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Abstract
The ability to sense and localize sound is so advantageous for survival that it is difficult to understand the almost 100 million year gap separating the appearance of early tetrapods and the emergence of an impedance-matching tympanic middle ear - which we normally regard as a prerequisite for sensitive hearing on land - in their descendants. Recent studies of hearing in extant atympanate vertebrates have provided significant insights into the ancestral state(s) and the early evolution of the terrestrial tetrapod auditory system. These reveal a mechanism for sound pressure detection and directional hearing in 'earless' atympanate vertebrates that may be generalizable to all tetrapods, including the earliest terrestrial species. Here, we review the structure and function of vertebrate tympanic middle ears and highlight the multiple acquisition and loss events that characterize the complex evolutionary history of this important sensory structure. We describe extratympanic pathways for sound transmission to the inner ear and synthesize findings from recent studies to propose a general mechanism for hearing in 'earless' atympanate vertebrates. Finally, we integrate these studies with research on tympanate species that may also rely on extratympanic mechanisms for acoustic reception of infrasound (<20 Hz) and with studies on human bone conduction mechanisms of hearing.
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Affiliation(s)
- Grace Capshaw
- Department of Biology, University of Maryland, College Park, MD 20742, USA
| | | | - Catherine E Carr
- Department of Biology, University of Maryland, College Park, MD 20742, USA
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2
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Aquatic birds have middle ears adapted to amphibious lifestyles. Sci Rep 2022; 12:5251. [PMID: 35347167 PMCID: PMC8960762 DOI: 10.1038/s41598-022-09090-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Accepted: 03/16/2022] [Indexed: 11/21/2022] Open
Abstract
Birds exhibit wide variation in their use of aquatic environments, on a spectrum from entirely terrestrial, through amphibious, to highly aquatic. Although there are limited empirical data on hearing sensitivity of birds underwater, mounting evidence indicates that diving birds detect and respond to sound underwater, suggesting that some modifications of the ear may assist foraging or other behaviors below the surface. In air, the tympanic middle ear acts as an impedance matcher that increases sound pressure and decreases sound vibration velocity between the outside air and the inner ear. Underwater, the impedance-matching task is reversed and the ear is exposed to high hydrostatic pressures. Using micro- and nano-CT (computerized tomography) scans of bird ears in 127 species across 26 taxonomic orders, we measured a suite of morphological traits of importance to aerial and aquatic hearing to test predictions relating to impedance-matching in birds with distinct aquatic lifestyles, while accounting for allometry and phylogeny. Birds that engage in underwater pursuit and deep diving showed the greatest differences in ear structure relative to terrestrial species. In these heavily modified ears, the size of the input areas of both the tympanic membrane and the columella footplate of the middle ear were reduced. Underwater pursuit and diving birds also typically had a shorter extrastapedius, a reduced cranial air volume and connectivity and several modifications in line with reversals of low-to-high impedance-matching. The results confirm adaptations of the middle ear to aquatic lifestyles in multiple independent bird lineages, likely facilitating hearing underwater and baroprotection, while potentially constraining the sensitivity of aerial hearing.
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Is Human underwater hearing mediated by bone conduction? Hear Res 2022; 420:108484. [DOI: 10.1016/j.heares.2022.108484] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/17/2021] [Revised: 03/08/2022] [Accepted: 03/14/2022] [Indexed: 11/17/2022]
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Russell AP, Bauer AM. Vocalization by extant nonavian reptiles: A synthetic overview of phonation and the vocal apparatus. Anat Rec (Hoboken) 2020; 304:1478-1528. [PMID: 33099849 DOI: 10.1002/ar.24553] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2020] [Revised: 08/13/2020] [Accepted: 09/16/2020] [Indexed: 12/19/2022]
Abstract
Among amniote vertebrates, nonavian reptiles (chelonians, crocodilians, and lepidosaurs) are regarded as using vocal signals rarely (compared to birds and mammals). In all three reptilian clades, however, certain taxa emit distress calls and advertisement calls using modifications of regions of the upper respiratory tract. There is no central tendency in either acoustic mechanisms or the structure of the vocal apparatus, and many taxa that vocalize emit only relatively simple sounds. Available evidence indicates multiple origins of true vocal abilities within these lineages. Reptiles thus provide opportunities for studying the early evolutionary stages of vocalization. The early literature on the diversity of form of the laryngotracheal apparatus of reptiles boded well for the study of form-function relationships, but this potential was not extensively explored. Emphasis shifted away from anatomy, however, and centered instead on acoustic analysis of the sounds that are produced. New investigative techniques have provided novel ways of studying the form-function aspects of the structures involved in phonation and have brought anatomical investigation to the forefront again. In this review we summarize what is known about hearing in reptiles in order to contextualize the vocal signals they generate and the sound-producing mechanisms responsible for them. The diversity of form of the sound producing apparatus and the increasing evidence that reptiles are more dependent upon vocalization as a communication medium than previously thought indicates that they have a significant role to play in the understanding of the evolution of vocalization in amniotes.
