Evidence for double acoustic windows in the dolphin, <i>Tursiops truncatus</i>

Vv, Popov; Supin, Alexander Ya.; Klishin, Vladimir O.; Tarakanov, Mikhail B.; Pletenko, Mikhail G.

doi:10.1121/1.2816564

Cited by 29 publications

(15 citation statements)

References 27 publications

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“…Anatomical studies have shown discrete fat lobes associated with the lower jaw that vary in size and shape in each species (Ketten, 1994). The mandibular fat hearing hypothesis is supported by physiological data, particularly for the concept of an additional pathway near the bulla, which preferentially receives lower frequency sounds (Popov et al, 2008).…”

Section: Introductionmentioning

confidence: 63%

“…While these data may not conclusively support a double acoustic window for the finless porpoise, they do indicate these porpoises hear low frequencies better from the side and higher frequencies better at anterior positions; and at least suggest the need for further investigations. Such a double-acoustic window has been proposed for the bottlenose dolphin (Popov et al, 2008). The porpoise's frequency-dependent general regions of low and high frequency sensitivity are less specific than in the bottlenose dolphin, which shows considerable (near 40 dB) differences across the head (Møhl et al, 1999).…”

Section: Relative Hearingmentioning

confidence: 99%

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Hearing pathways in the Yangtze finless porpoise,Neophocaena asiaeorientalis asiaeorientalis

Mooney

Ketten

et al. 2013

Journal of Experimental Biology

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How an animal receives sound may influence its use of sound. While 'jaw hearing' is well supported for odontocetes, work examining how sound is received across the head has been limited to a few representative species. The substantial variation in jaw and head morphology among odontocetes suggests variation in sound reception. Here, we address how a divergent subspecies, the Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) hears low-, mid-and high-frequency tones, as well as broadband clicks, comparing sounds presented at different locations across the head. Hearing was measured using auditory evoked potentials (AEPs). Click and tone stimuli (8, 54 and 120 kHz) were presented at nine locations on the head and body using a suctioncup transducer. Threshold differences were compared between frequencies and locations, and referenced to the underlying anatomy using computed tomography (CT) imaging of deceased animals of the same subspecies. The best hearing locations with minimum thresholds were found adjacent to a mandibular fat pad and overlaying the auditory bulla. Mean thresholds were not substantially different at locations from the rostrum tip to the ear (11.6 dB). This contrasts with tests with bottlenose dolphins and beluga whales, in which 30-40 dB threshold differences were found across the animals' heads. Response latencies increased with decreasing response amplitudes, which suggests that latency and sensitivity are interrelated when considering sound reception across the odontocete head. The results suggest that there are differences among odontocetes in the anatomy related to receiving sound, and porpoises may have relatively less acoustic 'shadowing'.

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Section: Introductionmentioning

confidence: 63%

Section: Relative Hearingmentioning

confidence: 99%

Hearing pathways in the Yangtze finless porpoise,Neophocaena asiaeorientalis asiaeorientalis

Mooney

Ketten

et al. 2013

Journal of Experimental Biology

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“…As this field of study advances, the evidence for how and where sounds are received suggests that this process is more complex than originally conceived (Møhl et al 1999;Popov et al, 2008;Cranford et al, 2008a,b). Regardless of the exact mechanism(s), it is clear that the hollow posterior portion of the mandibles is an integral part of sound reception in odontocetes.…”

