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Structure of the external auditory meatus of the Bowhead whale ( Balaena mysticetus ) and its relation to their seasonal migration
Author(s) -
Rehorek Susan J.,
Stimmelmayr Rafael,
George John C.,
Suydam Robert,
McBurney Denise M.,
Thewissen J. G. M.
Publication year - 2019
Publication title -
journal of anatomy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.932
H-Index - 118
eISSN - 1469-7580
pISSN - 0021-8782
DOI - 10.1111/joa.12908
Subject(s) - biology , epithelium , anatomy , glycogen , moulting , juvenile , whale , endocrinology , ecology , genetics , larva
The external auditory meatus ( EAM ) in many species of mysticete whales is filled with a waxy ear plug. Though this lamellated structure is often used to age a whale, its formation and development remain undescribed. It is thought that growth layer groups ( GLG s) are laid down annually, thereby increasing the size of this structure. Since some mysticete whales are migratory and many undergo molting, we hypothesized that the cyclical production of these GLG s may be related to these processes. The epithelia of both EAM and glove finger (a part of the tympanic membrane protruding into the EAM ) of one juvenile and multiple adult bowhead whales from both fall (October: non‐molting) and spring (May: molting) seasons were dissected and examined anatomically and histologically. These tissue samples were compared with the adult oral epithelia at the same time periods. These epithelia shared a similar basic broad structure, though there were differences in thickness and presence of intraepithelial structures. All epithelia in the October specimens were rich in both glycogen and lipid. The parakeratinized epithelium of the oral cavity in the juvenile and some May specimens shed via the production of several superficial epithelial fissures. Other adult May specimens exhibited deep epithelial fissures, reminiscent of pressure ulcers, which would cause the detachment of the entire epithelium from the dermis. We propose that sloughed epithelial lining is the source of the GLG s in the ear plug. Correlating a potential molting sequence with these observations explained the presence of epidermal glycogen, deep epidermal fissures and dermal glycolipid, and to some extent calls into question the origin and structure of the ear plug itself. Further morphological characterization of ear plugs in bowheads is needed to better understand cell origin and ear plug formation.