The story of the mammoths of Wrangel Island that survived 6,000 years after the mammoths in the rest of the world became extinct
The woolly mammoths on Wrangel Island, originating from a very small population, have survived for 6,000 years despite genetic difficulties. Their sudden extinction remains a mystery, providing lessons for contemporary conservation efforts.
The genetic analysis of the last woolly mammoths on Wrangel Island revealed a population that survived for 6,000 years despite severe interbreeding and low genetic diversity.
In the beginning, this population came from a number that did not exceed eight individuals and expanded to 200-300 individuals. Although the genetic problems did not directly cause their extinction, the reason for their final extinction is still unclear. The study provides insights into how such populations can assist contemporary conservation strategies for endangered species.
Ten thousand years ago, the last population of woolly mammoths remained isolated on Wrangel Island, located off the coast of Siberia, due to rising sea levels that separated the mountainous island from the mainland. A new genomic study shows that this isolated population, which lived on the island for the next 6,000 years, began with a number that did not exceed eight individuals and expanded to 200-300 within 20 generations. The study, published on June 27 in the journal Cell, shows that Wrangell Island mammoths showed signs of hybridization and low genetic diversity, but these factors alone do not explain their mysterious and final extinction.
Reevaluating extinction theories
"We can now confidently reject the idea that the population was too small and doomed to extinction for genetic reasons," says senior author Love Dalen, an evolutionary geneticist at the Center for Paleogenetics, a collaboration between the Natural History Museum in Sweden and Stockholm University. "It was probably a random event that caused them to go extinct, and if that random event hadn't happened, then we'd still have mammoths today."
Insights into contemporary conservation efforts
In addition to understanding woolly mammoth population dynamics, the analysis of Wrangel Island mammoths can help inform conservation strategies for today's endangered species.
"Mammoths are an excellent system for understanding the ongoing biodiversity crisis and what happens genetically when a species goes through a population bottleneck, because they mirror the fate of many modern-day populations," says lead author Marian Dasek of the Institute of Paleogenetics.
Genetic challenges and lasting legacy
To understand the genomic consequences of the bottleneck on the Wrangell Island mammoth population, the team analyzed the genomes of 21 woolly mammoths – 14 from the Wrangel Island and 7 from the land population that existed before the bottleneck. In total, the samples spanned the last 50,000 years of woolly mammoth existence, providing a window into the changes in mammoth genetic diversity over time.
Compared to their terrestrial ancestors, Wrangell Island mammoth genomes showed signs of hybridization and low genetic diversity. In addition to a generally low genetic diversity, they exhibited a decrease in diversity in the central histocompatibility system, a group of genes known for their critical role in the immune response of vertebrates.
Long-term genetic implications and future research
The researchers showed that the genetic diversity of the population continued to decline throughout the 6,000 years that the mammoths lived on Wrangel Island, albeit at a very slow rate, suggesting that the population size was stable until the end. And while the island's mammoth population gradually accumulated mildly harmful mutations over its 6,000 years, the researchers showed that the population slowly eliminated the most harmful mutations.
"If an individual has a very harmful mutation, it's actually not viable, so these mutations gradually disappeared from the population over time, but on the other hand, we see that the mammoths accumulated mildly harmful mutations almost until they became extinct," says Dasek. “It is important for contemporary conservation programs to remember that it is not enough to increase the population to a suitable number again; It also needs to be actively monitored genetically because these genomic effects can last more than 6,000 years."
The last remaining mystery about the extinction of woolly mammoths
Although the genomes of the mammoths analyzed in this study span a wide period of time, they do not include the last 300 years of the species' existence. However, the researchers found fossils from this period and plan to perform genomic sequencing in the future.
"What happened at the end is still a mystery - we don't know why they went extinct after being more or less fine for 6,000 years, but we think it was something sudden," says Dalen. "I think there is still hope to understand why they became extinct, but there are no promises."
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