Genetic misunderstanding leads to giant growth in whales

One has teeth, the other two baleen. They eat up to 6,000 kilograms of food per day. Its length is thirty meters, and one of them is the largest animal on Earth. Although whales capture the imagination of many people because of their “giganticity,” it has not been known for a long time why these beasts suffer such exponential growth. researchers Estadual University de Campinas In Brazil I posted a solution last week nature To that mystery: Four specific genes caused whales to grow into giants.

“When we look at the evolution of whales, it’s kind of strange that they’re so big,” said Mariana Freitas Neri, a marine biologist and co-author of the publication. “Their predecessors were relatively young, so the question is where the huge growth spurt came from.” In addition, it is assumed that gigantic growth brings developmental defects. For example, large animals need more food. Concomitant competition leads to a smaller population, which reduces diversity in genes. This affects the ability of whales to adapt to changes in their habitat and food availability, among other things. “In addition, large animals are more likely to develop diseases such as cancer,” says Neary. “Large animals have a lot of cells and they often get very old, so the risk of cancer is higher than in small animals.”

Food quality is higher

Despite hypotheses opposing the evolution of sea giants, there are currently about two million whales swimming in our seas and oceans – although not all of them are huge. Some possible explanations have already been explored. “Animals in the sea have more space and a higher quality of food than they do on land,” says Neary. However, she believes that this only explains part of the giant growth of whales. After all, the disadvantages of their gigantic appearance take a toll. This is why Brazilian researchers looked at the formation of genes. “A lot of research has been done on growth genes in cattle because larger animals produce more meat,” Neary says. “In addition, cows are very similar to whales in terms of genetic makeup, so we took these growth genes for our research.” She also examined common growth genes found in many animals.

Neary and her colleagues examined nine developmental genes present in all 86 cetaceans.

As Pisces grows, the risk of developing cancer decreases

Mariana Freitas Neri marine biologist

Neary and her colleagues were the first to discover a so-called stop codon on the RNA strand in the epidermal growth factor (EGF) gene. This chain of RNA is made up of several amino acids and acts as a molecular messenger from DNA to cells that make proteins for growth. A stop codon in that chain causes part of the message to be deleted, causing the gene to partially lose its function. “The specific stop codon that we found caused the whales’ growth inhibition to disappear,” Neary says. “We found serendipitously that this gene also caused tooth loss and baleen bone development.” These baleen filter the water in which krill and other microorganisms swim. This evolution allowed baleen whales to catch a lot of food and this partly explains their massive body sizes.

Feeling hungry

The sperm whale is the only toothed whale with a giant overgrowth, but the stop codon was not found here. Neary explains that the GHSR gene plays a major role here. This gene stimulates the secretion of growth hormones and promotes feelings of hunger. In all giant whales, including baleen whales, this gene was more active than in mammals without giant undergrowth.

The IGFBP2 gene is another active growth gene that researchers have found in giant whales. It is almost three times as active here as in other mammals. This gene promotes cell growth and regulates cell division. “But the finding that really jumped out at us was that IGFBP7 gene overexpression increases with the higher whale BMI,” Neary says. After all, this gene not only promotes growth, but also suppresses cancer. “As the whale grows, the risk of cancer decreases,” Neary says. “This is in stark contrast to previous hypotheses that large animals are more susceptible to cancer.”

That cancer-suppressing growth genes in whales also promote additional growth is key to the evolution of the ocean giant. “These genes were very important in terms of natural selection,” Neary asserts. “In addition to large supplies of food and the formation of baleen whales, whales can afford to carry their large, heavy bodies.”

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