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Affiliation(s)
- Anthony P Russell
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Aaron M Bauer
- Department of Biology and Center for Biodiversity and Ecosystem Stewardship, Villanova University, Villanova, Pennsylvania, USA
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Larsen ON, Wahlberg M, Christensen-Dalsgaard J. Amphibious hearing in a diving bird, the great cormorant ( Phalacrocorax carbo sinensis). J Exp Biol 2020; 223:jeb217265. [PMID: 32098879 DOI: 10.1242/jeb.217265] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Accepted: 02/10/2020] [Indexed: 11/20/2022]
Abstract
Diving birds can spend several minutes underwater during pursuit-dive foraging. To find and capture prey, such as fish and squid, they probably need several senses in addition to vision. Cormorants, very efficient predators of fish, have unexpectedly low visual acuity underwater. So, underwater hearing may be an important sense, as for other diving animals. We measured auditory thresholds and eardrum vibrations in air and underwater of the great cormorant (Phalacrocorax carbo sinensis). Wild-caught cormorant fledglings were anaesthetized, and their auditory brainstem response (ABR) and eardrum vibrations to clicks and tone bursts were measured, first in an anechoic box in air and then in a large water-filled tank, with their head and ears submerged 10 cm below the surface. Both the ABR waveshape and latency, as well as the ABR threshold, measured in units of sound pressure, were similar in air and water. The best average sound pressure sensitivity was found at 1 kHz, both in air (53 dB re. 20 µPa) and underwater (58 dB re. 20 µPa). When thresholds were compared in units of intensity, however, the sensitivity underwater was higher than in air. Eardrum vibration amplitude in both media reflected the ABR threshold curves. These results suggest that cormorants have in-air hearing abilities comparable to those of similar-sized diving birds, and that their underwater hearing sensitivity is at least as good as their aerial sensitivity. This, together with the morphology of the outer ear (collapsible meatus) and middle ear (thickened eardrum), suggests that cormorants may have anatomical and physiological adaptations for amphibious hearing.
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Affiliation(s)
- Ole Næsbye Larsen
- Sound and Behaviour Group, Department of Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Magnus Wahlberg
- Sound and Behaviour Group, Department of Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Jakob Christensen-Dalsgaard
- Sound and Behaviour Group, Department of Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
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Brandt C, Brande-Lavridsen N, Christensen-Dalsgaard J. The Masked ABR (mABR): a New Measurement Method for the Auditory Brainstem Response. J Assoc Res Otolaryngol 2018; 19:753-761. [PMID: 30238407 DOI: 10.1007/s10162-018-00696-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2017] [Accepted: 09/04/2018] [Indexed: 11/26/2022] Open
Abstract
The auditory brainstem response (ABR) is relatively non-invasive, and in many species, the only practical way to assess auditory sensitivity. The two main methods for measuring ABR are using either transients or tone bursts as a stimulus. The transient stimulus produces strong neural responses that contain no frequency information. In contrast, tone bursts stimulate only a small part of the auditory system, eliciting weaker neural responses but supplying frequency information. Furthermore, short tone bursts become less and less frequency specific with increasing stimulus wavelength, making them unsuitable for testing low-frequency hearing. Here, we develop a method that can measure sensitivity to both low and high-frequency stimuli. The method is based on masking of a transient response by long-duration sinusoids. The measurement system is developed as a highly portable system that runs on battery power. It has been used in a variety of animals in our lab and in the field, including squid (Mooney et al. in J Exp Biol 213: 3748-3759, 2010), lungfish (Christensen-Dalsgaard et al. in J Neurophys 105: 1992-2004, 2011b), alligators (Bierman et al. in J Exp Biol 217: 1094-1107, 2014), and mink (Brandt et al. in J Exp Biol 216: 3542-3550, 2013). Here, we present data recorded from Tokay geckos and compare the results with tone burst ABR measurements. This method produces results comparable to tone burst stimulations at higher frequencies (above 1 kHz) but has several advantages: it is relatively insensitive to fluctuations in neural signal level, it allows measurements at very low frequencies, it allows constant monitoring of the state of the animal, and can be used to measure directional hearing.
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Affiliation(s)
- Christian Brandt
- Institute of Clinical Research, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark.
- Institute of Biology, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark.
| | - Nanna Brande-Lavridsen
- Institute of Biology, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark
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Comparative and developmental patterns of amphibious auditory function in salamanders. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2016; 202:879-894. [PMID: 27766381 DOI: 10.1007/s00359-016-1128-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Revised: 09/16/2016] [Accepted: 10/12/2016] [Indexed: 10/20/2022]
Abstract
Early amphibious tetrapods may have detected aquatic sound pressure using sound-induced lung vibrations, but their lack of tympanic middle ears would have restricted aerial sensitivity. Sharing these characteristics, salamanders could be models for the carryover of auditory function across an aquatic-terrestrial boundary without tympanic middle ears. We measured amphibious auditory evoked potential audiograms in five phylogenetically and ecologically distinct salamanders (Amphiuma means, Notophthalmus viridescens, Ambystoma talpoideum, Eurycea spp., and Plethodon glutinosus) and tested whether metamorphosis and terrestrial niche were linked to aerial sensitivity. Threshold differences between media varied between species. A. means' relative aerial sensitivity was greatest at 100 Hz and decreased with increasing frequency. In contrast, all other salamanders retained greater sensitivity up to 500 Hz, and in A. talpoideum and Eurycea, relative sensitivity at 500 Hz was higher than at 100 Hz. Aerial thresholds of terrestrial P. glutinosus above 200 Hz were similar to A. talpoideum and Eurycea, but lower than N. viridescens and A. means. Metamorphosis did not affect aerial sensitivity in N. viridescens or A. talpoideum. These results fail to support a hypothesis of terrestrial hearing specialization across ontogeny or phylogeny. We discuss methodological limitations to our amphibious comparisons and factors affecting variation in amphibious performance.
