Researchers have compared the genomes of woolly mammoths from different eras to those of modern elephants to gain new insights into the genetics and evolutionary history of the shaggy Ice Age voyages. Among other things, the genetic clues reflect how these special mammalian mammals developed smaller ears, woolier fur and more immunity over the course of their evolutionary history, the scientists report.
Up until about 20,000 years ago, they roamed the cold steppes of the north in large herds: the woolly mammoths (Mammuthus primigenius) were the cousins of our elephants, adapted to the harsh conditions of the Ice Age. More than 700,000 years ago, they had split off from other representatives of the mammoth group and produced special characteristics. Much is known about the appearance and biology of these animals from specimens found in the permafrost, and scientists have already been able to obtain and analyze genetic remains of some mammoths. But there are still some unanswered questions about the characteristics and history of the development of the symbolic animals of the Ice Age.
The code of the shaggy giants
“We wanted to know what makes a mammoth a woolly mammoth,” says first author David Díez-del-Molino from the Center for Paleogenetics in Stockholm. “Woolly mammoths have some very distinctive morphological features, like their thick fur and small ears, but there are also many other adaptations that aren’t as obvious because they’re happening at the molecular level,” says Díez-del-Molino. In order to identify hereditary factors that played a special role in the woolly mammoth, special patterns had to be observed, the researchers explain: Genes that were subject to a strong developmental process exhibit a comparatively large number of mutations. To track them down, the team compared the genomes of 23 woolly mammoths discovered in Siberia with 28 genomes of contemporary Asian and African elephants.
While previous studies have looked at the genomes of just one or two woolly mammoths, this is the first comparison of a large number of mammoth genomes, the researchers point out. Sixteen of the genomes had not previously been sequenced. However, the 23rd woolly mammoth genome was the key element of the study: It came from a very early representative of the species: the animal called “Chukochya” lived about 700,000 years ago. “Using the Chukochya genome, we were able to identify a set of genes that evolved as a species during the lifespan of the woolly mammoth,” says senior author Love Dalén of the Center for Paleogenetics.
Evolution in the mirror of ancient DNA
As the researchers report, their genetic analyzes revealed that many genes that show significant adaptations in the woolly mammoth are associated with life in cold environments. Interestingly, similar genetic traits are also found in unrelated modern arctic mammals: “We found some genetic adaptations related to lipid metabolism and fat storage that are also found in other arctic species such as reindeer and polar bears, meaning that it there is likely parallel evolution for these genes in cold-adapted mammals,” says Díez-del-Molino.
As far as the changes in the woolly mammoth over the course of its evolutionary history are concerned, it became apparent that the 700,000-year-old early specimen “Chukochya” was in principle already equipped with the typical characteristics of the species. The systems were probably already present in the steppe mammoth, from which the woolly mammoth had previously split off. However, the genetic development in the descendants of Chukochya went much further, as can be seen from the genetic comparisons. This is particularly reflected in the genetic basis of ear development and fur: “The very first woolly mammoths were not yet fully developed,” says Dalén. “They may have had even larger ears, and their wool was different – perhaps less insulating and fluffy than that of later woolly mammoths.”
The researchers report that there are also genetic clues that relate to the development of the immune system: Later woolly mammoths therefore had several mutations in their hereditary traits that are linked to characteristics of immune cells that did not yet occur in their ancestors. The researchers suspect that this could have resulted in improved resistance to specific viral pathogens that eventually afflicted the proboscidea.
The team now wants to look further into the genetics of the mammoths for traces of their characteristics and history. According to them, one aspect is that they have only examined woolly mammoths from Siberia so far. But the animals once also trudged through North America. However, these representatives could have been special: “North American woolly mammoths could also have carried genes from non-woolly mammoths. So that’s something we need to take into account if we want to include these animals in our studies in the future,” says Dalén.
Source: Cell Press, Article: Current Biology, doi: 10.1016/j.cub.2023.03.084