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Aquatic skin adaptation of whales and hippos evolved independently

Paintings of dolphins (top), early extinct whales (center), hippos (bottom) Credits: Carl Buell

New studies show that the similarly smooth, almost hairless skin of whales and hippos has evolved independently. This work suggests that their last common ancestor was probably land-dwelling mammals, and now that skin has been fine-tuned for underwater life from a shared amphibious ancestor. I have uprooted the idea of.The study was published in the journal today Current biology It was led by a researcher at the American Museum of Natural History. University of California, Irvine; University of California, Riverside; Maxplanck Institute for Molecular Cell Biology and Genetics; and LOEWE-Centre for Translational Biodiversity Genomics (Germany).


“How mammals left Terrafarm and became completely aquatic is one of the most fascinating evolutionary stories, perhaps the way animals first exchanged water for land, or in flight. It is comparable only by evolution, “said the author of the American Museum of Natural History’s Department of Vertebrate and Zoology and the corresponding study. “Our latest findings contradict the current doctrine in this area that amphibious hippo relatives may have been part of the transition when mammals re-entered underwater life. . “

In contrast to their appearance, completely aquatic cetaceans (a group that includes whales, dolphins, and porpoises) and semi-aquatic hippos are the closest living relatives to each other and lived about 55 million years ago. They share a common ancestor. They also share many features that are strange to most mammals: they give birth and lactate in water and lack the scrotal testes and sebaceous glands (secreting oily sebum) and most of their hair. I will. Since these traits are rarely found in other mammals, it is speculated that they were already present in the common ancestor of hippos and whales. However, when and how cetacean ancestors became completely aquatic remains a subject of intense debate.

Paleontological studies of transient extinct cetaceans suggest that water invasion was a gradual process involving the amphibious phase. So did hippos and whales independently develop adaptations to aquatic lifestyles? Or did their common ancestors already amphibious, from which the cetaceans diverged to become completely aquatic?

“The simplest hypothesis is that whale and hippo ancestors were already amphibious, but evolution is not always the shortest distance between two points,” said the lead author of a study, a professor of biology at the University of California, Riverside. Mark Springer said.

To solve this problem, researchers turned to animal skin. This shows a major evolutionary change depending on the aquatic organism.

“When a group of animals becomes aquatic, the skin becomes much more streamlined and uniform overall,” said Maksim Plikus, co-author and skin biologist at the University of California, Irvine. “Complex derivatives such as hair, nails, and sweat glands are no longer needed, and in fact they can interfere with life in the water, so they are gone, and the barrier function performed by the outer layers of the skin. Lose. Terrestrial mammals are essential to prevent water from evaporating out of the body and to prevent pathogens from invading. “

Researchers compare the anatomical structures of hippo and whale skin based on histology and use genomic screening to provide a comprehensive list of “skin genes” inactivated in both hippopotamus and whales. is created. This was supported by the first examination of the genome of Choeropsis liberiensis, one of the two living hippopotamus species of Pygmy hippopotamus.

“Looking at the molecular signatures, we have an impressive and clear answer,” said Michael Hiller, co-author of the Max Planck Institute of Molecular Cell Biology and Genetics and LOEWE-Centre for Translational Biodiversity Genomics. In German. “Our results strongly support the idea that the” aquatic “skin traits found in both hippos and whales have evolved independently. Not only that, it turns out that the gene loss of the hippopotamus line occurred much later than that of the whale line. “

The results of these genes are consistent with the examination of the skin itself. Unlike whales, hippos actually have a very special type of sweat glands that produce “blood sweat.” This is an orange substance that is presumed to have natural antibacterial agents and sunscreen. Property. Also, although there are only a few cetacean whiskers, the hippopotamus is completely bearded, but the hair is sparse and the tips of the ears and tail are most noticeable. The latter is used when the hippopotamus defecates. In the meantime, the hippopotamus spins its tail quickly, and brush-like hair helps crush the dung as a way to mark the territory. In addition, whale skins are much thicker than hippo skins, and only hippos have hooves.

“These differences are in perfect agreement with the evolutionary history records written in the genome, which show independent knockouts of skin genes in cetacean and hippo evolutionary lines,” Springer said. .. “None of the inactivated mutations that would suggest a common aquatic ancestor are not shared between these two strains.”


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For more information:
Current biology (2021). DOI: 10.1016 / j.cub.2021.02.057

Courtesy of the American Museum of Natural History

Quote: Skin Depth: Whale and Hippo Aquatic Skin Adaptation Evolved Independently (April 1, 2021) April 1, 2021 https://phys.org/news/2021-04-skin- Obtained from deep-aquatic-whales-hippos.html

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Aquatic skin adaptation of whales and hippos evolved independently

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