Julie Arruda

The influence of cochlear shape on low-frequency hearing

The conventional theory about the snail shell shape of the mammalian cochlea is that it evolved essentially and perhaps solely to conserve space inside the skull. Recently, a theory proposed that the spirals graded curvature enhances the cochleas mechanical response to low frequencies. This article provides a multispecies analysis of cochlear shape to test this theory and demonstrates that the ratio of the radii of curvature from the outermost and innermost turns of the cochlear spiral is a significant cochlear feature that correlates strongly with low-frequency hearing limits. The ratio, which is a measure of curvature gradient, is a reflection of the ability of cochlear curvature to focus acoustic energy at the outer wall of the cochlear canal as the wave propagates toward the apex of the cochlea.

Hyperbaric computed tomographic measurement of lung compression in seals and dolphins.

SUMMARY Lung compression of vertebrates as they dive poses anatomical and physiological challenges. There has been little direct observation of this. A harbor and a gray seal, a common dolphin and a harbor porpoise were each imaged post mortem under pressure using a radiolucent, fiberglass, water-filled pressure vessel rated to a depth equivalent of 170 m. The vessel was scanned using computed tomography (CT), and supported by a rail and counterweighted carriage magnetically linked to the CT table movement. As pressure increased, total buoyancy of the animals decreased and lung tissue CT attenuation increased, consistent with compression of air within the lower respiratory tract. Three-dimensional reconstructions of the external surface of the porpoise chest showed a marked contraction of the chest wall. Estimation of the volumes of different body compartments in the head and chest showed static values for all compartments except the lung, which showed a pressure-related compression. The depth of estimated lung compression ranged from 58 m in the gray seal with lungs inflated to 50% total lung capacity (TLC) to 133 m in the harbor porpoise with lungs at 100% TLC. These observations provide evidence for the possible behavior of gas within the chest of a live, diving mammal. The estimated depths of full compression of the lungs exceeds previous indirect estimates of the depth at which gas exchange ceases, and concurs with pulmonary shunt measurements. If these results are representative for living animals, they might suggest a potential for decompression sickness in diving mammals.

Anatomical predictions of hearing in the North Atlantic right whale

Some knowledge of the hearing abilities of right whales is important for understanding their acoustic communication system and possible impacts of anthropogenic noise. Traditional behavioral or physiological techniques to test hearing are not feasible with right whales. Previous research on the hearing of marine mammals has shown that functional models are reliable estimators of hearing sensitivity in marine species. Fundamental to these models is a comprehensive analysis of inner ear anatomy. Morphometric analyses of 18 inner ears from 13 stranded North Atlantic right whales (Eubalaena glacialis) were used for development of a preliminary model of the frequency range of hearing. Computerized tomography was used to create two‐dimensional (2D) and 3D images of the cochlea. Four ears were decalcified and sectioned for histologic measurements of the basilar membrane. Basilar membrane length averaged 55.7 mm (range, 50.5 mm–61.7 mm). The ganglion cell density/mm averaged 1,842 ganglion cells/mm. The thickness/width measurements of the basilar membrane from slides resulted in an estimated hearing range of 10 Hz–22 kHz based on established marine mammal models. Additional measurements from more specimens will be necessary to develop a more robust model of the right whale hearing range. Anat Rec, 290:734–744, 2007.

BIOMECHANICAL AND STRUCTURAL MODELING OF HEARING IN BALEEN WHALES

Anthropogenic noise may be a major source of habitat degradation for cetaceans. To assess and mitigate the effects of noise pollution on marine mammals, we need information on how and what they hear. Although hearing in odontocetes, or toothed whales, is well studied, few data are available for mysticetes, or baleen whales. Behavioural and electrophysiological hearing tests are presently impractical for mysticetes, but biomechanical, structural modelling provides hearing estimates based on auditory system anatomy. In this research, three101 dimensional models were produced for minke Balaenoptera acutorostrata, blue Balaenoptera musculus, and humpback Balaenoptera novaeangliae whale inner ears from CT scans and histology to measure key features for estimating hearing ranges, e.g., basilar membrane thickness-towidth ratios. Full head reconstructions were also produced for minke whales based on head CT images and dissections.

Great Ears: Low-Frequency Sensitivity Correlates in Land and Marine Leviathans.

Like elephants, baleen whales produce low-frequency (LF) and even infrasonic (IF) signals, suggesting they may be particularly susceptible to underwater anthropogenic sound impacts. Analyses of computerized tomography scans and histologies of the ears in five baleen whale and two elephant species revealed that LF thresholds correlate with basilar membrane thickness/width and cochlear radii ratios. These factors are consistent with high-mass, low-stiffness membranes and broad spiral curvatures, suggesting that Mysticeti and Proboscidea evolved common inner ear adaptations over similar time scales for processing IF/LF sounds despite operating in different media.

