Toothed Whale Echolocation Organs Evolved From Jaw Muscles, New Research Suggests
taylorvich writes:
https://phys.org/news/2024-04-toothed-whale-echolocation-evolved-jaw.html
Dolphins and whales use sound to communicate, navigate and hunt. New research suggests that the collections of fatty tissue that enable toothed whales to do so may have evolved from their skull muscles and bone marrow.
Scientists at Hokkaido University determined DNA sequences of genes which were expressed in acoustic fat bodies-collections of fat around the head that toothed whales use for echolocation. They measured gene expression in the harbor porpoise (Phocoena phocoena) and Pacific white-sided dolphin (Lagenorhynchus obliquidens). Their findings were published in the journal Gene.
The evolution of acoustic fat bodies in the head-the melon in the whale forehead, extramandibular fat bodies (EMFB) alongside the jawbone, and intramandibular fat bodies (IMFB) within the jawbone-was essential for sound use such as echolocation. However, little is known about the genetic origins of those fatty tissues.
"Toothed whales have undergone significant degenerations and adaptations to their aquatic lifestyle," said Hayate Takeuchi, a Ph.D. student at Hokkaido University's Hayakawa Lab and first author of the study. One adaptation was the partial loss of their sense of smell and taste, along with the gain of echolocation to enable them to navigate in the underwater environment.
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"This study has revealed that the evolutionary tradeoff of masticatory muscles for the EMFB-between auditory and feeding ecology-was crucial in the aquatic adaptation of toothed whales," said Assistant Professor Takashi Hayakawa of the Faculty of Environmental Earth Science, who led the study."It was part of the evolutionary shift away from chewing to simply swallowing food, which meant the chewing muscles were no longer needed."
More information: Hayate Takeuchi et al, A tradeoff evolution between acoustic fat bodies and skull muscles in toothed whales, Gene (2024). DOI: 10.1016/j.gene.2024.148167
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