Acoustic allometry and vocal learning in mammals

Garcia, Maxime; Ravignani, Andrea

doi:10.1098/rsbl.2020.0081

Cited by 41 publications

(30 citation statements)

References 90 publications

(146 reference statements)

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“…Unfortunately, the relative contribution of both sound production mechanisms is unclear. Here, we provide support for a hypothesis trying to segregate anatomical vs. learning mechanisms (Garcia & Ravignani, 2020;Ravignani & Garcia 2021). We find that harbour seals are mechanistically constrained by their vocal anatomy, and their large vocal flexibility (Ralls et al, 1985;Borda et al, in press) thus points towards extensive volitional control over their vocalisations.…”

Section: Discussionsupporting

confidence: 79%

Vocal tract allometry in a mammalian vocal learner

Reus

Carlson

Lowry

et al. 2021

Preprint

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Acoustic allometry occurs when features of animal vocalisations can be predicted from body size measurements. Despite this being considered the norm, allometry sometimes breaks, resulting in species sounding smaller or larger than expected. A recent hypothesis suggests that allometry-breaking animals cluster into two groups: those with anatomical adaptations to their vocal tracts and those capable of learning new sounds (vocal learners). Here we test this hypothesis by probing vocal tract allometry in a proven mammalian vocal learner, the harbour seal (Phoca vitulina). We test whether vocal tract structures and body size scale allometrically in 68 individuals. We find that both body length and body weight accurately predict vocal tract length and one tracheal dimension. Independently, body length predicts vocal fold length while body weight predicts a second tracheal dimension. All vocal tract measures are larger in weaners than in pups and some structures are sexually dimorphic within age classes. We conclude that harbour seals do comply with allometric constraints, lending support to our hypothesis. However, allometry between body size and vocal fold length seems to emerge after puppyhood, suggesting that ontogeny may modulate the anatomy-learning distinction previously hypothesised as clear-cut. Species capable of producing non-allometric signals while their vocal tract scales allometrically, like seals, may then use non-morphological allometry-breaking mechanisms. We suggest that seals, and potentially other vocal learning mammals, may achieve allometry-breaking through developed neural control over their vocal organs.

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Section: Discussionsupporting

confidence: 79%

Vocal tract allometry in a mammalian vocal learner

Reus

Carlson

Lowry

et al. 2021

Preprint

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“…Nevertheless, we maintain the plausibility of such a scenario, however, as even the simplest (monotonic) rhythms still appear to occur more frequently in terrestrial rather than arboreal primate species (Table 6). Furthermore, it is worth emphasizing that artificially deep tones, as some other mammals produce (Garcia and Ravignani, 2020), are vastly more readily enabled via hominin bipedality by virtue of free-to-drum arms and hands. Being terrestrial also likely enabled hominins to use the ground as a sturdy and unyielding acoustic platform, permitting even more vigorous striking of inanimate, and perhaps resonant, objects-such as hollow logs.…”

Section: Discussionmentioning

confidence: 99%

Singing behavior via reduced predation risk

Schruth¹,

Jordania²

2020

Preprint

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A surprisingly diverse array of animals produce sounds with song-like qualities in order to communicate who and where they are to conspecifics when their senses of smell, and in some cases vision, are rendered ineffectual across long or occluded distances. Social factors are typically considered to drive the evolution of such calls, but here we consider broader effects of habitat which are often difficult to observe, measure, and analyze, and are thus typically neglected. We tested the hypothesis that ecological protections from predation enabled animals to call by neutralizing the risk inherent in vocally forfeiting position. We compiled data on human and non-human singing species that live in arboreal, aerial, or aquatic (i.e. non-planar) habitats, to measure the degree to which each presumably helps to reduce predation and thereby allow singing. We find that singing species also forfend predation via larger size as well as increased levels of arboreality and flight. Arboreal primates and birds do appear to sing significantly more so than terrestrial ones. Hunting and warfare in humans, respectively, likewise correlate with the musical features of rhythmic and melodic tension. In all species explored, however, only body size universally correlates positively with singing behavior. We conclude that effects of predation, especially when viewed in a larger, food-web context, play a central role in determining who sings and who does not.

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“…It has been previously shown that elaborate control over the vocal apparatus provides a biophysical mechanism for vocal learning. Thus, laryngeal plasticity and vocal flexibility may provide indirect evidence for vocal learning in harbour seals' puppyhood [ 28 , 38 , 75 ].…”

Section: Discussionmentioning

confidence: 99%

Vocal plasticity in harbour seal pups

Borda

Jadoul

Rasilo

et al. 2021

Phil. Trans. R. Soc. B

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Vocal plasticity can occur in response to environmental and biological factors, including conspecifics' vocalizations and noise. Pinnipeds are one of the few mammalian groups capable of vocal learning, and are therefore relevant to understanding the evolution of vocal plasticity in humans and other animals. Here, we investigate the vocal plasticity of harbour seals ( Phoca vitulina ), a species with vocal learning abilities observed in adulthood but not puppyhood. To evaluate early mammalian vocal development, we tested 1–3 weeks-old seal pups. We tailored noise playbacks to this species and age to induce seal pups to shift their fundamental frequency ( f 0 ), rather than adapt call amplitude or temporal characteristics. We exposed individual pups to low- and high-intensity bandpass-filtered noise, which spanned—and masked—their typical range of f 0 ; simultaneously, we recorded pups' spontaneous calls. Unlike most mammals, pups modified their vocalizations by lowering their f 0 in response to increased noise. This modulation was precise and adapted to the particular experimental manipulation of the noise condition. In addition, higher levels of noise induced less dispersion around the mean f 0 , suggesting that pups may have actively focused their phonatory efforts to target lower frequencies. Noise did not seem to affect call amplitude. However, one seal showed two characteristics of the Lombard effect known for human speech in noise: significant increase in call amplitude and flattening of spectral tilt. Our relatively low noise levels may have favoured f 0 modulation while inhibiting amplitude adjustments. This lowering of f 0 is unusual, as most animals commonly display no such f 0 shift. Our data represent a relatively rare case in mammalian neonates, and have implications for the evolution of vocal plasticity and vocal learning across species, including humans. This article is part of the theme issue ‘Voice modulation: from origin and mechanism to social impact (Part I)’.

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Acoustic allometry and vocal learning in mammals

Cited by 41 publications

References 90 publications

Vocal tract allometry in a mammalian vocal learner

Vocal tract allometry in a mammalian vocal learner

Singing behavior via reduced predation risk

Vocal plasticity in harbour seal pups

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