Secrets of Survival and Mysterious Extinction on Wrangel Island

Last Wrangel Mammoth

The woolly mammoths on Wrangel Island, from a tiny original population, persisted for 6,000 years despite genetic obstacles. Their sudden extinction remains a mystery, offering lessons for modern conservation efforts. Credit: Beth Zaiken

Genetic analysis of the last woolly mammoths on Wrangel Island has revealed a population that managed to survive for 6,000 years despite severe inbreeding and low genetic diversity.

This group initially consisted of just eight individuals, but grew to 200-300 members. Although genetic problems did not directly cause their extinction, it remains unclear what ultimately led to their demise. The study provides insight into how such populations may influence current conservation strategies for endangered species. kind Today.

Ten thousand years ago, the last population of woolly mammoths became isolated on Wrangel Island, located off the coast of Siberia, as rising sea levels separated the mountainous island from the mainland. New genomic research indicates that this isolated population, which lived on the island for the next 6,000 years, began with just eight individuals and grew to between 200 and 300 within 20 generations. Published in the journal Cell On June 27, the study showed that the Wrangel Island mammoths showed signs of inbreeding and low genetic diversity. However, these factors alone are not the cause of their mysterious and eventual extinction.

Siberian mainland tusk

Siberian mainland tusk. Credit: Love Dalén

Re-evaluation of extinction theories

“We can now confidently reject the idea that the population was simply too small and that they were genetically doomed to extinction,” said lead author Love Dalén, an evolutionary geneticist at the Centre for Paleogenetics, a joint collaboration between the Swedish Museum of Natural History and Stockholm University. “This means that it was probably just a random event that wiped them out, and if that random event hadn’t happened, we would still have mammoths today.”

Love Dalen

I love Dalén. Photo: Ian Watts

Insights for current conservation efforts

This analysis of the Wrangel Island mammoths could not only provide further insight into the dynamics of the woolly mammoth population, but could also contribute to conservation strategies for endangered species that are still threatened with extinction today.

“Mammoths provide an excellent system to understand the ongoing biodiversity crisis and what happens from a genetic point of view when a species goes through a population bottleneck, because they reflect the fate of many current populations,” said first author Marianne Dehasque of the Centre for Palaeogenetics.

Marianne Dehasque Ancient DNA Lab

Marianne Dehasque at work in the Ancient DNA Lab. Credit: Love Dalén

Genetic Challenges and Lasting Legacy

To understand the genomic consequences of the Wrangel Island bottleneck on the mammoth population, the team sequenced the genomes of 21 woolly mammoths: 14 from Wrangel Island and seven from the mainland population that preceded the bottleneck. In total, the samples spanned the last 50,000 years of the woolly mammoth’s existence, providing a glimpse into how the genetic diversity of mammoths changed over time.

Compared to their mainland ancestors, the Wrangel Island mammoth genomes showed signs of inbreeding and low genetic diversity. In addition to overall low genetic diversity, they showed reduced diversity in the major histocompatibility complex, a group of genes known to play a crucial role in the immune response of vertebrates.

Wrangel Island Tusk

Tusk of Wrangel Island. Credit: Liefde Dalén

Long-term genetic effects and future research

The researchers showed that the population’s genetic diversity continued to decline over the 6,000 years that the mammoths inhabited 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 moderately deleterious mutations over its 6,000-year existence, the researchers showed that the population slowly purged the most harmful mutations.

“If an individual has an extremely deleterious mutation, it’s basically not viable, so those mutations gradually disappeared from the population over time, but on the other hand, we see that the mammoths accumulated mildly deleterious mutations almost to the point of extinction,” Dehasque said. “It’s important for current conservation programs to keep in mind that it’s not enough to get the population back to a decent size; you also need to actively and genetically monitor it, because these genomic effects can last for more than 6,000 years.”

The Last Mystery of the Woolly Mammoth Extinction

Although the mammoth genomes analyzed in this study cover a large time frame, they do not include the last 300 years of the species’ existence. However, the researchers have unearthed fossils from the last period of the mammoth and plan to perform genomic sequences in the future.

“What happened in the end is still a bit of a mystery. We don’t know why they went extinct after doing more or less well for 6,000 years, but we think it was something sudden,” Dalén says. “I would say there is still hope to find out why they went extinct, but there are no promises.”

Reference: “Temporal dynamics of woolly mammoth genome erosion prior to extinction” June 27, 2024, Cell.
DOI: 10.1016/j.cell.2024.05.033

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