nationalfonds (SNF)
• Cooperation Partners: Dr. Stefan Gstöhl; Professor Dr. Friedrich Ladich; Dr. Christian Schlepütz