Vocal changes accompanying the descent of the larynx during ontogeny from neonates to adults in male and female goitred gazelles (Gazella subgutturosa)

Abstract

The pronouncedly enlarged and descended larynx in male goitred gazelles (Gazella subgutturosa), Mongolian gazelles (Procapra gutturosa) and fallow deer (Dama dama) represents an interesting parallel to the ‘Adam’s apple’ of human males. Goitred gazelles, as humans, are not born with a descended larynx. Therefore the sexual dimorphism of larynx size and position develops during ontogeny. In this study, the vocal ontogeny of male and female goitred gazelles was investigated across five age classes from neonates to adults. The acoustic variables of nasal contact calls were measured in 53 (24 male, 29 female) individuals, body mass and neck dimensions in 63 (31 male, 32 female) live individuals and nasal vocal tract and vocal fold lengths in 26 (16 male, 10 female) anatomical specimens. Call fundamental frequency (f0), the acoustic correlate of the ontogenetically enlarging larynx, decreased significantly in either sex. Call formants (second, third and forth), the acoustic correlates of the ontogenetically elongating vocal tract, did not differ significantly between sexes up to early adulthood, but clearly diverged in adults. Significant differences between sexes in neck circumference at the level of the larynx emerged already at 2–3 months of age, whereas body mass, neck circumference at the neck–body transition and the degree of larynx descent significantly differed in adults only. We discuss that, in contrast to humans, the accelerated enlargement of the larynx in male goitred gazelles starts early in ontogeny. A moderate descent of the larynx develops equally in both sexes before early adulthood, whereas the additional prominent descent of the larynx in males is shifted to late ontogeny. This might avoid selective disadvantages of this sexually dimorphic trait on males during their period of growth. As has been previously proved for humans, the emergence of the strong male-specific descent of the larynx in goitred gazelles may go along with the increasing social status and the males’ increasing chances of siring offspring. Similar to the Adam’s apple of human males, this may indicate the important role of the enlarged and descended larynx for signaling male status via masculine voice.