Section: Introductionmentioning

confidence: 99%

Shape analysis of odontocete mandibles: Functional and evolutionary implications

Barroso¹,

Cranford²,

Berta³

2012

Journal of Morphology

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Odontocete mandibles serve multiple functions, including feeding and hearing. One hypothesis is that sound enters the hearing apparatus via the pan bone of the posterior mandibles (Norris, 1968). Another viewpoint, based on computer models, suggests that sound enters primarily through the gular apparatus and the opening created by the absent medial wall of the posterior mandibles. The posterior region of each mandibular ramus has a large, hollow cavity called the mandibular foramen that contains a bulging mandibular fat body (MFB), which terminates on the bony tympanoperiotic complex. The acoustic properties of these fat bodies suggest that they refract sound. This unambiguous link between form and function has catalyzed this current study of mandibular shape. Previous studies have described odontocete mandibles using linear morphometrics and focused on multiple populations within single genera. Geometric Morphometrics (GM) is used to avoid some limitations of linear morphometric studies, using relative 3-D landmark positions instead of lengths. This technique measures shape only, excluding any scaling, rotational, and positional effects.The primary objective of this study is to use GM to quantify mandibular shape across all major lineages of Odontoceti. Eighty-five mandibles, comprised of 40 species, representing all major lineages were included in the shape analysis. Twelve landmarks found on each mandible represent regions of the symphysis and mandibular foramen. The majority of shape variation was found in Jaw Flare and Symphysis Elongation (85.5%). Shape differences in the mandibular foramen also accounts for a portion the total variation (10.9%). The mandibles are an integral component of the sound reception apparatus in toothed whales and the geometry of the mandibular foramen likely plays a role in hearing.The second objective of this study is to assess correlates of hearing and mandibular foramen geometry derived from the GM shape analysis, as well as from linear morphometrics. Echolocation peak frequency (EPF) was used as a measure of sound reception. Odontocete anatomy may emphasize frequencies they need to hear and suppress others in a returning echo during echolocation. Frequencies can be characterized by corresponding wavelengths. Surface area between the four landmarks that represent the mandibular foramen was calculated to assess the relationship between EPF and dimensions of a receiving structure (i.e. mandibular foramen and corresponding MFB). A significant relationship between size of the foramen and EPF was found, suggesting that size of the foramen may limit lower frequencies (longer wavelengths) from propagating through the mandibular fat body.

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“…The signals were monitored using an oscilloscope (Tektronix TDS1002C, Beaverton, OR, USA) before being projected through a Reson TC-4040 hydrophone (Reson, Slangerup, Denmark), which was positioned at a distance of ~2m and a depth of 0.5m in front of the subject's 'acoustic windows' along the body axis. The 'acoustic windows' are located at the lower jaw area of the subject, through which sound is assumed to travel to the inner ear (Norris, 1968;Popov et al, 2008). Sound pressure levels (SPLs, dB re.…”

Section: Hearing Measurementmentioning

confidence: 99%

“…On the same day, the dolphin was transported to the rescue centre of the Pearl River Estuary Chinese White Dolphin National Nature Reserve, Zhuhai, China (Fig.1B) (C)The dolphin was positioned in a stretcher at the water surface while wearing electroencephalography (EEG) electrodes attached to the skin by soft silicone suction cups. The sound projector was positioned ~2m from the animal's 'acoustic windows', where the sound is assumed to travel to the animal's inner ear (Norris, 1968;Popov et al, 2008).…”

Section: Subjectmentioning

confidence: 99%

Possible age-related hearing loss (presbycusis) and corresponding change in echolocation parameters in a stranded Indo-Pacific humpback dolphin

Wang

et al. 2013

Journal of Experimental Biology

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SUMMARYThe hearing and echolocation clicks of a stranded Indo-Pacific humpback dolphin (Sousa chinensis) in Zhuhai, China, were studied. This animal had been repeatedly observed in the wild before it was stranded and its age was estimated to be ~40years. The animal's hearing was measured using a non-invasive auditory evoked potential (AEP) method. Echolocation clicks produced by the dolphin were recorded when the animal was freely swimming in a 7.5m (width)×22m (length)×4.8m (structural depth) pool with a water depth of ~2.5m. The hearing and echolocation clicks of the studied dolphin were compared with those of a conspecific younger individual, ~13years of age. The results suggested that the cut-off frequency of the high-frequency hearing of the studied dolphin was ~30-40kHz lower than that of the younger individual. The peak and centre frequencies of the clicks produced by the older dolphin were ~16kHz lower than those of the clicks produced by the younger animal. Considering that the older dolphin was ~40years old, its lower high-frequency hearing range with lower click peak and centre frequencies could probably be explained by age-related hearing loss (presbycusis).

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Evidence for double acoustic windows in the dolphin, Tursiops truncatus

Cited by 29 publications

References 27 publications

Hearing pathways in the Yangtze finless porpoise,Neophocaena asiaeorientalis asiaeorientalis

Hearing pathways in the Yangtze finless porpoise,Neophocaena asiaeorientalis asiaeorientalis

Shape analysis of odontocete mandibles: Functional and evolutionary implications

Possible age-related hearing loss (presbycusis) and corresponding change in echolocation parameters in a stranded Indo-Pacific humpback dolphin

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