Comparative physiology of vocal musculature in two odontocetes, the bottlenose dolphin (Tursiops truncatus) and the harbor porpoise (Phocoena phocoena)
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The mechanism by which odontocetes produce sound is unique among mammals. To gain insight into the physiological properties that support sound production in toothed whales, we examined myoglobin content ([Mb]), non-bicarbonate buffering capacity (β), fiber-type profiles, and myosin heavy chain expression of vocal musculature in two odontocetes: the bottlenose dolphin (Tursiops truncatus; n = 4) and the harbor porpoise (Phocoena phocoena; n = 5). Both species use the same anatomical structures to produce sound, but differ markedly in their vocal repertoires. Tursiops produce both broadband clicks and tonal whistles, while Phocoena only produce higher frequency clicks. Specific muscles examined in this study included: (1) the nasal musculature around the phonic lips on the right (RNM) and left (LNM) sides of the head, (2) the palatopharyngeal sphincter (PPS), which surrounds the larynx and aids in pressurizing cranial air spaces, and (3) the genioglossus complex (GGC), a group of muscles positioned ventrally within the head. Overall, vocal muscles had significantly lower [Mb] and β than locomotor muscles from the same species. The PPS was predominately composed of small diameter slow-twitch fibers. Fiber-type and myosin heavy chain analyses revealed that the GGC was comprised largely of fast-twitch fibers (Tursiops: 88.6%, Phocoena: 79.7%) and had the highest β of all vocal muscles. Notably, there was a significant difference in [Mb] between the RNM and LNM in Tursiops, but not Phocoena. Our results reveal shared physiological characteristics of individual vocal muscles across species that enhance our understanding of key functional roles, as well as species-specific differences which appear to reflect differences in vocal capacities.
KeywordsAerobic metabolism Anaerobic capacity Myoglobin Fiber-type Myosin heavy chain Sound production
We thank Joy Reidenberg, Ted Cranford, Bill McLellan, Ann Pabst, Mario Muscedere, Sarah McHugh, Megan Murphy, and Adrienne White, as well as the Long Marine Lab Marine Mammal Stranding Network, the Marine Mammal Center, the UNCW Stranding Network, and the Southwest Fisheries Science Center. This research was conducted under NMFS Scientific Research Permit #19590 to TMW, and NOAA Parts Authorization 110314 to RCD.
Compliance with ethical standards
This research was supported by the Office of Naval Research (N000141410460 to TMW and RCD; and N0001416IP00023, N0001415IP00039, and N0001414IP20045 to DPN and MMH).
Conflict of interest
The authors declare no conflict of interest.
This article does not contain any studies with live animals performed by any of the authors.
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