Inner ear morphology in elasmobranchs: implications for auditory capacity and ecology

Elasmobranchs (sharks, rays, and skates) represent the majority of Chondrichthyan species, a clade of cartilaginous fishes that first appeared over 400 million years ago. Given their basal position in the evolutionary tree of gnathostomes, elasmobranchs can provide key insights into the early evolutionary history of the vertebrate nervous system. Sharks and their relatives were some of the first vertebrates to evolve the capacity for sound detection, and their auditory system is part of the impressive array of sensory systems they possess. However, relatively little is known about the elasmobranch auditory system and its importance compared to other sensory systems within and across species, despite the fact that underwater sound can convey important biological information and likely plays a key role in elasmobranch ethology. Anatomical comparisons are often the first step in better understanding the links between form and function. This thesis investigates the morphology of elasmobranch inner ears, focusing on variation from both an intraspecific (ontogenetic) and interspecific perspective. Using fluorescence microscopy to examine the ultrastructure of the inner ear, two shark species (Galeorhinus galeus and Cephaloscyllium isabellum) exhibit substantial ontogenetic changes to inner ear hair cell organisation in all four hearing end organs (saccule, lagena, utricle, and macula neglecta). Further, there is variation in hair cell organisation between shark species with different feeding strategies, primarily attributed to vertically oriented hair cells. Lastly, using magnetic resonance imaging (MRI) to obtain in situ characterisations of fish inner ears for the first time, I employ broad comparative analyses across 26 elasmobranch species to understand interspecific variation and the ecological factors that potentially influence morphology across species. Diet and primary habitat partially explain inner ear morphology, suggesting that the functional requirements of prey capture and environmental soundscapes influence inner ear structure and auditory capacity in elasmobranchs. Throughout my thesis, findings consistently demonstrate that the elasmobranch auditory system is dynamic and diverse, with morphological variation that correlates with various ecological and/or behavioural parameters. Therefore, selective pressures on auditory capacity have likely shaped the inner ears of elasmobranchs to reflect the life history and ecological characteristics associated with different species.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Marine Science

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2023

Author dc:creator

• Sauer, Derek Jason

Advisors dc:contributor.advisor

• Radford, Craig
• Yopak, Kara

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/65993

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/65993