Search

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Society for Marine Mammalogy for personal use, not for redistribution. The definitive version was published in Marine Mammal Science 30 (2014): 1549–1563, doi:10.1111/mms.12120., In an underwater environment where light attenuates much faster than in air, cetaceans have evolved to rely on sound and their sense of hearing for vital functions. Odontocetes (toothed whales) have developed a sophisticated biosonar system called echolocation, allowing them to perceive their environment using their sense of hearing (Schevill and McBride 1956, Kellogg 1958, Norris et al. 1961). Echolocation has not been demonstrated in mysticetes (baleen whales). However, mysticetes rely on low frequency sounds, which can propagate very long distances under water, to communicate with potential mates and other conspecifics (Cummings and Thompson 1971)., Funding to pursue this work came from the National Science Foundation Graduate Research Fellowship, Woods Hole Oceanographic Institution (WHOI) Coastal Ocean Institute Award, WHOI Ocean Life Institute Fellowship, Massachusetts Institute of Technology Student Assistance Fund, Joint Industry Program, Office of Naval Research, and the WHOI Academic Programs Office., 2015-03-07

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2012., Cataloged from PDF version of thesis., Includes bibliographical references., Despite widespread concerns about the effects of anthropogenic noise on baleen whales (suborder Mysticeti), we lack basic information about their auditory physiology for comprehensive risk assessments. Hearing ranges and sensitivities could be measured if customized equipment and methods were developed based on how baleen whales receive sound. However, sound reception pathways in baleen whales are currently unknown. This thesis presents an integrative approach to understanding hearing in baleen whales through dissections, biomedical imaging, biochemical analyses, and modeling sound propagation through a whale head using the Finite Element Method (FEM). We focused on the minke whale (Balaenoptera acutorostrata) because it is one of the smallest and most abundant mysticete species, reducing logistical difficulties for dissections and experiments. We discovered a large, well-formed fat body extending from the blubber region to the ears and contacting the ossicles. Although odontocetes, or toothed whales, are thought to use specialized "acoustic fats" for sound reception, no such tissues had been described for mysticetes to date. Our study indicates that the basic morphology and biochemical composition of the minke whale "ear fats" are very different from those of odontocete acoustic fats. However, the odontocete and mysticete fatty tissues share some characteristics, such as being conserved even during starvation, containing fewer dietary signals compared to blubber, and having well-defined attachments to the tympano-periotic complex, which houses the middle and inner ears. FE models of the whale head indicated that the ear fats caused a slight increase in the total pressure magnitude by the ears, and this focusing effect could be attributed to the low density and low sound speed of the ear fats in the models. Fatty tissues are known to have lower densities and sound speeds than other types of soft tissues, which may explain why they are an important component of the a, by Maya Yamato., Ph.D.

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/B978-0-12-394282-1.00004-1, Sound 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.

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., The original document contains color images.

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2012, Despite widespread concerns about the effects of anthropogenic noise on baleen whales (suborder Mysticeti), we lack basic information about their auditory physiology for comprehensive risk assessments. Hearing ranges and sensitivities could be measured if customized equipment and methods were developed based on how baleen whales receive sound. However, sound reception pathways in baleen whales are currently unknown. This thesis presents an integrative approach to understanding hearing in baleen whales through dissections, biomedical imaging, biochemical analyses, and modeling sound propagation through a whale head using the Finite Element Method (FEM). We focused on the minke whale (Balaenoptera acutorostrata) because it is one of the smallest and most abundant mysticete species, reducing logistical difficulties for dissections and experiments. We discovered a large, well-formed fat body extending from the blubber region to the ears and contacting the ossicles. Although odontocetes, or toothed whales, are thought to use specialized “acoustic fats” for sound reception, no such tissues had been described for mysticetes to date. Our study indicates that the basic morphology and biochemical composition of the minke whale “ear fats” are very different from those of odontocete acoustic fats. However, the odontocete and mysticete fatty tissues share some characteristics, such as being conserved even during starvation, containing fewer dietary signals compared to blubber, and having well-defined attachments to the tympano-periotic complex, which houses the middle and inner ears. FE models of the whale head indicated that the ear fats caused a slight increase in the total pressure magnitude by the ears, and this focusing effect could be attributed to the low density and low sound speed of the ear fats in the models. Fatty tissues are known to have lower densities and sound speeds than other types of soft tissues, which may explain why they are an important component of the a, This study was funded by the National Science Foundation Graduate Research Fellowship Program, WHOI Academic Programs Office, WHOI Ocean Life Institute Fellowship, Ocean Ventures Fund, WHOI Coastal Ocean Institute Award, WHOI Summer Student Fellowship, WHOI Minority Fellowship, the MIT Student Assistance Fund, the Joint Industry Program, the Marine Mammal Program of the Office of Naval Research, and the Naval Operations Energy and Environmental Readiness Division.

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.