145.2 Monday, Jan. 7 Hearing of the Yangtze finless porpoise: Form and function in an ‘unrepresentative’ species MOONEY, T.A.*; LI, S.; KETTEN, D.R.; WANG, K.; WANG, D.; Biology Department, Woods Hole Oceanographic Institution; Hawaii Institute of Marine Biology, University of Hawaii; Biology Department, Woods Hole Oceanographic Institution; Institute of Hydrobiology, The Chinese Academy of Sciences ; Institute of Hydrobiology, The Chinese Academy of Sciences firstname.lastname@example.org
While it is broadly accepted that odontocetes receive sound through tissues near the lower jaw, there are important species differences in the tissue shapes potentially related to what it hears. This paper addresses the hearing of a divergent cetacean species, the Yangtze finless porpoise (Neophocaena phocaenoides). Hearing was measured using auditory evoked potentials. Clicks and low-, mid- and high-frequency (8, 54, 120 kHz) tones were presented through adapted jawphone transducers at nine locations on the body. Thresholds were related to underlying anatomy determined from CT and MR images. Results showed ‘acoustic fat’ regions coincident with lowest thresholds (best hearing) at locations adjacent to the auditory bullae. Response latencies were shortest from this region, indicating subtle preferential sound pathways. Mean thresholds did not vary significantly along a line from the rostrum to the ear (11.6 dB). This is quite different from the bottlenose dolphin and beluga, in which 30-40 dB threshold differences were found across their heads. Greater stimulus levels produced higher amplitude and faster auditory responses suggesting sound pathways influence hearing in multiple ways. Yet, finless porpoises have relatively less ‘shading’ of sounds compared to some odontocetes, implying they hear well from many directions. These distinctions indicate sound reception differences among odontocetes which likely influence vital bio-acoustic behaviors of these sound specialists, and supports caution when attempting to generalize from limited auditory data across cetacean species.