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Nourbakhsh H, Adams A, Raverty S, Vogl AW, Haulena M, Skoretz SA. Microscopic Anatomy of the Upper Aerodigestive Tract in Harbour Seals (Phoca vitulina): Functional Adaptations to Swallowing. Anat Rec (Hoboken) 2022; 306:947-959. [PMID: 35719006 DOI: 10.1002/ar.25025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Revised: 05/05/2022] [Accepted: 05/31/2022] [Indexed: 11/07/2022]
Abstract
Abandoned harbour seal pups (Phoca vitulina) are frequently recovered by rehabilitation centres and often require intensive nursing, gavage feeding and swallowing rehabilitation prior to anticipated release. Seal upper aerodigestive tract (UAT) histology descriptions relevant to deglutition are limited, impacting advances in rehabilitation practice. Therefore, we examined the histological characteristics of the harbour seal UAT to understand species-specific functional anatomy and characterize adaptations. To this end, we conducted gross dissections, compiled measurements and reviewed histologic features of the UAT structures of 14 pre-weaned harbour seal pups that died due to natural causes or were humanely euthanized. Representative samples for histologic evaluation included the tongue, salivary glands, epiglottis, and varying levels of the trachea and esophagus. Histologically, there was a prominent muscularis in the tongue with fewer lingual papillae types compared to humans. Abundant submucosal glands were observed in lateral and pharyngeal parts of the tongue and rostral parts of the esophagus. When compared to other mammalian species, there was a disproportionate increase in the amount of striated muscle throughout the length of the esophageal muscularis externa. This may indicate a lesser degree of autonomic control over the esophageal phase of swallowing in harbour seals. Our study represents the first detailed UAT histological descriptions for neonatal harbour seals. Collectively, these findings support specific anatomic and biomechanic adaptations relevant to suckling, prehension and deglutition. This work will inform rehabilitation practices and guide future studies on swallowing physiology in harbour seals with potential applications to other pinniped and otariid species in rehabilitation settings. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Hirad Nourbakhsh
- School of Audiology & Speech Sciences, University of British Columbia, Vancouver, BC
| | - Arlo Adams
- Life Sciences Institute & Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC
| | - Stephen Raverty
- Animal Health Center, 1767 Angus Campbell Road, Abbotsford, BC
| | - A Wayne Vogl
- Life Sciences Institute & Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC
| | - Martin Haulena
- Vancouver Aquarium Marine Mammal Rescue Centre, Vancouver, BC
| | - Stacey A Skoretz
- School of Audiology & Speech Sciences, University of British Columbia, Vancouver, BC.,Department of Critical Care Medicine, University of Alberta, Edmonton, AB
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de Reus K, Carlson D, Lowry A, Gross S, Garcia M, Rubio-Garcia A, Salazar-Casals A, Ravignani A. Vocal tract allometry in a mammalian vocal learner. J Exp Biol 2022; 225:275049. [PMID: 35483405 PMCID: PMC9124484 DOI: 10.1242/jeb.243766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Accepted: 03/14/2022] [Indexed: 11/20/2022]
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. Summary: Harbour seals are vocal learners that can escape acoustic allometry despite complying with anatomical allometric constraints. Advanced neural control over their vocal organs may allow them to break acoustic allometry.
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Affiliation(s)
- Koen de Reus
- Comparative Bioacoustics Group, Max Planck Institute for Psycholinguistics, 6525 XD Nijmegen, The Netherlands.,Artificial Intelligence Lab, Vrije Universiteit Brussel, 1050 Brussels, Belgium.,Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands
| | - Daryll Carlson
- Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands.,Department of Earth System Science, Stanford University, Stanford, CA 94305-4216, USA
| | - Alice Lowry
- Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands.,School of Environmental Sciences, University of Liverpool, Liverpool, L3 5DA, UK
| | - Stephanie Gross
- Institute for Terrestrial and Aquatic Wildlife Research (ITAW), University of Veterinary Medicine Hannover, Foundation, 25761 Büsum, Germany
| | - Maxime Garcia
- Animal Behaviour, Department of Evolutionary Biology and Environmental Studies, University of Zurich, 8057 Zürich, Switzerland.,Center for the Interdisciplinary Study of Language Evolution, University of Zurich, CH-8050 Zürich, Switzerland
| | - Ana Rubio-Garcia
- Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands
| | - Anna Salazar-Casals
- Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands
| | - Andrea Ravignani
- Comparative Bioacoustics Group, Max Planck Institute for Psycholinguistics, 6525 XD Nijmegen, The Netherlands.,Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands.,Center for Music in the Brain, Department of Clinical Medicine, Aarhus University & The Royal Academy of Music Aarhus/Aalborg, 8000 Aarhus C, Denmark
