The auditory anatomy of the minke whale (Balaenoptera acutorostrata) : a potential fatty sound reception pathway in a baleen whale

Author Posting. © John Wiley & Sons, 2012. This article is posted here under terms and conditions set forth in the Wiley Online Library. The definitive version was published in The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology 295 (2012): 991-998, doi:10.1002/ar.22459.Cetaceans possess highly derived auditory systems adapted for underwater hearing. Odontoceti (toothed whales) are thought to receive sound through specialized fat bodies that contact the tympanoperiotic complex, the bones housing the middle and inner ears. However, sound reception pathways remain unknown in Mysticeti (baleen whales), which have very different cranial anatomies compared to odontocetes. Here, we report a potential fatty sound reception pathway in the minke whale (Balaenoptera acutorostrata), a mysticete of the balaenopterid family. The cephalic anatomy of seven minke whales was investigated using computerized tomography and magnetic resonance imaging, verified through dissections. Findings include a large, well-formed fat body lateral, dorsal, and posterior to the mandibular ramus and lateral to the tympanoperiotic complex. This fat body inserts into the tympanoperiotic complex at the lateral aperture between the tympanic and periotic bones and is in contact with the ossicles. There is also a second, smaller body of fat found within the tympanic bone, which contacts the ossicles as well. This is the first analysis of these fatty tissues' association with the auditory structures in a mysticete, providing anatomical evidence that fatty sound reception pathways may not be a unique feature of odontocete cetaceans

The anatomy, physiology, functional significance and evolution of specialized hearing organs of gerbilline rodents

Middle and inner ear anatomy correlates with neurophysiological responses to a wide range of sound frequencies for species of the Gerbillinae representing generalized, intermediate, and specialized anatomical conditions. Neurophysiological data were recorded from 81 specimens of 13 species representing six genera. Anatomical parameters involved in the process of hearing were correlated with the neurophysiological data to assess the effects of different degrees of anatomical specialization on hearing. The 13 species tested in this manner have graphic curves of auditory sensitivity of remarkably similar disposition over the frequencies tested and to those published for Kangaroo Rats. Ears with anatomical specializations show greater auditory sensitivity. The natural history of the Gerbillinae, particularly the kinds of predators, degree of predation, and habitat is reviewed and utilized to interpret the significance of the degree of auditory specialization in the forms studied and to evaluate the prevailing hypothesis that these specializations enhance the ability of these rodents to survive in open desert situations by detecting and evading predators. The middle ear anatomy of five additional genera and species was also studied. Thus, data on the entire spectrum of gerbilline middle ear morphology provide an evolutionary sequence. Certain anatomical parameters of the organ of Corti show a degree of specialization parallel to that of features of the middle ear. The morphological changes and possible functional roles of these features are considered. A very high correlation exists for degree of specialization and aridity of habitat, thus specialization increases with increasing aridity. This increased specialization may result from more effective predation in open xeric environments. Auditory acuity for a wide range of low frequency sounds augmented by auditory specialization is hence more advantageous here. There does not appear to be selection for hearing at particular frequencies in this range. The peaks of greatest auditory sensitivity appear to correspond to the resonant frequencies of the different components of the middle ear transformer and cavity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50256/1/1051380103_ftp.pd

A New Acoustic Portal into the Odontocete Ear and Vibrational Analysis of the Tympanoperiotic Complex

Global concern over the possible deleterious effects of noise on marine organisms was catalyzed when toothed whales stranded and died in the presence of high intensity sound. The lack of knowledge about mechanisms of hearing in toothed whales prompted our group to study the anatomy and build a finite element model to simulate sound reception in odontocetes. The primary auditory pathway in toothed whales is an evolutionary novelty, compensating for the impedance mismatch experienced by whale ancestors as they moved from hearing in air to hearing in water. The mechanism by which high-frequency vibrations pass from the low density fats of the lower jaw into the dense bones of the auditory apparatus is a key to understanding odontocete hearing. Here we identify a new acoustic portal into the ear complex, the tympanoperiotic complex (TPC) and a plausible mechanism by which sound is transduced into the bony components. We reveal the intact anatomic geometry using CT scanning, and test functional preconceptions using finite element modeling and vibrational analysis. We show that the mandibular fat bodies bifurcate posteriorly, attaching to the TPC in two distinct locations. The smaller branch is an inconspicuous, previously undescribed channel, a cone-shaped fat body that fits into a thin-walled bony funnel just anterior to the sigmoid process of the TPC. The TPC also contains regions of thin translucent bone that define zones of differential flexibility, enabling the TPC to bend in response to sound pressure, thus providing a mechanism for vibrations to pass through the ossicular chain. The techniques used to discover the new acoustic portal in toothed whales, provide a means to decipher auditory filtering, beam formation, impedance matching, and transduction. These tools can also be used to address concerns about the potential deleterious effects of high-intensity sound in a broad spectrum of marine organisms, from whales to fish

Hearing in cetaceans : from natural history to experimental biology

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Advances in Marine Biology 63, edited by Michael Lesser, :197-246. Academic Press (Elsevier), 2013. ISBN: 9780123942821. doi:10.1016/B978-0-12-394282-1.00004-1Sound is the primary sensory cue for most marine mammals, and this is especially true for cetaceans. To passively and actively acquire information about their environment, cetaceans have perhaps the most derived ears of all mammals, capable of sophisticated, sensitive hearing and auditory processing. These capabilities have developed for survival in an underwater world where sound travels five times faster than in air, and where light is quickly attenuated and often limited at depth, at night, and in murky waters. Cetacean auditory evolution has capitalized on the ubiquity of sound cues and the efficiency of underwater acoustic communication. The sense of hearing is central to cetacean sensory ecology, enabling vital behaviors such as locating prey, detecting predators, identifying conspecifics, and navigating. Increasing levels of anthropogenic ocean noise appears to influence many of these activities. Here we describe the historical progress of investigations on cetacean hearing, with a particular focus on odontocetes and recent advancements. While this broad topic has been studied for several centuries, new technologies in the last two decades have been leveraged to improve our understanding of a wide range of taxa, including some of the most elusive species. This paper addresses topics including how sounds are received, what sounds are detected, hearing mechanisms for complex acoustic scenes, recent anatomy and physiology studies, the potential impacts of noise, and mysticete hearing. We conclude by identifying emerging research topics and areas which require greater focus.In compiling this review, TAM was supported by the John E. and Anne W. Sawyer Endowed Fund and the Penzance Endowed Fund

Decalcifying odontocete ears following a routine protocol with RDO (R)

The study of the organ of Corti is essential to assess the impact of underwater noise on cetaceans. While classical histology techniques (including EDTA decalcification) have been previously considered, the process is time consuming. Independently from the histological technique, one of the challenging steps after extraction and fixation of the samples is to decalcify the bone envelope to access the cochlea without damaging the soft tissues. Here, we propose to use a fast commercial decalcifier (RDO (R)). 93 ears from 11 different odontocetes species stranded in the Mediterranean, Spanish North Atlantic and North Sea were used to precisely determine the decalcification time. Depending on the tympanic-periotic volume of the species, the decalcification time ranged from several hours to a few days, allowing a subsequently faster observation of the cochlear structures through routine microscope techniques. (C) 2009 Elsevier B.V. All rights reserved