Changes in ear bone development in the womb paralleled changes observed throughout whale evolution, providing new insight about how whales adapted to hearing underwater, according to a study published March 11, 2015 in the open-access journal PLOS ONE by Maya Yamato and Nicholas Pyenson from Smithsonian Institution National Museum of Natural History.
Whales receive underwater sounds through a different mechanism than their close terrestrial relatives. Instead of hearing through the ear canal, cetaceans hear through specialized fatty tissues leading to an evolutionarily novel feature: an acoustic funnel located anterior to the tympanic aperture. The acoustic funnel is thought to be a critical component to understanding how baleen and toothed whales hear underwater. Using non-invasive X-ray computed tomography (CT) imaging techniques, the authors of this study traced the development of fetal ear bones in 56 specimens from 10 different families of toothed and baleen whales. They observed how ears develop in unborn whales of modern species, and compared these changes with those reflected in the fossilized ears of extinct whales over the course of millions of years.
Their findings confirmed that changes in the development of ear bones in the womb paralleled changes observed throughout whale evolution, providing new insight about how whales shifted from land to sea and adapted to hearing underwater.
"Whale ears are incredibly complex organs. Although scientists know that hearing is one of the most important senses that whales use to communicate, navigate and search for food in their underwater world, we are still searching for clues about how their ears actually work," said Maya Yamato. "This research provides a window into evolutionary processes that took place millions of years ago, and helps explain how whales evolved to hear after they moved from living on land to thriving in today's oceans."
Whales rely on sound to communicate with each other, forage, and navigate through water.
Understanding how whales hear is essential to protecting populations in the future as ocean noise from human activities, including global shipping, seismic surveys, and sonar training, continues to rise.
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Citation: Yamato M, Pyenson ND (2015) Early Development and Orientation of the Acoustic Funnel Provides Insight into the Evolution of Sound Reception Pathways in Cetaceans. PLoS ONE 10(3): e0118582. doi:10.1371/journal.pone.0118582
Funding: Support for this work came from a NMNH Peter Buck Postdoctoral Fellowship to MY, and the NMNH Remington Kellogg Fund to NDP (http://www. mnh.si.edu/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: NDP is an academic editor for PLOS ONE. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.