Selective Inner Hair Cell Loss in a Neonate Harbor Seal (Phoca vitulina)

Area of Science:

• Marine Mammal Health
• Otolaryngology
• Congenital Malformations

Background:

• Congenital hearing loss is documented in terrestrial species but poorly understood in pinnipeds.
• Establishing baseline data on marine mammal inner ear malformations is crucial for distinguishing congenital from acquired conditions.
• Potential causes of acquired abnormalities include pathogens, aging, and anthropogenic factors like noise exposure.

Purpose of the Study:

• To investigate the prevalence and pathophysiology of congenital hearing loss in pinnipeds.
• To document inner ear malformations in a neonate harbor seal.
• To differentiate congenital abnormalities from acquired conditions in marine mammals.

Main Methods:

• Ultrastructural evaluation of the cochlea using scanning electron microscopy.
• Analysis of a neonate harbor seal (Phoca vitulina).
• Histological examination of inner ear structures.

Main Results:

• Bilateral loss of inner hair cells with intact outer hair cells was observed.
• Selective inner hair cell loss was more pronounced in the cochlea's basal turn, associated with high-frequency sound encoding.
• Hair cell loss began approximately 40% from the apex, with up to 84.6% loss at 80-85% of cochlear length.

Conclusions:

• This case represents the first report of selective inner hair cell loss in a marine mammal neonate, likely congenital.
• The findings highlight the importance of understanding congenital hearing defects in marine wildlife.
• Further research is needed to explore the etiologies and consequences of such conditions.