Vocal tract allometry in a mammalian vocal learner

Abstract

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 for their size. A recent hypothesis suggests that allometry-breaking mammals cluster into two groups: those with anatomical adaptations to their vocal tracts and those capable of learning new sounds (vocal learners). Here, we tested which mechanism is used to escape from acoustic allometry by probing vocal tract allometry in a proven mammalian vocal learner, the harbour seal (Phoca vitulina). We tested whether vocal tract structures and body size scale allometrically in 68 young individuals. We found that both body length and body mass accurately predict vocal tract length and one tracheal dimension. Independently, body length predicts vocal fold length while body mass 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 anatomical allometric constraints. 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. We suggest that seals, and perhaps other species producing signals that deviate from those expected from their vocal tract dimensions, may break allometry without morphological adaptations. In seals, and potentially other vocal learning mammals, advanced neural control over vocal organs may be the main mechanism for breaking acoustic allometry.

The paradox of learned song in a semi‐solitary mammal

“…Duration is not used in mate choice, though highly variable among individuals and populations (Bjørgesæter et al, 2004; Nikolich et al, 2016; Van Parijs, Corkeron, et al, 2003), thereby arguing against the lungworm hypothesis (Sabinsky et al, 2017). Harbor seals follow acoustic allometry (de Reus et al, 2022), that is, an individual's vocalization accurately encodes their body size. Yet, these animals break allometry by vocal production learning, suggesting vocal control (de Reus et al, 2022).…”

“…Harbor seals follow acoustic allometry (de Reus et al, 2022), that is, an individual's vocalization accurately encodes their body size. Yet, these animals break allometry by vocal production learning, suggesting vocal control (de Reus et al, 2022). Harbor seals show vocal plasticity, a building block of vocal learning, extremely early in life, at 1–3 weeks of age: Seal pups lower their fundamental frequency when exposed to noise specifically overlapping with this frequency (Torres Borda et al, 2021).…”

The paradox of learned song in a semi-solitary mammal

“…Duration is not used in mate choice, though highly variable among individuals and populations (Bjørgesaeter et al, 2004;Nikolich et al, 2016;Van Parijs, Corkeron, et al, 2003), thereby arguing against the lungworm hypothesis (Sabinsky et al, 2017). Harbor seals follow acoustic allometry (de Reus et al, 2022), that is, an individual's vocalization accurately encodes their body size. Yet, these animals break allometry by vocal production learning, suggesting vocal control (de Reus et al, 2022).…”

“…Harbor seals follow acoustic allometry (de Reus et al, 2022), that is, an individual's vocalization accurately encodes their body size. Yet, these animals break allometry by vocal production learning, suggesting vocal control (de Reus et al, 2022). Harbor seals show vocal plasticity, a building block of vocal learning, extremely early in life, at 1-3 weeks of age: Seal pups lower their fundamental frequency when exposed to noise specifically overlapping with this frequency (Torres Borda et al, 2021).…”

Analysis of the role and influence of sight-singing and ear training on vocal learning skills

“…Sight-singing and ear training from the initial type of development has nearly a thousand years of history. China's sight-singing and ear training teaching, from the initial school music to the current music colleges and universities of the basic subjects, has nearly a hundred years of history, its curriculum, teaching objectives, teaching content, teaching methods, and so on, have a full range of improvements in all aspects of the teaching [4][5][6]. Sight-singing and ear training are mainly the practice of basic skills that can effectively learn and use sight-singing and ear training, which will have a greater role in promoting vocal singing [7][8].…”