Computerized tomography of the otic capsule and otoliths in the oyster toadfish, Opsanus tau

The neurocranium of the toadfish (Opsanus tau) exhibits a distinct translucent region in the otic capsule (OC) that may have functional significance for the auditory pathway. This study used ultrahigh resolution computerized tomography (100 µm voxels) to compare the relative density of three sites along the OC (dorsolateral, midlateral, and ventromedial) and two reference sites (dorsal: supraoccipital crest; ventral: parasphenoid bone) in the neurocranium. Higher attenuation occurs where structural density is greater; thus, we compared the X‐ray attenuations measured, which provided a measure of relative density. The maximum attenuation value was recorded for each of the five sites (x and y) on consecutive sections throughout the OC and for each of the three calcareous otoliths associated with the sensory maculae (lagena, saccule, and utricle) in the OC. All three otoliths had higher attenuations than any sites in the neurocranium. Both dorsal and ventral reference sites (supraoccipital crest and parasphenoid bone, respectively) had attenuation levels consistent with calcified bone and had relatively small, irregular variations along the length of the OC in all individuals. The lowest relative attenuations (lowest densities) occurred consistently at the three sites along the OC. In addition, the lowest attenuations measured along the OC occurred at the ventromedial site around the saccular otolith for all seven fish. The decrease in bone density along the OC is consistent with the hypothesis that there is a low‐density channel in the skull to facilitate transmission of acoustic stimuli to the auditory endorgans of the ear. J. Morphol. 276:228–240, 2015.

Morphometric analyses of hearing in two families of pinnipeds

Pinniped (seal and sea lion) auditory systems operate in two acoustically distinct environments, air and water. Otariids (sea lions and fur seals) generally divide their time evenly between land and water while phocids (true seals) spend the majority of their time in water. These pinniped families therefore offer an exceptional opportunity to investigate aquatic versus terrestrial hearing mechanisms. Recent reports indicate differences in hearing ranges and sensitivities among species from these families [D. Kastak and R. Schusterman, J. Acoust. Soc. Am. 1303, 2216–2228 (1998); P. W. B. Moore and R. Schusterman, Marine Mammal Sci. 3, 31–53 (1987)]. In this project, ear anatomy of three representative pinniped species (Otariidae: California sea lion, Zalophus californianus; Phocidae: northern elephant seal, Mirounga angustirostris; and harbor seal, Phoca vitulina) was examined using computerized tomography (CT scans) and gross dissection. Three‐dimensional reconstructions of heads and ears from CT data wer...

DIAGNOSIS AND MANAGEMENT OF INTESTINAL PARTIAL OBSTRUCTION IN A LOGGERHEAD TURTLE (CARETTA CARETTA)

Abstract: A loggerhead sea turtle (Caretta caretta) was suspected of ingesting rubber suction cups during rehabilitation following a cold-stun event. Survey radiographs were inconclusive. Computed tomography (CT) was performed to determine whether the objects had been ingested after traditional radiographs failed to resolve the material. The items were identified, and a partial obstruction was diagnosed. The case was managed with medical therapy using white petrolatum and light mineral oil administered to the turtle in fish for 3 wk. The CT exam was repeated 2 wk into the therapy. A persistent partial obstruction was identified; however, progression of the foreign objects through the intestinal tract was evident and continued medical mangement was deemed appropriate. The foreign bodies were passed with feces 26 days after ingestion.

Non anthropogenic deafness in marine mammals: Hearing that is going, going, gone.

In humans, hearing is absent or diminished as a result of congenital defects, aging, noise exposures, traumatic events, and disease. Until concern arose about anthropogenic noise impacts on marine mammals, little was known about the mechanisms or incidence of marine mammal hearing losses. Over the past decade, we have gained substantial information from behavioral and electrophysiologic audiometres, in vivo imaging, and postmortem examinations. Dr. Sam Ridgway has been a pivotal element in these investigations, pioneering many of the techniques and facilitating broad collaborative studies. In this paper, the results of computerized tomographic and histologic studies of pinniped and cetacean ears, the majority of which Dr. Ridgway supplied, will be presented. The data show that marine mammals sustain precipitous and progressive hearing loss from multiple etiologies, including labyrinthitis, infestations, trauma, chronic multistage otitis, and presbycusis. In particular, older dolphins and seals develop deg...

Hearing in the North Atlantic right whale: Anatomical predictions

Understanding the hearing abilities of large whales is important to determine the impacts of anthropogenic sources of sound. Right whales are not amenable to traditional physiological techniques to test hearing. Previous research on the hearing of marine mammals has shown that functional morphometric models are reliable estimators of hearing sensitivity in marine species. Morphometric analyses of 18 inner ears from 13 stranded right whales were used in the development of a preliminary model of the frequency range of hearing. All ears were scanned with computerized tomography (CT). Four ears showing the best preservation were processed into slides for measurements of the basilar membrane. Calculated basilar‐membrane length averaged 55.7 mm (range 50.5–61.7 mm). The ganglion cell density/mm averaged 1842 ganglion cells/mm. Membrane length and ganglion cell density were used to predict a total ganglion cell count of approximately 102 500 ganglion cells for right whales. The thickness/width measurements of the basilar membrane from slides resulted in an estimated frequency range of approximately 10 Hz–22 kHz based on established marine mammal models. Additional measurements from more specimens will be necessary to develop a more robust model of the right whale hearing range. a)Currently at Cornell University Bioacoustics Research Program.