Wednesday, March 29, 2023

Whales’ eyes offer glimpses of their evolution from land to sea: U of T researchers

University of Toronto researchers have shed light on the evolutionary transition of whales’ early ancestors to deep-sea shore dwellers, suggesting that these ancestors had visual systems that quickly adapted to darkness. Could.

Their findings suggest that the common ancestor of living whales was already a deep diver, capable of seeing in the blue twilight zone of the ocean, with eyes that rapidly adjusted to dim conditions as whales were exposed to the surface air. She went down on a deep breath.

“In the evolution of whale diving, there has been a long-standing question of whether deep-sea foraging evolved,” says Belinda Chang, a professor in the Faculty of Ecology and Evolutionary Biology, and the Departments of Arts and Sciences of Cell and Systems Biology. “And it seems that based on our data, this happened before the divergence of toothed and baleen whales. The common ancestor of all living cetaceans was deep-diving – and then later species all the diversity seen in modern whales and dolphins.” Developed forging expertise.”

Chang worked with all dangA former member of Chang’s lab, who has a PhD in ecology and evolutionary biology from Yu KT, on a study describing his experiments, computational analysis and results Proceedings of the National Academy of Science,

Deep diving by marine mammals is a great evolutionary transition, along with powered flight and living on land, and tells a lot about how quickly life can adapt to a changing world.

Whales evolved from mammals that share a common ancestor with hippos and that were partially aquatic. The great mystery of their transition to deep-sea pasture was how quickly this ability developed. Dungan and Chang looked at whale fossils at the molecular level and focused on the rhodopsin protein, which absorbs light and sends a signal that travels through the retina to the brain.

“One of the most intriguing aspects of this iconic land-to-sea evolutionary transition is that the properties of the visual environment have completely changed,” Chang says. “This helped define which genes would be most interesting to us to target in our study.”

Dungan applied robust data science models to rhodopsin proteins from a variety of living whales and related mammals. This computerized analysis revealed a gene sequence representing rhodopsin found in the common ancestor of all living whales. He expressed this gene in cells grown in the laboratory to “regenerate” the predicted proteins and to perform experiments on pure samples.

Dungan says, “The fossil record is the gold standard for understanding evolutionary biology. But Jurassic Park notwithstanding what you believe, it is rare to extract DNA from fossil specimens because the situation worsens. So, if you are interested in genes and You rely on mathematical modeling and a robust sampling of the genes of living organisms to complement what you understand from the fossil record of how DNA is evolving.”

Whales' Eyes Offer Glimpses Of Their Evolution From Land To Sea: U Of T Researchers

Belinda Chang (back left) leads a lab that focuses on the evolutionary transition of animal vision. Sarah Dungan (Chang’s right) researched whale vision as a former member of Chang’s lab (Photo by Diana Tyzko)

Dungan and Chang were astonished by the biochemical properties of the regenerated proteins compared to land mammals. Early whale rhodopsin was more sensitive to blue light that penetrates deeper into the ocean, to an extent that exceeded expectations. Its biochemical properties also suggested that the retinas of early whales may have responded rapidly to changes in light levels.

Early whales eventually evolved into the many types of toothed whales and baleen whales we see today. As different species of whales evolved, they established ecological niches at different levels of the ocean and even in freshwater rivers. Dungan and Chang’s work suggests that there were further evolutionary adaptations as members of both groups were either exposed to prey closer to the surface from early deep levels or specialized to become even more extreme divers.

Dungan says, “I’ve always been fascinated by whales. The idea that there was a land mammal like mine that eventually evolved to live underwater blew my mind as a child, even though I really Didn’t understand the meaning of it. In those days.

“It’s amazing that we can now gain this level of insight into the lifestyle of a long-extinct organism, just by performing laboratory experiments on a single protein. An incredibly powerful way for us to interrogate ancestral protein resurrection.” That’s how ancient organisms evolved that most people don’t know about,” she adds.

Next, Dungan and Chang plan to regenerate the ancestral whale protein that transmits rhodopsin light signals from the retina to the brain to provide insight into the neurological adaptations associated with deep diving. They will investigate ancient evolutionary adaptations associated with new behaviors and hope to learn more about how animals can adapt to a changing world.

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