Fig 1.
Spectrogram illustrating high-frequency and low-frequency vocalization modes in domestic dog (A), dhole (B) and red fox (C).
(A) Dog (7-kg dachshund): left–low-frequency whine; middle–high-frequency squeak; right–biphonic whine-squeak (S1 Audio). (B) Dhole: left–low-frequency yap; middle–high-frequency squeak; right–biphonic yap–squeak (S2 Audio). (C) Red fox–low-frequency whine (S3 Audio). Designations: f0 –low fundamental frequency; f1 and f2 –harmonics of f0; g0 –high fundamental frequency; g0–f0 and g0+f0 –the linear combinations of f0 and g0. The spectrogram was created at 22050 Hz sampling frequency, Hamming window, FFT 1024, frame 50%, overlap 93.75%.
Fig 2.
Gross morphology of the vocal apparatus, tongue and hyoid of an adult male dhole in near-natural position.
Overlay reconstruction based on CT scans and macroscopic anatomical dissection. Skull, skeletal parts of the neck and thoracic inlet and contours of a typical head-and-neck posture of a live animal are provided in addition to facilitate an integrative view of the dhole vocal organs. Constrictor muscles of the pharynx removed. *** = lateral edge of neck musculature. Scale bar = 10 mm.
Fig 3.
Computed 3-D reconstruction based on a CT scan of a female dhole head and neck specimen.
In-situ resting positions of hyoid apparatus and larynx. Mediosagittal virtual section, right half, medial view. The arrow points to the flexible nostril region. Scale bar = 50 mm.
Table 1.
Measured acoustic variables and corresponding abbreviations.
Fig 4.
Mediosagittal section of the head and the region of the larynx of an adult male dhole.
Illustrating the difference between nasal and oral vocal tract (vt) length including respective topographical relationships. The nasal vt is constantly longer than the oral vt in both adult male and adult female. The laryngeal entrance is depicted in a position for a nasal call. For production of an oral call, the soft palate is raised, the larynx slightly retracted and the epiglottis pulled ventrally to a position close to the root of the tongue, i.e. below the red line. Scale bar = 10 mm.
Fig 5.
Intra-pharyngeal ostium in the dhole.
During quiet respiration (not panting) and nasal call production the laryngeal entrance protrudes through the intra-pharyngeal ostium into the nasal portion of the pharynx. The intra-pharyngeal ostium is the sole connection between the ventral oral portion and the dorsal nasal portion of the pharynx. Mediosagittal section of pharynx and larynx of an unpreserved specimen, right half, medial view. Scale = 50 mm.
Fig 6.
Mucous membrane relief of the larynx including the vocal and vestibular folds in the dhole.
The contour of the lateral laryngeal ventricle is indicated. The position of the ventricle is rostral to the vestibular fold and lateral to the cuneiform process. The red arrow points into the caudally directed entrance to the lateral laryngeal ventricle. Mediosagittal section of the formalin-fixed larynx of a two-years-old female, right half, medial view. White scale bar = 10 mm.
Fig 7.
Hyoid apparatus (A) and laryngeal cartilages (B) of the dhole.
(A) Excised hyoid apparatus and larynx; overlying muscles partly reconstructed on the basis of macroscopic dissection. The thyrohyoid 'articulation' is established by a cartilaginous connection. (B) Left half of hyoid apparatus and laryngeal cartilages. The interarytenoid cartilage is intercalated between left and right arytenoid cartilage. A sesamoid cartilage supports the transverse arytenoid muscles at their dorsomedian fusion along the transverse furrow between the corniculate and medial processes of the arytenoid cartilages. Colours in (A): green = M. cricopharyngeus; blue = M. thyropharyngeus; red = M. thyrohyoideus; orange = termination of M. sternothyroideus; yellow = termination of M. sternohyoideus. ** in (B): thyrohyoid connection. (A) and (B): Left lateral view. Scale bar = 10 mm, respectively.
Fig 8.
Intrinsic laryngeal muscles of the dhole (A) and position of lateral laryngeal ventricle (B).
(A) Larynx after removal of the left cricothyroid muscle and the left half of the thyroid cartilage. Dorsal and lateral cricoarytenoid muscles and thyroarytenoid muscle exposed. The thyroarytenoid muscle is not divided into a rostral ventricularis and a caudal vocalis muscle. (B) Larynx after removal of its intrinsic muscles. Reconstruction of the thyroarytenoid muscle (black line, shaded in translucent red) shows how its wider ventral portion covers the ventral end of the cuneiform process and the ‘neck’ of the laryngeal ventricle rostrally. Contour of the cuneiform process indicated by faint black line. The vocal ligament marks position and angle of the medially located vocal fold. (A) and (B): Left lateral view. Scale bar = 10 mm.
Fig 9.
Extrinsic laryngeal muscles and ventral hyoid muscles of the dhole.
The sternohyoid and sternothyroid muscles are fused between their joint origin from the sternal manubrium up to a tendinous inscription. At this point both muscles separate to reach their terminations on the basihyoid and on the thyroid cartilage, respectively. * = position of tendinous inscription. Left lateral view. Scale = 50 mm.
Fig 10.
Right nasal cavity (A) and its flexible rostral portion (B) of an adult male dhole.
(A) Middle nasal concha and nasal septum removed to expose the dorsal, the alar and the basal folds. ** = cut edge of the nasal septum. (B) Detail of (A). The arrow points to the flexible rostral portion of the nose, which can be variably constricted by differential action of the rostral nasal muscles. This will narrow particularly the space between the dorsal and the alar folds and, in concert with movements of the nostril wings, might influence nasal call characteristics. Mediosagittal section of the nasal region, right half, medial view. Scale bar = 10 mm in (A) and (B), respectively.
Fig 11.
Lateral laryngeal ventricle (A) and larynx (B) in red fox.
(A) Artificially inflated pharynx and laryngeal ventricle after removal of the left half of the thyroid cartilage. The thyroarytenoid muscle is not divided into a rostral ventricularis and a caudal vocalis muscle. Its wider ventral portion covers the ‘neck’ of the laryngeal ventricle rostrally. (B) Mucous membrane relief of the larynx including the vocal and vestibular folds in the red fox. In (A): * = cricothyroid articulation; ** = temporomandibular articulation. Left lateral view; in (B): Mediosagittal section of pharynx and larynx of an unpreserved specimen, right half, medial view. Scale = 50 mm in (A) and (B), respectively.
Table 2.
Values (mean ± SD) of acoustic variables measured in calls of 4 dholes which served postmortem as anatomical specimens for this study.
Table 3.
Controlled for individual identity two-way ANOVA results for comparison of low-frequency component variables between the yap and yap-squeak call types in the dhole.
Table 4.
Controlled for individual identity two-way ANOVA results for comparison of high-frequency component variables between the squeak and yap-squeak call types in the dhole.
Fig 12.
Spectrogram illustrating the acoustic similarity between the high-frequency squeaks of a dhole (A) and the whistles of a human (B).
(A) A natural series of a captive male dhole. (B) A natural series of an adult male zoo visitor, imitating the dhole calls (S4 Audio). A 5 kHz high-pass filter was applied to remove background noise. Spectrogram settings as in Fig 1.