Secrets of survival and mysterious extinction on Wrangel Island

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

Originally consisting of no more than eight individuals, this group expanded to 200-300 members. While genetic issues did not directly cause their extinction, it remains unclear what ultimately led to their demise. The study provides insight into how such populations can inform current conservation strategies at risk species today.

Ten thousand years ago, the last population of woolly mammoths became isolated on Wrangel Island, located off the coast of Siberia, due to rising sea levels that separated the mountainous island from the mainland. New genomic research shows that this isolated population, which lived on the island for the next 6,000 years, began with no more than eight individuals and expanded to between 200 and 300 within 20 generations. Published in the journal Cell On June 27, a study shows that mammoths from the Wrangel Islands showed signs of inbreeding and low genetic diversity, but these factors alone do not explain their mysterious and final extinction.

Extinction theories revisited

“We can now confidently reject the idea that the population was simply too small and that it was doomed to extinction for genetic reasons,” says lead author Love Dalén, an evolutionary geneticist at the Center for Paleogenetics, a collaboration between the Swedish Museum. of Natural History and Stockholm University. “That means it was probably just some random event that killed them, and if that random event hadn’t happened, then we’d still have mammoths today.”

Statistics for current conservation efforts

In addition to shedding light on woolly mammoth population dynamics, this analysis of mammoths on Wrangel Island could help inform conservation strategies for the endangered animals today.

“Mammoths are an excellent system for understanding the ongoing biodiversity crisis and what happens genetically when a species passes through a population bottleneck because they mirror the fate of many contemporary populations,” says first author Marianne Dehasque of the Center for Paleogenetics.

Genetic challenges and enduring legacies

To understand the genomic consequences of the Wrangel Island bottleneck on the mammoth population, the team analyzed the genomes of 21 woolly mammoths—14 from Wrangel Island and 7 from the mainland population that preceded the bottleneck. Overall, the samples covered the last 50,000 years of the woolly mammoth’s existence, providing a window into how mammoth genetic diversity has changed over time.

Compared to their mainland ancestors, the mammoth genome from Wrangel Island 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 critical role in the vertebrate immune response.

Long-term genetic effects and future research

The researchers showed that the genetic diversity of the population continued to decrease during 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 very end. And although the island’s mammoth population has gradually accumulated moderately harmful mutations over its 6,000-year lifespan, researchers have shown that the population slowly clears 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 mammoths accumulated mildly deleterious mutations almost to the point of extinction,” he added. says Dehasque. “It is important for current conservation programs to remember that it is not enough to get the population back to a decent size; you also have to monitor it actively and genetically because these genomic effects can last over 6,000 years.

The last mystery of the mammoth extinction

Although the mammoth genomes analyzed in this study cover a large span of time, they do not include the last 300 years of the species’ existence. However, scientists have discovered fossils from the last mammoth period and plan to perform genome sequencing in the future.

“What happened at the end is still a bit of 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 Dalén. “I’d say there’s still hope to find out why they went extinct, but no promises.

Reference: “Temporal dynamics of pre-extinction mammoth genome erosion” 27 Jun 2024, Cell.
DOI: 10.1016/j.cell.2024.05.033