Auditory System of the Minke Whale (Balaenoptera Acutorostrata): A Potential Fatty Sound Reception Pathway in a Mysticete Cetacean.

摘要

Cetaceans possess highly derived auditory systems adapted for underwater hearing. Odontocetes, or toothed whales, are thought to use specialized acoustic fats for sound reception. However, sound reception pathways in baleen whales, or mysticetes, are unknown. We investigated the auditory system of the minke whale (small mysticete species) through dissections, biomedical imaging, biochemical analyses, and sound propagation models using the Finite Element Method (FEM). We discovered a large, well- formed fat body extending from the blubber region to the ears and contacting the ossicles. The basic morphology and biochemical composition of the minke whale ear fats were very different from those of odontocete acoustic fats. However, the two tissues shared some subtle characteristics. FE models showed that the presence of the ear fats help to focus sound by the ears, which could be attributed to the low sound speed of the tissue. Sound bends towards regions of minimum sound speed, and fats are known to have lower sound speeds than other soft tissues. In an aquatic habitat where the air-filled ear canal is no longer effective, we propose that both odontocete and mysticete cetaceans have incorporated fatty tissues into their auditory systems for underwater sound reception.