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Torres Borda L, Jadoul Y, Rasilo H, Salazar Casals A, Ravignani A. Vocal plasticity in harbour seal pups. Philos Trans R Soc Lond B Biol Sci 2021; 376:20200456. [PMID: 34719248 PMCID: PMC8558775 DOI: 10.1098/rstb.2020.0456] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/28/2021] [Indexed: 12/22/2022] Open
Abstract
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 (f0), 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 f0; simultaneously, we recorded pups' spontaneous calls. Unlike most mammals, pups modified their vocalizations by lowering their f0 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 f0, 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 f0 modulation while inhibiting amplitude adjustments. This lowering of f0 is unusual, as most animals commonly display no such f0 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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Affiliation(s)
- Laura Torres Borda
- Comparative Bioacoustics Group, Max Planck Institute for Psycholinguistics, Wundtlaan 1, 6525 XD Nijmegen, The Netherlands
- Research Department, Sealcentre Pieterburen, Hoofdstraat 94-A, 9968 AG Pieterburen, The Netherlands
| | - Yannick Jadoul
- Comparative Bioacoustics Group, Max Planck Institute for Psycholinguistics, Wundtlaan 1, 6525 XD Nijmegen, The Netherlands
- Artificial Intelligence Lab, Vrije Universiteit Brussel, 1050 Elsene/Ixelles, Belgium
| | - Heikki Rasilo
- Artificial Intelligence Lab, Vrije Universiteit Brussel, 1050 Elsene/Ixelles, Belgium
| | - Anna Salazar Casals
- Research Department, Sealcentre Pieterburen, Hoofdstraat 94-A, 9968 AG Pieterburen, The Netherlands
| | - Andrea Ravignani
- Comparative Bioacoustics Group, Max Planck Institute for Psycholinguistics, Wundtlaan 1, 6525 XD Nijmegen, The Netherlands
- Research Department, Sealcentre Pieterburen, Hoofdstraat 94-A, 9968 AG Pieterburen, The Netherlands
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Varola M, Verga L, Sroka MGU, Villanueva S, Charrier I, Ravignani A. Can harbor seals ( Phoca vitulina) discriminate familiar conspecific calls after long periods of separation? PeerJ 2021; 9:e12431. [PMID: 34820184 PMCID: PMC8601051 DOI: 10.7717/peerj.12431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Accepted: 10/12/2021] [Indexed: 11/20/2022] Open
Abstract
The ability to discriminate between familiar and unfamiliar calls may play a key role in pinnipeds' communication and survival, as in the case of mother-pup interactions. Vocal discrimination abilities have been suggested to be more developed in pinniped species with the highest selective pressure such as the otariids; yet, in some group-living phocids, such as harbor seals (Phoca vitulina), mothers are also able to recognize their pup's voice. Conspecifics' vocal recognition in pups has never been investigated; however, the repeated interaction occurring between pups within the breeding season suggests that long-term vocal discrimination may occur. Here we explored this hypothesis by presenting three rehabilitated seal pups with playbacks of vocalizations from unfamiliar or familiar pups. It is uncommon for seals to come into rehabilitation for a second time in their lifespan, and this study took advantage of these rare cases. A simple visual inspection of the data plots seemed to show more reactions, and of longer duration, in response to familiar as compared to unfamiliar playbacks in two out of three pups. However, statistical analyses revealed no significant difference between the experimental conditions. We also found no significant asymmetry in orientation (left vs. right) towards familiar and unfamiliar sounds. While statistics do not support the hypothesis of an established ability to discriminate familiar vocalizations from unfamiliar ones in harbor seal pups, further investigations with a larger sample size are needed to confirm or refute this hypothesis.
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Affiliation(s)
- Mila Varola
- Comparative Bioacoustics Research Group, Max Planck Institute for Psycholinguistics, Nijmegen, The Netherlands
- Research Department, Sealcentre Pieterburen, Pieterburen, the Netherlands
| | - Laura Verga
- Comparative Bioacoustics Research Group, Max Planck Institute for Psycholinguistics, Nijmegen, The Netherlands
- Department of Neuropsychology and Psychopharmacology, Maastricht University, Maastricht, The Netherlands
| | - Marlene Gunda Ursel Sroka
- Research Department, Sealcentre Pieterburen, Pieterburen, the Netherlands
- Department of Behavioral Biology, University of Münster, Münster, Germany
| | - Stella Villanueva
- Research Department, Sealcentre Pieterburen, Pieterburen, the Netherlands
| | - Isabelle Charrier
- Paris Saclay Institute of Neuroscience, Université Paris-Saclay, Orsay, France
| | - Andrea Ravignani
- Comparative Bioacoustics Research Group, Max Planck Institute for Psycholinguistics, Nijmegen, The Netherlands
- Research Department, Sealcentre Pieterburen, Pieterburen, the Netherlands
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