Dolphins and whales use sound to communicate, navigate and hunt. New research suggests that the fatty tissue deposits that allow toothed whales to do this may have evolved from cranial muscles and bone marrow.

Scientists from Hokkaido University identified the DNA sequences of genes expressed in acoustic fat bodies, which are clusters of fat around the head that toothed whales use for echolocation. They measured gene expression in the harbor dolphin (Phocoena phocoena) and the Pacific white-sided dolphin (Lagenorhynchus obliquidens). Their findings were published in a journal Gene.

The evolution of acoustic fat bodies in the head (the melon on the whale’s forehead, extramandibular fat bodies (EMFBs) near the mandible, and intramandibular fat bodies (IMFBs) in the mandible) was important for the use of sound. echolocation However, little is known about the genetic origin of these fatty tissues.

Ph.D. “Toothed whales have gone through a significant process of degeneration and adaptation to their aquatic lifestyle,” said Hayate Takeuchi. student at Hokkaido University Hayakawa Laboratory and first author of the study. One of the adaptations was the development of echolocation, as well as the partial loss of smell and taste, so that they could navigate the underwater environment.

Researchers found that genes normally associated with muscle function and development were active in melon and EMFB. There was also evidence of an evolutionary link between extramaxillary fat and the masseter muscle in humans, which connects the lower jaw to the cheekbones and is an important muscle in chewing.

“This study showed that the evolutionary shift of masticatory muscles for EMBF (between auditory and food ecology) was crucial in the adaptation of toothed whales to water,” said Associate Professor Takashi Hayakawa from the Faculty of Environmental Earth Sciences, who led the study. . .

“This was part of the evolutionary transition from chewing to just swallowing, which meant that chewing muscles were no longer needed.”

Analysis of gene expression in intramaxillary adipose tissue revealed the activity of genes related to immune functions, such as activation of some elements of the immune response and regulation of T cell formation.

Stranding Network Hokkaido (SNH) is another important aspect of the study as the samples used in this study were collected by them. SNH collected samples from whales stranded on shore and at the mouth of the Hokkaido River.

“Long-term contact with local people and communities in Hokkaido allowed researchers to conduct a variety of studies on whale biology, including our unexpected discoveries,” said Professor Takashi Fritz Matsuishi, director of SNH.