DOI: 10.5061/dryad.5qfttdzj3
title: Individual vocal identity is enhanced by the enlarged external nose in male proboscis monkeys (Nasalis larvatus)

description: Adult male proboscis monkeys, Nasalis larvatus, develop an enlarged
 external nose. Males often produce loud, long-distance calls filtered
 through the nasal passage. The enlarged nose likely functions as a visual
 badge of social status and a visual key representing the owner’s physical
 and sexual quality and thus is useful for females in selecting mates. In
 addition to such visual signaling, a larger external nose enhances the
 lower frequencies in calls, possibly exaggerating acoustic signals related
 to body size. Here, we used computational simulations with
 three-dimensional models of the nasal passage to show how the external
 nose modifies the acoustic property, indicating that the external nose
 develops to enhance lower frequencies in adults but varies in a specific
 formant position among adult males. This finding suggests that the
 external nose generates acoustic signals about physical–sexual maturity in
 adult males and individual identity among them. The unusual features of
 the social organisation in this species, a patrilineality of a multilevel
 community consisting of one-male-multi-female units, may reinforce the
 functional importance of individual male recognition for males and females
 to monitor the location of both their own units and those of other males.
description: # Individual vocal identity is enhanced by the enlarged external nose in
 male proboscis monkeys (Nasalis larvatus) Dataset DOI:
 [10.5061/dryad.5qfttdzj3](10.5061/dryad.5qfttdzj3) ## Description of the
 data and file structure CT scans, STL data of 3D model, and acoustic
 property calculated ### Files and variables #### **File: CTscans.zip**
 **Description:** Frozen specimens of two male proboscis monkeys (adult
 Jaka and juvenile Niko) were thawed and scanned using a 320-row area
 detector CT scanner (Aquilion One™, Canon Medical Systems Corporation,
 Otawara, Japan) at Nihon University in Fujisawa, Japan, in 2016. The scans
 are in DICOM format. The scanning and reconstruction parameters are
 described in the header of each file. **File: STL.zip**
 **Description:** The nasal passage from the posterior and anterior naris
 area was extracted from each CT scans and the extracted area was
 transformed into a three-dimensional surface image in stereolithography
 (STL) format. The left and right nasal passages of each proboscis were
 computationally separated, and the side with few water and tissues was
 used for study after smoothing rough surfaces. **File:
 SweeptoneMeasurement.zip** **Description:** The acoustic properties of a
 replica model of the nasal passage which was created from the STL data
 were measured based on the method of Kitamura et al. (2009). The models
 were based on the geometric data used for computational estimation and
 created by a three-dimensional printer using
 acrylonitrile–butadiene–styrene resin. A sweep tone sound was generated
 from a loudspeaker (W3-881SJ; TB Speaker, Taipei, Taiwan) with an
 amplifier (PC200USB-HR; Fostex, Tokyo) and was inputted from the external
 nostril side. The distance between the loudspeaker and the external nose
 was set to 30 mm. The nasopharyngeal side was covered with a silicone
 plate (Smooth-Sil 940; Smooth-On, Macungie, USA), into which a probe
 microphone (Type 4182; Brüel & Kjaer, Naerum, Denmark) was inserted
 through a small hole and linked to a Nexus conditioning amplifier (Brüel
 & Kjaer). By covering the output, direct injection of the source sound
 into the microphone was avoided. Acoustic effects below the posterior
 nostril, such as the ventricle and the vocal tract, were also avoided so
 that only the acoustic effect of the nasal passage was measured. Before
 measurement, the sweep tone sound was recorded externally to the nasal
 passage. To minimize environmental effects (e.g., frequency response and
 directivity of the microphone, reverberation, and room reflection), the
 input signal was corrected so that the sweep tone sound was generated with
 equal power at all frequencies. The corrected signal was applied to the
 nasal passage, and the output sound was recorded by a digital recorder
 with a sampling frequency of 44.1 kHz. air_f.csv: Original sweep tone
 sound generated from a loudspeaker (W3-881SJ; TB Speaker, Taipei, Taiwan)
 with an amplifier (PC200USB-HR; Fostex, Tokyo). The frequency was
 increased from 100 Hz to 6000 Hz in 120 seconds. This sound was recorded
 by a probe microphone (Type 4182; Brüel & Kjær, Naerum, Denmark) in
 the absence of the replica model of the nasal cavity. The sampling
 frequency is 44.1 kHz. The physical unit for the recording time is
 seconds, whereas that of the microphone signal is voltage. air_f.wav:
 Sound file converted from "air_f.csv." jaka.csv: Output sound
 recorded from the replica model of Jaka by the probe microphone (Type
 4182; Brüel & Kjær, Naerum, Denmark). The sweep tone sound was input
 to the replica model from the external nostril side. The sampling
 frequency is 44.1 kHz. The physical unit for the recording time is
 seconds, whereas that of the microphone signal is voltage. niko.csv:
 Output sound recorded from the replica model of Niko by the probe
 microphone (Type 4182; Brüel & Kjær, Naerum, Denmark). The sweep tone
 sound was input to the replica model from the external nostril side. The
 sampling frequency is 44.1 kHz. The physical unit for the recording time
 is seconds, whereas that of the microphone signal is voltage.