Description of cochlear morphology and hair cell variation in the beluga whale

Abstract

Environmental change and decreased ice cover in the Arctic make new areas accessible to humans and animals. It is important to understand how these changes impact marine mammals, such as beluga whales (Delphinapterus leucas Pallas, 1776). Hearing is crucial in the daily lives of cetaceans. Consequently, we need normal baselines to further understand how anthropogenic noise affects these animals. Relatively little is known about the inner ear morphology of belugas, particularly the organ of Corti, or hearing organ, found within the cochlea. The base of the cochlea encodes for high-frequency sounds, while low frequencies are detected in the apex. We showed differences between the apex, or centremost point of the cochlea, and the base, the region closest to the stapes. Our results showed that average outer hair cell density changed from 148 cells/mm in the apex to 117 cells/mm in the base. Cell width varied between the two regions, from 5.8 µm in the apex to 8.4 µm in the base. These results revealed variation throughout the cochlea, and thus the need to understand the basic morphology, to give further insight on hearing function in belugas and allow us to recognize damage if or when we find it.

Keywords

• beluga (delphinapterus leucas)
• cochlea
• inner ear
• odontocetes
• organ of corti