Wrangel Island Mammoths Were Inbred but Not Destined for Extinction

Many species around the world are on the brink of extinction. A recent study, published in Cell, used genomic analysis on the last surviving population of woolly mammoths to explore the potential causes of their extinction.

Investigating the impact of a population bottleneck

The last population of woolly mammoths resided on Wrangel Island, off the coast of Siberia, over 10,000 years ago. When sea levels rose, the mountainous island was cut off from the mainland, isolating the species, which then survived for another 6,000 years. Originating from just 8 individual mammoths, the population grew to around 200–300 individuals over 200 generations. Researchers believe that inbreeding and a lack of genetic diversity may have led to the species’ extinction.

“Mammoths are an excellent system for understanding the ongoing biodiversity crisis and what happens from a genetic point of view when a species goes through a population bottleneck because they mirror the fate of a lot of present-day populations,” said Marianne Dehasque, lead author and doctoral candidate at the Centre for Palaeogenetics.

The Wrangel Island mammoths had low genetic diversity

Genomic analysis was performed on 21 woolly mammoths, 14 from the Wrangel Island and 7 from the mainland population that predated the bottleneck. The samples provided insight into how the mammoth's genetic diversity transformed over time, spanning the last 50,000 years of the species' existence.

The genomes of the Wrangel Island mammoths exhibited signs of inbreeding and a lack of genetic diversity. Examination of the major histocompatibility complex, a group of genes crucial for the vertebrate immune response, revealed that the Wrangel population had reduced diversity compared to their mainland ancestors.

Despite a gradual decline in genetic diversity over their 6,000 years of existence, the Wrangel Island mammoth population managed to maintain stability. Researchers observed that while moderately harmful mutations had accumulated, the population was slowly purging the most detrimental ones. The mammoths recovered swiftly from the severe bottleneck, indicating that low genetic diversity alone does not explain their mysterious demise.

“We can now confidently reject the idea that the population was simply too small and that they were doomed to go extinct for genetic reasons. It was probably just some random event that killed them off, and if that random event hadn't happened, then we would still have mammoths today,” said Dr. Love Dalén, senior author and evolutionary geneticist at the Centre for Palaeogenetics.

Present day conservation programs

“What happened at the end is a bit of a mystery still, we don't know why they went extinct after having been more or less fine for 6,000 years, but we think it was something sudden. I would say there is still hope to figure out why they went extinct, but no promises,” said Dalén.

The results have strong implications for conservation programs working on species that have recently recovered from near extinction.

“It’s important for present day conservation programs to keep in mind that it’s not enough to get the population up to a decent size again; you also have to actively and genetically monitor it because these genomic effects can last for over 6,000 years,” said Dehasque.

The genomes analyzed in the study spanned a significant portion of the population's existence but did not include the final 300 years before the species went extinct. Researchers have recently unearthed fossils from this last period and plan to analyze their genomes in the future.

Reference: Dehasque M, Morales HE, Díez-del-Molino D, et al. Temporal dynamics of woolly mammoth genome erosion prior to extinction. Cell. 2024;187:1-10. doi: 10.1016/j.cell.2024.05.033

This article is a rework of a press release issued by Cell. Material has been edited for length and content.