Investigation on acoustic reception pathways in finless porpoise (Neophocaena asiaorientalis sunameri) with insight into an alternative pathway

Abstract

Sound transmission and reception are both vital components to odontocete echolocation and daily life. Here, we combine computed tomography (CT) scanning and Finite Element Modeling to investigate the acoustic propagation of finless porpoise (Neophocaena asiaorientalis sunameri) echolocation pulses. The CT scanning and FEM wave propagation model results support the well-accepted jaw-hearing pathway hypothesis and suggest an additional alternative auditory pathway composed of structures, mandible (lower jaw) and internal mandibular fat, with different acoustic impedances, which may also conduct sounds to the ear complexes. The internal mandibular fat is attached to the ear complex and encased by the mandibles laterally and anteriorly. The simulations show signals in this pathway initially propagate along the solid mandibles and are transmitted to the acoustically coupled soft tissue of the internal mandibular fat which conducts the stimuli posteriorly as it eventually arrives at ear complexes. While supporting traditional theories, this new bone-tissueconduction pathway might be meaningful to understand the hearing and sound reception processes in a wide variety of odontocetes species.

Numerical-modeling-based investigation of sound transmission and reception in the short-finned pilot whale (Globicephala macrorhynchus)

“…Using finite element modeling, Cranford et al (2008) identified an additional sound-reception pathway-the so-called "gular pathway"-by which sounds enter the internal mandibular fat through the ventral margin of the mandible; these findings were based on a case study of a Cuvier's beaked whale (Ziphius cavirostris). In addition, sound-reception channels in which the solid mandible may play a significant role were introduced in both the experiments and numerical models (Castellote et al, 2014;Mooney et al, 2008;Mooney et al, 2015;Mooney et al, 2018;Song et al, 2018). These results indicate that the entire head may function as an antenna system for sound reception (Popov et al, 2019).…”

“…The sound-transmission and -reception pathways were not located in the same sagittal plane. In previous twodimensional models, these two systems were typically separated into their respective models (Zhang et al, 2017;Song et al, 2018). However, this restricts our understanding of the bio-sonar target-detection capabilities.…”

“…No studies have sought to analyze odontocetes' echo-reception systems because it is unethical to implant sensors into live animals. The problem can be approached via numerical modeling (Cranford et al, 2008;Song et al, 2018).…”

“…Sounds can reach the odontocetes' ear complex via various pathways (Norris 1964(Norris , 1968Cranford et al, 2008;Song et al, 2018;Popov et al, 2019). The external mandibular fat located between the skin and a thin portion of the posterior mandible known as the "pan-bone" constitutes an important sound entrance.…”

Contribution of bone-reverberated waves to sound localization of dolphins: A numerical model

“…Importantly, bone heterogeneity, neglected in other similarlyminded numerical studies (e.g. [17,18]) is accounted for in our simulations. While it is impossible (for a number of technical reasons that we discuss) to reproduce Reinwald et al's [2] experiment exactly, our results share all the important features of their data.…”