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Womack MC, Christensen-Dalsgaard J, Hoke KL. Better late than never: effective air-borne hearing of toads delayed by late maturation of the tympanic middle ear structures. ACTA ACUST UNITED AC 2016; 219:3246-3252. [PMID: 27520654 DOI: 10.1242/jeb.143446] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Accepted: 08/05/2016] [Indexed: 11/20/2022]
Abstract
Most vertebrates have evolved a tympanic middle ear that enables effective hearing of airborne sound on land. Although inner ears develop during the tadpole stages of toads, tympanic middle ear structures are not complete until months after metamorphosis, potentially limiting the sensitivity of post-metamorphic juveniles to sounds in their environment. We tested the hearing of five species of toads to determine how delayed ear development impairs airborne auditory sensitivity. We performed auditory brainstem recordings to test the hearing of the toads and used micro-computed tomography and histology to relate the development of ear structures to hearing ability. We found a large (14-27 dB) increase in hearing sensitivity from 900 to 2500 Hz over the course of ear development. Thickening of the tympanic annulus cartilage and full ossification of the middle ear bone are associated with increased hearing ability in the final stages of ear maturation. Thus, juvenile toads are at a hearing disadvantage, at least in the high-frequency range, throughout much of their development, because late-forming ear elements are critical to middle ear function at these frequencies. We discuss the potential fitness consequences of late hearing development, although research directly addressing selective pressures on hearing sensitivity across ontogeny is lacking. Given that most vertebrate sensory systems function very early in life, toad tympanic hearing may be a sensory development anomaly.
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Affiliation(s)
- Molly C Womack
- Department of Biology, Colorado State University, Fort Collins, CO 80523, USA
| | | | - Kim L Hoke
- Department of Biology, Colorado State University, Fort Collins, CO 80523, USA
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Carr CE, Christensen-Dalsgaard J. Sound Localization Strategies in Three Predators. BRAIN, BEHAVIOR AND EVOLUTION 2015; 86:17-27. [PMID: 26398572 DOI: 10.1159/000435946] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
In this paper, we compare some of the neural strategies for sound localization and encoding interaural time differences (ITDs) in three predatory species of Reptilia, alligators, barn owls and geckos. Birds and crocodilians are sister groups among the extant archosaurs, while geckos are lepidosaurs. Despite the similar organization of their auditory systems, archosaurs and lizards use different strategies for encoding the ITDs that underlie localization of sound in azimuth. Barn owls encode ITD information using a place map, which is composed of neurons serving as labeled lines tuned for preferred spatial locations, while geckos may use a meter strategy or population code composed of broadly sensitive neurons that represent ITD via changes in the firing rate.
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Affiliation(s)
- Catherine E Carr
- Department of Biology, University of Maryland Center for the Comparative and Evolutionary Biology of Hearing, College Park, Md., USA
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Bierman HS, Carr CE. Sound localization in the alligator. Hear Res 2015; 329:11-20. [PMID: 26048335 DOI: 10.1016/j.heares.2015.05.009] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Revised: 05/12/2015] [Accepted: 05/24/2015] [Indexed: 10/23/2022]
Abstract
In early tetrapods, it is assumed that the tympana were acoustically coupled through the pharynx and therefore inherently directional, acting as pressure difference receivers. The later closure of the middle ear cavity in turtles, archosaurs, and mammals is a derived condition, and would have changed the ear by decoupling the tympana. Isolation of the middle ears would then have led to selection for structural and neural strategies to compute sound source localization in both archosaurs and mammalian ancestors. In the archosaurs (birds and crocodilians) the presence of air spaces in the skull provided connections between the ears that have been exploited to improve directional hearing, while neural circuits mediating sound localization are well developed. In this review, we will focus primarily on directional hearing in crocodilians, where vocalization and sound localization are thought to be ecologically important, and indicate important issues still awaiting resolution.
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Affiliation(s)
- Hilary S Bierman
- Center for Comparative and Evolutionary Biology of Hearing, Department of Biology, University of Maryland College Park, College Park, Maryland 20742, USA.
| | - Catherine E Carr
- Center for Comparative and Evolutionary Biology of Hearing, Department of Biology, University of Maryland College Park, College Park, Maryland 20742, USA.
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