Sound Generating Structures of the Humpback Dolphin Sousa plumbea (Cuvier, 1829) and the Directionality in Dolphin Sounds

Abstract

The macroscopic morphology of structures involved in sound generation in the Indian Ocean humpback dolphin (Sousa plumbea) were described for the first time using computed tomography imaging and standard gross dissection techniques. The Indian Ocean humpback dolphin may represent a useful comparative model to the bottlenose dolphin (Tursiops sp.) to provide insights into the functional anatomy of the sound production in dolphins, since these coastal dolphins exhibit similar body size and share similarities on acoustic behavior. The general arrangement of sound generating structures, that is, air sacs and muscles, was similar in both the bottlenose dolphin and the Indian Ocean humpback dolphin. The main difference between the two species existed in a small left posterior branch of the melon in the Indian Ocean humpback dolphin, which was not found in the bottlenose dolphin and might reflect an adaptation of directionality for high frequency communication sounds as seen in some other delphinids (e.g., Lagenorhynchus sp., Grampus griseus). Thus, this may be the main reason for the asymmetry of the sound production structures in dolphins. Additionally, the longer rostrum in Indian Ocean humpback dolphins might suggest a more directional echolocation beam compared to the Lahille's bottlenose dolphin. Anat Rec, 302:849–860, 2019. © 2018 Wiley Periodicals, Inc.

Head adaptation for sound production and feeding strategy in dolphins (Odontoceti: Delphinida)

“…The late transformation of the rostrum might reflect shifts in the feeding and/or behavioural (acoustic) patterns of these species (Plön et al, 2015;Troina et al, 2016) and potentially indicate higher vulnerability when facing a changing environment. Young individuals of coastal NBHF species and S. plumbea (i.e., mainly male adolescents) seem to be more susceptible to die in gill nets (Atkins et al, 2013;Reeves et al, 2013) and this might be related to, among other things, the late development of an important structure to modulate biosonar clicks (i.e., rostrum) (Song et al, 2016) and their restricted field of perception compared to other coastal forms such as T. gephyreus (Frainer et al, 2019b).…”

“…plumbea (i.e., mainly male adolescents) seem to be more susceptible to die in gill nets (Atkins et al, 2013; Reeves et al, 2013) and this might be related to, among other things, the late development of an important structure to modulate biosonar clicks (i.e., rostrum) (Song et al, 2016) and their restricted field of perception compared to other coastal forms such as T . gephyreus (Frainer et al, 2019b).…”

Raven Calls Indicate Sender’s Neural State

“…With respect to the animal communication, the pronunciation is not only depending on a series of pronounced organ coordination work [40][41][42], but also depending on the control of central nervous system [43]. The animals have been adapted to the environment after a long time evolution process via a series of successful constructed conditional reflexes [44].…”

Blowhole anomaly in pantropical spotted dolphin (Delphinidae: Stenella attenuata)

“…The epicranial or nasal complex of dolphins have a lip‐like valve at the nasal passage called monkey‐lips, which given air pressure and interaction with the skull, melon, and air sacs can produce directional sound beams (Frainer, Plön, Serpa, Moreno, & Huggenberger, 2018). Mead (1975) examined the nasal passages and diverticula in Stenella , and showed that the premaxillary sac in Stenella was quite uniform in the species examined and was like that of Tursiops truncatus .…”