Researchers Discover the Genetic Secrets of Woolly Mammoths: Uncovering the Unique Traits That Defined the Species, from their Iconic Coats to their Tiny Ears, and How They Evolved Over 700,000 Years.

By comparing the genomes of modern-day elephants with those of woolly mammoths, a research team sought to uncover the distinct genetic characteristics that made woolly mammoths unique as individuals and as a species.

The team’s findings, published in Current Biology on April 7th, reveal that many of the distinguishing features of woolly mammoths, such as their thick coats and substantial fat reserves, were already present in the earliest specimens genetically.

However, these traits and others were further refined over the 700,000-year lifespan of the species. Additionally, the researchers identified a gene with multiple mutations that may have been responsible for the small ears of the woolly mammoth.

First author David Díez-del-Molino says they “wanted to know what makes a mammoth a woolly mammoth.

“Woolly mammoths have some very characteristic morphological features, like their thick fur and small ears, that you obviously expect based on what frozen specimens look like, but there are also many other adaptations like fat metabolism and cold perception that are not so evident because they’re at the molecular level.”

The research team aimed to pinpoint genes that had undergone significant evolution in woolly mammoths, which meant that they had accumulated numerous mutations. To accomplish this, they compared the genomes of 23 Siberian woolly mammoths with 28 modern-day Asian and African elephant genomes. Among the woolly mammoths were 22 relatively recent specimens that lived within the last 100,000 years, with 16 of these genomes previously unsequenced. The 23rd genome belonged to Chukochya, one of the oldest woolly mammoths on record, who lived around 700,000 years ago.

“Having the Chukochya genome allowed us to identify a number of genes that evolved during the lifespan of the woolly mammoth as a species,” remarks senior author Love Dalén. “This allows us to study evolution in real time, and we can say these specific mutations are unique to woolly mammoths, and they didn’t exist in its ancestors.”

It comes as no surprise that numerous genes that proved advantageous to woolly mammoths are associated with survival in frigid climates. Certain genes are even common to modern Arctic animals that aren’t related.

According to Díez-del-Molino, they “found some highly evolved genes related to fat metabolism and storage that are also found in other Arctic species like reindeer and polar bears, which means there’s probably convergent evolution for these genes in cold-adapted mammals.”

Prior research has focused on examining the genomes of just one or two woolly mammoths. In contrast, this study represents the first extensive comparison of a substantial number of mammoth genomes. With a large sample size, the researchers were able to pinpoint genes that were shared by all woolly mammoths and thus more likely to have been adaptive, as opposed to genetic mutations that might have been unique to a single specimen.

“We found that some of the genes that were previously thought to be special for woolly mammoths are actually variable between mammoths, which means they probably weren’t as important,” points out Díez-del-Molino.

In total, the genome of Chukochya, which dates back 700,000 years, exhibited around 91.7% of the mutations that resulted in changes to protein-coding in the more recent woolly mammoths. This suggests that many of the distinctive features of woolly mammoths, such as their dense fur, fat metabolism, and cold-sensing abilities, were likely present at the time of the species’ divergence from its ancestor, the steppe mammoth.

Nonetheless, these traits are believed to have undergone further refinement in subsequent generations of woolly mammoths.

“The very earliest woolly mammoths weren’t fully evolved,” adds Dalén “They possibly had larger ears, and their wool was different—perhaps less insulating and fluffy compared to later woolly mammoths.”

Compared to their ancestor, the more contemporary woolly mammoths had a number of immune mutations in T cell antigens that were not present before. The researchers suggest that these mutations may have provided a superior cell-mediated immune response to counter new viral pathogens.

Extracting and studying ancient mammoth DNA presents numerous challenges. As Díez-del-Molino notes, “Every step of the way, things are a bit more difficult, from fieldwork, to lab work, to bioinformatics.”

“Apart from the field work, where we have to battle both polar bears and mosquitos, another aspect that makes this much more difficult is that you have to work in an ancient DNA laboratory, and that means that you have to dress up in this full-body suit with a hood and face mask and visor and double gloves, so doing the lab work is rather uncomfortable to put it mildly,” adds Dalén. “I would like to highlight Marianne Dehasque, the second author of this paper, who did the herculean effort of performing lab work on most of these samples.”

Although the mammoths whose genomes were analyzed in this study were obtained from Siberia, the researchers aspire to expand their investigation to include North American woolly mammoths in the future.

“We showed a couple of years ago that there was gene flow between woolly mammoths and the ancestors of Colombian mammoths, so that’s something that we will need to account for because North American woolly mammoths might have been carrying non-woolly mammoth genes as well,” adds Dalén.

Featured Image Credit: KAZUHIRO NOGI/AFP via Getty Images